· 2009. 5. 19. · enc software user’s guide revision 3.3, april, 2009 © causal systems table...

ENGINEERING NOISECONTROL SOFTWARE

With references to 3rd Edition textbook

User GuideVersion 3.3, April, 2009

By Colin H Hansen and Xiaojun Qiu

Causal SystemsA companion to the textbook,

“Engineering Noise Control, 3rd Edn., by DA Bies and CH Hansen

ENC Software User’s Guide Revision 3.3, April, 2009 © Causal Systems

User's Guide for Engineering Noise Control Softwareby Colin H Hansen and Xiaojun Qiu

© Copyright 2009 Causal Systems

33 Parsons StMarion SA 5043AUSTRALIAPhone: 61 8 8377 1641Fax: 61 8 8377 0217Email: [email protected]

http://www.causalsystems.com

ALL RIGHTS RESERVED

PRODUCT AND DOCUMENTATION NOTICE: The authors reserve the right tochange this product and its documentation without prior notice.

Information furnished by author and company is believed to be accurate and reliable.However, no responsibility is assumed by Causal Systems.

PRINTING HISTORYFirst release by Causal Systems (1.0) 2/2002First update (1.1) 9/2002Second update (1.183) 6/2003Third update (1.185) 8/2003 Fourth update (1.186) 9/2003Fifth Update (1.187) 10/2003sixth Update (1.188) 10/2003seventh update (1.189) 11/2003eighth update (1.189) 12/2003ninth update (1.20) 3/2004tenth update (1.30) 7/2004version 2 update (2.0) 11/2004version 2 update (2.1) 3/2005version 2 update (2.2) 3/2006version 3 update (3.0) 9/2006version 3 update (3.1) 3/2007version 3 update (3.2) 10/2007version 3 update (3.3) 04/2009


Table of Contents

About this Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1General guidelines for use (essential reading) . . . . . . . . . . . . . . . . . . . . . . . . 1On-Line Help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Main menu at top of screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Software Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Plotting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Fundamentals and Criteria (Module 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Fundamental Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Conversions of levels to linear quantities . . . . . . . . . . . . . . . . . . . . . . . 10Decibel addition and subtraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Wavenumber, wavelength and frequency . . . . . . . . . . . . . . . . . . . . . . . 11Wave Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Level reduction combination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Speed of sound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Hearing Damage Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Noise exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Hearing damage risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Noise Level Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Loudness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Noise criterion curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Loudness Calculator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Weighting Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Spectral plotting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Noise Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Occupational and environmental noise descriptors . . . . . . . . . . . . . . . . 20

Flow resistivity and flow resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Speech privacy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Sound Sources and Sound Power (Module 2) . . . . . . . . . . . . . . . . . . . . . . . . . 23Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Sound Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Monopole, Dipole and Quadrupole sources . . . . . . . . . . . . . . . . . . . . . 23Radiation from a vortex impinging on a rigid body in flow . . . . . . . . . . 24Line source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Radiation field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Plane Sound Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Incoherent plane radiator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Coherent piston source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Radiation from a building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Sound Propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28


Left panel (source type) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Centre Panel (excess attenuation) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Barrier attenuation calculation panel . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Attenuation due to housing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Attenuation due to process equipment . . . . . . . . . . . . . . . . . . . . . . . . . . 39Attenuation due to forests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Right panel (air absorption, ground and meteorological effects) . . . . . . 41

Air absorption effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Ground effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Meteorological effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Sound Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Free and semi-free field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Reverberant field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

substitution method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46absolute method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Field Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48reference source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48substitution method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48two test surfaces method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Near field measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Determination of sound power from surface vibration measurements . . 52Easy SPL Averager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Room Acoustics and Sound Absorption (Module 3) . . . . . . . . . . . . . . . . . . . 55Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Room Modal Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Rectangular room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Cylindrical room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Sound in rooms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65Steady-state response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Sabine Rooms (steady-state response) . . . . . . . . . . . . . . . . . . . . . . . 65Flat Rooms (steady-state response) . . . . . . . . . . . . . . . . . . . . . . . . . 67Long Room (steady-state response) . . . . . . . . . . . . . . . . . . . . . . . . . 68

Transient Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Porous Material Sound Absorbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Calculations based on flow resistance data . . . . . . . . . . . . . . . . . . . . . . 72Calculations based in impedance tube measurements . . . . . . . . . . . . . . 75Calculation summary and results presentation . . . . . . . . . . . . . . . . . . . . 75

Panel Absorber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

TL, Enclosures, Barriers & Pipe Lagging (Module 4) . . . . . . . . . . . . . . . . . . 83Partition Transmission Loss (Single wall) . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Isotropic Panel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85Multi-leaf walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87Composite material wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87Orthotropic Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89


Double Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91Multi-leaf Panels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93Composite Material. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

STC, Rw and IIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96Composite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98Enclosures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101Outdoor Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104Indoor Barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111Pipe Lagging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Reactive and Dissipative Mufflers (Module 5) . . . . . . . . . . . . . . . . . . . . . . . 116Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116Duct Modal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116Impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

tube/orifice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1191/4 wave tube calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122volume/expansion chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123Helmholtz resonator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124perforated sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

Reactive Mufflers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127Helmholtz resonator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1301/4 wave tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131expansion chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132Low Pass Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133Small Engine Exhaust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

Dissipative Mufflers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136Liner Attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139Inlet Attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140Exit Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140Expansion Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140Duct Bend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

Lined Plenum Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141Pressure Drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145Flow Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146Exhaust Stack Directivity and Noise Reduction . . . . . . . . . . . . . . . . . . . . 147Duct break-out/Break-in Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

Vibration Isolation (Module 6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154SDOF System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

4-Isolator System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156Flexible Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1582-stage Vibration Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161Vibration Absorber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164


Sound Power of Equipment (Module 7) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167Sound Power and SPL Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170Air Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171Refrigeration Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172Cooling Towers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174Jet Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174Control Valves (Gases) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175Control Valves (Liquid) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179Control Valves (Steam) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180Pipe Flow Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180Boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183Turbines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183Diesel and Gas Driven Engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

Exhaust Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184Casing Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185Inlet Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185Electric Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189Gears . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

Transportation Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192Traffic noise - CoRTN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192Traffic noise - FHWA-TNM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195Rail Traffic noise - UK DoT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

Errata, third Edition text book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223


1.

About this Software

Thank you for purchasing a license for the software, "ENC" for engineering noisecontrol. The purpose of this software is to provide an easy way of numericallyevaluating many of the equations and algorithms incorporated in the third edition ofthe book, "Engineering Noise Control", by DA Bies and CH Hansen. It is essentialthat the software is used with the textbook as a reference so that the theoretical basisfor the calculations can be understood. This software is intended purely as acalculation aid. It is not intended to produce report-ready documentation, althoughthe screen can be copied using the "Print Screen" button your keyboard and pastedinto an application such as Adobe Photoshop or Corel Photopaint. The graphs canthen be cut and pasted into a document. Using ENC can replace hours of tedioushand calculations and lead to a more efficient work environment. In addition tosaving time, the advantage of the software is that the calculations are correct everytime and there is no need for them to be checked by someone else.

The software provided with this manual can be used to solve all kinds of problemsencountered in engineering noise control work, including most of the exampleproblems provided in the book, "Example Problems in Engineering Noise Control",2nd Edn., by C.H. Hansen.

Installation

To install the software, copy the files from the CD-ROM to a directory on your harddrive and double click on the file, "setup.exe". Follow the installshield instructionson the screen. You will need approximately 50 Mbytes of free disk space. If youaccept the default directories, you should be able to access the program immediatelyafter installation from the "Start" menu of your computer. It is called "ENC". If youare installing a network version or are using a USB dongle, please look carefully atthe "readme.txt" file that is on the software CD.

General guidelines for use (essential reading)

NOTE THAT MANY CALCULATIONS USE THE DENSITY OF THE GAS ANDSPEED OF SOUND IN THE GAS (USUALLY AIR) AS PART OF THE

Chapter 1: About ENC 2


CALCULATION. VALUES FOR THESE QUANTITIES ARE SET IN THETOOLS MENU (SEE BELOW). YOU MUST SET THESE VALUESCORRECTLY TO GET CORRECT RESULTS. DEFAULT VALUES ARE1.205 kg/m3 and 343 m/s RESPECTIVELY.

Another important item to note is that ENC ALWAYS uses the correction10log10(ρc/400) when calculating sound power level from sound pressure level andvice versa. The text book sometimes ignores this correction as it is often onlybetween 0.1 and 0.2 dB at room temperature in air.

Graphical as well as numerical output is provided. Numerical data can be stored onfile for later access and plotting by a spreadsheet program such as excel. A quickerway of getting a graph in your word processor document is to double left click onany graph in ENC and then you can paste it into any application.

Alternatively the graphs and other on-screen results presented by the software canbe printed directly and any part of the screen can be imported into a word processorby importing it first into Corel PhotoPaint. This is done by pressing the "printscreen" key on your keyboard (sometimes requires pressing the "shift" key as well).Then in PhotoPaint click on "file", then "new from clipboard". Then select the partof the screen you would like to import and click on "edit" followed by "copy visible".Then paste it into your document. The result is of good quality and suitable for areport. All graphics in this manual were produced in this way. If Microsoftphotoeditor is used, the results obtained are of marginal quality. However, AdobePhotoshop should also be suitable.

Many of the calculations give a new result immediately any input data value ischanged. However, more complex calculations and especially those involving theproduction of charts, require that you click on the "run" icon in the tool bar (orchoosing the "run" option from the main menu) after you have changed all the inputvalues to those wanted for the particular problem.

When a variable is labelled in blue type, that means it is a calculation result andshould not be typed over. You can change the result by typing in a new value but itwill not be valid, as it will not be reflected by the input data values. If you do makethe mistake of typing in a box corresponding to a result, you can rectify the problemby changing one of the input values and/or clicking on the "run" symbol in the toolbar menu.

There are many places where some input data are redundant. In these cases, whenyou change one data entry, another may change to remain consistent with the others.For example, if you enter the percent open area and hole diameter for a perforatedpanel, the number of holes is defined and need not be entered. If you enter thenumber of holes as well, then one of the other items of input data will change.



When you enter a number in a data box and press "enter" or "run", you may see thenumber of decimal places truncated in your input data. However, do not worry: ENCwill use the accurate number you typed in for any calculations.

At the very top of the screen is the software name, "Engineering Noise ControlDesign" followed by the name of the file currently open. Typically, this file containsthe input data for what you see on the screen, if you have saved it. It is also the nameof the file you may have opened to obtain the input data on the screen. This file canbe one of the example files included with the software or one saved from a previoussession. If you see the word "Untitled", then you currently have no file open.

If you wish to save data that you see plotted, then click on the "Save" button at thebottom of the graph. Both 1/1 octave and 1/3 octave band data will be written to afile that you can open using Microsoft Excel or Word. Alternatively, in many partsof ENC, you can double left click on the graph and paste it directly into your wordprocessor with a high quality result.

Where equation numbers are given in this user guide, they refer to equations in"Engineering Noise Control", 3rd edn. by D.A. Bies and C.H. Hansen.

Note that in most cases there are restrictions on allowable input data. This is toavoid program crashes as much as possible. Input data in many cases can be typeddirectly in the data box or the increment arrows on the side of the data box can beused.

On-Line Help

Extensive on-line help can be activated by right-clicking on the grey part of anyscreen for which help is required. In addition, more illustrative html help can beobtained by hitting the F1 key on yourkeyboard.

Main menu at top of screen

The menu is made up of the six items shownabove. The file menu is shown in the figure tothe right and allows data for any window in anymodule to be saved (a .enc extension isnecessary) and later retrieved using the "open"choice on the menu.

The name of the current file appears in the title bar right at the top of the ENCwindow. If this name is "Untitled New", then selecting "new" from the file menu will



have no effect. However, if the current set up has been saved using a different filename, selecting "new" will allow you to start a new file based on the current setup.

It is often useful to have more than one ENC window open at one time so thatcalculations done in one module can be easily transferred to anotherand this is what the "launch ENC" button is for. If you need to doa calculation in another module for use in the current module, youcan launch another ENC from within your existing ENC. You canthen use the new ENC to do the calculation needed withoutupsetting the data already entered in the ENC that was being usedoriginally. To do this, click the "launch ENC" button in the "file"menu at the top of the screen.

The "options" menu shown at right is used to select the module(from a choice of 7) that you want to work with.

The "run" button on the main menu can be clicked on instead of the icon on theright of the tool bar to make sure that the results reflect new input data that you haveentered.

The "tools" menu at right includes anumber of items. The first item, “Export toexcel”, which is also activated by pressingthe F8 key, allows most tables of values tobe exported to excel. Generally the tablethat is visible is the one that is exported toan .xls file.

The next item, "Constants Set-up", allows adjustment of some physical constantssuch as the speed of sound and density of air. When clicking on this item, the paneltitled "Constants Set-up and Calculation" shown on the next page appears. You canthen type in the parameters that are appropriate for your problem. You can do thisfrom any module or you can click on the "Constants" button on any page that youfind it or you can key in [Cntrl] H from anywhere. All ENC calculations use thevalues in the "Constants Set-up and Calculation" window. The "speed of sound" and"gas density" are in blue font to indicate that they are calculated quantities. Thespeed of sound is calculated from the values you enter for molecular weight, ratio ofspecific heats and temperature of the gas in which the sound is travelling. The ENCdefault values are for air at 20 degrees C and may be reinstated by clicking on the"Default" button in this window. To calculate the density of the gas in which thesound is travelling you need to enter the gas pressure (often but not alwaysatmospheric) in addition to the other quantities mentioned above. Practically allcalculations use the speed of sound and gas density data from this panel. Todetermine the speed of sound and gas density corresponding to the parameters youhave selected, click on the "Calculate" button. The gas viscosity data is only used in



module 5 and in module 3, "Porous Material Absorber". In module 7, the speed ofsound in the ambient medium surrounding the sound source is assumed to be 343m/s and the product of air density and speed of sound has been approximated asρc = 400. The relative humidity datum is only used in calculations involving outdoorsound propagation. In a number of cases (principally module 5), 1/3 octave bandvalues are calculated by averaging data corresponding to a number of singlefrequencies in the band. The number of intervals used in numerical integration in anumber of calculations can be set here. It is recommended that it be left at the defaultvalue. However, the default value may be increased if computation time is not anissue and high accuracy is important. The number of single frequencies used for aband average can also be set using the "Constants Set-up and Calculation" window.When you have completed entering the values for the various constants, click on"Finish".

The tools menu (see previous page) also has a list of conversion factors forconverting quantities expressed in the SI system of units to the British system ofunits. The "Unit conversion" window is shown on the next page, and includes, forconvenience, a simple calculator for multiply, divide, add and subtract operations.

The tools menu can also be used to select the optimum display resolution as there issome distortion on a few wide screen displays.

The Debug ON / OFF item on the menu allows users to see the results ofintermediate calculations. However, this is not recommended for general use and nosupport is provided to users for this option.



The "help" menu (see left) containsinformation about various general topics, someof which are also covered elsewhere in thismanual. Information about the various menusmay be obtained simply by clicking on the menuname in the Help menu. Topics that are notincluded elsewhere in the manual are discussedbelow.

The “html help” item is activated by the “F1"key. You are then provided with an index, atable of contents and a search facility.

The "New Release Notes" item displays all ofthe improvements made to ENC since the firstcommercial release (Version 1.183). The"Windows Display Mode" item explains how toset up windows to get the best

out of ENC. Finally, the "About ENC Design" tells you what version of ENC youhave.

Software Modules

The software is divided into seven modules that roughly follow the layout of thebook, Engineering Noise Control, 3rd Edition, by D.A. Bies and C.H. Hansen. Each



module is associated with unique tool bar symbols (see example below) thatrepresent different calculation procedures from different sections of the book chapteror chapters associated with the particular module. You can select the module youwant from the "Options" menu at the top of the screen. Each module has a numberof windows which can be selected by clicking on the appropriate symbol on the toolbar. Each window has a number of panels, each of which represents a particularcalculation.

The modules and the chapters of the book that they represent are listed in thefollowing table.

Module number Book chaptersrepresented

1 1, 2, 3, 4

2 5, 6

37, App. C

4 8

5 9

6 10

7 11

When you select a particular module, you will find that a page will pop up thatrepresents one particular window in that module. Each window in the module isrepresented by an icon in the tool bar (see an example above for the module 4 toolbar). You can tell which window you are currently in because the correspondingicon in the tool bar will appear in one of the corners of the screen.

The symbol on the far right is the "run" symbol on which you often need to click tomake sure a new calculation occurs after you change some input parameters. Thethree icons to the left on the tool bar allow you to respectively, start a newcalculation, open an old calculation previously stored on a file, and save the currentcalculation parameters to file.



Plotting

In most windows of the software, the calculated results are shown plotted on a graph.An example is shown below. Multiple curves can be plotted by clicking on the"Overlap" button so it shows "ON". Different colours for each curve can be selectedby clicking on the arrows on the "Colour" button prior to doing a new calculation.Clicking on the "Print" button allows you to print the entire ENC window, includingthe graph. Clicking on the "Save" button allows you to save the data used toconstruct the entire ENC window. Clicking on "Clear" will clear all curves from thegraph.

Many graphs also have a cursor button that can be turned "ON" by clicking on it,thus allowing you to obtain accurate values from the graph. Above many graphs youwill also have the option of selecting the quantity to be plotted (Display Contents"box).

In modules 4 and 7, the graphs have arrows on the left side so you can adjust therange of the scale on the y-axis.Other graphs have a "y-axis setup" button which allows you to adjust the upper andlower limits of the scale so that sensible numbers appear on the y-axis and the scale



can be compressed or expanded (see below). There is also an "auto/manual" switchin the pop-up window. When set to "auto" ENC will select the y-axis scale for you.


2.

Fundamentals and Criteria(Module 1)

Overview

The software in module 1 calculates all of the quantities discussed in chapters 1-4 ofthe text, ranging from the speed of sound in any medium to addition and subtractionof sound levels, A-weighting and noise criteria evaluation. The module consists offive separate windows, all of which are accessed by clicking on an appropriate iconon the tool bar. Each window is discussed separately below.

Fundamental Calculations (Chapter 1)

This window contains eight panels for eight separate calculations. The green"Constants" button near the middle of the page allows constants such as airtemperature to be set up for any of the eight panels.

Conversions of levels to linear quantities. The top left panel of this window at thetop allows you to convert SPL to Pascals (Eq. 1.78), Sound power level to watts (Eq.1.80) and Sound intensity level to Watts/m2 (Eq. 1.82) and vice versa (see below).Decibel addition and subtraction. The next panel below and on the left (see next

page) allows you to add and subtract decibel levels for coherent (tonal - Eqs. 1.90,1.78) and incoherent sound (see below Eqs. 1.94, 1.78). You would normally usethe incoherent sound button unless the two sounds to be added were tonal, of thesame frequency and from synchronised sound sources. This procedure is discussedon pages 45-47 in the text.

Chapter 2: Fundamentals and criteria (module 1) 11


Wavenumber, wavelength and frequency. The next panel below and on the left,titled "wavelength" (see below) allows you to calculate wavelength and wavenumberfrom frequency and speed of sound. In fact frequency or wavelength, may be variedto give wavenumber and speed of sound.

Wave Properties. The next panel belowand on the right (see below) is titled"Wave Properties" and allows you to

calculate the following quantities (shown in blue) for plane and spherical waves fora specified sound pressure level, Lp. For spherical waves, the distance from the pointsource and frequency must also be specified.

• rms acoustic pressure (Eq. 1.78)• Acoustic particle velocity (Eq. 1.43)• Sound intensity (Eq. 1.74)• Sound intensity level (IL) (Eq. 1.81)• Reactive intensity amplitude (A.R.I.) (Eq. 1.74, second term)• Total energy density (ED) (Eq. 1.56)• Potential energy density (Eq. 1.55)• Kinetic energy density (Eq. 1.54)

Note that this panel also includes the "Constants" button.



Level reduction combination. At the bottom of the left panel (see below), you cancombine level reductions (Page 49, text). You may need to do this when you havemany paths from the source to the receiver and each path is characterised by adifferent noise reduction to the direct path. Combining level reductions allows youto calculate the sound level at the observer when the noise comes from a source viamore than one path and you know the noise reduction associated with each path.

You can also do complex calculations such as calculating the overall noise reductiondue to the insertion of a finite size barrier if you know the reduction attributable toeach path from source to receiver both before and after insertion of the barrier. Thisis discussed in detailon pages 49-50 ofthe text.

Speed of sound. Onthe right hand panel(see right), the speedof sound in gases(Eqs. 1.4, 1.5), bulkliquids (Eqs. 1.1,1.2), liquids in athin-walled tube(corrected Eqs. 1.1,1.3) and solids (Eq.1.1, Appendix B) iscalculated from basicphysical propertiesof the substance.The equations usedare on pages 15-18and 610 of the textbook.



Hearing Damage Risk (text, pp. 133-139)

Noise exposure. The table at the top of the panel (see below) is for specifying a noiseexposure environment for an individual or group of people for whom hearingdamage risk and allowed exposure time is to be calculated. All you need do is enterthe noise level in a particular area and the amount of time per day that the individualspends in that area. The total time need not add up to 8 hours.

The right hand panel, second from the top (see below) is for presenting the resultsof calculations of the traditional equivalent continuous noise level (Eq. 3.17, with

L(t) replaced by the A-weighted sound pressure level, LA(t)), the normalized (8 houraverage) continuous level (Eq. 4.2), the 8-hour Equivalent continuous level (Eq.4.39), the maximum allowed exposure time (Eq. 4.42) to a particular noiseenvironment that is specified in the table at the top of the screen and the daily noisedose (Eq. 4.43). There is an error in Eq. 4.43; the "Θ" should be replaced with an"8". (done in ENC) and for exposures greater than 8 hours, the "8" in Eqs 4.42 and4.43 should be replaced with the actual exposure time. The rules used for thecalculation are specified in the panel immediately to the left of the above panel andthis panel is illustrated below. The calculations done here are described in the texton pages 124, 142 and 143.



Hearing damage risk. The two panels, third from the top (see above) are forcalculating a group of people’s risk of hearing damage when exposed to theenvironment described in the table at the top of the panel. Alternatively a new valuefor LAeq,8h can be selected from the box in the left panel. Two calculation procedures(Eqs. 4.16-4.25 (ISO 1999) and Eqs. 4.26-4.30 (Bies and Hansen, 2003)) are usedand each is described in the text, pages 134-138.

The bottom two panels shown below allow the calculation of the daily noise dose forimpact and impulsive noise. The procedures are described on pages 145-148 in thetext. Enter values in three out of the four boxes and then double left click on thefourth box to get the result for the unknown quantity. Note that impulse noise



follows the USA 5dB trading rule for large numbers of impulses (text, fig 4.6). Notethat the figure in the text is slightly inaccurate but ENC is accurate.

Noise Level Criteria (text, pages 82-89, 100-102 , 150-151 and 154-163)

The top left panel on this page (see below) provides the opportunity to enter 1/3octave or octave band linear or A-weighted spectrum levels. If 1/3 octave band

levels are entered, they are converted to octave band levels prior to plotting and theresulting octave band levels are also included in the table in the bottom panel.However, there is one exception to this. If 1/3 octave NR curves are desired, then the“1/3 octave NR” button is clicked and the 1/3 octave band values are plotted togetherwith 1/3 octave band NR curves (which are the octave band NR curves shifted downby 4.8 dB (10 log 3).

Note that only the linear band levels are plotted. If the "A-weighting" switch isselected in the top left panel, the values in the table in the top left panel will be A-weighted values and will not be the ones that are plotted. The panel (including thefigure) can be printed by clicking on the "print" button below the figure. The "clearbackground curves" button is used to clear the NC, NR, NCB, RC or RNC curvesfrom the figure when they are plotted by clicking on the NC, NR, NCB, RC or RNCletters at the bottom left of the panel (see text, p.118-120 and ANSI S12.2).

Next to each curve rating number is a letter. “O” means “overrange - the data exceedthe highest permissible rating curve. “R”, “N” and “H” mean the sound isrespectively “rumbly”, “neutral” or “hissy”. It is possible to have “R” and “H”simultaneously but “N” will always appear alone. For RNC curves, the allowed rangeis between 10 and 50. If any octave spectrum value in the frequency range 63 Hz and



above exceeds the 50 curve, ENC writes “NA: >50" and if either the 16 Hz or 31.5Hz spectrum values exceed the black line, ENC writes “NA: noisy”. Also for RNCcurves, the values at 31.5 Hz, 63 Hz and 125 Hz must be corrected prior to plottingas outlined in the text book.

Note that for NR curves, both octave and 1/3 octave versions are available.

A plot of NR curves is illustrated in the figure below. Clicking on "y-axis setup" (seefigure below the graph) allows you to choose the y-axis maximum and minimumvalues.



Loudness (text, p82-89). The bottom left panel (see below) lists A-weighted levelscorresponding to the linear spectrum. A-weighted levels are calculated using the 1/3octave band linear spectrum, or the octave spectrum entered in the top left panel (andthe procedure in Example 3.1 in the text). If 1/3 octave band levels are entered in thetop left panel, they are converted to octave band levels for use in the bottom panel.If A-weighted levels are entered in the top left panel, then the corresponding linear

levels are calculated for the first line in the table below.

The loudness level in sones is calculated from the octave band data and in the topline in the table. The data in the top three lines of the table will appear on the graphat right if you click on the coloured button adjacent to the line of data which youwant plotted. The plot will have the same colour as the button you clicked on tomake it. Click on the button a second time to remove the curve from the graph.

Overall linear and dB(A) levels as well as loudness (sones and phons - Figures 2.9and 2.10 and Eqs. 2.32 and 2.33 in the text) are provided in boxes beneath the tablein the bottom left panel (see previous page). Note that the letters "PE" next to theloudness calculation indicate a "poor estimate" due to being out of the range of theformula (Eq. 2.32) that is used for the calculation.

Noise criterion curves. In the bottom boxes are NR (text, p.154-156), NC (text,p.156-157), RC (text, p.157-159, ANSI S12.2), NCB (text, p.159-160, ANSI S12.2)and RNC (text, p. 161-163) values corresponding to the spectra in the table. Theblue letter next to the NCB and RC values describe the character of the noise. "R"is rumbly, "H" is hissy, "N" is neutral and "RV" indicates that feelable vibrationexists. The letter "O" indicates that the spectrum exceeds the range of thecorresponding set of curves. It is possible for "R" and "RV" and “H” characters toco-exist. Any of the sets of curves corresponding to the 4 types of criteria mentionedabove can be made to appear on the graph by clicking on "NC", "NCB", "RC", "NR"or RNC characters immediately above the data boxes. Clicking the characters asecond time will make the curves disappear. NC, NR and RNC curves are notassociated with hissy /rumbly calculations. The frequency numbers to the right of the



NR box and the RNC box refer to the octave band where the level intersected thehighest NR or RNC curve.

Note that before the RNC plot is valid, appropriate corrections must be calculatedfor the 31.5 Hz, 63 Hz and 125 Hz octave bands by measuring time series data and

following the procedure outlined on pages 162 and 163 of thetext. The corrections can beentered by clicking on the"Corrections" button which willbring up the window shownbelow. Enter the values andthen click on "finished".

The next from bottom rightpanel (shown at right) is forcalculating speech interferencecriteria as described on pages 150-151 of the text book (and ANSI S3.14). You havethe choice of using the spectrum already entered at the left or you may enter a newA-weighted sound pressure level in the box.

Loudness Calculator. Thebottom right panel is a simplecalculator for convertingSones to Phons and vice-versa as described on page 86(Eq. 2.32) in the text book.

Weighting Networks (text, pages 44-49, 100, 101)

Spectral plotting. This window allows you to enter two octave or 1/3 octave bandspectra, apply A, B or C weighting to them and plot both the linear and weightedspectra. You can also add the two spectra together logarithmically or subtractspectrum 2 from 1. If a value in spectrum 2 is greater than or equal to a value inspectrum 1, then the result of the subtraction operation will be "-inf". The spectrum



values are entered in the appropriate table - the octave bandtable is shown above - the 1/3 octave band table is not shownhere but it is similar to the octave one.

The octave band results and weighting curves may both beplotted on the graph. You can select the curve you wish to plotby clicking on the appropriate coloured button beneath the graph. Clicking on thecoloured button a second time will make the curve disappear. The graph is illustratedbelow.



Note that you can set the plot limits to what is convenient and you can choose to plot1/3 octave or octave band data. There are always 10 horizontal divisions so theincrement from one horizontal division to the next will be the value you choose asthe maximum minus the value you choose as the minimum, all divided by 10. Thisis how you can force the dB scale values to what you want them to be.

You can add or delete each one of the five curves on the graph by clicking on theappropriately coloured button below the graph.

Noise Descriptors (text, pages 52-53, 124-126, 165, 172-173)

Occupational and environmental noise descriptors(text, p. 172-173) can be calculated using this windowby entering either hourly Laeq data in a table of (forenvironmental noise descriptors) or exposure time(hours) vs exposure level (dBA) in a separate table (foroccupational noise). The following page illustrates thetables that need to be filled in with data. Results arelabelled in blue font. Noise impact is calculated bydetermining how many people are exposed to particularranges of Ldn and then filling in the table at right (seetext, p. 172-173).



Flow resistivity and flow resistance (text, p. 52-53) of a specified thicknessof a fibrous porous material can be calculated using the panel on the centre right ofthis window (see below) by entering the density of the material and the fibres makingit up together with the fibre diameter. The "material thickness" label in ENC refersto the bulk material thickness. The "constants" button is used to set ambienttemperature and speed of sound parameters.

Speech privacy (text, table 4.9, p165) between two spaces separated by apartition can be estimated using the panel illustrated below. Enter the 1/3 octaveband transmission loss value for the partition separating the two spaces of interestand then enter the ambient sound level (dBA) in the receiving room (containing thelistener).


3.

Sound Sources and SoundPower (Module 2)

Overview

The software in module 2 is concerned with the calculations in Chapters 5 and 6 ofthe text. The software is divided into 3 separate windows, each of which is discussedbelow and each of which is represented by a unique icon on the tool bar. Simplyclick on the appropriate icon to select the window you want.

Sound Sources (text, pages 128-157, 193-196)

This window allows you to calculate the sound pressure level at a specified distancefrom a sound source ignoring the effects of excess attenuation and the presence ofreflecting planes, which are calculated on the "sound propagation" window. Thetypes of source considered are monopole, dipole, quadrupole, line and vortexshedding. The relationship between source volume velocity and sound power isdependent on the source type. Clicking on the "Constants" button allows you to setthe speed of sound and gas density for the calculations - see pages 4 -5 for a fulldescription. IMPORTANT: you must set the frequency and speed of soundbefore proceeding with any calculations in this panel (see below). Clicking on the"constants" button allows you to calculate the speed of sound by specifying thedensity, temperature and ratio of specific heats (1.4 for air).

Monopole, Dipole and Quadrupole sources (text, pages 175-188). For a specifieddistance from the source, you can calculate the relationship (equations 5.13, 5.30 and5.48-5.50) between the source volume velocity (Q), the sound power level (PWL)and the sound pressure level (SPL) (as shown below). Simply enter in any one ofthese quantities, then for the distance, r, shown, the other two quantities will becalculated. For the dipole and quadrupole sources, the volume velocity, Q, is the

24Chapter 3: Sound sources and sound power (module 2)


volume velocity of each of themonopoles making up the source.For the dipole source, you also needto define the distance, 2h, betweenthe monopole sources making up thedipole and the angle, θ, at which thesound pressure is measured. Forthe quadrupole source, which ismade up of 2 dipole sources, youneed to define the separation, 2h,between the monopole sourcesmaking up each dipole and thedistance, 2L, between the two dipolesources. You also need to enter theangle, α, between the axis of the twodipoles making up the quadrupoleand the quadrupole axis, as well asthe angles, θ and ψ, that define thelocation of the sound pressuremeasurement. If the angle, α = 0,then you have a longitudinalquadrupole and if α = 90 degrees,you have a lateral quadrupole.

Radiation from a vortex impingingon a rigid body in flow (text, p.184). Here Eq. 5.41(b) is evaluated.You may enter Sound power level,power in watts or force exerted bythe vortice on the downstream body.ENC will then calculate the othertwo quantities. The 1/K factor is 9for Curle's prediction, 3 to describesome experimental data reported by Zinoviev and Bies and 1 for a vibrating spheresolution (that is, the downstream body vibrates rather than being subject to a vortex).



Line source (text, pages 188-192).For the line source (see next page),there are 4 types of basic source,incoherent infinite, coherent infinite,incoherent finite and coherent finite(equations 5.63, 5.66, 5.69 and5.70). Each source may be eithercontinuous or made up of discretesources. You must choose theoption that suits your application.An example of a continuous sourceis a pipeline and an example of adiscrete line source is traffic. If theline source is finite in length andmade up of discrete monopoles, thenyou need to specify the separation distance, b, betweenadjacent monopoles, one of the angles, (αl or αu) subtendedby the source at the observation location and 2 out of 3 ofthe quantities: normal distance, r, from the source axis tothe observer; length, D, of the line source; and the otherangle (αl or αu) not already entered. Note that for a source of infinite length, thesoftware ignores the input data mentioned above, except for the (closest) distance,r, of the observer from the source axis and the source separation, b. Once the abovedata are entered, you can enter either the sound pressure level (dB) at themeasurement location (observer) and read the source sound power level or enter thesource sound power level and read the sound pressure level (dB) at the measurementlocation.

For a finite length coherent source, at distances greater than 0.5D, the calculation isthe same as for an incoherent finite length line source. For small distances (< 0.1D)from the line source axis, the calculation is the same for an infinite coherent linesource. At in between distances, linear interpolation (dB vs distance) between theabove two cases is used.

Radiation field (text, pages 249-251). As we move further from a sound source, wemove from the near field to the far field. The near field is made up of ahydrodynamic part and a geometric part. This panel (see below) indicates whichtype of field the observer is in for a specified frequency, source size and distancefrom the acoustic centreof the source. Thefrequency is entered inthe top right panel.



Plane Sound Sources (text, pages 192-204)

This panel calculates sound radiation fields for plane piston sources and also planerectangular incoherent sources. IMPORTANT: you must set the frequency andspeed of sound before proceeding with any calculations in this panel (use the topright panel). Clicking on the "constants" button allows you to calculate the speedof sound by specifying the density, temperature and ratio of specific heats (1.4 forair).

Incoherent plane radiator (text,pages 200-204). This calculation(done in the left panel of thewindow) assumes that the source isan incoherent radiator, mounted in alarge baffle and radiating from onlyone side. It is not for singlefrequency modal radiation, but is agood approximation for broadbandsound radiation.

To calculate the relationshipbetween the sound power radiated bya plane source and the soundpressure at the measurement point,you need to specify the distance ofthe centre of the source from theorigin of the coordinate axes, whichin turn are defined as being parallel to each of the two sides of the rectangular sourceand normal to its surface. The observer is assumed to lie in the plane formed by thevertical and normal axes and the source is assumed off-set from this plane along thehorizontal axis by a distance, d. The location of the observer (or measurement point)is defined by a distance, r, along the normal axis (see figure). You also need to enterthe dimensions, H ×L, of the plane source and the height, h, of the receiver above thebase of the rectangular source. If the source is not rectangular in shape, then you willobtain excellent results by approximating it as a rectangular source of the same area.Having input the data, you can enter either the sound pressure level (dB) at theobserver location and read the source sound power level or enter the source soundpower level and read the sound pressure level (dB) at the measurement location(calculated using Eq. 5.104).

Coherent piston source (text, pages 200-204). For a plane source vibrating with auniform velocity amplitude (U), this panel allows you to calculate the sound powerlevel, the sound power in watts, the on-axis sound pressure amplitude in Pa (Eq.*p*5.89) and the sound pressure level (dB) at distance r from the plane surface, thephase of the sound pressure (relative to the surface velocity), and both the real and



imaginary parts of the radiationimpedance (Eq. 5.95) which is theradiation efficiency multiplied by

. The normalised radiationπa 2ρcimpedance which is numerically thesame as the radiation efficiency isplotted as a function of frequencyas shown below and the soundpressure level as a function ofangular location is also plotted (seenext page). Note that you can selectthe maximum and minimum valueson the y-axis by clicking on "y-axissetup" button under the graph.

The coherent piston source panelalso provides the far field soundpressure amplitude and level aswell as the sound intensity andlevel at a specified distance fromthe piston surface and specifiedangle θ, from the normal to thepiston surface (see figure at right).

Note the "Field" button on thesecond line under the figure. Thequantity to the right of this button tells you whether the specified distance, r (m) isin the far field or near field of the piston source (uses relations on page 250 of thetext book). If the location is in the near field, the far field parameters at the bottomof the window are "greyed out".



Radiation from a building (text, p.204). Thispanel allows you to calculate the sound pressurelevel at a distance, r, from a building. Thiscalculation assumes that the building is on hardground so the excess attenuation due to theground is -3dB. The distance from the buildingfor which the calculation is valid is greater thanthe maximum building dimension. Excess

attenuation effectswould have to beincluded using module2 - sound propagation.The excess attenuationdue to the ground (if itis not concrete orasphalt) could beincluded by calculatingit according to module2 and then subtracting3 dB.

Sound Propagation (text pages 217-244)

This panel calculates all of the excess attenuation factors of equation 5.165 in thetext and uses the result to calculate the sound pressure level at a distance from asource that is specified at the top of the "sound sources" window and repeated in thiswindow. You must enter the correct "distance from source" in the top left panel.The window is divided into three sections: left, centre and right panels. This windowalso allows calculation of plane and spherical wave reflection coefficients.



Left panel (source type).The left panel (illustratedat left) allows you toenter the distancebetween the source and

receiver and information about thesource type (constant power, constantvolume velocity or constant pressure andmonopole, line or plane) as well as any directivityeffects due to close proximity ofreflecting surfaces, EXCLUDING theground. Note that the reflecting surfacesmust be such that they do NOT block theline of sight from the source to thereceiver. It is assumed that the reflectingsurfaces are much closer to the sourcethan the receiver (by a factor of at least10). If the reflecting surface is closer tothe receiver than this, the sound level atthe receiver must be calculated by addingthe contribution of the reflected wavewith that of the direct wave(incoherently) as done in Module 1 ofENC. If the source is a constant volumevelocity source and less than a quarter ofa wavelength from the reflecting plane,

then select "constant volume velocity source" and the DIm value will be 6dB for eachreflecting surface (as the reflecting surface will increase the power of the source by3 dB as well as the directivity by 3dB - see discussion at the beginning of Chapter6 in the text). If the source is an aerodynamic constant pressure type and closer thanone quarter of a wavelength to the reflecting surface, select "constant pressureaerodynamic source" and the DIm value will be 0 dB. If the source is of constantvolume velocity type or constant pressure type and further than a quarter of awavelength from the reflecting surface, select "constant power source". For constantpower sources, the distance from the reflecting surface is not important as long as itis less than 1/10 of the receiver distance.



You also need to enter whether the source is approximated by a monopole, linesource or plane radiator. Depending on the source type selected, various parametersneed to be entered to fully define it as shown on the panel.

Centre Panel (excess attenuation). The centre panel (top part shown below)contains calculation results culminating in the sound pressure level at the receiver fora known source sound power level. You need to enter in the top section of the centrepanel (see below) the sound power level of the source in octave bands (dB) and thesource directivity index, DIM, (dB), which does NOT include directivity due to theground. If you have selected "calculating DIm with below" in the top left panel, thenthe appropriate quantity for DIM will be entered by ENC into the middle panel in therow labelled "DIm (dB)". If you have a situation where there are additionaldirectivity effects due to the sound source characteristics, then you should unselect"calculating DIm with below" so that is greyed out and manually enter the directivityvalues in the middle panel near the top. The values you enter will also include theeffect of any nearby reflecting surfaces but will NOT include the effect of the ground.This is included in the "ground effects" section.

The top part of the table (see above figure) evaluates the right side of Eq. 5.158 inthe text except for the excess attenuation part. The constant K in that equation isdependent on the source type that you selected in the left hand panel and thepresence or otherwise of reflecting surfaces that you specified in that panel.

Clicking on the "Constants" button (see preceding figure) allows you to set the speedof sound and gas density for the calculations - see pages 4-5 for a full description.

The second to top panel in the centre section (see next page) evaluates the OCMAexcess attenuation model described in the text on pages 222-224 as shown below.This model only applies to a point source in the ground plane and allows only twotypes of barrier shielding, K2_m for minimal shielding (figure 5.16 in the text) andK2_s for significant shielding (Fig. 5.17). You must click on the appropriate box toensure that the correct shielding is selected for your particular case. The value ofsound power from the top centre panel is used with Eq. 5.166 to find Lp (dB).



The bottom half of the centre panel (see below) shows results for excess attenuationcalculations using various prediction schemes described in the "right panel" (see nextpage) and implemented by entering the correct parameters in that panel. You mustselect the excess attenuation to be included by clicking on the appropriate box andmaking sure a tick appears in the box. The line second to bottom of the table is thesound pressure level (Lp in blue type) at the observer, calculated using equation5.158, which includes the excess attenuations, Aa plus those corresponding to theticked boxes subtracted from the third line of the table at the top of the window. Thetwo total sound pressure level boxes at the bottom of the table give overall dB anddB(A) levels at the receiver location. The line at the bottom of the table only appearswhen the ISO calculation is chosen for meteorological effects. In this case it is notalso possible to tick the box above corresponding to meteorological effects as thisis already taken into account.



Note that the ground effect attenuation is not included separately when barrierattenuation is included, except for the ISO9613 case. This is because for all casesexcept the ISO case, it is included in the barrier excess attenuation. Also, ifmeteorological effects (wind and temperature gradients) are included in the barriercalculation, they should not also be added separately.

The "plot" button allows you to obtain a graph of the sound pressure level at thereceiver as a function of octave band centre frequency. You can choose the maximumand minimum values for the y-axis scale by simply typing the value you want intothe appropriate box at the bottom of the graph (see figure below).



Barrier attenuation calculation panel (text, pages 235-236, 398-399). If you clickon the blue Ab(dB) button on the left column of the above table, a new screen (seenext page) will appear in place of the table. This screen is designed to allow you tocalculate the attenuation corresponding to a particular barrier configuration.

The configuration used in the calculations is illustrated below. When you click on

"NOTE", a message will appear toexplain the location of the origin of thecoordinate system as shown below.

As noted in the figure above, the z-axisis normal to the ground surface andparallel to the plane of the barrier andthe y-axis is parallel to the ground surface and the barrier surface. The coordinatesof the source and receiver as well as the top corners of the barrier are entered in thetable at the bottom of the window as illustrated at right. Note that the ground heightis the height at the base of the barrier. It is assumed that the ground height isconstant between source and receiver. Negative values of z are not allowed for anyparameter.



Before undertaking a calculation, you must enterthe particular barrier diffraction model you wish touse from a total of 4 different choices as shown inthe figure at right. Then, depending on thediffraction model chosen, you will need to enterthe type of wave (plane cylindrical or spherical) orthe type of source (point incoherent line orcoherent line). The spherical wave of theMenounou model is equivalent to the point sourceof the Maekawa model and the cylindrical waveMenounou model is equivalent to the coherent linesource of the Maekawa model. The ISO and Kurzemodels provide the same results for any source orwave type.

The barrier thickness can also be entered at thebottom right of the screen (see text, page394). Forthe ISO method, this thickness is taken intoaccount by using a double diffraction model. Inthis case, the second diffractionedge is on the receiver sideseparated from the first edge by thenumber entered as the thicknessparameter. You can also enter theheight of the second barrier here.For barrier attenuation calculationmethods other than the ISOmethod, the effect of the barrierthickness on the insertion loss iscalculated using Eq. 8.98 and Fig.8.17.

If the barrier is a building greater than 10 m high, the excess attenuation term, Ag,which is the ground effect in the absence of the barrier, is omitted from Eq. 8.101.In most cases, this means that the barrier will be slightly less effective than if theterm were included. In any case, you have a choice here, you can click on th box toselect the option or not select the option which removes the Ag term from Eq. 8.101.This is explained on page 400 in the text book.



The calculation of the barrier attenuation requires a knowledge of the sonic gradient(text, pages 398-399, Eqs 5.190, 8.100) and this in turn is dependent on the windgradient which in turn is dependent on the ground cover. So it is necessary to enterthe ground cover type for the wind gradient calculation separately from the groundtype for the ground reflection calculation. Apologies for the different list of groundtypes here, but that is what is available in the literature and in each case, you willneed to select the one that best matches your situation. The radius of curvature, R (inmetres) (see Eq. 5.190) of the sound wave going over the top of the barrier as a resultof wind and temperature gradients and the value of the exponent ξ (see Eq. 5.186 andTable 5.6) are provided for your interest in blue font at the bottom of the barrierpanel (see below).

A negative radius of curvature implies that the sound rays will be curved upwardsand the resulting barrier attenuation will increase. This is in contrast to the decreasein barrier attenuation which occurs when there is a positive radius of curvature andcorresponding downward curved rays. Wind and temperature gradients are taken into



account automatically if you enter a non-zero value for the wind speed ortemperature gradient. The procedure calculates an effective source height based onthe sound ray curvature calculated from the wind and temperature gradients. If theeffective source height is less than zero, it is set equal to zero. Interestingly, the effecton the overall attenuation of the barrier is not great in most cases. You need to enterthe wind speed at 10m and the temperature gradient in degrees C per 1000m (seefigure on previous page).

It is IMPORTANT to note that the barrier noise reduction will not be accurate untilyou have entered the wind speed at a specified height (speed component in thedirection from the source to the receiver - negative values represent a componentblowing from the receiver to the source) and temperature gradient. However, youmay exclude the effect of a sonic gradient by entering zero for the wind speed andtemperature gradient.

As the barrier attenuation depends on the type of ground either side of the barrier,you must first choose the ground type from the "ground type" menu located in thepanel below the barrier figure. Just click inside the box and a menu of ground typeswill pop up as shown at right.

Note that you can also define your own ground surface by clicking on the "Selfdefined" item at the bottom of the menu. When you do this the box below pops upand all you need do is enter the flow resistivity of the ground surface in MKSRayls/m and then click on "finished".

You also need to select which ground model you want to use (the hard/soft modelfor which the reflection loss is 3 dB or 0 dB respectively; the plane wave reflectionmodel - Eq. 5.129; or the spherical wave model without turbulence - Eq. 5.133). Itis not possible to include turbulence in the barrier attenuation model here. Thereflection loss is -20log(Rp) or -20log(Rs). The effect of paths around all sides of thebarrier as well as attenuations due to reflections from the ground are included in thefinal attenuation value you find in the table. For each path the attenuation iscalculated using Figs. 8.13 & 8.14, and Eqs. 8.85 & 8.88. The ISO method is not yetavailable. For paths involving ground reflections, the loss due to that is also added



to the barrier attenuation. The attenuations for each path are combined together togive an overall barrier excess attenuation using Eq. 1.97 in the text. Note that Eq.1.97 requires the calculation of a reflection loss for when no barrier is in place. InENC, if the barrier is closer to the receiver than the source, the ground properties forthe source side of the barrier are used and if the barrier is closer to the source thanthe receiver, the ground properties for the receiver side of the barrier are used. Theactual reflection loss will be a bit different to the equivalent one with the barrier inplace due to the different angle of incidence of the sound with the ground. If youclick the box that asks if the barrier is a building more than 10 m high (or if thesource is more than 10 m above the ground), the reflection loss without the barrieris set at infinity (implied by ISO9613-2). When you have entered the barrierparameters, click on "back" to return to the table and you will see the barrierattenuation entered in the correct place in the table.

The window for calculating the speed of sound and other parameters can be can beactivated by clicking on the "constants" button.

After all of the barrier parameters have been entered, click on "run" in the tool barand the 1/3 octave band attenuations will appear plotted on the graph to the left ofthe screen. Octave band results are output on the table beneath the graph (see nextpage). The octave band results are averages of the three third octave bands makingup the particular octave band.



Attenuation due to housing (text, pages 226-227). This panel (shown below) isactivated by clicking on the "Ah(dB)" button on the left side of the centre panel. The

attenuation due to housing is calculated according to ISO 2613-2 (1996). Thequantities r1 and r2 represent the distances that the sound rays actually travel throughbuildings and these quantities are affected by the radius of curvature of the soundwave. To be able to estimate r1 and r2, it is necessary to use ENC to calculate theradius of curvature and then do a scale drawing similar to that done for theattenuation due to forests and shown in the figure on the next page. Note that the"percentage of the length......" data box should only be non-zero for road or rail noisewhere houses are in defined rows.

Attenuation due to process equipment (text, page226). This panel (shown below)is activated by clicking on the "Ap(dB)" button on the left side of the centre panel.The attenuation due to process equipment is calculated according to ISO 2613-2

(1996). The quantities r1 and r2 represent the distances that the sound rays actuallytravel through buildings and these quantities are affected by the radius of curvatureof the sound wave. To be able to estimate r1 and r2, it is necessary to use ENC tocalculate the radius of curvature and then do a scale drawing similar to that done forthe attenuation due to forests and shown in the figure above.



Attenuation due to forests (text, page 227-228). This panel (shown below) isactivated by clicking on the "Af(dB)" button on the left side of the centre panel. Theattenuation due to forests and foliage is calculated according to ISO 2613-2 (1996).The quantities r1 and r2 represent the distances that the sound rays actually travelthrough trees and these quantities are affected by the radius of curvature of the soundwave. To be able to estimate r1 and r2, it is necessary to use ENC to calculate theradius of curvature and then do a scale drawing similar to that shown in the figurebelow. Data shown in ENC corresponding to Eq. 5.172 are for information only andare not used in other ENC calculations.



Right panel (air absorption, ground and meteorological effects). The right handpanel is where the calculations of excess attenuation due to air absorption, groundeffects and meteorological effects are carried out.

Air absorption effects. The excessattenuation due to air absorption, Aa, iscalculated using the panel shown at right(Sutherland’s method). All that is needed isthe air temperature and relative humidity(see text, Table 5.3).

Ground effects. The excess attenuation due toground effects, Ag, may be calculated usingany one of four methods as described onpages 228-233 in the text (see panel at right).In the ground effects panel, you need to enterthe source and receiver heights and thehorizontal separation distance between thesource and receiver. All that are needed (inaddition to the source/receiver separation) arethe source and receiver heights above theground and the flow resistivity of the groundsurface (see Table 5.2, page 209 for somerepresentative values of flow resistivity). Thedistance, L, is calculated from the source andreceiver heights and the distance, r, given in the leftpanel near the top. Alternatively, if L is entered, rwill be calculated by the software. You then need tochoose which of the four ground effect calculationmethods are to be used. The detailed results for eachof the 4 methods may be obtained by clicking on the "Results" button or clicking on"Ag" in the centre panel. When you do this, the window on the next page appears.In this window, all equations from the text which are used in the calculations areidentified.

For the "plane wave" method, the ground effect is calculated by estimating the planewave reflection coefficient. The reflection coefficient is calculated for the two casesof local reacting ground and extended reacting ground. You are able to selectwhether you wish the calculations to assume extended reaction ground or locallyreacting ground If unsure, use the extended reactive model.

Values of reflection coefficients and the ground effect in dB averaged over 10 singlefrequencies in each octave band are shown in the table. Values of reflectioncoefficient (both locally reactive and extended reactive) are listed for any frequencyyou specify in the box beneath and to the left of the table. Also are shown, values of



the transmission coefficient (Eq. 5.132), complex propagation constant (Eq. C.4) andcomplex characteristic impedance of the ground (Eq. C.3). These latter quantities area function only of the flow resistivity of the ground.

For the "spherical wave" method, the ground effect is calculated by estimating thespherical wave reflection coefficient. The reflection coefficient is calculated for bothextended reaction and local reaction models and also for turbulence included in orexcluded from each model. You are also able to select whether you wish thecalculations to assume extended reaction ground or locally reacting ground as wellas whether to include turbulence or not. If unsure use "extended reactive withturbulence". The relevant equations are on pages 213-217 in the text book.Calculations averaged over 10 single frequencies in each octave band are shown inthe table and values corresponding to a single specified frequency are shown to theright of the table. The desired frequency is selected by typing it into the box abovethe reflection coefficient values for single frequencies.

The quantity, Φ, of equation 5.156, which is used to calculate the turbulenceparameter and is displayed in the table illustrated on the previous page. For Φ > 1.0,incoherent reflection from the ground is assumed and equation 5.171 is used tocalculate the ground effect. For Φ < 0.1, coherent reflection is assumed. For0.1 < Φ < 1.0, the reflection is somewhere between coherent and incoherent.However, the coherent reflection equation 5.182 is used for Φ < 1.0.



For the ISO method, the ground effect is calculated corresponding to the values ofthe G parameters that you enter as well as the source / receiver layout. Note that foreach region (source, mid and receiver), the value of G is the fraction of ground in theregion which is soft and values vary between 1.0 and 0. The method is explained onpages 230-232 of the text.

The "simple method" is explained on page 230 of the text and results in a groundeffect (or excess attenuation) of -3 dB for hard ground and 0 dB for soft ground. The“CONCAWE” method is encapsulated in Figure 5.19 in the text.

Meteorological effects. The excess attenuation, Am, due to meteorological effectsmay be calculated using one of six different methods and the panel shown below.



Detailed results for all methods are available when you click on "Am" in the centrepanel, which results in the window below popping up.

The first model for calculating the excess attenuation due to meteorological effectsis based on a calculation of the atmospheric sonic gradient from your input of theatmospheric temperature gradient (which can be negative as well as positive, withpositive representing a temperature inversion or increasing temperature withincreasing altitude), wind speed, and height at which the wind speed was measured(preferably 10m). These data are entered in the panel shown above. Note that thewind speed is positive if blowing from the source to the receiver and is theproportion of the wind vector pointing from source to receiver.

Note that the type of ground also needs to be selected from the drop down menu(shown at right hand part of the panel shown above) as this affects the sonic gradient.The empirical constant from Table 5.6 in the text is used to calculate the sonicgradient caused by the wind gradient.



The calculated sonic gradient is used together with interpolation/ extrapolation oftable 5.7 on page 240 in the text to give the excess attenuation due to meteorologicaleffects for the wind and temperature conditions that you entered.

The second model is based on the CONCAWE method described on pages 239-243of the text. The required input data are the time of day and wind speed at groundlevel (usually 1.8 metres height) and is the proportion of the wind vector pointingfrom source to receiver. For daytime, the incoming solar radiation value is requiredand for nighttime, the extent of cloud cover (with 8 octas being overcast and 4 octasbeing half cloudy) is required. These are selected from the dialog boxes illustratedon the previous page. The temperature gradient value is not used in this calculation.

The third and fourth models are simply a restatement of table 5.10 in the text.

The fifth model is specified by ISO 9613-2.

The sixth model is only applicable to upwind propagation and is based on shadowzone theory as outlined in the text book on page2 237 and 238.

Detailed results for all methods are shown in the pop up panel that appears when youclick on "Am" in the centre panel of the main window (see above figure).

Sound Power (text, pages 253-272)

This panel enables you to calculate machine sound power levels from sound pressuremeasurements for a range of test methods. The test methods are divided intoanechoic room, reverberationroom, field and near field. Eachof these are discussed below. Thecalculation can be done for anyfrequency by entering appropriatevalues into this panel or it can bedone for all octave bandssimultaneously by clicking on"octave".

Free and semi-free field (text,pages 254-258). For measurements in free orsemi-free field, equations 6.8 and 6.9 in thetext are used. The average sound pressurelevel measured on a test hemispheresurrounding the source is entered in the panelalong with the test hemisphere radius.



The average sound pressure level is calculated from a number of discretemeasurements using Equation 6.9, which is evaluated in the "Easy SPL averager"panel shown below. Clicking on the "Constants" button in this figure allows you toset the speed of sound and gas density for the calculations - see pages 4 -6 for a fulldescription.

Reverberant field (text, pages 258-260). The two distinct methods for determiningthe sound power level from reverberant field measurements are described in thefollowing paragraphs.

The substitution method (text, page260) involves placing a referencesource of known sound power level inthe octave or 1/3 octave band ofinterest in the room and measuringthe resulting sound pressure level.The reference source is then replacedwith the source to be tested and thesound pressure level is measuredagain. Equation 6.12 in the text isthen implemented in this panel todetermine the sound power level forthe tested source.

The absolute method (text, page 260)involves measuring the roomreverberation time with the machine tobe tested in place and measuring thesound pressure level in the room withthe machine in operation. There is adialog box at the top asking whetherthe tests are in octave bands, 1/3 octavebands or discrete frequencies. Theroom volume and total area of allreflecting surfaces (including the roomboundaries) must also be entered. Thelowest frequency at which the test willprovide valid results is calculated bythe software using the discussion onpages 258 and 259 of the text.

Octave band data can be calculated and plotted by clicking on "octave" at the top ofthe panel. When you do this the windows shown on the next page appear. The graphautomatically plots the selected spectrum. You can adjust the upper and lower limitsof the plot to suit your data.



Field Measurement (text, pages 261-269). There are three choices of method formaking far field sound power measurements on a machine in-situ. These are eachdescribed below. The calculation can be done for any frequency by enteringappropriate values into this panel or it can be done for all octave bandssimultaneously by clicking on "octave" which produces the windows shown on thenext page.

The reference source method (pages261-262) uses a reference source ofknown sound power output and thecorresponding measured soundpressure level averaged over the roomvolume to determine the room constant(with the test machine switched off).This is then used with the soundpressure measurements with only thetest source operating to determine thesound power level of the test source.Note that this method requires that allother equipment in the room be turnedoff during the measurements. The"location" information (see drop downmenu at right) is needed so that thepresence of 1 or more reflecting planeson the sound pressure level can betaken into account. This is done byadding 3dB to the direct fieldcomponent for each reflecting plane.

The substitution method (page 263)essentially replaces the test machinewith a reference sound source of knownsound power level. The sound pressuredue to the machine and then due to thesubstituted reference source operatingalone are then used to calculate thesound power of the machine (text,equation 6.19).

The two test surfaces method (text,pages 263-265) involves taking soundpressure level measurements over twotest surfaces that completely surroundthe machine. The area of one test surface should be at least twice that ofthe other.



Near field measurement (text, pages265-269). This method evaluatesequation 6.25 and allows the user toselect one of three possible ways ofdetermining the value of the constant,Δ1. The three methods are discussed indetail in the text and each requiresdifferent input data. The methodsdecrease in reliability from the top of thepanel to the bottom. The method at thetop of the panel requires sound pressurelevel measurements on two test surfaces,with the larger test surface having atleast twice the area of the smaller one.The next method uses knowledge of theroom surface area and average Sabineabsorption coefficient to calculatecorrection term, Δ1. Module 3 can beused to find the average absorptioncoefficient for cases where they aredifferent for each of the room surfaces.The third method uses the values inTable 6.4 in the text. The constant, Δ2 iscalculated using the values in Table 6.3in the text. The panel used for thecalculations is shown at right.

The calculation can be done for any frequency by entering appropriate values intothis panel or it can be done for all octave bands simultaneously by clicking on"octave" which produces the window shown on the next page.



Determination of sound power fromsurface vibration measurements(pages 269-271). This panel (shown atright) effectively evaluates Equation6.31 in the text for sound radiationfrom a simply supported steel oraluminium panel. The calculation canbe done for any frequency by enteringappropriate values into this panel or itcan be done for all octave bandssimultaneously by clicking on "octave"which produces the window shownbelow.

The most difficult parameter to estimateis the radiation efficiency, so this panelcan only be used for sound radiationfrom rectangular shaped panels. Inpractice, most machine and enclosurepanels have edge conditions that maybe approximated as simply supported.For the radiation efficiency calculation,instead of using the somewhatinaccurate figure on page 270 in thetext, equations from page 295 of therevised edition of Beranek’s Noise andVibration Control book (see also text,pages 309-310) have been used, asthese are the corrected versions of the original Maidanik equations.

For clamped plate radiation efficiency calculations, the fundamental resonancefrequency, f11, for clamped plates is set equal to Q*f11 for simply supported plates,where Q=1.83 for a square plate, Q=1.89 for a=1.5b, Q=1.99 for a=2b, Q=2.11 fora=3b, Q=2.23 for a=6b, Q=2.25 for a=8b and Q=2.26 for a>=10b, where a and b arethe plate dimensions. Interpolation is used to calculate f11 for in between values ofthe a/b ratio. Also for clamped edge plates in the frequency range below fc, the



radiation efficiency is set as 3 dB higher than that calculated for a simply supportedplate (equations on page 309-310 of the text).

As input data, you must enter the frequency of interest and either the space averagedacceleration or the space averaged velocity. If acceleration is selected, velocity iscalculated by the software and vice versa. You must also enter the longitudinal wavespeed in the panel and the panel area, thickness and perimeter. The outputs are thepanel radiation efficiency (or radiation ratio), the critical frequency and the radiatedsound power. The radiated sound power is plotted in the window that appears whenyou click on "octave" (see figure below).

To see a plot of the radiation efficiency as a function of frequency for the panel youhave specified, click on the "Plot" button and the figure shown below appears.



Easy SPL AveragerTo find the energy average of a number of sound pressure level or sound power levelmeasurements (or any dB measurements), enter the number of measurements ofinterest and the dB values of each in the table (see discussion under free fieldmeasurement).


4.

Room Acoustics and SoundAbsorption (Module 3)

Overview

This software may be accessed by choosing "module 3" from the "options" dialogbox. The software automates all of the calculations in Chapter 7 of the textbook aswell as the calculations implicit and explicit in Appendices C, D and E. Thetreatment is divided into sections, each of which are represented by a unique icon inthe tool bar. To access a particular section, just click on the appropriate icon in thetool bar. Each section will be described in the text to follow.

Room Modal Properties

This section calculates modal properties of rectangular and cylindrical rooms. Thewindow is divided into two sections, each of which is discussed below.

Rectangular room. This section calculates the first 100 resonance frequencies andmode type (axial, tangential or oblique) for a rectangular room of any shape. It alsoapplies to long and flat rooms. Mean free path, crossover frequency (from modalresponse to diffuse response), number of modes in a band, modal density at the bandcentre frequency, modal overlap (see page 282-284 in the text) and spatial standarddeviation of the SPL (Eq. 7.25) are all calculated. Note that you have a choice asto how many modes are needed to be resonant in a defined band for the sound fieldto be considered diffuse (usually between 3 and 6) for the purposes of calculating thecross-over frequency. For noise of a bandwidth narrower than 1/3 octave the cross-over frequency should be defined as when the modal overlap is equal to 3. You needto select this criterion by clicking on the pop-up box beneath "mean free path"

Entering the reverberant field sound pressure level allows you to calculate timeaveraged energy density and time averaged intensity for sound travelling in any givendirection (Eqs. 7.32 and 7.33 respectively). The bandwidth used for calculating thenumber of modes can be selected in terms of Hz or as octave or 1/3 octave. Do notchange values in boxes with no arrows at the side.

Chapter 4: Room acoustics and sound absorption (module 3) 56


Clicking on the "Constants" button in the following figure allows you to set thespeed of sound and gas density for the calculations of the entire window - see pages4 -5 for a full description.

Note that at the top of the left and right panels, blue typeface indicates whether or notthe room dimensions satisfy the Sabine room criterion that no dimension should bemore than three times any other. For non-Sabine rooms, the last 4 items calculatedat the bottom of the table may be inaccurate. Note that these last terms do not includeany contribution from the direct fields of the sound sources contributing to the soundfield.



f (nz , m , n) 'c2

nz

R

2

%ψmn

a

2

Cylindrical room. These rooms are not discussed in the text, although there is anexample problem in the "Example Problems in Engineering Noise Control" book byC.H. Hansen.

For the cylindrical room, the same expressions as used for a rectangular room areused for calculating mean free path (Eq. 7.34), cross over frequency, number ofmodes within a band , modal density (Eq. 7.21), modal overlap, spatial standarddeviation (Eq. 7.25), time averaged energy density (Eq. 7.32) and effective timeaveraged intensity (Eq. 7.33). Note that for a cylindrical room, the effectiveperimeter, L, is given by L = 4(πa + R), where R is the cylinder length and a is theradius.

The mean free path calculation is accurate as Eq. 7.34 in the text applies to anyshaped room. The other calculated quantities are only approximate as the formulaestrictly only apply to rectangular shaped rooms. However, experience shows theapproximations to be good ones.

The cross-over frequency is calculated on the basis of the specified number of modesin a band (3 to 6 for 1/3 or octave band analysis) or a modal overlap greater than 3for narrower bands. The number of modes in a band is calculated using Eq. 7.20.

For a cylindrical room, the resonance frequencies are given as:

where nz is the number of axial nodes, R is the cylinder length and a is the cylinderradius.

The characteristic values ψmn are functions of the mode numbers m, n, where m is thenumber of diametral pressure nodes and n is the number of circumferential pressurenodes.

Values of ψmn are given in the following tables. The quantity nz is the number ofnodal planes normal to the axis of the cylinder.

Note that the expressions for mode numbers and modal density are approximate onlyand become more accurate as the room shape becomes more irregular. However,even for rooms of regular shape, the actual mode number and modal density fluctuateabout the theoretical prediction plotted as a function of frequency and the predictionbecomes more accurate as the frequency increases.



Values of ψmn

m\n 0 1 2 3 4

0123456789

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0.00000.58610.97221.33731.69262.04222.38772.73043.07093.40963.74684.08284.41784.75185.08515.41775.74976.08116.41216.74257.07267.40227.73168.06058.38928.71769.04589.37369.7013

10.0287

1.21971.69712.13462.55132.95473.34863.73534.11654.49314.86595.23555.60235.96676.32906.68947.04817.40527.76108.11558.46888.82109.17239.52269.8721

10.220710.568610.915811.262311.608211.9535

2.23312.71723.17343.61154.03684.45234.86005.26155.65766.04946.43726.82177.20317.58197.95848.33268.70499.07549.44439.8116

10.177610.542210.905511.267811.629011.989112.348312.706613.064113.4208

3.23833.72614.19234.64285.08155.51085.93256.34776.75747.16247.56337.96058.35448.74549.13379.51969.9032

10.284910.664611.042611.419011.793912.167412.539512.910413.280113.648714.016214.382714.7483

4.24114.73125.20365.66236.11036.54946.98117.40657.82638.24148.65239.05949.46309.8636

10.261310.656511.049311.439911.828512.215212.600112.983413.365213.745414.124314.501914.878315.253515.627616.0007



Values of ψmn (Cont.)

m\n 5 6 7 8 9

0123456789

1011121314151617181920212223242526272829

5.24285.73456.21126.67577.13057.57698.01638.44958.87749.30069.7194

10.134510.546110.954511.360011.762912.163312.561412.957413.351413.743514.133914.522714.909915.295615.680016.063016.444816.825417.2049

6.24396.73687.21667.68568.14558.59769.04319.48279.9170

10.346710.772211.193911.612112.027112.439212.848613.255513.660014.062314.462614.861015.257515.652416.045616.437316.827617.216417.604017.990318.3754

7.24487.73858.22078.69319.15719.6139

10.064310.509110.948811.384011.815012.242312.666213.086813.504613.919614.332014.742115.150015.555815.959616.361616.761817.160317.557317.952818.346818.739519.130919.5210

8.24548.73999.22399.6990

10.166410.626911.081411.530611.974812.414712.850513.282613.711414.136914.559614.979515.396915.811916.224616.635317.043917.450717.855718.259018.660619.060819.459519.856820.252720.6474

9.24599.7409

10.226410.703811.173911.637712.095712.548512.996713.440513.880514.316814.749815.179615.606616.030916.452616.872017.289117.704118.117018.528118.937419.345019.750920.155320.558220.959621.359721.7585




m\n 10 11 12 13 14

0123456789

1011121314151617181920212223242526272829

10.246310.741711.228611.707812.180212.646713.107613.563714.015214.462614.906115.346115.782916.216616.647417.075517.501217.924418.345418.764319.181219.596220.009320.420820.830621.238821.645522.050822.454722.8573

11.246611.742412.230312.711113.185613.654314.117914.576715.031215.481615.928416.371716.811817.248817.683118.114718.543918.970619.395219.817620.238020.656621.073321.488321.901622.313322.723523.132323.539723.9457

12.246912.743013.231813.714014.190114.660915.126715.588016.045116.498316.947817.394117.837218.277318.714719.149519.581820.011720.439520.865221.288821.710622.130522.548822.965323.380323.793724.205724.616325.0255

13.247113.743514.233114.716415.194115.666616.134416.597917.057317.512917.965118.413918.859719.302619.742820.180520.615721.048521.479221.907922.334522.759223.182223.603424.022924.440924.857325.272325.685926.0981

14.247314.744015.234215.718616.197616.671717.141217.606618.068118.525918.980419.431619.879920.325320.768121.208321.646222.081722.515122.946523.375823.803324.229024.653025.075325.496025.915226.333026.749327.1643




m\n 15 16 17 18 19

0123456789

1011121314151617181920212223242526272829

15.247515.744416.235216.720417.200617.676118.147318.614419.077819.537619.994120.447520.898021.345821.790922.233522.673823.111823.547723.981524.413524.843525.271725.698326.123226.546526.968327.388627.807528.2250

16.247716.744717.236017.722118.203418.680119.152719.621420.086420.548121.006521.461921.914522.364322.811623.256423.698924.139224.577425.013625.447825.880226.310926.739827.167127.592828.017028.439728.861129.2810

17.247817.745018.236818.723619.205819.683720.157520.627721.094321.557622.017722.475022.929423.381223.830424.277324.721925.164325.604626.043026.479426.914027.346927.778028.207628.635529.062029.487029.910630.3328

18.247918.745319.237519.724920.208020.686921.161921.633422.101422.566223.028023.486923.943024.396624.847725.296525.743026.187426.629727.070127.508527.945228.380128.813429.245029.675130.103630.530830.956531.3809

19.248019.745520.238120.726221.210021.689822.165922.638623.107923.574124.037324.497824.955525.410825.863626.314126.762427.208627.652828.095128.535428.974029.410929.846130.279730.711831.142431.571531.999332.4257




m\n 20 21 22 23 24

0123456789

1011121314151617181920212223242526272829

20.248120.745721.238721.727322.211822.692523.169623.643324.113824.581325.045925.507825.967026.423826.878327.330427.780428.228328.674229.118329.560430.000830.439530.876631.312131.746032.178532.609533.039133.4674

21.248221.745922.239222.728323.213423.694924.172924.647725.119325.588026.053826.517026.977727.435927.891828.345528.797129.246629.694230.139830.583731.025831.466231.905032.342232.777933.212233.645034.076434.5066

22.248322.746123.239623.729224.214924.697225.176025.651726.124326.594127.061127.525627.987528.447128.904429.359629.812630.263630.712731.159931.605432.049132.491132.931633.370533.807834.243834.678335.111435.5433

23.248423.746324.240124.730025.216325.699226.178826.655427.129027.599828.067928.533528.996729.457629.916230.372630.827131.279531.730032.178732.625733.070933.514533.956534.396934.835935.273435.709536.144336.5778

24.248424.746425.240525.730826.217626.701127.181527.658828.133328.605129.074329.540930.005230.467330.927131.384931.840632.294432.746333.196333.644734.091434.536434.979935.421835.862336.301336.739037.175337.6103




m\n 25 26 27 28 29

0123456789

1011121314151617181920212223242526272829

25.248525.746626.240826.731527.218827.702928.183928.662029.137329.610030.080130.547831.013231.476431.937432.396332.853333.308333.761534.212934.662635.110635.557036.001936.445336.887237.327637.766838.204538.6410

26.248626.746727.241227.732228.219928.704529.186229.665030.141130.614631.085631.554332.020732.484932.947033.407033.865234.321434.775835.228535.679436.128736.576537.022737.467437.910638.352538.793039.232239.6700

27.248627.746828.241528.732829.221029.706130.188330.667831.144631.618932.090832.560433.027733.492933.956034.417134.876435.333735.789336.243136.695337.145837.594838.042338.488338.932839.376039.817840.258340.6976

28.248728.746929.241829.733430.221930.707531.190331.670432.147932.623033.095633.566134.034334.500434.964535.426735.886936.345336.802037.257037.710338.162038.612239.060939.508139.953940.398340.841441.283141.7237

29.248729.747030.242030.733931.222831.708832.192132.672833.151033.626834.100234.571435.040535.507535.972536.435636.896937.356337.814138.270138.724539.177339.628640.078540.526840.973841.419441.863742.306742.7485



The cylindrical room panel is illustrated below.

Note that at the top of the left and right panels, blue typeface indicates whether or notthe room dimensions satisfy the Sabine room criterion that no dimension should bemore than three times any other. For non-Sabine rooms, the last 4 items calculatedat the bottom of the table may be inaccurate. Note that these last terms do not includeany contribution from the direct fields of the sound sources contributing to the soundfield. All the items shown in the figure above are fully described in the "rectangularroom" section immediately preceding this section.



Sound in rooms

This section calculates sound pressure levels and reverberation times in rooms of anyshape. It is divided into two main sections. The section including the left hand sideand bottom of the window applies to the steady state sound field in a room and isused to relate the sound pressure level to the sound power level for sound sources inthe room for various types of room. It is also used to calculate direct field andreverberant field sound pressure levels for specified source sound power levels.

The panel on the right of the window applied to transient or decaying sound fieldsin rooms and is used to relate absorption coefficients to reverberation times forvarious room types.

Steady-state response. This section is divided into three panels: Sabine rooms, flatrooms and long rooms. Each will be discussed in turn below.

Sabine Rooms (steady-state response). This panel (located at the bottom of thewindow and shown below), is intended for Sabine rooms; that is, rooms whosedimension in one direction is no greater than three times the dimension in any otherdirection. Given the source sound power level and room properties (entered in thepanel by the user), the total, direct and reverberant sound pressure levels may becalculated at any given distance from the source using Eqs. 7.40 to 7.42 in the text.

Any one of the quantities, "room constant", "average Sabine absorption coefficient"or "T60" may be entered and the other two will be calculated automatically. However,choosing T60 values that are too small can result in unreasonable values for thereverberant sound field level. The average Sabine absorption coefficient and totalroom surface area may be calculated using the table in the "Transient response"panel. Alternatively, the reverberant field sound pressure level may be entered and



the corresponding average absorption coefficient and reverberation time will then becalculated.

Clicking on the green button duplicated at right, results in thewindow below popping up , which is used to calculate soundabsorption coefficients from reverberation time measurementsin a reverberation room. Measured reverberation times may beinput with and without absorbing material and the absorbingmaterial area is also input. Then two equations are used tocalculate the absorption coefficient. Eq. 7.75a gives an exactresult and Eq. 7.75b in the text gives the result according tomost current national and international standards (labelled"standard"). The min and max boxes beneath the graph allow you to change the scaleon the graph y-axis. You can also select which absorption coefficient curve todisplay.



Flat Rooms (steady-state response). A flat room is one for which two dimensionsare more than three times the third dimension. Both reverberant and direct soundlevels are calculated in a flat room for a specified distance between the source andreceiver and a specified source sound power level for various reflection conditionsof the floor and ceiling. The results provided by the software follow the analysis onpages 311-321 in the text.

Where the floor and ceiling are either both specular reflective or both diffuselyreflective, results are only provided for cases where the source and receiver are



located mid-way between the floor and ceiling. For specularly reflecting floor andceiling, Eq. 7.91 is used for the reverberant field and for diffusely reflecting floor andceiling where the two reflection coefficients β1 and β2 are equal, Eq. 7.101is used,otherwise Eq. 7.97 is used. For the calculations corresponding to the case of onesurface diffusely reflecting and the other specularly reflecting, equation 7.111 in thetext is used for the reverberant field for r/a > 1 and Table 7.2 is used for r/a < 1.Thisresults in up to 2 dB error in the region of r = a. The direct field is calculated usingEq. 5.13(b). Remember not to change values in boxes without arrows on the sidesas these are results boxes and not input data.

Long Room (steady-state response). A long room (see next page) is one for whichone dimension is more than three times greater than the other two. Both reverberantand direct sound levels are calculated in a long room for a specified distance betweenthe source and receiver and a specified source sound power level for variousreflection conditions of the side walls, floor and ceiling. The results provided by thesoftware follow the analysis on pages 322-327 in the text. Remember not to changevalues in boxes without arrows on the sides as these are results boxes and not inputdata. Where line sources are considered, they are assumed to occupy the full widthof the room and be orientated perpendicular to the room axis. All calculations arefor the source and receiver to be on the main axis of the tunnel-shaped space. Forthe case of a circular cross-section room and specularly reflecting walls and a pointsource, Eq. 7.112 is used to calculate the direct and reverberant sound pressures andfor the case of specularly reflecting walls and a line source, Eq. 7.114 is used. Fora circular cross-section, a point source and diffusely reflecting walls, Eq. 7.116 isused for the reverberant field and Eq. 5.13(b) for the direct field.

When a square cross-section room is selected, the value entered for the height is alsoused for the width and the width value is ignored. For a rectangular section room forwith specularly reflecting side walls and diffusely reflecting floor and ceiling andeither a point source, Eq. 7.119 is used to calculate the reverberant field component



and the term outside the brackets in Eq. 7.115 is used to calculate the direct field.

Transient Response. This panel (right side of the window and illustrated below)calculates reverberation times and average absorption coefficients for any shaperoom, given the room volume and surface area and the absorption coefficient of allroom surfaces (in tabular form, associating each area with a particular absorptioncoefficient). You may also add absorption areas that are not necessarily room walls,floor nor ceiling. For calculations using the Sabine formula (equation 7.51 in thetext), the absorption coefficient entered in the table must be the Sabine absorptioncoefficient. For calculations using the Norris-Eyring or Millington-Sette equations(7.56 and 7.57 in the text) or the Kuttruff non-Sabine room (equation 7.63 in thetext), the absorption coefficients entered in the table must be statistical coefficientsand none can be greater than 0.95. If they are, then they are set equal to 0.95 priorto the calculations. The final result can include air absorption (Eq. 7.37) if you tickthe indicated box.



Clicking on the "Constants" button allows you to set the speed of sound and gasdensity for the calculations of the entire window - see pages 4 -6 for a fulldescription.

Clicking on the green box labelled, "Reverberation calculations using Fitzroy andFitzroy-Kuttruff equations" results in the window shown below (and continued onthe following page) popping up. In this window, the room volume, surface areas ofopposite walls and total wall/ceiling/floor surface area are calculated from the roomdimensions. The average sound absorption coefficient of opposite walls in the roommust be entered as well. With these data ENC will calculate the room reverberationtime using two alternative empirical equations for Sabine type rooms and anotherempirical equation for flat or long rooms (one dimension less than or greater thanthree times the other two). The two equations for the Sabine room correspond to Eq.(7.59) (Fitzroy equation) and Eq. (7.60) (Fitzroy-Kuttruff equation) and the equationfor flat or long rooms corresponds to Eq. (7.64) (Neubauer equation) in the text.These equations are often preferred by practitioners for architectural spaces as theyseem to give more accurate results than obtained with equations derived from firstprinciples. Note that the room dimensions that are selected will determine whichresults are available. This if the room dimensions are such that it is a Sabine room,the flat and long room calculations will be "greyed out" and not accessible.



Clicking on the "back" button will return you to the main screen.



Porous Material Sound Absorbers

This window calculated random incidence absorption coefficients and normalimpedances of fibrous acoustic material. The user may choose between flowresistance measured data or impedance tube measurements as the basis for thecalculations by clicking the switch illustrated below.

Calculations based on flow resistance data. These calculations are explained in fullin Appendix C of the text. The calculations involve calculating in octave bands, thestatistical absorption coefficient associated with a porous acoustical material with orwithout the following:• backing cavity (can be specified as partitioned or non-partitioned)• impervious protective covering (such as plastic sheet)• perforated panel (assumed to be spaced from the impervious covering with a mesh

(at least 2mm thick and 13mm size squares).

You may choose any one or more of the above options simultaneously and when theinput data are correct, the "run" symbol in the tool bar may be clicked on to producea result. A partitioned backing cavity is one for which solid partitions normal to thesurface of the sound absorbing material divide the backing cavity. The partitionsmust be closer together than half a wavelength at the highest frequency of interest.The impervious membrane may be defined in terms of speed of sound and densityor selected from a list. You must enter the membrane thickness. For the perforatedpanel, you must enter the hole diameter, % open area and whether the holes arestaggered or parallel. The hole spacing and density are then calculated by thesoftware. You may also choose whether you wish the porous acoustic material to betreated as locally reactive or non-locally reactive.

For a simple layer of fibreglass or rockwool, you have a choice of calculationmethod. The Bies and Hansen method first calculates the characteristic impedanceand propagation constant for the material using Eqs. C.3 to C.15 in Appendix C ofthe text. The other method available is the Delaney and Bazely method which isinaccurate at high and low values of flow resistance. For both methods, you must



enter whether the material is locally or bulk reacting (as this affects the statisticalabsorption coefficient calculation), the material flow resistivity (defined page 53 ofthe text) and the material thickness (see preceding figure).

The next choice to make is whether the material is backed by a cavity which in turnhas a rigid termination (see figure below). If the "backing cavity" option is notselected, ENC will assume that the material is backed by a rigid wall. For thiscalculation, the impedance used in Eq. 5.131 is the normal impedance calculatedusing Eq. C.41.

Note that for a material that is infinitely thick, the specific normal acousticimpedance is equal to the characteristic impedance. For a locally reactive material,Eq. 5.131 is used with Eq. C.36 to calculate the statistical absorption coefficient, fora given mounting condition. For an extended reaction (or bulk reacting) material,Eq. 5.131 is replaced with Eq. 5.129 and 5.130.

Calculations in this panel are based on some constants with assumed values.Clicking on the "Constants" button (see above figure) allows you to set the speed ofsound and gas density for the calculations of the entire window - see pages 4 -5 fora full description. Note that the value for viscosity is also used here.

If the material is backed by a cavity, then you must enter the backing cavity depthand whether it is partitioned or non-partitioned (see following figure). If non-partitioned, then the angle of incidence of the incoming sound must be entered. Forthese cases, Eqs. C38-C41 are used to calculate the normal impedance that is usedin Eq. 5.131. For an extended reaction (or bulk reacting) material, Eq. 5.131 isreplaced with Eqs. 5.129 and 5.130.

For a porous acoustic material covered in a limp impervious membrane (such aspolyethylene - see figure below), the normal impedance used in Eqs 5.129 or 5.131

is calculated using Eq. C.42. You must click on the smallsquare box in this panel, enter the layer thickness and select amaterial from the list (see figure at right). If your material isnot in the list, select the "self defined" button and enter thematerial density.



If a perforated sheet is added (spaced away from an impervious membrane if oneexists), you need to click on the empty box labelled "if covered with a perforatedpanel facing" and enter whether the holes in the panel are circular or non-circular.If circular, you need to enter the diameter and if non-circular, you need to enter thehole aspect ratio, area and perimeter. Next, enter whether the hole pattern is parallelor staggered. ENC will calculate the distance between holes. Next select theperforated panel material type from the list. If your material is not there, select "selfdefined" and enter the material density (see figure below). Finally, enter theperforated panel thickness (mm) and the Mach number of any grazing flow acrossthe perforations.

If a perforated sheet is added, then the specific normal impedanceused in Eqs. 5.129 or 5.131 is calculated using Eq. C.43 in the text,where the effective length of the holes is given by Eq. 9.25.

Note that calculation of the effect of the perforated panel inENC is only valid for a panel open area of less than 20%. Also,the condition fL/c < 0.1 must be satisfied, where L is the depthof backing cavity behind the perforated sheet.

The total number of holes calculation is only accurate if the aspect ratio of the holesos close to unity. For other aspect ratios, the estimate will be incorrect. However,only the % open area is used in the sound absorption calculations, not the numberof holes.

As well as the final result of statistical absorption coefficient being produced, anumber of intermediate results are also provided (see following figure). You mayselect any frequency for which you desire to know impedance or statisticalabsorption coefficient values.



Calculations based in impedance tube measurements. All of the impedance andstatistical absorption coefficients described above can also be calculated usingstanding wave measurements made in an impedance tube. The switch on the top leftof the window is set to "Impedance tube measurements". Then enter the measureddata (standing wave ratio, Lo and distance, D1, from the face of the test material ofthe first minimum sound pressure level in the tube) for each octave band centrefrequency in the table reproduced here below. The equations used to calculate thenormal impedances and statistical absorption coefficients for each octave band centrefrequency are C30-C37 in the text book.

Clicking on the "Constants" button allows you to set the speed of sound and gasdensity for the calculations of the entire window (including those based on flowresistance measurements) - see pages 4 -6 for a full description.

Calculation summary and results presentation. The absorption coefficientscalculated using either method are also provided in a table of values correspondingto octave band centre frequencies (see figure below). The table also provides the

NRC value for the material. You can switch between normal incidence and statisticalabsorption coefficient, and the values shown in the table depend on the position ofthe flow resistivity/impedance tube switch at the top of the window.For convenience there is an NRC calculator at the bottom right of the window whichcan be used with any known values of absorption coefficients for the octave bandcentre frequencies, 250 Hz to 2 kHz (see below).



All of the calculated quantities are also available for display as a graph for octaveband centre frequencies from 31.5 Hz to 8 kHz (see following figure). The screencan be dumped to a printer or to the clipboard and/or the numerical results can besaved to a file for later use by a spreadsheet program such as Excel. If dumped to theclip board (by pressing the "print Scrn" key on your keyboard), you can cut out theparts you need for a report using software such as Corel PhotoPaint (which producesexcellent results).

The y-axis maximum andminimum values can also be set byclicking on "y-axis setup" asshown at left.



Panel Absorber

This section is for the calculation of sabine absorption coefficients produced by asound absorber made using a solid panel. There are two ways of doing thecalculation. One relies on an empirical model and is based on figures 7.8 and 7.9 inthe text (3rd edition). The other method is analytical (text, p. 308-310) but requiresmuch more detailed knowledge of the characteristics of the room and the panel usedas the absorber. Both methods provide values of Sabine absorption coefficient. Forthe empirical method, all that is needed is the desired frequency of maximumabsorption and the corresponding absorption coefficient (see following figure).

Clicking on the "Constants" button (see above figure) allows you to set the speed ofsound and gas density for the calculations of the entire window - see pages 4 -5 fora full description.

For the analytical method, the data indicated in the figure on the next page must beinput. The required input data are either the room dimensions or its volume, surfacearea and perimeter. In addition, the room reverberation time, the absorbing panelmaterial, absorbing panel area, thickness, perimeter and reverberation time as wellas the number of panels must be entered. The statistical absorption coefficient iscalculated using Eq. 7.82 in the text. The panel radiation ratio is calculated usingequations from pages 309-310 in the text. For clamped plate radiation efficiencycalculations, the fundamental resonance frequency, f11, for clamped plates is set equalto Q*f11 for simply supported plates, where Q=1.83 for a square plate, Q=1.89 fora=1.5b, Q=1.99 for a=2b, Q=2.11 for a=3b, Q=2.23 for a=6b, Q=2.25 for a=8b andQ=2.26 for a>=10b, where a and b are the plate dimensions. Interpolation is used tocalculate f11 for in between values of the a/b ratio. Also for clamped edge plates inthe frequency range below fc, the radiation efficiency is set as 3 dB higher than thatcalculated for a simply supported plate (equations on page 309-310 of the text book).For the analytical calculation, a number of useful intermediate results are provided(see figure on the next page).



For both calculation methods, the octave band values of the Sabine absorptioncoefficient are included in the table (see following figure) and the valuecorresponding to any frequency can be obtained by typing the desired frequency intothe "single frequency" box (preceding figure and also figure below) and reading the

corresponding Sabine absorption coeff. in the "Absorpt. coeff. " box.



The absorption coefficients are also provided in graphical form. The graph reflectswhat is indicated by the switch, "Analytical Method / Empirical Method" in theabove figure. The screen can be dumped to a printer and/or the numerical results canbe saved to a file for later use by a spreadsheet program such as Excel. The empiricalmethod seems to give more realistic results. The graph shows 1/3 octave band resultsas well as octave band results and values can be read accurately using the cursor.Maximum and minimum values for the y-axis are user selectable. For the analyticalcalculations, the 1/3 octave band results are calculated using the correspondingoctave band reverberation times which represents an approximation, albeit a goodone.



Applications

There are two applications of reverberation and sound absorption for whichcalculations are provided. The first application (see below) provides a rough guide(equation 7.121 in the text) for estimating optimum reverberation times in anoccupied auditorium subject to various uses and a class room (both occupied andunoccupied). The optimum octave band values of T60 are plotted on the graph andincluded in the table and the value corresponding to any frequency can be obtainedby typing the desired frequency into the "single frequency" box and reading thecorresponding reverberation time in the "Optimum T60 " box (see figure below). Theoptimum reverberation time at 250 Hz is set at 10% above the value calculated usingequation 7.121 in the text. At 125 Hz it is 50% and at 63 Hz it is 100% and at 31.5Hz it is 120%. For the optimum reverb times in occupied classrooms, the discussionfollowing Eq. 7.121 in the text is used and for unoccupied classrooms, the optimumreverberation time is calculated from that for an occupied classroom using Eq. 7.122in the text.



The second calculation (see below) allows three quantities of interest for an occupiedauditorium to be calculated from the measured quantities in an unoccupiedauditorium (most applicable to a concert hall). The quantity of interest may beselected from t he drop down menu and the choice is between early decay time,clarity and total sound pressure level.

The third calculation (see below) allows one to estimate the reverberant field noisereduction as a result of adding a fixed amount of absorption (Eqs. 7.120 and 7.43 inthe text). Remember, only type in boxes with black numbers in them. In the table,you can enter either the room constant or the room average Sabine absorptioncoefficient but not both. You need to click on "Run" for the calculation to proceedafter you have entered the appropriate numbers in all the boxes.

The fourth calculation (see next page) allows actual reverberation times in auditoriato be calculated with a reasonable degree of accuracy using Eq. 7.124 in the text anda knowledge of the average absorption coefficients for the bare auditoria and also forthe treated surfaces (and corresponding areas). The total absorption for each memberof the audience and number of people in the audience also need to be entered for



each octave band. The default absorption coefficients used in ENC are generallyaccepted values for seated people.

In the bottom right of the section is a calculator (Eq. 7.78) for averaging soundabsorption coefficients (see figure below).


5.

TL, Enclosures, Barriers &Pipe Lagging (Module 4)This module allows you to do the calculations described in chapter 8 of the text.There are separate windows (and sections below) for single partition transmissionloss (isotropic and orthotropic), double partition transmission loss, compositetransmission loss, enclosures, outdoor barriers, indoor barriers and pipe lagging. Allwindows have the same left hand panel, which is illustrated on the next page. Foreach type of calculation, the results appear plotted on the graph, either as 1/3 octaveband or octave band data. The octave band values (which are averages of thecorresponding 1/3 octave bands) are listed in the table below the figure. There area number of aspects associated with the figure that are worthy of note.• A number of curves can be plotted on the figure simultaneously, allowing you to

observe the effect of changing some parameters. However, to plot more than onecurve on the figure, the "overlap" button at the bottom of the figure must be"ON". If it is "OFF", only the curve corresponding to the current data in the rightpanel will appear when the "run" icon is clicked on in the tool bar.

• Each curve can be assigned a unique colour using the "color" button beneath thefigure.

• The cursor may be turned on so that the 1/3 octave band levels can be readaccurately for each frequency. For cases such as the TL for composite panelswindow, the cursor will only read octave band values as these are the only inputdata available. The frequency and graph TL value corresponding to thatfrequency are displayed in boxes beneath the figure. To make the cursor registerwhen it is first turned "ON", it is necessary to click somewhere on the figure andthis is also how you move the cursor around. Note that if the cursor is "OFF",these numbers have no meaning.

• The STC as well as the ISO single number descriptors, Rw, C and Ctrcorresponding to the TL curve are given in a box beneath the figure. Thesedescriptors apply to the curve which has the cursor on it rather than the last onedrawn. However, if the cursor is never turned on, the descriptors apply to the lastcurve drawn. If the cursor is turned on and then off, the descriptors will apply tothe curve where the cursor was located prior to it being turned off.

• Clicking on "Clear" beneath the figure clears all curves from the figure.• Clicking on "Save" will prompt the user for a file name to which the data

corresponding to the current screen will be saved. These data can then beimported into Excel.

Chapter 5: TL, Enclosures, Barriers and Pipe Lagging (Module 4) 84


• Double clicking on the graph will save it to the clipboard from where it can bepasted into any application.

• Clicking on "Print" will result in the screen on the next page being printed.

In some cases the cursor may not display the same value as in the table below thefigure. This is because the cursor value is a 1/3 octave band value and the tablevalue is an octave band value, which is the average of three 1/3 octave band values.

In all windows of this module (except the "Composite" and "Enclosure"windows), you will find a button, labelled "Constants". Clicking on this bringsup a window that allows you to set the speed of sound and gas density for thecalculations - see pages 4 -5 for a full description.



Partition Transmission Loss (Single wall) (text, pages 281-289)

In this calculation, you have a choice between an isotropic (uniform) panel and anorthotropic panel (stiffened or corrugated). The window allows you to calculate theTL of a single partition that is isotropic or orthotropic and which has one or morelayers (or leaves) of the same material connected rigidly of viscoelastically. There isalso provision for different materials to be used in a two leaf panel (select "compositematerial" provided that the two different materials are rigidly connected). For eachpanel type, there is a choice of two different models for the calculations. Theadvantages of each model are outlined below.

Isotropic Panel. For the isotropic panel, you canchoose between the Sharp and the Davy models.The latter model is considered more realistic andis dependent on the area of one side of the panel.As the Sharp model does not depend on panel area, thisquantity is "greyed out" when the Sharp model option isselected. The model currently selected is displayed on thebottom right of the screen (see figure to right). Note that thepanel critical frequency is displayed in the green box at thebottom of the screen. Click on "Constants" (see figure below) to set the speed ofsound in air to be used in the calculations.



There are two lists of materials (current list displayed in the "Selectmaterial/config.window and in the window to the right of this box) that you can loadby clicking on "file" in the tool bar and then "open" or by clicking on the "open file"icon that is second from the left beneath the tool bar. The list, "material_list1.enc"is from Appendix B in the text and "material_list2.enc" is from the internet.

The TL is calculated for the panel material that is highlighted in the "selectmaterial/config" box. You will notice that you can change the material properties ofthe currently selected material by typing in values in the appropriate boxes. You canproceed with the calculation with the new material properties and you can also savethem by clicking on "file" then "save" or "save as".

To enter properties of a new material, you must click on the "insert material/config"button to obtain the screen shown below, then name and define a new material withthe properties you want. Do not worry about "greyed out" items. Click on"finished" when you have finished entering the material properties and you willreturn to the main panel where you can run the TL calculation. Note that the newmaterial is added to the bottom of the current materials list when you click on"finished". You can then save the new list to a new file by clicking on "file" in thetool bar and then "save as" or you can click on the "save" button to overwrite theexisting file.

Be careful with the "delete material/config" button as it will delete the materialhighlighted in the "select material" box from your current working file. If you do not"save" the file or save the file as a different name, then you can still retrieve theoriginal data by clicking on "open" in the tool bar. You can also retrieve the lastdeletion by clicking on "undo" in the "Edit" menu. If you wish to save your newmaterials property list as a new file click on "file" in the tool bar and then "save as".



The calculations for the Sharp analysis use Eqs. 8.2, 8.3, 8.36 and 8.38 in the texttogether with the procedure described under Figure 8.8. For the Davy analysis, Eqs.8.39-8.41 are used. Note that the TL values calculated using the Davy analysis andSharp analysis deviate from one another around the panel critical frequency.Experimental data agree better with the Sharp analysis for values of loss factor nearthe low end of the expected range whereas the Davy analysis agrees better withexperimental data for values of loss factor near the low end of the expected range.

Multi-leaf walls describesingle walls that aremade up of single panelseither nailed or gluedtogether or held togetherwith viscoelastic material such as silastic. These wallshave the same weight as a wall made up of a singlepanel equal to the combined thicknesses of theindividual panels. However, the critical frequency for the multi-leaf wall, withflexibly connected leaves of identical material, is equal to that of the thickest leaf, sothe TL behaviour of the two wall types is very different. The connection type caneither be "flexible", "visco-elastic" or "rigid". If "flexible" (ie connected by a gridof glue spots or even nailed), the loss factor is doubled over that of a single panel.If "visco-elastic", the loss factor is set equal to 0.2. The word "rigid" used here refersto panels bonded so tightly together that they behave as a single panel. In this case,ENC automatically uses the total thickness and mass of the panel rather than thethickness of the thickest leaf, in the calculations of critical frequency and TL.

For the other two connection types (flexible and visco-elastic), the data specified inthe data box apply only to the thickest leaf and the critical frequency calculation isbased on these data. Note that this part of ENC can only calculate the TL forconstructions for which the leaves are made of identical material, but the leaves donot have to have the same thickness.

Composite material wall. If it is desired to calculate the TL of a panel made up oftwo leaves of differentmaterial and if thematerials are rigidlyconnected, then it isnecessary to use the"composite material" boxshown at right, whichproduces results based onEqs. 8.7, 8.8, and 8.9 inthe text.

Clicking on this tick box will automatically bring up



the two layer titles above the data boxas shown on the figure on the previouspage. Note that the “loss factor” line inthe two column table is greyed outbecause you need to enter the value forloss factor of the compositeconstruction in a second box as shownon the previous page.

Clicking on the arrow at the top ofeither column will produce a pop uppanel to allow you to select the materialproperties for each layer as shownbelow on the right. You can modify anymaterial properties and you can alsoadd a new material for either layer 1 orlayer 2 by following the proceduredescribed on the previous page andmaking sure that the "compositematerial" box is ticked. However, don'tforget to save these new materials to thelist before exiting this window byclicking on "file", "save as". Then youwill be able to use these data later.

Note that an estimate of the loss factorfor the composite construction must beentered.

It is possible to have composite andmu l t i - l e a f o p t i o n s s e l e c t e dsimultaneously. When this is done, itmeans that each leaf in the multi-leafconstruction is made up of two layers,each of a different material bondedrigidly together

You can add new materials to the layer1 and layer 2 lists by clicking on the"Ins material/config" button and then inthat window clicking on the "compositematerial" tick box and entering the dataas for a single leaf panel. The newmaterial name will appear in the "selectmaterial / config" window.



A number of intermediate calculations are provided as shown on the panel on theprevious page. Note that you need to enter the frequency for which you desire thebending wave speed to be calculated.

Orthotropic Panels. For the orthotropic panel, youcan choose between the Heckl model (Eqs. 8.3,8.10, 8.11, 8.5, 8.42-8.44 and the explanationfollowing them) and the Hansen model (Eqs. 8.3,8.10, 8.11 and 8.24-8.33). You can specify anypanel cross sectional profile by clicking on the green "more properties" button toproduce the screen shown below. Basically the idea is to define x and y coordinatesof each bend point (up to a maximum of 13) in the panel until they start to repeatagain. Note that both start and end points of the repeating cycle need to be defined.For curved sections, you can define several points on the curve and that will be agood enough approximation for the purposes of the TL calculation. The y-coordinateis normal to the panel surface and the x-coordinate is in the plane of the panel normalto the corrugations. After you have defined a panel profile, click on the "draw"button to see it drawn in the small window. You need to specify whether or not the



panel is covered with damping material by clicking on the appropriate button. Whenyou have finished specifying the panel profile, click on the "back" button to returnto the TL calculation. The TL is plotted out on the graph and octave band values aregiven in the table beneath the graph.

Note that multi-leaf, orthotropic panels are not considered here. However, it ispossible to use ENC to calculate the TL of a composite orthotropic panel made upof two leaves of different material bonded rigidly together. Although the calculationsare based on Eqs. 8.7, 8.8, and(8.9 in the text, some additional manipulations arenecessary in order to be able to use these equations for an orthotropic panel. Toderive the necessary relationships, Eq 8.7 is used to calculate the quantity, Beff whichis then substituted for B in Eq. 8.2 and an equivalent Young's modulus is thusobtained. This equivalent Young's modulus is then used in Eqs. 8.10 and 8.11 in thetext to calculate the two bending stiffnesses for the orthotropic panel. Again anestimate of the loss factor for the composite construction must be entered.

A number of intermediate calculation results are also provided as shown below.



Double Wall (text, pages 356-365)

For the double wall, the properties of each paneland the way the two panels are connectedtogether need to be specified. Also you have achoice of using either the Sharp or Davy models for the TL calculations. If the Davymodel is chosen, the surface area of one side of the wall must be entered as well. Forthe Sharp method, Eqs. 8.37-8.41 are used together with the procedure in the captionof Figure 8.7. For the Davy method, Eqs. 8.42-8.52 are used.

Both single and multi-leaf panels are allowed. Each panel making up the doublepanel may be a composite panel with each composite panel made up of two differentmaterials bonded rigidly together as for the single partition case. The panelmaterial/configuration can be selected by clicking on "layer 1" (and/or layer 2 if"composite material" is selected) and then selecting the desired material from the list(see figure below).

If the desired material is not there, then you can enter your own material by directlyediting the data table containing the properties of a material in the list. If you wishto save this new material to the list, then you can either save the new list to a new fileby clicking on "file" in the top tool bar followed by "save as" or overwrite the currentfile by clicking on "save". After selecting the material, you may choose the Davymethod or the Sharp method to calculate the TL for the double wall. Note that forthe calculations here using Davy’s method, the 1.8 empirical correction factormentioned in the equation for f0 on page 290 of the text has been excluded. Priorto doing the calculation, you must select the type of connection between the panels



by clicking on the "Panel/studconnection type" box at the topright of the screen (see image atright). A pop-up menu willappear if you click inside the boxrather than on the arrows to theleft of the box. See figure at rightfor the buttons corresponding toselection of the Sharp model.There are different buttons whenthe Davy model is selected.Other data must be entered asshown on the figure below.These data include gap between

the two partitions (panel separation distance)making up the wall, the stud spacing (distancebetween supports), whether the studs arewood or steel or something for which youknow the compliance (enter compliance ifknown). For steel studs the compliance used

by ENC is 10-6 m2/N and for wood it is 0. Note that the stud type is only needed if theDavy model is selected for the calculations.

Next, enter whether or not there is sound absorbing material in the cavity betweenthe two partitions. Note that acceptable sound absorbing material consists ofrockwool or fibreglass flexible batts, the thickness of which is at least 50% of the gapwidth between the panels. It is also assumed that the sound absorbing material isonly in contact with one of the two partitions making up the double wall.

Click on "Constants" to set the speed of sound in air to be used in the calculations.

When you are ready for the TL calculation to proceed, click on "run" in the tool barat the top of the window. The critical frequencies of each panel, the bendingwavespeeds in each panel at the frequency you specified and the frequencies, f0

(mass-air-mass resonance frequency), fc and f1 are given in the blue box at thebottom of the screen (shown on the next page).

The TL is plotted out on the graph and octave band values are given in the tablebeneath the graph.



Multi-leaf Panels. Note that multi-leaf panels are made up of leaves of the samematerial but not necessarily the same thickness. When the "multi-leaf wall" optionis selected (see image below), you must enter the total thickness of all the leavesmaking up one panel and then in the data boxes you need to enter the detailed datafor the thickest leaf as this is used to calculate the critical frequency of the panel. Asfor the single partition, if the rigid connection option is selected, the panel is treatedas a single leaf panel of thickness equal to the sum of the thicknesses of all theleaves.



Composite Material. The "composite material" option (see below) allows for panelsmade up of a maximum of two leaves but the leaves may be of different materials andthey must be bonded rigidly together. For this option the loss factor also needs to beselected. Note that if the multi-leaf panel is selected at the same time as thecomposite panel, then ENC will assume that each leaf in the multi-leaf panel is madeup of two layers, each of a different material, bonded rigidly together and you willthen need to enter the properties for each layer.

An example of the plotted results is shown on the next page.



STC, Rw and IIC (text, pp. 343-346)

This window allows the calculation of STC, Rw and IIC using either directly enteredTL or Ln data or from measurements of the sound pressure level in the receivingroom and also in the source room (for STC and Rw). In the latter case the averageabsorption coefficient of the receiver room is needed. This can be entered directly orreverberation times can be entered and ENC will calculate the correspondingabsorption coefficient.Choices of input data aremade by selecting from themenu shown at right or byclicking appropriate tick boxas shown below.

As shown in the figure above, it is also necessary to know the receiver room surfacearea and volume. This can be calculated by ENC from dimensions for a rectangularroom or entered directly.

Once the choices are made, the appropriate data must be entered in the appropriate1/3 octave and/or octave band table as shown below. Note that Lp, the spaceaveraged sound pressure level in the receiver room, must also be measured andentered in the table below if the calculated TL and Ln option is selected.

All of the above values apply to the receiverroom and only need to be entered if theoption, "Using calculated TL and Ln frommeasured Lp" is selected. Note that in orderto calculate TL, it is also necessary to enterthe test partition area (see text, Eq. 8.16).This is not needed for the impact isolationcase (see Eq. 8,19).



To calculate the TL from measured data, it is necessary to enter the space averagedsound pressure level, Li, that is measured in the source room so that NR can becalculated. The NR is the difference between Lp and Li and Lp (the average soundpressure level in the receiver room) must also be measured. The TL is then calculatedusing Eq. 8.16 in the text. The calculation of STC and Rw is done as described onpages 343 and 344 of the text.

If the "Using directly entered TL and Ln"option is chosen at the top of the window, thenyou only need to enter the TL values in thetable above in order to determine thecorresponding STC and Rw values. The STCvalues are the USA standard and they aresimilar to the Rw values which are calculatedaccording to the ISO standard. The maindifference between STC and Rw is that the firstcriterion on page 344 in the text does not apply to the ISO calculation. The otherdifference is that Rw is qualified by two correction numbers, C and Ctr that dependon the characteristics of the noise. However, the values of these correction terms alsodepend on the frequency range for which measured data are available, which is whyENC gives users a choice between 4 frequency ranges. However, the Rw value is thesame for all frequency ranges and is based on 1/3 octave band data for the frequencybands 100 Hz to 3150 Hz inclusive and octave band data from 125 Hz to 2000 Hzinclusive.

Note that only the ISO standard allows octave band calculations which is why STCis not listed for octave bands

To determine Impact Insulation Class (IIC), you can either used the measured Lp andabsorption coefficient values as for TL calculations or you can enter the Ln valuesdirectly into the table. Remember to select the option you want at the top of thewindow. The ISO equivalent to IIC is referred to as Ln,w. There is also a descriptormentioned in the ISO standard, which is based on the measurement of reverberationtime in the receiving room, which is called, LnT,w and ENC calculates this as well.



Note that only ISO allows use of octave band data to calculate the single numberdescriptor so no IIC value appears under the octave band table. The main differencebetween IIC and Ln,w is that the first criterion on page 346 in the text does not applyto the ISO calculation. Note that according to the relevant standards, all singlenumber descriptors are reported as values rounded to the nearest integer.

Composite (text, pages 366, 373)

The purpose of this calculation is to determine theoverall TL of a partition made up of severalsegments, all with different TLs (eg a wall with awindow and door), using Eq. 8.65 in the text. The firstthing to do is enter the number of elements withdifferent values of TL that you wish to combine toobtain an overall TL (see figure above right). Next youshould select whether you want to present octave bandor 1/3 octave band data on the graph (see figure at right). If youwish to work with 1/3 octave band values in the table, you mustclick on the "1/3 octave" button shown at right. Next the TL values (in octave or 1/3octave bands) for each segment are input into the table. The table for octave bands



is shown below and the one for 1/3 octave bands is shownabove on this page. The area of each segment is also inputin the right hand column in the octave band table and intoa separate table for the 1/3 octave band calculations(illustrated at right). Note the second to bottom line for bothoctave and 1/3 octave cases contains TL calculations for acrack which are done in the panel below this one (seeillustration below). The crack TL calculations may beincluded or excluded depending on whether the tick box isticked.

The total composite TL at the bottom of the table is plottedout on the graph on the left of the screen and as statedpreviously, you may select to plot octave or 1/3 octave bandvalues on the graph.

In the centre of the right side of this window is a calculator for determining the TLof a crack (see figure below). The TL is calculated using Fig 8.11 and Eq 8.12 as abasis. If the question, "Is the crack adjacent to a plane surface (eg under a door)?" isanswered yes, then the effective width of the gap is doubled when calculating the TLbut the actual width is used when calculating the crack area. Note that the crack TLvalues are automatically entered by ENC into the composite table illustrated on theprevious page.

At the bottom of the panel is a calculator for enabling you to calculate in bothdirections for a 2 or 3 element system (see next page). That is, you could determinethe required TL of a door, given the overall TL needed and the TL of the wall that



is to contain the door. Using this calculator is a bit complicated, but worthmastering. First you enter the areas of each element in the top line. Then you enterthe TLs that you know. If you know the total TL, but not one of its constituents, thento find the unknown TL, double left click on the box that is to contain it. If you wantto calculate the total TL after filling 2 or 3 of the constituent boxes on the left, thenjust click on the right pointing arrow. The same operation can be done with theareas, but note that the TL calculation only updates when clicking on the right arrow.For calculations based on knowing the totals and wishing to find one of theconstituents, the area and TL calculations must be done separately. It is notnecessary to click on "run" in the tool bar to use this calculator.



Enclosures (text, pages 375-387)

This panel is used to calculate the expectednoise reduction of an enclosure, given the TL of itswalls and its internal acoustic conditions. The internalacoustic conditions can be specified in terms ofabsorption coefficients (entered in the table at thebottom of the window) or in a general sense by clickingon the "Enclosure internal acoustic conditions" box asshown in the figure at right.

The noise reduction of the enclosure is then calculated using Eq. 8.79 in the text,where the quantity, C, is based on the selected enclosure internal conditions (Table8.4 in the text) and listed as "Correction (dB)" in the table below.

If the enclosure is lined with acoustically absorbing material, the TL of the enclosurewall will increase slightly at higher frequencies (see Table 8.3 in the text which islinearly adjusted for different thickness blankets). For a medium density blanket,ENC will include this effect in the NR value in the table above. The user may enterany thickness desired for the blanket - 50mm is shown as an example below.

The enclosure noise reduction calculation (Eq. 8.67) is performed by clicking on"run" in the tool bar and the result is displayed on the graph to the left of the screen.

When the internal enclosure conditions are "user defined", it is necessary for the userto enter the enclosure external surface area, “Ext. area, exclude floor (m2)”, as wellas absorption coefficients and corresponding surface areas (inside the enclosure) inthe table at the bottom of the screen (see next page). The correction is thencalculated using Eq. 8.71.

Note that the "number of internal elements" refers to the number of rows in the table(working from the top row downwards) that are to be included in the calculations.



In addition to calculating the enclosure noise reduction, it is also possible to getsound pressure levels on the enclosure outer surface (Lp1) or at some distant pointeither in free space or in a large room (Lp2), as well as at the same location withoutthe enclosure in place (Lp2p). You need to select from the menu, observation point= "outdoors" or observation point = "in a large building" (see below). If the latter ischosen, the building dimensions and the mean Sabine absorption coefficient must beentered. Note that none of these outdoor sound predictions include the excess

attenuation effects. If the observation point is more than 50 m from the enclosure,then it is necessary to include the excess attenuation effects by using module 2 andcalculating the enclosure radiated sound power by using the first 2 terms on the RHSof Equation (8.72) in the text.

You can also apply a directivity factor (NOT directivity index) to the source insidethe enclosure (to be used for calculations for the "no enclosure" case) or a directivityfactor may be applied to the enclosure sound radiation itself. You also need to enterthe distance, R(m) of the observer from the enclosure surface or from the source for



the case with no enclosure. As an input to the calculation, you must input, for eachoctave band, one of the following (chosen by clicking on the corresponding tickbox):Source sound power level (Lw);Sound pressure level at the receiver location with no enclosure (Lp2p);Sound pressure level at the receiver location with the enclosure in place (Lp2);Sound pressure level immediately outside the enclosure (Lp1)

Cooling air requirements for enclosures containing heat generating equipment suchas electric motors can be determined by clicking on the bright blue button at thebottom of the window, labelled "Cooling air requirement". This brings up thewindow shown below, which evaluates Eq. 8.84.

Partial Enclosures. When a sound source is only partially enclosed, it is possible tocalculate the overall sound power reduction of the enclosure for a specified wall TL.This is not the sound pressure level reduction as this will vary, depending on theorientation of the observer to the enclosure opening(s). To calculate the sound powerreduction, you need to enter the wall TL and the ratio of covered to open area areaas shown in the figure below.



Outdoor Barriers (text, pages 387-401)

This panel calculates the insertion loss due to the insertion of a barrier of finiteheight and length between a sound source and a receiver. The configuration used inthe calculations is illustrated below. When you click on "NOTE", a message willappear to explain the location of the origin of the coordinate system as shown below.

As noted in the figure above, the z-axis isnormal to the ground surface and parallelto the plane of the barrier and the y-axis isparallel to the ground surface and thebarrier surface. The coordinates of thesource and receiver as well as the topcorners of the barrier are entered in thetable at the bottom of the window asillustrated at right. Note that the groundheight is the height at the base of the barrier. It is assumed that the ground height isconstant between source and receiver. Negative values of z are not allowed for anyparameter.



Mid-ResultsIf you are interested it is possible to view intermediateresults of a calculation for the 1000 Hz band byclicking on this button. The screen shown below is then shown in place of the graph.



Before undertaking a calculation, you must enterthe particular barrier diffraction model you wish touse from a total of 4 different choices as shown inthe figure at right. Then, depending on thediffraction model chosen, you will need to enterthe type of wave (plane cylindrical or spherical) orthe type of source (point incoherent line orcoherent line). The spherical wave of theMenounou model is equivalent to the point sourceof the Maekawa model and the cylindrical waveMenounou model is equivalent to the coherent linesource of the Maekawa model. The ISO and Kurzemodels provide the same results for any source orwave type.

The barrier thickness can also be entered at thebottom right of the screen (see text, page394). Forthe ISO method, this thickness is taken intoaccount by using a double diffraction model. Inthis case, the second diffractionedge is on the receiver sideseparated from the first edge by thenumber entered as the thicknessparameter. You can also enter theheight of the second barrier here.For barrier attenuation calculationmethods other than the ISOmethod, the effect of the barrierthickness on the insertion loss iscalculated using Eq. 8.98 and Fig.8.17.

If the barrier is a building greater than 10 m high, the excess attenuation term, Ag,which is the ground effect in the absence of the barrier, is omitted from Eq. 8.101.In most cases, this means that the barrier will be slightly less effective than if theterm were included. In any case, you have a choice here, you can click on th box toselect the option or not select the option which removes the Ag term from Eq. 8.101.This is explained on page 400 in the text book..



The calculation of the barrier attenuation requires a knowledge of the sonic gradient(text, pages 398-399, Eqs 5.190, 8.100) and this in turn is dependent on the windgradient which in turn is dependent on the ground cover. So it is necessary to enterthe ground cover type for the wind gradient calculation separately from the groundtype for the ground reflection calculation. Apologies for the different list of groundtypes here, but that is what is available in the literature and in each case, you willneed to select the one that best matches your situation. The radius of curvature, R (inmetres) (see Eq. 5.190) of the sound wave going over the top of the barrier as a resultof wind and temperature gradients and the value of the exponent ξ (see Eq. 5.186 andTable 5.6) are provided for your interest in blue font at the bottom of the barrierpanel (see below).

A negative radius of curvature implies that the sound rays will be curved upwardsand the resulting barrier attenuation will increase. This is in contrast to the decreasein barrier attenuation which occurs when there is a positive radius of curvature and



corresponding downward curved rays. Wind and temperature gradients are taken intoaccount automatically if you enter a non-zero value for the wind speed ortemperature gradient. The procedure calculates an effective source height based onthe sound ray curvature calculated from the wind and temperature gradients. If theeffective source height is less than zero, it is set equal to zero. Interestingly, the effecton the overall attenuation of the barrier is not great in most cases. You need to enterthe wind speed at 10m and the temperature gradient in degrees C per 1000m (seefigure on previous page).

It is IMPORTANT to note that the barrier noise reduction will not be accurate untilyou have entered the wind speed at a specified height (speed component in thedirection from the source to the receiver - negative values represent a componentblowing from the receiver to the source) and temperature gradient. However, youmay exclude the effect of a sonic gradient by entering zero for the wind speed andtemperature gradient.

As the barrier attenuation depends on the type of ground either side of the barrier,you must first choose the ground type from the "ground type" menu located in thepanel below the barrier figure. Just click inside the box and a menu of ground typeswill pop up as shown at right.

Note that you can also define your own ground surface by clicking on the "Selfdefined" item at the bottom of the menu. When you do this the box below pops upand all you need do is enter the flow resistivity of the ground surface in MKSRayls/m and then click on "finished".

You also need to select which ground model you want to use (the hard/soft modelfor which the reflection loss is 3 dB or 0 dB respectively; the plane wave reflectionmodel - Eq. 5.129; or the spherical wave model without turbulence - Eq. 5.133). Itis not possible to include turbulence in the barrier attenuation model here. Thereflection loss is -20log(Rp) or -20log(Rs). The effect of paths around all sides of thebarrier as well as attenuations due to reflections from the ground are included in thefinal attenuation value you find in the table. For each path the attenuation is



calculated using Figs. 8.13 & 8.14, and Eqs. 8.85 & 8.88. The ISO method is not yetavailable. For paths involving ground reflections, the loss due to that is also addedto the barrier attenuation. The attenuations for each path are combined together togive an overall barrier excess attenuation using Eq. 1.97 in the text. Note that Eq.1.97 requires the calculation of a reflection loss for when no barrier is in place. InENC, if the barrier is closer to the receiver than the source, the ground properties forthe source side of the barrier are used and if the barrier is closer to the source thanthe receiver, the ground properties for the receiver side of the barrier are used. Theactual reflection loss will be a bit different to the equivalent one with the barrier inplace due to the different angle of incidence of the sound with the ground. If youclick the box that asks if the barrier is a building more than 10 m high (or if thesource is more than 10 m above the ground), the reflection loss without the barrieris set at infinity (implied by ISO9613-2). When you have entered the barrierparameters, click on "back" to return to the table and you will see the barrierattenuation entered in the correct place in the table.

The window for calculating the speed of sound and other parameters can be can beactivated by clicking on the "constants" button.

After all of the barrier parameters have been entered, click on "run" in the tool barand the 1/3 octave band attenuations will appear plotted on the graph to the left ofthe screen. Octave band results are output on the table beneath the graph (see nextpage). The octave band results are averages of the three third octave bands makingup the particular octave band.



Indoor Barrier (text, pages 402-403)

This window is used to calculate the noise reduction due to a barrier mountedindoors. The barrier configuration used is shown in the figure below. The room isassumed to be rectangular and the origin of the coordinate system used for definingthe source, receiver and barrier locations is at a room corner on the source side of thebarrier as shown in the figure. The barrier is assumed to be a plane partition, restingon the floor and normal to the floor as shown in the figure. The room dimensionsand the coordinates of the top corners of the barrier as well as the source and receivermust be defined and input in the table shown on the next page. Make one corner ofthe room the origin of your coordinate system such that all coordinate locations arepositive.

You need to enter the for the bareαroom (room boundaries only) for eachoctave band and also the for eachαside of the added partition. Thesoftware will use the room surface areato calculate the for the bare roomSαand for each side of the barrier for theroom with the barrier. The value ofsurface area, S, used in the calculationsis the room surface area for the bare room and the room surface area plus barrier areafor each side of the barrier for the room with barrier. It is assumed that the in theSαroom without the barrier is uniformly distributed. If this is not the case or if there areadditional surfaces in the room you may enter the of the additional area that shouldαbe added to each side of the barrier to account for these effects (see following table).



Beneath the table you also need to include thesource directivity in the direction of thereceiver (see figure below) and whether or notthe ceiling is treated with sound absorbingmaterial. The barrier insertion loss is thencalculated using Eqs. 8.80-8.82. The"Constants" button may be clicked on tocalculate and set the speed of sound used inthe calculations.

The additional surface areas corresponding to the of the additional area on eachαside of the barrier (see previous figure) is input in the bottom right section of thepanel (see at right). The bottom three lines are calculated from the data input for theroom (see figure on previous page). There you must enter the room size and thecoordinates of the source and receiver locations as well as the two top corners of thebarrier. It is assumed that the barrier is resting on the floor.

Ceiling absorption prevents the wave reflected from the ceiling from having asignificant influence on the sound level at the receiver. So if ceiling absorption isused, the increase in noise reduction is the minimum of the following two quantities:• 1/3 of the noise reduction with no ceiling treatment; • 4 dB for 250 Hz, 5 dB for 500 Hz, 6 dB for 1000 Hz and 7 dB for 2000 Hz and

higher frequencies. (see text, page 332)

When you are satisfied with all input parameters, click on "run" in the tool bar. Thenthe barrier IL results will be plotted on the graph on the left of the screen and listedin the table beneath the graph.



Pipe Lagging (text, pages 403-405)

This window is intended to provide an estimate of the noise reduction achieved whena pipe is covered with a layer of sound absorbing material which, in turn, is coveredwith a limp, impervious skin. Care must be taken in the choice of rockwool andfibreglass as the binder sometimes disintegrates in service, leaving the imperviousskin resting on the original pipe, resulting in very little residual noise controlperformance. Also you should consider using shaped acoustic foam in place ofshaped rockwool or fibreglass as its performance is often better. However, thecalculation procedures used here are not applicable to acoustic foam wrappings (asno satisfactory theory exists) and the two procedures used here for the rockwool andfibreglass wrappings are semi-empirical and approximate at best.

The calculations are based on the assumption that the fibreglass or rockwool materialhas a density of between 70 and 120 kg/m3. The actual density is not used in eithercalculation procedure. It is also assumed that the fibreglass or rockwool material iscovered with a limp impervious membrane (jacket) of substantial mass. Usually asurface weight of 5-10 kg/m2 is used and the material is usually aluminium or abonded lead/aluminium sheet. The porous material (fibreglass or rockwool)thickness and the bare pipe diameter are entered in the section at the top, right sideof the panel (see figure below). Clicking on "Constants" allows you to calculate andset the speed of sound to be used in these calculations.

You can enter the properties of either type of jacket in the table on the bottom rightof the screen (see next page) and you can specify whether the jacket is made of oneor two materials using the toggle above the table (see next page).

You have two choices of calculation method, the Hale method (Eqs. 8.112-8.119 inthe text) or the Michelson method (shown on next page, Eq. 8.120). The lattermethod is more reliable, but when compared to measured data it is a bit conservative.It also has a lower frequency limit below which the calculations are invalid (seefigure below).



The Hale method is unreliable and often overestimates the actual IL. The calculationmethod is selected by clicking on the "method selection" switch in the middle of thewindow. Note that the Michelson method is characterized by a lower limitingfrequency below which the results are not valid. This must be remembered wheninterpreting the plotted and tabulated results in the graph (see below) and table to theleft of the screen. These results appear when you click on the "run" button in the toolbar.



Note that you can scroll the scale for the IL by clicking on either of the green squaresto the left of the graph. A number of curves can be plotted on the same axes byturning overlap to "ON". For the jacket material, results are provided at the bottomof the right side of the panel for mass per unit area, speed of sound, critical frequencyand ring frequency.

Enc Software User’s Guide Revision 3.3, April, 2009 © Causal Systems

6.

Reactive and DissipativeMufflers (Module 5)

Overview

This module enables calculation of the impedances of individual reactive mufflerelements, the Insertion Loss of reactive and dissipative mufflers, flow noise, ductbreak-in / break-out noise, exhaust stack directivity and the Insertion Loss of plenumchambers using the procedures described in chapter 9 of the text.

Duct Modal (text, pages 456-459, 463)

This panel enables you to calculate the cut on frequency of a specified higher ordermode in a rectangular or cylindrical duct. In addition you can calculate the phasespeed of the specified mode at a specified frequency as well as the number of cut-onmodes that are propagating at the specified frequency. This panel also allows you tocalculate the speed of sound in gases, solids and liquids, which is a duplicate of thespeed of sound panel in "Module 1 -Fundamentals" (see page 12).

To use this module simply enter the cross-sectional dimensions of the duct, thefrequency of interest and the mode index of the mode you wish to consider as shownon the figure.

117Chapter 6: Reactive and Dissipative Mufflers (Module 5)


cn 'c

1 & [ (cαmn ) / (rω ) ] 2

fm,n ' αm,n c /2πr

For rectangular ducts, the analysis uses Equations 9.95 and 9.96 in the text. Forcylindrical ducts, the phase speed is given by:

and the cut-on frequency is:

where r is the radius of the cylinder, c is the speed of sound in free space and αm,n isa constant dependent on the modal index and is listed in the table below.

m n0 1 2 3 4

0 0 3.83 7.02 10.17 13.321 1.84 5.33 8.53 11.71 14.862 3.05 6.71 9.97 13.17 16.353 4.20 8.02 11.35 14.59 17.794 5.32 9.28 12.68 15.96 19.205 6.42 10.52 13.99 17.31 20.586 7.50 11.73 15.27 18.64 21.937 8.58 12.93 16.53 19.94 23.278 9.65 14.12 17.77 21.23 24.59

where m is the number of diametral nodes and n is the number of cylindrical nodesparallel to the x-axis.

The panel also allows you to calculate the attenuation due to an unlined duct withand without lagging on the outside. To calculate the unlined duct attenuation for theduct cross sectional dimensions entered above, enter the duct length (see below) andindicate whether or not external insulation exists. This is discussed on page 463 ofthe text book.



Impedance (text, pages 409 - 420)

This panel enables you to calculate the impedance for elements that make up reactivemufflers. The first thing to do is specify the properties of the gas flowing in or pastthe element by clicking on the "Constants" button to bring up the "Constants set-upwindow. In addition, the flow speed needs to be entered.

There are 5 elements for which you can calculatethe impedance: tubes/orifices, 1/4 wave tubes,volumes/expansion chambers, Helmholtzresonators and perforated sheets. When inputtingparameters, please note carefully the units foreach quantity. Generally SI units are used but inmany cases millimetre units are used instead ofmetres. The type of object to be analysed is selected from the drop down menushown at right.



For the tube/orifice panel shown below, the input parameters need some explanation(text, pages 411 - 418). The reactive part of the acoustic impedance for specified gasproperties and flow is calculated using the first term on the right of Eq. 9.15 in thetext, where the effective length of the hole is given by Eq. 9.7. The resistive part iscalculated using Eq. 9.29 in the text.

The length parameter in ENC is the actual tube length with no end correction or thethickness of the orifice plate for an orifice. The edge radius parameter is used forcalculating the resistive part of the impedance (Eq. 9.29 in the text). If it isunknown, use 10mm. Next you must specify whether the tube or orifice is circularor not - this is necessary to allow the end correction to be calculated correctly. If thecross-sectional shape is circular, you need to specify its diameter; if it is non-circular,then you need to specify the cross-sectional area and perimeter. Equation 9.18 in thetext is then used by ENC to calculate an equivalent radius of the orifice or tube. Forall cross-sectional shapes, you need to specify the diameter of the baffle around eachend of the tube or around each side of the orifice. If the baffle is non-circular, thenyou can use figure 9.5 and equation 9.18 in the text to calculate the diameter of acircle of the same area. If the orifice or tube pierces a baffle in another largerdiameter tube, then the orifice diameter cannot be more than 0.6 times the larger tubediameter, and ENC uses equation 9.16 in the text to calculate the end correction. If



the orifice or tube is not in a larger tube and the baffle is bigger than three times theorifice diameter, then ENC uses equation 9.16 with ξ = 0 to calculate the effectivelength. If the orifice or tube is radiating into free space with no baffle, then ENCuses equation 9.19. For baffles of diameter smaller than three times the orificediameter, linear interpolation between the above two cases is used to calculate theeffective length.

If you enter "yes" to the "inside another tube" question, then it is assumed that thebaffle is in another tube and the tube diameter should be entered. To select theoption corresponding to a baffle in free space, select"no" for the "inside anothertube" question and then select "yes" for the "have baffle" question. If there is nobaffle and the orifice is not inside a tube, enter "no" to the "inside another tube"question and "no" for the "have baffle" question. Note that if "yes" is selected for the"inside another tube" question, then the "have baffle" question is "greyed out".

The software calculates the effective length increase for each side of an orifice oreach end of a tube, which is why input data are needed for each end. The resultingeffective length of the tube or orifice calculated by ENC is given at the bottom of thepanel. Also at the bottom of the panel, is given the real, imaginary and modulus ofthe impedance for any frequency entered in the "frequency" box.

With the required input data entered, click on "run" in the tool bar and the impedancewill be plotted at 1/3 octave band intervals on the graph (shown on the next page).Note that you must select the desired parameter to be plotted from the data windowabove the graph as shown in the figure below. The maximum valid frequency for theresults, corresponding to the orifice diameter being equal to λ/4, is also calculatedby the software and displayed above the graph. The values plotted on the graph arenot 1/3 octave band averages - they are single frequency values at the 1/3 octaveband centre frequencies.

Values at the octave band centre frequencies are displayed below the graph. Notethat the values are single frequency values with no band averaging.



For the 1/4 wave tube calculations (see figure below and text, pages 419 - 420), theinlet edge radius is the radius of the edge where the 1/4 wave tube joins the structure(usually a duct) on which it is mounted. If you do not know the value, use 10mm.After specifying the tube diameter, you may specify the length and have the softwarecalculate the corresponding resonance frequency or you may specify the resonancefrequency you desire and the software will calculate the required length. Just clickon the appropriate circle to the right of the data boxes. The quantity calculated by thesoftware is in blue type. Equation 9.37 in the text (2nd term on the right) is the basisof the calculation of the reactive impedance and Eq. 9.29 is used for the resistiveimpedance. Note that the effective length of the tube is the actual length plus an endcorrection calculated using Eqs. 9.16 to 9.20. As it is a calculated quantity, itappears in ENC in blue type. The maximum allowed value is the radius of the ductto which the 1/4 wave tube is attached. For a 1/4 wave tube not attached to a ductwall, the end correction for no baffle (or baffle diameter equal to the tube diameter)is calculated using Eq. 9.19 and for a very large baffle (of diameter greater than 3times the tube diameter, Eq. 9.16 is used with ξ = 0. Linear interpolation for the endcorrection is used for baffle diameters between one and three times the tube diameter.For a quarter wave tube attached to the side of a duct, the end correction is calculatedusing Equation (9.16) (multiplied by (1 - M)2 to account for flow) where in this case,ξ is set = 0. For a 1/4-wave tube attached to a duct wall, the maximum allowed endcorrection is the radius of the duct to which it is attached (or half the duct depth).Note that all end corrections calculated for no flow using the equations in the text aremultiplied by (1-M)2 in ENC to account for flow.



The quality factor at resonance is provided at the bottom of the panel and iscalculated using Eq. 9.41b in the text.

With the required input data entered, click on "run" in the tool bar and the impedancewill be plotted at 1/3 octave band intervals on the graph. Note that you must selectthe desired parameter to be plotted from the data window above the graph. Themaximum valid frequency for the results, corresponding to the 1/4 wave tubediameter being equal to λ/4, is also calculated by the software and displayed abovethe graph. Values corresponding to intermediate frequencies can be determined bytyping in the frequency of interest in the 1/4 wave panel illustrated on the previouspage.

The data required for the volume/expansion chamber (see figure below) (text, pages419 - 420) impedance calculations are the volume, and the diameters and edge radiiof the inlet and exit ducts. The inlet and exit duct diameter data are only used fordetermining the quality factor (see Eq. 9.41b in the text) and acoustic resistanceassociated with the expansion chamber at a specified frequency. However, rememberthat the quality factor is only valid at a resonance frequency of the expansionchamber and attached ducts. The acoustic resistance used in the quality factor



calculation is the sum of the resistances associated with the inlet and outlet ducts.The reactive impedance is calculated Eq. 9.35 in the text. The flow Mach numberis that corresponding to flow through the inlet and exit ducts.

In this panel, you are also able to calculate the acoustic impedance of a closed endtube that is not designed specifically as a quarter wave tube at some specifiedfrequency. To use this option click on the circle next to the tube specifications.

With the required input data entered, click on "run" in the tool bar and the impedancewill be plotted at 1/3 octave band intervals on the graph. Note that you must selectthe desired parameter to be plotted from the data window above the graph. Valuescorresponding to intermediate frequencies can be determined by typing in thefrequency of interest in the volume/expansion chamber panel illustrated above.

The upper frequency limit of this lumped analysis (indicated above the graph) is thesmaller of the frequency corresponding to the cube root of the volume being equalto λ/4 and the diameter of the tube being equal to λ/4.

The Helmholtz resonator panel (see figure below) (text, pages 412 - 420) enablesyou to design a Helmholtz resonator by specifying its resonance frequency orcalculate the resonance frequency of a specified design. First, you must specify the



neck inlet edge radius. If it is unknown, use 10mm. You must also enter anapproximate effective diameter of the resonator volume. This value is used toestimate the effective end correction for the neck attached to the volume. Note thatthe effective length of the neck is the actual length plus an end correction calculatedusing Eqs. 9.16 to 9.20. As it is a calculated quantity, it appears in ENC in bluetype. For a resonator not attached to a duct, the end correction for no baffle (orbaffle diameter equal to the neck diameter) is calculated using Eq. 9.19 and for avery large baffle (of diameter greater than 3 times the neck diameter, Eq. 9.16 is usedwith ξ = 0. Linear interpolation for the end correction is used for baffle diametersbetween one and three times the tube diameter. For a Helmholtz resonator attachedto the side of a duct, the end correction is calculated using Eq. 9.16 wherein thiscase, for the duct end of the neck, the end correction is calculated using ξ =0 and forthe other end ξ is calculated as the ratio of neck diameter to the equivalent diameterof the resonator volume. If ξ exceeds 0.6, it is set equal to 0.6. For the duct end theend correction cannot exceed half the duct diameter.

Next, you need to click on the circle corresponding to the quantity you wish thesoftware to calculate. The text corresponding to this quantity will turn blue and allother text will be black. You need to input data for all the values described by blacktext. However, you have a choice between entering "neck diameter" or "neck cross-sectional area" and "neck perimeter". The latter two quantities are used for necks ofnon-circular cross section. Use the switch to the left (see figure on previous page)to indicate your choice. Note that if you choose "neck diameter" as the quantity forthe software to calculate, it is assumed circular in cross-section and you will not beable to move the switch to the non-circular cross-section option.

The upper frequency limit of this lumped analysis is limited to frequencycorresponding to the cube root of the volume being equal to λ/10 or the tubediameter being equal to λ/4. This frequency is indicated above the graph.

With the required input data entered, click on "run" in the tool bar and the impedancewill be plotted at 1/3 octave band intervals on the graph. Note that you must selectthe desired parameter to be plotted from the data window below the graph. Valuescorresponding to intermediate frequencies can be determined by typing in thefrequency of interest in the Helmholtz resonator panel shown above. Note that the software also calculates the quality factor for the resonator (atresonance only). The equation used for this is 9.40a in the text.



The perforated sheet panel (see figure on next page) enables you to calculate theimpedance looking into a perforated panel backed by a cavity and rigid wall. Thereactive impedance for the perforated sheet is calculated using Eq. 9.24 in the text.The resistive impedance, Ra for a single hole is calculated for a hole of area, A, usingEq. 9.29 in the text.

You need to enter the length of each hole (the perforated facing panel thickness), thehole edge radius (use 10mm if unsure) and whether the holes are staggered orparallel. If the holes are circular, click in the circle next to "Circular" and enter thediameter. If the holes are another shape, click on the circle next to "non-circular"and enter the hole cross sectional area, perimeter and aspect ratio. For non-circularholes, Eq. 9.17 is used to calculate an effective radius. If a backing cavity exists,click on the square box next to "if backed by a cavity" and enter its depth andwhether it is partitioned or not to prevent propagation parallel to the plane of thefacing. It is assumed that the cavity behind the perforated sheet is terminated by arigid wall. If no backing cavity is selected, the impedance is calculated for theperforated panel backed by infinite free space (see Eq. 9.24 in the text). If a backingcavity is selected, the impedance of the cavity (Equation C.30 or C.40 in the textmultiplied by the cavity cross sectional area) is added arithmetically to that of theperforated sheet.



Reactive Mufflers (text, pages 420 - 438)

This panel enables you to calculate as a function of frequency, the Insertion Loss ofa 1/4 wave tube, a Helmholtz resonator, an expansion chamber, a low pass filter anda small engine exhaust system as described on pages 420 - 438 in the text. Note thatnone of the calculations provide accurate results once any dimension in the mufflerexceeds one quarter of a wavelength of sound.

The first thing to do is to enter the properties of the duct connecting the muffler tothe noise source (source end) and the duct between the muffler outlet and theatmosphere (outlet end), as shown in the figure below. Each of the ducts has twoends (end 1 being nearest the source), and you need to select whether the duct iscircular or non-circular. If the ducts are circular, select the "Circular" option andenter the diameters of each. If the ducts are non-circular, enter cross-sectional areaand perimeter of each.

The equivalent diameter of a baffle or an outer tube (if any) at each end of each ductneeds to be entered (see text page 415 for equivalent diameter calculations). Theletter "B" corresponds to the tube terminated in a baffle and the letter "T"corresponds to the tube being in a baffle inside another tube. Click on the letter totoggle between "B" and "T". This allows the effect on the effective lengths of thetubes of expansion chambers and low pass filter mufflers that may be connected tothe ends of the tubes.

For side branch mufflers such as 1/4-wave tubes and Helmholtz resonators, the baffleor outside tube diameter should be set equal to the duct diameter on which theresonator is mounted for 'source end, end 2' and for 'outlet end, end 1'. No endcorrection is calculated for the duct ends nearest the side branch resonator as theupstream and downstream ducts effectively join together at the side branch.



Note that for all muffler types, if the duct end is not in a baffle or a tube, select "B"and set the baffle diameter equal to the duct diameter (or the equivalent diameter ifthe duct is non-circular).

End corrections are calculated using Eqs 9.16 and 9.20 in the text multiplied by (1-M2) to account for the effects of flow (whether through or grazing flow).

You also need to enter the length of each duct and the edge radii where they connectto the muffler and exhaust to atmosphere - use 0.01 m for the edge radius if unsure.

You can also specify if the upstream pipe isterminated by the source (fan or compressor).If so, ENC assumes a reflection coefficient of1.0 at that end. If not, ENC assumes that theend is open. If you select the "absorbingliner", the analysis assumes that no wavesreflected from the end of the duct reach themuffler.

Note that if a small engine exhaust is beingdesigned, none of the data in the "ductproperties" panel are used.

The next thing to do is to enter the properties of the gas flowing through the muffler(top right panel) by clicking on the "Constants" button to bring up the "Constantsset-up window. In addition, the volume flow rate must be entered (see figure below).

The next step is to select the type of noisesource: constant volume velocity(reciprocating compressor) or constantpressure (axial or centrifugal fan) by clickingon the box to the right of "Select noisesource"as shown in the figure at right.

Next select the muffler type (1/4 wave tube, Helmholtz resonator, expansionchamber, low pass filter or small engine exhaust) as shown on the next page.



One third octave average Insertion Loss valuesare plotted on the graph (see below) for themuffler type selected. Octave band values(averaged over 20 single frequencies in eachband) are provided in the table below the graph.

The upper frequency limit of this lumpedanalysis is limited to the largest dimension ofany component being λ/4. The frequencycorresponding to λ/4 is indicated below thegraph as the "maximum valid frequency". On the graph, the 1/3 octave band valueshave been averaged over 7 frequencies in each band.



Helmholtz resonator (See text, pages 421 - 425). This part enables you to designa Helmholtz resonator by specifying its resonance frequency or calculate theresonance frequency of a specified design. It then calculates and plots the InsertionLoss as a function of frequency.

First, you must specify the neck inlet edge radius (see fig. below). If it is unknown,use 0.01 m. Then you need to enter the effective diameter of the resonator chamberwhere the neck is attached and in the same plane as the neck cross-section, so thatthe end correction for the neck at the resonator end can be calculated using Equation9.16 in the text multiplied by (1-M2) to account for the effects of grazing flow.

Next, you must enter the diameter of the part of the duct to which the resonator isattached. This is usually the same as the diameter of the inlet and outlet ducts enteredin the "Duct Properties" section of the panel. This information is used to calculatethe effective length of the neck at the duct end as described on page 119 of thismanual.

Next you need to click on the circle corresponding to the quantity you wish thesoftware to calculate. The text corresponding to this quantity will turn blue and allother text will be black. You need to input data for all the values described by blacktext. However, you have a choice between entering "neck diameter" or "neck cross-sectional area" and "neck perimeter". The latter two quantities are used for necks ofnon-circular cross section. Use the switch to the left (see above figure) to indicateyour choice. Note that if you choose "neck diameter" as the quantity for the softwareto calculate, it is assumed circular in cross-section and you will not be able to movethe switch to the non-circular cross-section option. The neck end correction is usedin the calculations, but you need to use the "impedance" panel of this module to see



it displayed. The neck length shown here is the physical length, not the effectivelength.

The equations used for the insertion loss calculations are 9.45 and 9.48 in the text.The quality factor is calculated using Eq. 9.40 in the text. The resistive and reactiveimpedances and the quality factor for the resonator are calculated during the insertionloss calculations, but you need to use the "Impedance" panel of this module to seethe impedance values. Sometimes ENC calculates quality factors that, based onexperience, seem too high, so if you prefer, you may enter a value for the qualityfactor and ENC will use that to calculate the resistive impedance and Insertion Loss.ENC then calculates the acoustic resistance at the resonance frequency of theresonator using Eq. 9.28 in the text. The resistance values at other frequencies arethen calculated by multiplying the resistance at the resonance frequency calculatedusing Eq. 9.28 by the ratio of the resistance calculated using Eq. 9.29 at frequencyof interest to the resistance calculated using Eq. 9.29 at the resonance frequency.

With the required input data entered, click on "run" in the tool bar and the 1/3 octaveaverage Insertion Loss will be plotted at 1/3 octave band intervals on the graph.Values corresponding to intermediate frequencies can be determined by typing in thefrequency of interest in the Helmholtz resonator panel shown above.

For the 1/4 wave tube (see below) Insertion Loss calculations (pages 421 - 424 intext), the inlet edge radius is the radius of the edge where the 1/4 wave tube joins the

structure (usually a duct) on which it is mounted. If you do not know the value, use10mm. After specifying the tube diameter, you may specify the length and have thesoftware calculate the corresponding resonance frequency or you may specify theresonance frequency you desire and the software will calculate the required length.Just click on the appropriate circle to the right of the data boxes. The quantitycalculated by the software is in blue type. Equations 9.37, 9.46 and 9.48 are in thetext are the basis of this calculation. The end correction for the tube may be



calculated using the "impedance" panel.

The quality factor at resonance is provided at the bottom of the panel and iscalculated using Eq. 9.41b in the text

The resistive and reactive impedances for the 1/4 wave tube are calculated during theinsertion loss calculations, but you need to use the "Impedance" panel of thismodule to see the impedance values. If you prefer, you may enter a value for thequality factor and ENC will use that to calculate the resistive impedance andInsertion Loss.

With the required input data entered, click on "run" in the tool bar and the 1/3 octaveaverage Insertion Loss will be plotted at 1/3 octave band intervals on the graph withoctave band averages tabulated below the graph. Values corresponding tointermediate frequencies can be determined by typing in the frequency of interest inthe 1/4 wave panel illustrated on the previous page. The maximum valid frequencycorresponding to the largest dimension being equal to λ/4 is also calculated by thesoftware and displayed under the graph.

The expansion chamber (see figure below) (text, pages 427 - 431) panel calculatesthe Insertion Loss for an expansion chamber inserted into a duct. The input datarequired are the expansion chamber volume or the diameter, length and inlet radiusof a closed tube. In the latter case, the insertion loss is the same as for a 1/4-wavetube discussed previously.

Note that the flow speed is in cubic metres per second, not metres per second!



The upper frequency limit of this lumped analysis is limited to the largest dimensionof any component being λ/4. The frequency corresponding to λ/4 is indicatedbeneath the graph.

You may see displayed the impedance of the components used to make up theexpansion chamber muffler by using the "Impedance" panel of this module.

The quality factor at resonance is provided at the bottom of the panel and iscalculated using Equation 9.40b in the text, where Rs is the acoustic resistance of thetail pipe, R is the tail pipe length, A is the tail pipe cross-sectional area and V is theexpansion chamber volume, all in consistent units. Note that this expression isapproximate and the error increases as the tail pipe length increases.

Alternatively, you may enter a value for the quality factor in the panel above if youwish and ENC will calculate the corresponding resistance and use that to calculatethe insertion loss. It is realised that the closed end tube option is not a very practicalway to implement an expansion chamber muffler, but it is interesting nevertheless.The quality factor for the expansion volume muffler corresponds to its first resonancefrequency (the first minimum in the TL curve).

With the required input data entered, click on "run" in the tool bar and the 1/3 octaveaverage Insertion Loss values will be plotted at 1/3 octave band intervals on thegraph with octave band averages tabulated below the graph. Values correspondingto intermediate frequencies can be determined by typing in the frequency of interestin the expansion chamber panel illustrated above.

Low Pass Filter (text, pages 433 - 438). This panel (see figure on next page) is usedfor the design of a low pass filter to remove pressure pulsations from piping systems(usually due to reciprocating compressors). You need to enter the volumes of thetwo chambers involved and the choke tube dimensions. Then you have a choice ofeither entering the fundamental frequency of the pressure pulsations or the choketube cross-sectional area. If you enter the former, ENC will calculate an appropriatechoke tube diameter so that resonance frequency of the filter is 0.65 times thefrequency of the pulsations. If the resulting choke tube diameter is too small (tosatisfy pressure drop considerations) you will have to use a longer choke tube and/orlarger volumes. If you choose to enter the choke tube diameter, ENC will calculatethe frequency of pressure pulsations, which is 1.54 times the resonance frequency ofthe filter.

Click on "run" in the tool bar and the software will calculate the Quality factor,resonance frequency, pressure drop and Insertion Loss for the selected frequency.The quality factor corresponds to the resonance frequency of the entire system (muffler and connecting ductwork). The resonance frequency corresponds to thefirst minimum in the TL curve. The frequency calculated using Eq. 9.70 in the textis usually an overestimate (by up to 50%).



Calculated 1/3 octave average Insertion Loss values will be plotted at 1/3 octaveband intervals on the graph with octave band averages tabulated below the graph.The quality factor at resonance is provided at the bottom of the panel and iscalculated using Equation 9.40b in the text, where Rs is the acoustic resistance of thechoke tube, R is the choke tube length, A is the tail pipe cross-sectional area and V isthe expansion chamber volume, all in consistent units. Note that this expression isapproximate and the error increases as the choke tube length increases. You mayalso enter a value for the overall quality factor and in this case ENC will calculate theeffective acoustic resistance using the above equation for use in calculating theinsertion loss.

The maximum valid frequency corresponding to the largest dimension being equalto λ/4 is also calculated by the software and displayed under the graph.

Note that the flow speed input is a volume flow in cubic metres per second, notmetres per second!

Small Engine Exhaust. (See text, pages 431 - 432). The configuration for the smallengine exhaust is the same as used in the expansion chamber panel, except that aconstant volume velocity source is assumed and an attempt is made to optimise theinsertion loss while minimizing the pressure loss.

You must input the parameters in black type (see following figure) and the softwarewill calculate those in blue type. The required inputs are engine speed and theInsertion Loss that you desire for this engine speed as well as the maximumallowable expansion chamber volume. The quality factor is calculated as for the



Helmholtz resonator using the impedance of the exhaust pipe as the inductance andthe expansion chamber volume as the capacitance. The duct properties data for thediameter of the tail pipe are not used. However, the edge radius from the ductproperties panel and the tail pipe diameter calculated in this panel are used forcalculating the quality factor. If you do not know what this is, enter 10 mm in theduct properties panel.

Note that you will get nonsensical results if you use a zero volume flow rate.

With the required input data entered, click on "run" in the tool bar. The software willcalculate the tail pipe diameter and length as well as the resonance frequency of theexhaust system. The calculated 1/3 octave band averaged Insertion Loss will beplotted at 1/3 octave band intervals on the graph and octave band averages will beprovided in the table beneath the graph. Insertion Loss values for individualfrequencies are output for any frequency value entered in the box at the bottom of thesmall engine exhaust panel (see preceding figure). The maximum valid frequencycorresponding to the largest dimension being equal to λ/4 is also calculated by thesoftware and displayed under the graph.

If you wish to calculate the insertion loss for a fixed expansion chamber volume andtail pipe parameters, then use the expansion chamber selection in this panel.



Dissipative Mufflers (text, pages 445 - 463)

Attenuation calculations are plotted on the graphas a function of frequency. The actual quantityplotted on the graph below is selected using themenu displayed at right. The term "Selected totalattenuation" means that the total attenuation onlyincludes the items selected by the dot inside thecircle in the bottom left panel.

The "overlap" switch allows multiple curves (use"color" to select color of each) to be plotted on the same set of axes. Note that the

values plotted on the graph are energy averages of ten frequencies over a 1/3 octaveband of frequencies (see text, example 5.1, p.233 for averaging method). Beneaththe graph, the octave band attenuations (energy average of the appropriate 1/3 octaveband values shown in the graph) are presented in a table (see below).



To do a lined duct attenuation calculation, the procedure outlined in the paper Bieset. al (1991) (after correction for a factor of 2 error in the attenuation result) isfollowed. The first step is to type in the density and speed of sound in the gas in theduct, the flow speed of the gas in the duct, the lined duct length, whether the duct iscircular or rectangular in cross section and the cross sectional dimensions (see figurebelow). If the duct is circular in cross-section, the diameter is required and if it isrectangular, the height and width of the section is required. Of course, good resultscan be obtained for ducts of other section shapes by treating them as rectangular orcircular ducts of the same cross sectional area. If the other section shape is linedaround its entire perimeter, it is best to treat it as a circular duct of the same area. In

all cases, the dimensions refer to the open area of duct, and do not include the liner.Note that if the duct is divided by lined baffles (or partitions) as in a typicaldissipative muffler, the dimensions required are the open cross sectional dimensionsbetween each baffle, not the overall dimensions. In this case the muffler attenuationis equal to the attenuation through one airway between two of the baffles. Do notadd the attenuations for each airway. The software will calculate the open ductcross-sectional area, the perimeter of the open area and the expected pressure dropdue to the lined duct. ENC will also calculate the duct cross sectional area, perimeterand pressure loss due to the specified flow speed.

Clicking on the "Constants" button in the above figure allows you to set the speedof sound and gas density for the calculations of the entire window - see pages 4 -5for a full description.

Next in the "perforated facing" panel, enter details (panel thickness and percentopen area) about the liner facing (see following figure). Click on the box on the left



side of the "perforated facing" panel to select whether or not there is a perforatedpanel. If the box is not ticked, the perforated panel details will be "greyed out" andnot used in the calculations. Enter also the surface density (mass per square metre -kg/m2) of any protective impervious membrane such as polyethylene. If there is nomembrane, enter 0.0 here. Note that if both the membrane and perforated panel areused together, it is essential that a spacer (e.g. 25mm mesh) is used to keep the twoseparated. Otherwise, the attenuations calculated here will be greater than thoserealised in practice, especially at higher frequencies.

Next, in the "Liner" panel (see below) enter the number of sides that are lined(rectangular duct only) and the location of the lined side(s) if there are less than 4.Note that "2 sides" refers to two opposite sides lined and you can choose between"across height" or across width". If only two adjacent sides are lined, then you mustdo two calculations for "1 side" lined and add the two results arithmetically (lineronly results). Do not add the total attenuations in each case, only the attenuationsfor the liner. If three sides are lined, do the calculations for 2 opposite sides and thenthe remaining side and add the two results (liner attenuation only). For circularducts, it is assumed that the liner extends the full circumference of the duct. If itdoes not, then use a square duct of the same cross-sectional area with the equivalentnumber of sides lined.

Also in the "liner" panel, enter the flow resistivity (rayls/m - see page 53 in the text)of the liner material in the direction normal to the axis of the duct ("normal") and inthe direction parallel to the duct axis ("parallel"). Although the analysis is strictlyfor isotropic materials, good results are obtained for orthotropic materials whichmake up the majority of fibre glass and rockwool materials. The switch on the topof this panel (locally reactive / extended reactive) is used to select between a linerthat has closely spaced solid partitions normal to the duct axis so that soundpropagation in the liner parallel to the duct axis is prevented (locally reactive) anda liner that allows axial sound propagation within it (extendedreactive). For the locally reactive case, only the normal flowresistivity value is used. For the extended reaction case, thesoftware will only give good results if the flow resistivity in theparallel direction is different from the normal direction by lessthan a factor of 2.

The attenuation due only to the liner is given in the grey box atthe right of the panel for the frequency selected above it.



In calculating the total attenuation of the lined duct, the following quantities need tobe calculated and added: liner attenuation (grey colour, discussed above), inletattenuation (yellow), exit loss (blue - select whether the outlet terminates flush witha wall/ceiling or free space), expansion loss (green) and duct bend attenuation, if oneexists (orange). Each quantity can be selected by clicking in the circle to the rightof the panel. The numbers in the box next to the circle are the attenuationscorresponding to the frequency selected in the box under "Frequency". The "totalattenuation" if it is selected for display in the graph and attenuation table is onlycalculated using the quantities selected (with a dot inside the circle - see below). Values are tabulated in octave bands in the table below the graph and may be readfrom the graph for 1/3 octave bands using the cursor.

Liner Attenuation (see pages 448 - 455 in the text). The required input data hasbeen discussed above. If there is an air space between the back of the liner and theduct wall, you need to add this depth to the liner thickness (within reason).

Note that the liner attenuation calculation (Bies et al, 1991) is very complex andsometimes the calculating program converges incorrectly. To be sure of correctresults, the software should only be used in the range represented by figures 9.15 -9.20 in the third edition of the textbook. If the calculated attenuations exceed 7dBper length of duct equal to half the duct width, then please change the inputparameters (flow resistivity or duct size) slightly and rerun the calculation. If theresults show an exponential tendency or a step change as shown in the followingfigure, then again the software has failed to converge to the correct solution and youshould change one of the input parameters by a small amount and try again.

The problem seems to be more prevalent when an impervious membrane orperforated panel (low percent open) is used. The correct curve shape, whichindicates that the software tracked the correct modal solution is shown in the secondfigure on the next page.



The attenuation plotted onthe curve is the total linerattenuation for thespecified length.

Note that ENC calculatesthe attenuation of the leastattenuated duct mode.When that mode isattenuated by more thanabout 40 dB as mayhappen in a long linedduct, other propagationmodes become importantso the amount ofattenuation given by ENCwill be an overestimate.

Inlet Attenuation (seepage 459 in text). Theattenuation due to soundhaving to enter a duct(assuming that theincident angle of thesound is random) iscalculated here using Figure 9.21 in the text. This is usually only applicable if amuffler is used as an inlet or outlet attenuator for cooling air for an enclosure and notif it is inserted into an existing duct.

Exit Loss (see text, pages 463 - 464). When sound exits from a muffler to free space,there is an exit loss, which can be calculated using Table 9.5 in the text. Again, thisis usually only applicable to the addition of a muffler to an enclosure to attenuatesound that is associated with the discharge or inlet of cooling air. If added to anexisting duct, the duct will already have exit losses. However, if the muffler crosssectional area is different to that of the existing duct, then the exit loss associatedwith the muffler will be different and it should be calculated here for both cross-sectional area cases (with and without muffler) and the difference used to calculatethe muffler insertion loss.

Expansion Loss (see text, page 460). When a liner is added to a duct and the opencross section area remains the same, there will exist an effective expansion as theliner is porous. The additional attenuation as a result of this expansion is calculatedhere using Figure 9.22 from the text. Note that you need to define a liner (see linedduct above) and enter the cross sectional area of the open duct plus liner to be ableto use this part. The open duct area is calculated when the liner is specified in thetop left of the panel.



Duct Bend (see text, page 462). Where a duct bend exists, this section can be usedto calculate the attenuation, following figure 9.23 in the text. Note that there areswitches for lined/unlined (referring only to the duct bend and the adjacent duct inthe close vicinity), and plane wave / diffuse input. Results are different forrectangular and circular duct and the calculations in the duct bend section are basedon the type of duct section (rectangular or circular) defined near the top of themodule. If the upstream duct is lined for a length equal to at least several duct crosssectional dimensions or if it is large enough in section that several modes arepropagating (in the software we use a frequency of 2.5 times the cut on frequency ofthe first higher order mode) then it can be characterised as a diffuse field input ratherthan a plane wave input. This is worked out by the software and is transparent to theuser. However the user must enter whether or not the upstream duct is lined priorto the bend (for a distance exceeding three times the largest duct cross sectionaldimension).

When all the parameters have been entered, the "run" button must be clicked for thesoftware to execute a calculation. The liner calculation is very complex so somewaiting time may be needed, especially if your computer is not a Pentium 4 orbetter.

Lined Plenum Chamber (text, pages 466 - 468)

In some air handling systems a plenum chamber is used to reduce mean pressurefluctuations. There have been a number of models published for calculating thetransmission loss of a plenum chamber and these are summarised in the paper,"Comparison of models for predicting the transmission loss of plenum chambers",by Li and Hansen, Applied Acoustics, 66, pp.810–828 (2005). In the text book, onlythe so-called Wells model is presented. However, ENC presents a number of models:the Well's model, Cummings model and Ih's model and the user must first selectwhich model is to be used (see below).

The Wells model is the simplest and leastaccurate and is only applicable to linedchambers. Ih's model is accurate but onlysuitable for an unlined chamber. Cummingsmodel is accurate and is intended for linedchambers. However, it also gives accurateresults when a thin liner with high flow



resistivity (effectively no liner) is used. All models give the option of circular orrectangular ports. However, results for a rectangular port are similar to those for acircular port of the same area. The Cummings model is more accurate than the Wellsmodel over the entire frequency range even though it is based on the so-calledCummings low frequency model (see above reference).

After selecting which model you wish to use, you must choose whether the inlet andoutlet ports are round or rectangular in cross section and the cross-sectionaldimensions of the inlet and outlet ports.

Next you need to enter the plenum size (which is effectively determined when youenter the coordinate location of "M"). Note that only rectangular section plenums canbe analysed here. If you have a cylindrical plenum, then you can only use the Wellsmodel and a square cross section of equivalent area to the actual cylinder crosssection. Next you need to enter the x, y and z coordinates of the inlet and outlet portcentres and the coordinates of the top corners of the barrier (if one exists) (seebelow). Note that both the Cummings and Ih models are quite sensitive to the actuallocations of the inlet and outlet ports.

As can be seen from the above figure, for both the Ih and Cummings models, youhave the option of adjusting the number of frequency lines. Increasing them willresult in longer calculation times but a more accurate 1/3 octave band average whichis plotted on the graph and used to calculate the octave band average in the table. Forthe Cummings model only, you also have the option of adjusting the number of



plenum chamber modes that are used to calculate the response. Increasing thenumber of modes increases the accuracy at high frequencies but the calculation timescan become quite long - up to minutes. Also for the Cummings model only, you willneed to enter the thickness and flow resistivity (Rayls/m) of the acoustical materialused to line the plenum chamber. What data are required for particular models canbe a bit confusing so to assist you, if data are not required, the place where it isentered is "greyed out".

The 1/3 octave band absorption coefficients of the plenum chamber liner must beentered in the table shown below. If a baffle or barrier exists, then move the switchat the top of the table to "Barrier present" and enter the absorption coefficients of thebarrier surface. The insertion loss of the barrier is calculated using the “IndoorBarrier” window in Module 4 and the result is added arithmetically to the InsertionLoss of the plenum chamber to get the total insertion loss. Note that in order tocalculate the barrier insertion loss, data are needed for the absorption coefficients ofthe plenum interior, even if it is for Ih's model with no sound absorbing material inthe plenum. With no barrier in place, no sound absorption coefficient data are neededfor the Ih model or the Cummings model and the table is greyed out. The formermodel is only applicable to an unlined plenum chamber and the latter model usesvalues of the plenum liner flow resistivity and thickness to calculate the plenumsound absorption effect.

Click on "run" after each change of data - sometimes it may take a short time for theresults to be calculated by ENC.

The 1/3 octave band Transmission Loss for the plenum chamber is plotted on thegraph and octave band results (which are energy averages of the 1/3 octave bandresults) are included in the table below the graph (see next page). The TransmissionLoss calculated here is very close to the insertion loss value, provided that there issome acoustic absorbing material on the interior walls of the chamber or the baffle.The additional transmission loss as a result of placing a baffle (or barrier) in thechamber between the inlet and outlet is simply added arithmetically to the TL of thechamber without a baffle which is difficult to justify theoretically. However, for



convenience it is also listed separately in the octave band results table and may beplotted separately or combined with the unbaffled chamber TL simply by clicking onthe appropriate empty boxes adjacent to the table (see figure below).



Pressure Drop (text, pages 438 - 441)

ENC also calculates thepressure drop for variouselements making updissipative mufflers asillustrated in the text, Fig.9.12 and Eqs. 9.81 - 9.84.To calculate the pressureloss in a straight duct, youneed to enter the ductlength, perimeter, cross-sectional area and flowspeed. The pressure dropis output in blue (see figureat left).

For calculating the pressuredrop due to an elementshown in Figure 9.12, youneed to select the elementtype and enter the elementtype, flow speed, gasdensity, pipe diameter andradius of curvature ofe x p a n s i o n s a n dcontractions as shown onFigure 9.12. The pressureloss outputs are given inblue at the bottom of thepanel (see at left).



Flow Noise (text, pages 442 - 444)

Noise generated by flow through a dissipative muffler or around a 90 degree bendor elbow can be calculated using this panel. Enter the gas density and flow speedand duct cross sectional area (see figure above). Click on "Dissipative muffler" or"Bend or elbow". If "Bend or elbow" is selected, enter the duct width in the planeof the elbow. ENC will calculate the free stream power level (dB) (see above figure)and the octave band flow generated sound power levels. The octave band flowgenerated sound power levels, calculated using Eqs. 9.85-9.88 in the text are plottedon a graph as shown in the figure below and also tabulated below the figure.



Exhaust Stack Directivity and Noise Reduction (see text, pages 469 -472)

This section calculates the directivity of an exhaust stack as well as the noisereduction that will occur as a result of installing one (see figure on next page), usingFigure 9.27 in the text and Eq. 9.119. The first line of data to be entered is theoctave band insertion loss of the stack itself. That is, the difference in soundpressure level at the duct outlet with and without the stack in place. Additional datathat must be entered include the distance between the outlet and observer, the anglesubtended by the observer to the exhaust duct axis and the duct exit cross sectionalarea for the outlet with and without the stack in place. The value of the subtendedangle is 90 degrees it the exhaust opening is pointed up and is at the same height asthe observer, at some horizontal distance away. The value is 0 degrees if the exhaustduct is pointed directly at the observer.

If desired, you can also insert the excess attenuation values from the duct opening tothe observer with and without the stack in place. These are calculated using module2. If the excess attenuation is the same with and without the stack in place, you mayenter zero for both rows of values. HOWEVER, IF YOU WANT TO CALCULATETHE SOUND PRESSURE LEVEL AT THE OBSERVER USING THE LOWERTABLE ON THIS WINDOW, YOU MUST ENTER ACCURATE EXCESSATTENUATION VALUES HERE AS THEY WILL BE USED IN THE LOWERTABLE CALCULATIONS.

The directivity from the exhaust opening to an observer location is calculated byENC for the exhaust opening at the top of the stack (DIs) and for the exhaust openingwithout the stack (DI). For this calculation, in addition to the data already discussedabove, you need to enter the speed of sound in the exhaust gas. Finally, the last linein the table (see following figure) is the noise reduction at the observer due to theinstallation of the stack. Note that although the directivity information used in thecalculations has not been averaged over octave bands, the octave band centrefrequency results given are very close to what would be obtained by band averaging.



Clicking on the "Constants" button in the above figure allows you to set the speedof sound and gas density for the calculations of the entire window - see pages 4 -5for a full description.

At the bottom of the table you can use the calculator to calculate results forindividual frequencies in addition to the octave band centre frequency results shownin the table. The input data are labelled in black and the calculated data in blue. The table at the bottom of the panel allows you to calculate the sound pressure levelat the observer location with the stack in place using Eq. 9.120. To do thiscalculation the sound power radiated by the duct prior to the installation of the stackis required. There are 3 methods ENC can use to determine the sound power levelvalues. Click on the box to the right of the title, ""PWL radiated by duct outletwithout stack" to select the method you wish ENC to use.

If you select "entered by user", then you must enter the octave band sound powerlevels in the first line of the table. If you select "calculated from SPL measured inthe plane of the duct outlet", you must enter these values of SPL (determined byaveraging the SPL over the plane of the duct outlet) in the first line of the table andENC will use these values and the duct outlet cross sectional area to calculate thesound power level radiated by the duct without the stack using Eqs. 9.116 and 9.117.



Note that taking measurements in the plane of the duct outlet is very difficult in thepresence of significant air flow which will contaminate the low frequencymeasurements.

If you select the third remaining option, "calculated from SPL measured at thefollowing location", ENC will use the measured sound pressure level at somedistance, r, from the stack to calculate the radiated sound power using Eq. 9.118.For this option you need to enter the distance from the duct outlet that themeasurement was made and the angle in degrees subtended to the measurementlocation from the duct axis. You also need to enter octave band values of excessattenuation, Aem, associated with sound propagation from the duct outlet to themeasurement location (calculated using module 2 of ENC). ENC will calculate thedirectivity associated with this measurement for the duct outlet, include the effect ofthe excess attenuation and calculate the radiated sound power level for the ductWITHOUT the stack.

As the sound power levels calculated using the information in the first line of thetable are for the duct WITHOUT the stack attached, the sound power radiated by theduct WITH the stack attached is determined by ENC by subtracting the insertion lossvalues entered in the upper table from the sound power levels calculated for the ductwithout the stack in the lower table. Similarly the insertion loss value entered belowthe upper table for the single frequency calculation is used for the single frequencycalculation under the lower table. The calculation in the lower table also uses values of excess attenuation (Aes) withthe stack in place from the upper table. For the individual frequency calculations,the value of Aes entered below the upper table will be used for the lower tablecalculations.



All of the data and results discussed above may be plotted on the graph on the rightside of the panel (see figure below). The parameter to be plotted is selected byclicking on the selection box above the graph (see below).



Duct break-out/Break-in Noise (text, pages 463 - 466)

This panel calculates the sound power that may be expected to break out of a ductsuch as an air conditioning duct, which contains an internal sound field. It will alsocalculate how much sound power that will break into a duct as a result of an externalsound field. The calculations are particularly useful for determining how much noisemay be carried by an air conditioning duct from a noisy area (such as a factory orplant room) to a quiet area (such as an office) as well as the importance of fan noisetransmission through the duct walls into an office space.

For both break-in and break-out noise, you need to enter the duct wall surface weight(kg/m2), the length of duct over which breakout or break in sound transmission willoccur, the speed of sound in the duct and the duct cross section dimensions (seefigure below).

For the break-out section (see figure below), the quantity, Lwi is the sound powerpropagating down the duct and entering the section from which it will breakout.This must be input by the user in octave bands. The quantity, Lwo is the sound



power that will break out of the duct (dB re 10-12 W) and this is calculated by ENCusing Eq. 9.100 in the text. The quantity, Δ, is the attenuation in dB/m of a linedduct (entered by the user) and the quantity, C, is defined by Eq. 9.101 in the text andTLout is defined by Eqs. 9.104-9.106. Both quantities are calculated by ENC.Below the table are output the cross over frequency (Eq. 9.103 in the text) and theminimum allowed value for TLout (Eq. 9.106). Note that the maximum allowed is45 dB.

In addition to the octave band values of power in the table, you can also obtainvalues at specific frequencies by entering the frequency of interest in the box belowthe table.

For the break-in section (see figure below), the quantity, Lwo is the sound powerincident on the duct walls from the external sound field (entered by the user). Thequantity, Lwi, is the sound power that will break into the duct (dB re 10-12 W) andTLin is the break in sound transmission loss. Both quantities are calculated by ENC.ENC also calculates the fundamental resonance frequency associated with the duct

cross section (line following Eq. 9.94 in the text). Single frequency calculations arealso done for the frequency entered in the box below the table.

Any of the outputs calculated by ENC may be plotted. Just select the requiredquantity from the drop down menu above the graph (see figure on next page).


7.

Vibration Isolation (Module 6)

Overview

This module carries out the calculations and procedures outlined in Chapter 10 of thetext. Single degree of freedom and multi-degree of freedom systems are bothconsidered in terms of vibration isolation. The effect of flexible foundations onvibration isolation performance, vibration absorbers, damping parameters and unitsof measurement are also included.

SDOF System (text, pages476 - 481)

This section calculates thedamped natural frequency aswell as the frequencycorresponding to maximumdisp lacemen t , ve lo c i ty,acceleration and transmittedforce for a single degree offreedom system using Eqs.10.2, 10.3, 10.6, 10.8, 10.10and 10.11. The traditionalundamped resonance frequencyis the same as the frequencycorresponding to the maximumvelocity.

You must enter the critical damping ratio and there is a choice of either entering thestatic deflection of the isolator or its stiffness and the mass that it supports (just clickon the appropriate dot). Note that if the spring mass is significant, then 1/3 of thespring mass should be added to the supported mass as the mass quantity to be enteredinto the software. Also note that for rubber isolators, you need to use the dynamicstiffness value corresponding to the expected amplitude of vibration. The static

155Chapter 7: Vibration Isolation (Module 6)


stiffness value is inappropriate. Note that the units of stiffness are MN/m = 106 N/m.The reduction in transmitted force (Tf Reduction) through the spring isolatorcompared to the situation without the isolator may be calculated for a specific valueof the ratio of excitation frequency to undamped resonance frequency, (f/f0), using

the calculator in the module illustrated below.

The transmitted force reduction is also plotted as a function of the frequency ratio,f/f0 in the figure below.

Units of Vibration (text, page 504). Enter the frequency of interest and any one of



acceleration, velocity or displacement (see figure on next page). The software willthen calculate the other two and the dB equivalents as well using the referencequantities on page 504 and Eqs. 10.56 - 10.59 in the text.

Damping Measurement (text, page 509). This part of the module allows you tocalculate two of the quantities logarithmic decrement, critical damping ratio and lossfactor, given the third one, using Equation 10.47 in the text. You can also relate thedamping to the 60 dB decay time (T60) of a single degree of freedom system (see Eqs7.22 and 7.23 in the text), given its resonance frequency (given in the panel 2 pages

back).

4-Isolator System (text, 482 - 484)

For this system (see below), the software will calculate the rotational andtranslational resonance frequencies using Eqs. 10.17, 10.18 and the procedure in thelast paragraph on page 482 in the text. You need to enter the mass and geometricalparameters requested (see next page).



You also need to enter the stiffnesses of the 4 isolators in all three translationaldirections. Note that if the spring mass is significant, then 1/3 of the spring massshould be added to the supported mass as the mass quantity to be entered into thesoftware. Also note that for rubber isolators, you need to use the dynamic stiffnessvalue corresponding to the expected amplitude of vibration. The static stiffness

value is inappropriate. Note that the combined spring stiffness is the one used in thecalculations. Note that the units of stiffness are MN/m = 106 N/m. You have achoice of entering the radii of gyration about 2 axes or the equivalent rectangulardimensions of the machine (enclose the machine in a rectangular box of the samevolume).



The outputs (see above) are all the translational and rotational resonance frequenciesfor the system. If the spring stiffnesses are different for the 4 isolators, the effectiveoverall stiffness for each direction is calculated by the software for use in theresonance frequency calculations. Note that if necessary, you can check the roots ofthe equation in the caption of Figure 10.5 in the textbook, used to determine theresonance frequencies. This is done by clicking on the "Check Roots" box and thepanel shown below appears.

Flexible Support (text, page 489)

In this part (see figure on the next page), the transmitted force as a function offrequency may be calculated for a flexible machine and support structure, using Eq.10.31 in the text.

Assuming a rigid isolated mass and a lightweight spring, the mobilities are calculatedusing Eqs. 10.32 - 10.34 I the text.

You may enter single values for the real and imaginary parts of the machine mobility(if the machine is non-rigid) and support structure or you may enter a table of valuesas a function of frequency. If the machine is relatively stiff, it is sufficient just toenter its mass instead of its mobility.

As can be seen in the figure below, the software calculates the transmitted forcereduction (in dB) for any frequency that is specified for the single value mobility dataor for the multiple value input data.

The graph (see below) gives a plot of transmitted force reduction as a function offrequency of excitation of the mass representing the machine.



2-stage Vibration Isolation (text, pages 484 - 486)

A 2-stage vibration isolator has an intermediate mass placed between the foundationand the equipment to be isolated with spring isolators between the intermediate massand the foundation and also between the intermediate mass and the equipment to beisolated.

You need to enter the mas of the machine to be isolated, the mass of the intermediatemass, the stiffnesses of the two isolators and the critical damping ratios of the twoisolators. ENC will output the static deflection and resonance frequency for eachsubsystem acting independently (see below), which assumes that the isolatorsconnected to it have their other end connected to a rigid foundation. In addition, forthis calculation the intermediate mass is assumed to be disconnected from themachine to be isolated.

ENC calculates the force transmissibility in dB (20log10[TF]) and plots it (see figureon the page after next) and also calculates the two frequencies of maximumtransmissibility, fa and fb (see figure on next page) as well as the resonance frequencyof the machine with the intermediate mass removed and the resonance frequency ofthe intermediate mass with the machine held fixed.



You can set up the graph to plot transmissibility or amplitude of the machine orintermediate mass complex displacement (modulus of the complex quantity) for aspecified driving force amplitude which you may specify as a peak or rms quantity(see below). The displacement is expressed in dB (peak to peak).



Vibration Absorber (text, pages 494 - 496)

This section allows you to design an optimum vibration absorber (using Eqs. 10.46 -10.48 in the text) to remove the influence of a particular structural or machineresponse frequency. You can also determine the performance of an absorber of anyparticular design using Eqs. 10.42 - 10.45. First the mass of the vibrating machine and the damping ratio of the machine supportis entered. The stiffness of the vibrating machine support or its resonance frequency(frequency of vibration to be reduced) is then entered. After entering the precedingquantities there are two options (specified or optimum absorber - see below).

The first option (specified absorber option - see above) calculates the absorber andmachine response as a function of frequency for the absorber parameters that areentered. This requires that the absorber mass and critical damping ratio be enteredand either the absorber stiffness or its resonance frequency on a hard surface. Theprogram outputs for this option are the two graphs mentioned above, thedisplacement of the absorber and the original and coupled resonance frequencies ofthe absorber and machine mass.



The second option (optimum absorber - see below) does not require that the absorberstiffness or critical damping ratio are entered. It calculates these quantities for anoptimised absorber configuration.

The vibration amplitude (peak, not rms or peak-peak) of the absorber or mass undercontrol is plotted in the graph on the right side of the panel (see next page). You can

choose the frequency range you wish to plot and also enter the peak or rms drivingforce amplitude (see below). You may choose other parameters to plot from themenu (see below).


8.

Sound Power of Equipment(Module 7)

Overview

This module is for the calculation of sound power and sound pressure levels of alarge number of sound sources, including process equipment and transport vehicles.There are 4 separate windows. The first, "sound power and SPL estimation" is for thecalculation of sound power and sound pressure levels of a large number of standardtypes of equipment. The second, "Road Traffic Noise", is for the estimation of roadtraffic noise levels using the UK DoT model, CoRTN. The third, "Highway Noise"is for the estimation of traffic noise using the USA, FHWA Traffic Noise Model(TN). The fourth, "Rail Traffic Noise" is for the estimation of train noise using theUK DoT model.

Sound Power and SPL Estimation

This window is for the calculation of sound power and sound pressure levels of alarge number of standard types of equipment. The estimations done here are usefulwhen manufacturer’s data are not available, but they are not intended to take theplace of measured data - use these calculations only when measured data areimpossible to obtain.

The items of equipment considered here are those discussed in chapter 11 of thetextbook. In many parts of the output, "SPL" is used as short notation for "soundpressure level" and "PWL" is used for "sound power level". Note that forcalculating PWL from SPL and vice versa, it has been assumed throughout thatρc . 400. Clicking on the constants button will simply bring up this message. Allcalculated sound power or sound pressure level data are displayed in a table andplotted on the right side of the screen. Click on the green arrows to the left of thegraph to change the scale on the y-axis and centre the curve on the display.

The data inputs for this module are very self explanatory and are also discussed indetail in the text book. The quantity plotted corresponds to the line in the table below the plot that has a tick on the square at the right end of the line of data (seenext page).

168Chapter 8: Sound Power of Equipment (Module 7)


Note that in many cases, subtracting the octave band corrections listed in thetextbook from the overall sound power or sound pressure level often results in octaveband values that do not add up to the overall level. ENC slightly adjusts the octaveband corrections so that the octave band values exactly add up to the total levelcalculated by the corresponding equation.

To begin, select the equipment of interest from the menu (see next page).



For each type ofequipment in the menu,there is a sub-menu.Each sub-menu itemwill be addressed in thefollowing discussion.For each item selected,ENC calculates anumber of outputs thatare shown in the"output panel" and alsotables of sound poweror sound pressurelevels in octave bands.These latter quantitiesa re a l s o s h o wngraphically.

An example outputpanel for control valvesis shown below. Alloutputs include overallsound power or sound pressure levels, both linear and A-weighted. Octave bandvalues for the same quantities are usually tabulated under the graph on the right ofthe screen.

Note that in some cases the octave band sound power or sound pressure levels willadd up to a little less than the overall level. This is because some energy is presentoutside of the frequency range of the specified octave bands.



Fans (text, pages 432-436)

There are a number of different types of fan from which to choose as shown in thesub-menu illustrated above.

For all of the fans listed in the menu, ENC uses Table 11.2 and Eqns 11.1 & 11.2in the text to calculate the sound power level in octave bands. You need to input thevolume flow rate, percentage of peak efficiency, static pressure, number of fanblades and running speed for each case to be considered.

For all fan types, ENC will output the blade passing frequency in the output panelas well as the octave band and A-weighted overall sound power levels both withinand outside the duct. The sound power and sound pressure levels are output beneaththe graph.



Air Compressors (text, pages 436-439)

The compressor sub-menu is shown below.

The sound pressure levels at 1 m distance from the compressor for the first threeitems on the above list are calculated using Table 11.4 in the text. No output isplaced in the output box for these three and no input data are needed.

The sound power levels for the second three items correspond to the inside of theexit piping. The compressor power in kW is needed as input for all three items. Forthe centrifugal compressor, the impeller tip speed is also needed as an input. For therotary or axial compressor, the number of impeller blades and impeller rpm areneeded as input in addition to the power. For the reciprocating compressor, thenumber of cylinders and crankshaft rpm are needed as input. In addition to theoctave band sound power levels, the outputs for these three items include thefrequency of maximum noise level. The equations used for these calculations are11.3-11.12 in the text. Note that when the octave band levels do not add up to theoverall level calculated according to Eq. 11.5, the octave band levels are correctedby ENC so that they add up to the overall level.

For items 4 to 6 on the list above, corresponding to exterior sound pressure levels,the additional item of input data needed over that required for the interior soundpower level estimates is the mass per unit area of the exit pipe wall. In addition tothe octave band sound power levels, the outputs for these three items include thefrequency of maximum noise level. The exterior sound power levels are calculatedfrom the interior levels using Eq. 11.13.



For the last three items on the list, the only input data needed is the compressorpower and the only outputs provided by ENC are the octave band sound powerlevels external to the exit pipe. These outputs correspond to the exterior soundpower levels calculated in items 4 to 6, except that a different calculation procedure(Eqs. 11.14-11.16) is used.

Refrigeration Compressors (text pages 439-440)

No input data are required for the5 types of compressor listed atright. ENC uses Tables 11.5 and11.6 to calculate the soundpressure levels in octave bands aswell as overall linear and A-weighted at 1 m.



Cooling Towers (text, pages 440-443)

There are four types ofcooling tower fromwhich to choose asindicated by the firstfour lines of the pop-up menu shown atright (three propellert y p e s a n d o n ecentrifugal type). Foreach one, the fanpower and direction ofinterest (front, rear, side or top)needs to be specified also usingthe menu shown at right. Theoutput consists of three linesunder the graph. One linecorresponds to the overallsound power levels in octavebands, the second line represents A-weighted values and the thirdline is a list of directivityindices corresponding to thedirection of radiation chosen (iefront, side, rear or top). Theappropriate directivity indexmust be added to the soundpressure level calculated usingthe sound power level in thefirst line and the excess attenuation effects calculated using module 2. Note that theoctave band corrections given in the text are slightly reduced by ENC to ensure thatthey add up to the overall level calculated using Eqs. 11.19 and 11.20. Note thatoverall linear and A-weighted levels are shown on the bottom left panel.

If any of the three "close in" options are chosen, ENC will give the sound pressurelevel at 1m for the intake and discharge of the cooling tower. The "Direction forDIm" menu disappears as it is no longer relevant. Corresponding octave band levelsare listed for each case beneath the graph and the tick box indicates whether theintake (In) or discharge (Dis) is plotted. Note that for these cases, the total levels inthe bottom left panel are sound pressure levels at 1m.



Pumps (text, pages 443, 444)

The only input data needed are the speed range and pump drive motor power. ENCuses 11.10 and 11.11 in the text to calculate the sound pressure levels at 1 m fromthe pump and these are output beneath the graph in octave bands. ENC alsocalculates and displays overall linear and A-weighted levels.

Jet Noise (text, pages 444-448)

For this calculation you need to input the data listed below. Note that the last twolines are not needed for the sound power calculations, they are only needed for thecalculation of SPL at a specified distance.

The Strouhal number requested for the input applies to the gas flow and is usuallyset at 0.2 in the absence of better information. The density and temperature of theambient gas refer to the gas that surrounds the jet but is not part of it (usually air).The density and temperature of the "gas in jet" refer to the fuel gas upstream of thenozzle exit.



In addition to the octave band sound pressure level at a specified distance and theoctave band sound power level (which are also plotted), ENC provides other outputsas illustrated below.

The outputs are calculated using Eqs. 11.21-11.26, Figure 11.2 and Table 11.11.Note that ENC includes the quantity 10l0g10[ρc/400] on the right hand side ofEquation 11.25 and the equation in item 5, page 527 in the text book.

Control Valves (Gases) (text, pages 449-457)

As there are some errors in the textbook formulation as a result of errors in thereferences used, ENC uses the IEC 60534/8/3 (2000) International standardformulation. Note that ENC provides means to calculate the sound power in andsound pressure radiated by the downstream piping attached to the valve. Radiationfrom the valve body or upstream piping is considered to be negligible according tothe IEC standard.

You may choose the type of valve from the list at right or decide to define allproperties yourself. Choosing a particular type of valve will fix the quantitieslabelled "required Cv", "Fl", "Fd" and "rw". These quantities are, respectively, thevalve flow coefficient,the valve pressurerecovery factor, thevalve style modifiercoefficient and theratio of acoustic powerp r o p a g a t e ddownstream of thevalve to the totala c o u s t i c p o w e rgenerated by thevalve. The quantitiesFlp and Fp in thesecond line are used inthe form Flp/Fl to



replace Fl when fittings are attached to the valve. You can specify "YES" or "NO"for fittings being attached (see figure below).

The quantity Dv is the valve discharge diameter. The "percentage of valve flowcapacity" is the ratio of flow through the valve to maximum rated flow through thevalve expressed as a percentage. The "pipe inside diameter" and "pipe wallthickness" are for the downstream piping. You are also asked to enter the length ofdownstream piping of interest and the longitudinal wave speed in the material (seemodule 1). You can select your gas type from a list of 37 gases, including steam oryou can specify the gas as "user defined". If you select the gas type, ENC willautomatically enter the gas molecular weight and ratio of specific heats.

Following selection of the gas type, there are three inputs required and for eachinput, there is a choice of two parameters to input. Only one of each choice isrequired (see below and the next page). The final two inputs required are the valveupstream and downstream pressures.



The outputs provided by ENC are quite extensive and are shown below.

All of the outputs (including sound power and sound pressure levels) refer to thepiping downstream of the valve. The jet diameter is the diameter of the venacontracta in the valve. The "int. Coinci frequency (Hz)" is the internal coincidencefrequency of the downstream pipe.

In addition to the outputs illustrated above, ENC provides 1/3 octave band plots andtables of octave band values for the following quantities:

• Internal sound power level (downstream piping only - upstream notimportant))

• external sound power level• external sound pressure level at 1m from the pipe wall (downstream piping

only)• pipe wall transmission loss

As for all items discussed in this section, the line corresponding to the ticked box isplotted on the graph. However, in this case, 1/3 octave instead of octave bandresults are plotted so the numbers on the graph (which may be read using the cursor)do not necessarily agree with the numbers in the table.



The pipe wall transmission Loss is calculated using the following procedure:1. Calculate the spectrum of internal sound pressure level using the

procedure described on pages 538 and 539 of the text book.2. Calculate the 1/3 octave band sound pressure levels at 1m using Eqs.

11.47, 11.60, 11.63, 11.65 and 11.67 to 11.69 in the textbook.3. Calculate the 1/3 octave band sound pressure levels immediately outside

the pipe by adding to the levels at 1 m, the second term on the right of Eq.11.65 in the text book.

4. Calculate the 1/3 octave band TL values by subtracting the sound pressurelevel immediately outside the pipe from the sound pressure level insidethe pipe for each 1/3 octave band and add the correction term, Lg (Eq.11.64 in the text book) to account for the internal fluid velocity.



The spectrum of radiated sound power is assumed to have the same shape as theradiated sound pressure.

Control Valves (Liquid) (text, pages 457, 458)

This panel follows the procedures outlined in the international standard, IEC60534-8-4. The procedures in the text book are no longer considered adequate. The inputdata required by ENC are shown in the table below. Note that all calculations arefor noise radiation from the downstream piping. The amount radiated from theupstream piping or the valve is considered negligible.

The outputs that are provided by ENC for the downstream piping are shown belowand on the next page.

The "TL" quantity refers to the Transmission Loss of the downstream piping,calculated according to the standard. The line in the above table that has a tickedbox to its right is plotted in the graph as illustrated at the beginning of this chapter.Note that numbers in boxes below 500 Hz are "greyed out" as the IEC procedure isnot valid at these frequencies.



Control Valves (Steam) (text, page 458)

As steam is a gas, the calculation procedures are the same as for "Control Valves(Gas)" discussed a few pages previously.

Pipe Flow Noise (text, page 459)

The sound power generated inside the pipe is calculated for gases using Eq. 11.60and for vacuum lines using Eq. 11.61. Note that for gases having a density equal tothat of ambient air, Eq, 11.60 underestimates the noise level by 2-4 dB, but for gaseshaving a density 30 times that of ambient air, Eq. 11.60 overestimates the noiselevels by 2-4 dB. The sound pressure level inside the pipe is calculated from thesound power level as for control valves.

The sound power and sound pressure levels external to the pipe can be calculatedfrom the internal levels and the pipe wall transmission loss. There are two possiblechoices for calculating the pipe wall TL. Eq. 11.13 in the text may be used or theIEC procedure that is used for control valve noise may be implemented. The choiceof calculation method is made on the main menu.

Regardless of the TL calculation method chosen, to begin, you need to enter whetherthe calculation is for normal gases or vacuum lines (see below).

If Eq 11.13 is to be used for the TL calculation, the input data specified on the nextpage are required.



If the IEC control valve noise calculation procedure is used for the TL calculations,the data listed in the figure below are needed.



The gas properties for many different gas types can be found in the "Control valves(gas)" panel. For the TL calculated using the IEC standard panel, the molecularweight and ratio of specific heats can be entered automatically by ENC if you selectthe gas of interest from the list.

The sound power and sound pressure outputs are tabulated beneath the graph andshown in the figure below.

In addition to the outputs shown above, ENC provides the frequency of maximumnoise output for the TL calculated using Eq. 11.13 and the outputs shown in thefigure below if the IEC calculation method is used for TL.

As for all items discussed in this chapter, the line corresponding to the ticked boxis plotted on the graph. However, in this case, 1/3 octave instead of octave bandresults are plotted so the numbers on the graph (which may be read using the cursor)do not necessarily agree with the numbers in the table.



Boilers (text, pages 459, 460)

Boiler noise is calculated using Eq. 11.62 for general-purpose boilers and Eq. 11.63for large power plant boilers. You need to choose the type of boiler (from the twobuttons) and enter the boiler power in MW. ENC outputs the overall boiler soundpower level and the octave band sound power levels calculated using Table 11.15in the text. The octave band levels are plotted on the graph.

Turbines (text, pages 460-462)

Gas turbine overall radiated sound power levels arecalculated using Eqs. 11.64, 11.65 and 11.66 for noiseradiated by the casing, inlet and exhaust respectively.For steam turbines, the total sound power level radiated by all parts is calculatedusing Eq. 11.67). The octave band sound power levels for both gas and steamturbines are calculated from the overall levelsusing Table11.16. ENC outputs the overallturbine sound power level (in dB linear anddB(A)) and the octave band sound powerlevels calculated using Tables 11.15 andallows for enclosures (see figure to right) asin Table 11.17 in the text. The octave bandlevels are plotted on the graph. Note that forthe inlet and casing noise, the octave bandlevels do not add up to the overall level - infact they add up to a larger number. This isbecause of the presence of intense tones forwhich the octave band containing them is notpredictable. So a conservative approach has been to assume that they occur in alloctave bands above 250 Hz and make the octave band corrections accordingly. Theunfortunate result is that the octave band noise levels then add up to more than the



overall level. However this is probably preferable to under predicting the noise insome octave bands.

Diesel and Gas Driven Engines (text, pages 462-465)

The noise radiated by this equipment isdivided into three components: exhaust,casing and inlet. Each component istreated separately by ENC and thecomponent of interest is selected from the"noise type" menu shown below.For all noise types, the overall soundpower levels are calculated by ENC as well as the octave band sound power levels.The latter are adjusted slightly so that they add up to the overall level (logarithmicaddition) and are plotted on the graph.

Exhaust Noise (text, pages 462, 463). If the "exhaust noise" option is chosen (withor without the turbocharger), the input data required are those shown below.

In addition, the type of muffler used can be specified using the menu illustratedbelow.



The outputs generated by this panel are calculated using Eq. 11.68 and tables 11.18and 11.19 in the text.

Casing Noise (text, pages 463, 464). If the casing noise option (with or without theroots blower) is chosen, the required input data are shown below.

As can be seen you are provided with a selection for each of four input parameters.ENC uses Eq. 11.69 and Tables 11.20 and 11.21 in the text to do the calculations.

Inlet Noise (text, page 463, 465). If the inlet noise option is chosen, the requiredinput data are shown below.

Equation 11.70 and Table 11.22 are used by ENC to provide the outputs.

Furnaces (pages 465, 466)

There are two types of furnace included in the equipment list. The first categoryincludes oil burners and low pressure drop gas burners and the second categoryincludes high pressure gas burners.



For the oil burner, the input data shown in the figure below are needed.

For the low pressure gas burner, the input data shown below are needed.

The sound power of the primary and secondary air in both cases is calculated usingEqs. 11.88 and Eq. 11.89 in the text. For the oil burner, fuel flow noise isnegligible, whereas for the low pressure drop gas burner, (less than 100 kPa), thefuel flow noise is calculated using Eqs. 11.21-11.26 in the text. The Strouhal numberrequested for the input applies to the fuel jet. The air jet Strouhal number is set at1.0 whereas the fuel gas Strouhal number may be entered by the user and is usuallyset equal to 0.2 in the absence of better information. The density and temperature ofthe ambient gas refer to the gas that surrounds the jet but is not part of it (usuallyair). The density and temperature of the "gas in jet" refer to the fuel gas upstreamof the nozzle exit. Octave band levels are calculated from the overall level by



following the procedure described on page 552 of the text and then adjusted so thatthey add up to the overall level calculated using the appropriate equation in the textbook.

The sound power of combustion noise is calculated using Eq. 11.91 in the text. Theoctave band values are calculated as described on page 553 of the text.

ENC outputs the overall sound power levels (both linear and dB(A)) for air flownoise, fuel flow noise and combustion noise as well as the overall levels arising fromall sources combined (see below).

Octave band levels for each case except the last case (SPL at 1m) are provided ina table below the graph. The spectrum shape for the SPL at 1m is the same as theoverall PWL and the levels at all frequencies are 9 dB lower for the SPL at 1 m.

For high pressure drop gas burners, the calculations are the same as above, exceptfor the fuel flow noise which must be calculated in the same way as for valve noise(using the IEC standard procedure). This is why there are many more parametersto enter than for the low pressure drop fuel flow (see next page). You should referto the discussion on valve noise for explanations of the parameters. The outputs arethe same as for the low pressure drop burners.



Electric Motors (text, pages 466,467)

First of all you need to select the type of electric motor from the menu shown above.In addition the motor power and speed needs to be entered (see next page).



ENC uses Equations 11.75 & 11.76 and Tables 11.23 & 11.24 to calculate the soundpressure level at 1 m (overall and in octave bands). The octave band sound pressurelevels are adjusted slightly so that they add up to the overall level (Eqs 11.75 and11.76) and they are also plotted on the graph. Note that ENC includes the quantity10l0g10[ρc/400] on the right hand side of Equations 11.92 and 11.93 in the textbook.

Generators (text, pages 467, 468)

For this equipment, only two input data items are needed (see below).

ENC uses Eq. 11.77 and Table 11.25 to calculate the overall and octave band soundpower levels. The octave band levels are plotted on the graph.

Transformers (text, pages 467, 468)

First you need to select the transformer location and then specify its NEMA ratingand surface area. ENC then uses Eq. 11.78 and Table 11.26 in the text to calculatethe octave band sound power levels which are added together to give the overalllevel and are also plotted on the graph.

ENC can also calculate the NEMA rating based on the transformer power (see table11.28 in the text and also the next page).



Gears (text, page 469)

First you need to select the type of gear mesh (only two buttons) and then specifythe power being transmitted and the rpm of the slowest wheel in the mesh.. ENCthen uses Eq. 11.79 and the procedure explained in the following lines in the text tocalculate the octave band sound pressure levels at 1 m from the gearbox and theselevels are also plotted on the graph. Note that ENC includes the quantity10l0g10[ρc/400] on the right hand side of Equation 11.96 in the text book.



Transportation Noise (text, pp. 557-568)

ENC calculates noise due to road and rail traffic. However, calculation of aircraftnoise is a very complex procedure and ENC does not calculate any aircraft noise.Specialised software should be used for this.

Traffic noise is calculated using 2 models. The first is CoRTN, developed in the UKby the Department of Transport and the second is TNM, developed in the USA bythe Federal Highway Administration (FHWA). Train noise is calculated using theUK model developed by the Department of Transport.

Traffic noise - CoRTN (text, pp. 557-560)

This window calculates L10 noise levels averaged over 1 hour intervals and over 18hours, using the UK Dept. of Transport CoRTN model. The noise levels arecalculated using a base level proportional to traffic volume with corrections addedto account for the percentage of heavy vehicles, the road gradient, the type andcondition of the road surface, the ground type, the distance to the observer, the angleof view and the presence of any barriers. In the text book, the corrections due toground and distance are lumped together, but in ENC they are treated separately asthey are in the published CoRTN model. Note that the road must be divided intosegments and the sound levels at the observer calculated for each segment using thisENC window. The overall noise level at any particular observer location is thenfound by adding the individual contributions together using module 1 of ENC.

To begin, decide onwhether you will bedefining the average vehicle speed or whether youwould prefer to enter the road type and then haveENC determine the average vehicle speedaccording to the CoRTN model (see right).

If you left click on "NOTE", the explanatory notebelow will appear.



Next, decide on whether single hour or 18-hour L10 noise levels need to becalculated. Enter the total number of vehicles if you want to calculate the 18-hourL10 noise levels (see below).

Enter the number of vehicles per hour for each hourly interval if you want tocalculate the single hourly L10 noise levels (see below).

Enter the percentage of heavy vehicles in the locations shown in the above twofigures. ENC uses this to calculate Cuse. Note that the 18-hour L10 noise level canalso be calculated from the single hourly L10 noise levels (see bottom of figureabove). The calculation is done by taking the logarithmic average of the singlehourly values and for the same number of vehicles is slightly different to the 18-hourvalue calculated in the upper figure.



The L10 noise levels are calculated using Equations 11.97 and 11.98 in the text book.These equations use the data in the previous tables plus some additional correctionfactors to account for the effects of road gradient, Cgrad , the type and condition ofthe road surface, Ccond , the ground type, Cground , the distance to the observer, Cdist ,the angle of view, Cview , the presence of any barriers, Cbarrier , and reflection effects,Creflection . The calculation of each of these is done as shown on the following panels.In the panel below, the measured speed would correspond to the "user defined"selection for the panels shown two pages back.

Following the approach ofCoRTN, which is slightlydifferent to the text book, thedistance correction is separatedfrom the ground correction (see below). Note that the distance entered by the useris the perpendicular distance from the observer to the road segment (or extendedroad segment).

Corrections for barriers, field of view subtended by the road segment to the observerand reflections are calculated using the panels illustrated in the following figure.



The total correction due to all the effects mentioned above is calculated byarithmetically summing them all, except that only the larger of the ground correctionand barrier correction is used.

If there are widely separated carriageways, the levels for each carriageway arecalculated separately and then added together using module 1.

Traffic noise - FHWA-TNM (text, pp. 561-562)

This window calculates road traffic noise according to the USA FHWA TrafficNoise Model (TNM). The user must enter the vehicle emission level, which is themaximum sound pressure level measured during a pass-by test at the nominatedspeed (also entered by the user) at a perpendicular distance of 15 m from the centreline of the traffic lane (or centre of the vehicle). There is a large data base ofemission levels for a large number of vehicle types and operating conditionsavailable from FHWA. Note that as for CoRTN, the noise level must be calculatedfor each lane of traffic and each vehicle type and the results combinedlogarithmically using module 1. The road must also be divided into segments thatsubtend no more than 10 degrees at the observer. Please click on "NOTE" near thetop of the screen and read it before starting (see below).

After entering the vehicle emission level for the particular vehicle type beingconsidered, enter the number of vehicles of this type for each hourly interval listedin the following table. Then enter the vehicle average speed for each hourly interval(many values will not vary from one hour to the next). The adjustment for shieldingand ground effects as described by the FHWA model is complex and not followedexplicitly by ENC. Instead, the user may use module 2 for these calculations andenter the overall ground and barrier correction in the column labelled "adjustmentfor shielding etc."



The adjustment for distance can be entered directly or calculated using the panel onthe right hand side of the window. If this is the case, then the "input directly optionmust be selected. If the other option, "usethe following calculated value" is selected,then the value, Adj. for distance (dB)calculated in the panel at right isautomatically entered by ENC into the column inthe left panel labelled, "Adjustment for distance".Note that the lower half of the panel at right isgreyed out unless the perpendicular distance of theobserver is less than 0.3m and the subtended angleis less than 20 degrees.

The quantities, "perpendicular distance fromobserver to segment line", "angle subtended atobserver by segment" and "distances from theobserver to each end of the segment are defined inthe figure on the next page. The latter twoquantities are defined by d1 and d2on the figure.



Angle subtendedby segment at receiver

Lane (or road) segment

Road segmentextension d1

d2

Observer

perpendicular distance of observer from lane centre

Rail Traffic noise - UK DoT (text, pp. 563-568)

This window calculates 6-hour and 18-hour equivalent noise levels at an observerlocation generated by a segment of railway track with a train running on it. Theobserver location must be at a normal distance greater than 10m from the tracksegment (or its extension). The track segments are selected so that the noisevariation at the observer location from one end of the track segment to another doesnot vary by more than 2 dB. Once the noise levels at the observer location due toeach train type on each track segment have been calculated, they are addedlogarithmically using the procedures in module 1 of ENC.

The first step is to divide the track into reasonable segments that satisfy the <2 dBnoise level variation. Next is to select the type of train or rolling stock for whichnoise levels are to be calculated. This is done by clicking on the two items shownbelow and selecting an item from each drop down menu. ENC calculates thecorrection term, C1, for train type, based onyour two selections. If "self defined" isselected in the lower drop downmenu, then you must enter your ownvalue for C1.

Next, you must enter the number ofvehicles of this type in each train thatpasses by (see figure atright).



The next step is toenter the track type(see right) and ENCwill calculate thecorrection C2 fortrack type. If the"self defined" optionis chosen fromthe drop downmenu, you willneed to enteryour own valueof C2 . For eithercase, you mustenter the speed of the train in km/hour.

With the vehicle data entered as described above, ENC can calculate values forsound exposure level (SEL) of a single vehicle (SELv or SELv in ENC), defined byEquations 11.110 and 11.111 in the text book. SEL is defined on page 125 in thetext book. SELTi (or SEL_Ti in ENC) for each vehicle type is then calculated usingEquation 11.109 together with the number of vehicles of this type entered by theuser. Note that this quantity has also been corrected for the track type by adding thecorrection, C2, from Table 11.32 in the text book. Note also that this result is foronly one vehicle type and one track segment. The quantity SEL (dBA) is calculatedby adding the total of all the correction terms calculated in the left hand panel toSEL_Ti.The total of all the correction terms is the quantity in the bottom left panel.

Calculation of the above-mentioned correction terms requires you to enter therequired data in the left hand panel. These correction terms account for the effectsof air absorption, Cabs , the ground type, Cground , the distance to the observer, Cdist ,the angle of view, Cview , the presence of any barriers, Cbarrier , and reflection effects,Creflection . In addition there is a correction to account for the presence of ballast tosupport the railway sleepers, Cothers , which applies to all segments of the track exceptthe one closest to the observer. The calculation of each of these is done as shownon the following panels. The first panel (shown on the next page) calculates thecorrections due to distance from the track (near side), the correction due to airabsorption and the correction due to the ground. You must enter the normalhorizontal distance from the track segment (or its extension if necessary) to theobserver, the height of the track above the ground between the track and observerand the height of the observer above the ground. Finally enter the percentage of softground between the track segment and observer. ENC will then calculate the straightline normal distance from the track to the observer. Note that this distance isdifferent for diesel locomotives as the effective source height in this case is 4 mabove the track. ENC will also calculate the corresponding three correction termsindicated in blue font.



R

segment length near side of track

line bisectingangle of view

In the above panel, note that all distances from the observer are to the rail on theNEAR side of the track. Note that normal distances are to the track segment wherepossible, or its extension when the line from the observer to the track segmentcannot meet the track at 90 degrees.

The next correction term is that for any barriers or buildings between the observerand track segment. This is a much simpler procedure than we use in module 2 andas such is not very accurate. The distances requested are all referenced to the nearside rail.

The next correction term is toaccount for the view angle, α,and the field of view, β, definedin the figure at right where R isthe observer.



The corrections due to reflections and ballast supporting the track sleepers arecalculated next and all that you need to do is click on the appropriate boxes (seebelow).

ENC then combines all the correction terms into a single number as shown below.

ENC will then calculate the overall SEL for that particular track segment and vehicletype, taking into account all of the correction terms as well as the number of vehiclesof that type. The overall SEL for a particular train and track segment is calculatedby combining logarithmically the SEL values for each vehicle type. This can be doneby opening another ENC window and using module 1. The overall SEL for all of thetrack segments is also calculated by combining the overall values for each tracksegment (including all vehicle types making up the train) using module 1.

If you enter the number of trains that pass by in a particular period (see panelbelow), ENC calculates the night-time and day-time LAeq,6h and LAeq,18h , respectivelyfor the particular vehicle type and track segment.



To get the overall noise levels, it is necessary to repeat the calculations for allvehicle types and all track segments and add the results together. Each train may alsohave to be treated separately as the number and type of vehicles may vary from trainto train. This just makes the procedure more tedious, but the end result is stillobtained by combining all of the individual results together using module 1. Pleaseread the note in ENC which is reproduced below.


φ 'f (k (ct ± r ))

r

TEXTBOOK ERRATA - 3rd Edn.FIRST PRINTING

p xi, Change "Noise Reduction Index (NRI)" to "Noise Reduction Coefficient(NRC)"

p xv, change "FWHA" to "FHWA"

p xviii In line 19, change "Noise Reduction Index" to "Noise ReductionCoefficient"

p16, In line 3, change the equation to (1 /hf) E /ρ > 2

p16, line 10, change DP = 1.346E to DP = 1.099E

p16, Change Eq. (1.3) to

p18, In Eq. (1.5), change "332" to "331"

p27, Change Eq. 1.40a to

p29, 3 lines above Eq, (1.50), change "1.36" to "1.41"

p34, Change the reference just above Eq. (1.69) to "Fahy, 1995" p35, First line under Eq. (1.67), change "1.65" to "1.64"

p41, 4 lines above Section 1.10., replace "pet" with "per"

p45, 2 lines under Eq. (1.89) and in Eq. (1.90), remove the subscript, " t "from pt.

p51, Table 1.3, line 3, replace "U " with "u"

p51, Table 1.3, line 5, replace "Zd " with "ZA "

p51, Heading 1.12.2, replace "Z " with "Zs"

p72, line immediately below the figure, add "is the" after the word, "ordinate"

p76, Line 13, change "sound" to "sounds"

DC 'DF

1 %DF

EW

2Rt

%ρw

ρν2

203Third edition textbook errata


DND ' 2(L )

Aeq,8h & 90) /L

Ta ' 8×2&(91.2 & 90.0) /3 ' 8/20.39 ' 6.1 hours

p87, 2 lines above Example 2.1, the text should read, "Figure 2.10(b) is analternative representation of Figure 2.10(a)"

p111, line 4, change "1252" to "61252".

p134, 3rd line, replace H with H )

p142, The number "3" and "0.3" should be replaced by "3.01" and "0.301"respectively in Equations (4.37) to (4.41) inclusive

p143, Replace equation 4.43 and the 2 lines preceding it with:The daily noise dose (DND), or "noise exposure", is defined as equal to 8 hoursdivided by the allowed exposure time, Ta with LB set equal to 90. That is:

p143, Replace the sentence following equation (4.42) with: "If the number ofhours of exposure is different to 8, then to find the actual allowedexposure time to the given noise environment, the "8" in Equation(4.42) is replaced by the actual number of hours of exposure."

p144, 3rd equation down should be:

p147, Replace Figure 4.6 with the more accurate figure below.



impact and steady state (equal energy)

5 dB / doublingsteady state

impulse180

170

160

150

140

130

120

110

100

90

0.1 1 10 10 10 10 10 10 10 10 102 3 4 5 6 7 8 92 5 5 5 5 5 5 5 5

8-hour dB(A)equivalent

B-duration x number of impulses (ms)

Peak

sou

nd p

ress

ure

leve

l (dB

re 2

0 Pa

)

p147, 4 lines under Figure 4.6, change "1414" to "1474".

p149, 5th and 6th lines from the top, change "645" to "60645" in four places.

p150, 13 lines from the bottom, change Figure 4.6 to Figure 4.7.

p153, First line after the headings in Table 4.6, change "0.06" to "0.6".

p157, Fig 4.9 caption, add "MAF" = minimum audible field.

p160, On y-axis, change label from "dB re 20 mPa" to "dB re 20 µPa"

p165, First paragraph in section 4.9, replace "1995" with "1995, 1999".

p176, Line above Eq. (5.6), change "r" to "r = a"

p176, In Eq (5.6), change "r" to "a"

p177, In Eq. (5.7), change "r" to "a"

p179, 2 lines under figure 5.2, replace "(x,y)" with "O" and label the observeras O in Figure 5.2

p192, 2 lines above Eq. (5.71), add "each of which has a radius of ai"immediately after "sources"



p192, 2 lines above Eq. (5.72), change "a" to "ai"

p192, Line above Eq. (5.72), change "ka" to "kai"

p192, In Eq. (5.72), change "a" to "ai" in 5 places

p192 Eq. 5.71 and below, change Q to in 4 placesQ

p192 last line add "amplitude" immediately after "velocity"

p193 Eq 5.73 and below change Q to in 2 placesQ

p225, In Table 5.3 caption, change "Sutherland et al., 1974" to "Sutherlandand Bass, 1979"

p226, 13 lines above Eq. (5.171), change "2613" to "9613".

p226, Paragraph beginning "Note that ISO" only applies to overall A-Weighted calculations and should be deleted here. The paragraphfollowing this one should also be deleted as the meteorological effectsshould not be taken into account in two separate places - either theyshould be included in the barrier calculations or calculated separatelybut not both.

p229, Interchange the 63 Hz and 2000 Hz labels on the curves in Fig. 5.19.

p232, Eq. 5.181, change "-0.09" to "-0.9"

p236, In Eq. (5.188) change "10.3" to "10.0"

p241, Table 5.9, -3.0<<<+0.5 should be replaced with -3.0<<<-0.5

p244, ISO 9613-2 procedures for calculating ground effects and shieldingeffects are based on an assumption of downwind propagation from thesound source to the receiver. Thus the only correction term (Equation(5.193)) that is offered by ISO for meteorological effects is a term toreduce the A-weighted calculated sound pressure level for long timeaverages of several months to a year. Thus section 5.11.12.4.should bedeleted and replaced with the paragraph above.

p251, In Figure 6.1, in the centre on the right hand side replaceγ ' 1/κ with γ ' κ

p253, 2 lines above section 6.6, change "1989" to "1995".



NRC 'α250 % α500 % α1000 % α2000

4(7.76)

p259, The equation numbered "6.12" should be numbered "6.11"

p264, The equation numbered "6.25" should be numbered "6.24"

p264, 2 lines below Eq. 6.20, replace S1 with 1/S1

p264, 3 lines below Eq. 6.20, replace S2 with 1/S2

p267, The first equation should be numbered "6.26"

p267, In Fig 6.3, there are two curves labelled "4". The lower curve should belabelled "5"

p292, 3 lines above Eq. 7.52, change to and add "at time t=0"¢p 2k (t) ¦ ¢p 2

k (0) ¦after "mode k"

p292, 2 lines above Eq. 7.52, change to ¢p 2k (t) ¦ ¢p 2

k (0) ¦p292, In Eq. 7.52, change to ¢p 2

k (t) ¦ ¢p 2k (0) ¦

p293, 3 lines above Eq. 7.55, change pk to pk(0)

p293 6 lines from the bottom, there should be a minus sign before loge

p294, 5 lines from the bottom, change (2000) to (2001)

p294, Eq. (7.59), replace 0.16V

Swith

0.16V

S 2

p295, Eq. (7.64), multiply each of the three terms in brackets by -1

p295, 2 lines beneath Eq. (7.62), add "energy" before "reflection"

p295, 2 lines above Equation (7.64), change "2001" to "2000"

p296, lines 2 and 3, change "Sx , Sx and Sx " to , "Sx , Sy and Sz "

p301, In each of the top two lines of the table, add "(m2)" after Sα

p303, Section 7.7.2, change "NRI" to "NRC" in three places and change"Noise Reduction Index" to "Noise Reduction Coefficient" in twoplaces. Also change Eq. 7.76 to:



p303, 2 lines from bottom, change "20 mm" to "20 µm"

p304, Caption of Figure 7.6, line 1, change "porous surface" to "rigidly backedporous material" and in the last line, change "L" to R

p310, Immediately following Equation (7.88), add the following: "Note thatfor square, clamped-edge panels, the fundamental resonance frequencyis 1.83 times that calculated using Equation (8.21). For panels withaspect ratios of 1.5, 2, 3, 6, 8 and 10 the factors are 1.89, 1.99, 2.11,2.23, 2.25 and 2.26 respectively."

p310, Equation 7.85 should be: ξc 'ffc

1/2

p311, End of second full paragraph, change "Elbert" to "Elfert"

p329, Eq. (7.122), replace T60u with1

T60u

p330, 10th line, change "2000" to "2001"

p339, 12th line from the bottom, change "1973" to "1988"

p343, 5 lines above the figure, change "ASTM E90-66T" to "ASTM E413-87"

p347, replace the line immediately above section 8.2.4 and the last word in theline above that with "contour value at 2000 Hz is increased by 1 dB."and add "Note that IIC, Rw and STC values are all reported as integers."

p352, 3 lines under Equation (8.36), change "below" to "above".

p353, change x-axis label to f (Hz) (log scale)"

p354, 2nd and 3rd lines from the bottom, replace "8.37" with "8.38"

p355, 2nd line after Eq. 8.44, replace fc2 /2 with fc1 /2

p355, 3rd line, replace "8.37" with "8.38"

p359, In Eq. 8.50, replace 10 log10 m1 with 20 log10 m1

p360, change x-axis label to "frequency (Hz) (log scale)"

p360, on the x-axis of the figure, change "0.5 fc2" to "0.5 fc1"

p360, first line of item (b) in the caption, change to "LineBpoint support ( fc2



20 % 20log10 (2500/100) & 6 ' 42.0 dB

h ' 1 &f

fc1

2 2

1 &f

fc2

2 2

D '

2h

if f < 0.9 × fc1

π fc1

8 fη1η2

fc2

fif f > 0.9 × fc1

is the critical frequency of the point supported panel)"

p360, Under "Point B", item (a), replace "30log10 fc2" with "20log10 fc1 +10log10 fc2"

p360, Under "Point B", items (b) and (c), replace "40log10 fc2" with "20log10 fc1

+ 20log10 fc2"

p360, Eq (a) under "Point C", add the term, "20 log10 (fc2 / fc1)" to the RHS ofthe equation

p360, last Eqn., change f l to fR

p361, replace Eq. 8.55 with:

p363, 6 lines from the bottom of the page, change the equation to:

p363, 4 lines from the bottom of the page, change "77" to "78" and "61" to"60" in 2 places

p363, last line, change "61" to "60" and "52" to "51"

p365, Section 8.2.6.2, 5 lines down, replace the sentence beginning with"Alternatively" with the following: "This mechanism can be consideredto approximately double the loss factor of the base panels. Alternatively,the panels could be connected together with a layer of visco-elasticmaterial to give a loss factor of about 0.2."

p365, Section 8.2.6.2, 9 lines down, after the words "(0.3 to 0.6 m)", add thewords, "or connected with a layer of visco-elastic material or evennailed together".



Ab ' 15.8 % 20log10[5.8/4.5] ' 18.0 dB; AR ' 1.3 dB; Ab % AR ' 19.3 dB

Ab ' 19.8 % 20log10[7.2 /4] ' 24.9 dB; AR ' 2.6 dB; Ab % AR ' 27.5 dB

Ab ' 19.5 % 20log10[7.5/4.5] ' 23.9 dB; AR ' 5 dB; Ab % AR ' 28.9 dB

p371, In the 500 Hz column, 7th number from the bottom, replace S1" with"51"

p379, 2 lines above "Example 8.4", change "Example 8.7" to "Example 8.8"

p380, replace the example table with the following table.

Octave band centre frequency (Hz)

63 125 250 500 1000 2000 4000 8000

TL from Table 8.2 30 36 37 40 46 54 57 59 from Table 7.1 0.013 0.013 0.015 0.02 0.03 0.04 0.05 0.06αw from Table 7.1 0.01 0.01 0.01 0.01 0.02 0.02 0.02 0.03α f

Si (m) 0.463 0.463 0.525 0.68 1.05 1.36 1.67 2.04α67 67 59 45.6 29.5 22.8 18.6 15.2SE /Siα i

10log10( ) 18 18 18 17 15 14 13 12SE /Siα iNR (dB) 12 18 19 23 31 40 44 47

p381, 3rd line down, Equation (8.75) should be (8.65), 6 lines down Equation(8.76) should be (8.66) and 8 lines down, Equation (8.6), should be(8.65).

p381, 4th Eq. in section 3, "30.5/30" should be "30.5/31"

p391, At the end of the paragraph above the figure, add the following sentences."When paths involving the ground reflected wave on the source side areconsidered, the straight line distance, d, used in Equation (8.85) is thedistance between the image source and the receiver. The same reasoningapplies to paths involving ground reflections on the receiver side."

p394, 3 lines following Eq. 8.98, replace "barier" with "barrier".

p395, replace the four equations for Ab with the following in the same order

Ab % AR ' 19.3 dB

p395, 6 lines from the bottom, replace "4.6" with "4.7"

p395, Solution, item 1, last line, change "5.18" to "5.20".



R)s ' R θ cosα

h )

s ' Hb & R θ sinα

α '12

(π & θ) & β

β ' cos&1 (Hb /A)

θ ' ±cos&1 [1 & (A 2 /2R 2 ) ], *R* > A /2

N ' ±2λ

X 2S % (hb & ZS )2 1/2

% X 2R % (hb & ZR )2 1/2

% b2% Y 2

1 /2& d

Ab ' 12.0 % 20log10[4.5/4] ' 13.0 dB

Ab ' 19.8 % 20log10[7.2/4] ' 24.9 dB

p396, replace the two equations for Ab with the following in the same order.

p396, Item 3, lines 2 and 3, change the numbers to 19.3 dB, 19.3 dB, 27.5 dB,28.9 dB, 28.9 dB, 13 dB, 24.9 dB and 24.9 dB

p396, Item 3, line 4, change "5.18" to "5.20".

p396, Item 3, line 4, change "10 dB" to "12 dB"

p399, Figure 8.19, replace r with R

p399, Replace Eq. (8.100) with:

p400, 1st paragraph, change "Figure 8.12" to "Figure 8.14"

p401, Eq. (8.107) should be:

p404, Figure 8.21 is missing (see following figure)



Xc ' [41.6(m /h )1/2ξc (1 & 1/ξc )&1/4 ] & [258h / Rξc )] (8.116)

Cc ' 0.232ξc R /h (8.117)

Xm ' [226(m /h)1/2ξc (1 & ξ 2c ) ] & [258h / (Rξc )] (8.119)

Octave band centre frequency (Hz)63 125 250 500 1000 2000 4000 8000

0

10

20

30

40

50O

ctav

e ba

nd in

serti

on lo

ss

Figure 8.21 Typical pipe lagging insertion loss for 50 mm glass-fibre, density 70-90 kg/m3, covered with a lead / aluminium jacket ofsurface density, 6 kg/m2. The I symbols represent variations inmeasured values for three pipe diameters (75 mm, 150 mm and 360mm).

p405, Replace Equations (8.116), (8.117) and (8.119) with the following:

p415, lines 6 and 7 under Eq 9.16, replace with, "the end correction. In this case,> = 0. For a"

p417, replace the text between Eqs. (9.25) and (9.26) with:"An alternative expression for the effective length, which may give slightlybetter results than Equation (9.25), for grazing flow across the holes, andwhich only applies for flow speeds such that , is (Dickey anduτ / (ωd ) > 0.03



Selamet, 2001)"

p429, Move Equation (9.52) up one line.

p432, Item 5, line 1, Replace "Equation (8.48)" with "Equation (9.52)"

p439, line following Equation (9.81), replace µ with fm

p444, In Table 9.2, "19" should be "-19"

p459, Figure 9.21, x-axis label, change "S" to "A" and in the caption add "open"immediately before "duct".

p461, In the equation in the centre of the page, change "6" to "5"

p461, 4 lines below the equation in the middle of the page, change "5.5" to "7"

p461, 8 lines below the equation in the middle of the page, change "12.5" to"13"

p462, line 1, change "1.2" to "1.0"

p462, Figure 9.23 caption, last line, change "1992" to "1987"

p464, Replace Table 9.5 with the following:

Octave band centre frequency (Hz)Ductdiameter (mm) 63 125 250 500 1000 2000

150 18(20) 13(14) 8(9) 4(5) 1(2) 0(1)200 16(18) 11(12) 6(7) 2(3) 1(1) 0(0)250 14(16) 9(11) 5(6) 2(2) 1(1) 0(0)300 13(14) 8(9) 4(5) 1(2) 0(1) 0(0)400 10(12) 6(7) 2(3) 1(1) 0(0) 0(0)510 9(10) 5(6) 2(2) 1(1) 0(0) 0(0)610 8(9) 4(5) 1(2) 0(1) 0(0) 0(0)710 7(8) 3(4) 1(1) 0(0) 0(0) 0(0)810 6(7) 2(3) 1(1) 0(0) 0(0) 0(0)910 5(6) 2(3) 1(1) 0(0) 0(0) 0(0)1220 4(5) 1(2) 0(1) 0(0) 0(0) 0(0)1830 2(3) 1(1) 0(0) 0(0) 0(0) 0(0)



p470, Figure 9.27, caption, and Eq. (9.115), replace "D" with "d"

p471, Eq. (9.116) and (9.117) and 2 lines below Fig. 9.28, replace "D" with "d"

p476, 3rd and 6th line of the first paragraph, change "1979" to "1978"

p478, line above Equation (10.14), change "1979" to "1978"

p479, Figure 10.2, replace the lowest y-axis label (currently 0) with 0.02

p483, In Equation (10.18) and 2 lines above it, replace "e" with "q" to avoidconfusion with the distance, e, between spring supports.

p484, In Figure 10.6, the force should be shown as acting on mass m2, not massm1.

p485In Eqs. (10.25a,b), the left hand side should be squared.

p487, line above Equation (10.31), change "1986" to "1988"

p495, Equation (10.42), remove the symbol "d" from the right hand side.

P496, Equation (10.48), replace "d" with |F|/ k1

p496, Equation (10.47), the numerator on the RHS should be 3( m2 /m1)3

p498, 8 lines from the top of the page, change "1979" to "1978"

p513, Table 11.2, 3rd line in 2000 Hz column should be "25"

p513, Table 11.2, the 8000 Hz column should be replaced with 13, 15, 18, 27,35, 35, 26, 32, 32, 34, 42 and 44 respectively and the BFI column for thetwo tubeaxial entries should be " 7 "

p513, Remove the paragraph containing Equation (11.2) and remove "(11.2)" inthe second to bottom line.

p514, last Equation, label (11.2)

p515, Example 11.1 table, replace "30" with "36"

p517, Equation (11.10), change to:



Lw ' 72 % 13.5 log10 kW (dB re 10&12 W)

p526, last line, change "8.8" to "8.3"

p528, replace the values in the table with the following.

0 72 77 80 81 80 76 69 6360 74 79 82 83 82 78 71 65120 61 66 69 70 69 65 58 52180 55 60 63 64 63 59 52 46

p535, 4 lines above Eq.(11.33), and 2 lines after Eq. (11.34), change "534" to"60534".

p536, 4 lines from the bottom, change "534" to "60534".

p541, Following Eq. 11.64, insert the statement, "If the second term in bracketsof Equation (11.64) exceeds 0.3, it is set equal to 0.3".

p542, line 3, change "534" to "60534".

p542, Immediately before Equation (11.67), add the following: "Note that thefinal spectrum levels must all be adjusted by adding or subtracting aconstant decibel number so that when A-weighted and added together, theresult is identical to the A-weighted overall levels form Equations (11.65)and (11.66)."

p543, 1 line and 4 lines above Eq. (11.70), change "534" to "60534".

p544, Equation 11.73, second term on the right should have the "log10" removedand "17.27" replaced with "17.37", so it reads "- 17.37(...........)"

p544, Replace the last paragraph with, "The octave band external sound pressurelevels may be calculated using Equations (11.73) and (11.76) with octaveband sound power levels used in Equation (11.76) instead of overallsound power levels."

p552, The constant in Equation (11.89) should be "55", not "53".

p558, Replace the paragraph following Table 11.29 with the following:"The road surface or condition correction is taken as zero for either sealedroads at speeds above 75 km/hr or gravel roads. For speeds below 75



SELref ' SELv % 10 log10 N % C2

km/hr on impervious sealed roads, the correction is -1 dB. For perviousroad surfaces, the correction is -3.5 dB. For concrete roads with deeprandom grooves greater than 5 mm in width, the correction is, Ccond = 4- 0.03P where P is the percentage of heavy vehicles."

p559, Replace the nine lines following Eq. 11.102 with the following:"Low barriers such as twin beam metal crash barriers can have less effectthan soft ground. So if these are used with any proportion, Pd , of softground, their effect should be calculated by looking at the lower noiselevel (or the most negative correction) resulting from the following twocalculations:

$ Soft ground correction (0 < Pd < 1.0), excluding the barriercorrection; and

$ hard-ground correction (Pd = 0) plus the barrier correction."

p560, Remove the sentence beginning 12 lines from the bottom of the page,"Note that the two values for $ must add up to 180E "

p561, In the heading and first line, change "FWHA" to "FHWA"

p561, 6 lines from the bottom, add "Menge, et al.," before "1998".

p562, 4 lines under Equation (11.108), add "Menge, et al.," before "1998".

p563, 5th line in first paragraph, and 3 lines under Equation (11.109), replace"1995" with "U.K. DOT, 1995a".

p563, 3 lines under Equation (11.111), replace "1995" with "U.K. DOT,1995a,b".

p563, p564, Replace the last two lines of page 563 and the top three lines of page564 with the following:"Note that different vehicle types must be considered as separatetrains. For any specific train type consisting of N identical units, thequantity SELref is calculated by adding 10log10N to SELv. In additionthe track correction, C2 from Table 11.32 must also be added so that:

p564, The second entry of "Freight vehicles, tread braked, 2 axles" shouldactually be "Freight vehicles, disc braked, 4 axles"



p565, Lines 1 and 3, change SEL to SELref.

p565, table 11.32, add ,C2, after "Correction" in the column 2 label.

p567, In Equation (11.121), remove the minus sign

p568, Add equation numbers, 11.122 and 11.123 to the equations at the top ofthe page.

p580, 10 lines above Equation (12.1), change "1985" to "1986".

p609, line 2 in the table for fresh water, change "988" to "998".

p609, line in the table for iron, Young’s Modulus = 206, density =7,600, =E /ρ4910, 0 = 0.0005 and < = 0.27.

p609, line in the table for Nylon, move the "6.6" next to "nylon" and Young’sModulus = 2, density =1,140, = 1,320.E /ρ

p609, line in table for lead, loss factor = 0.015

p609, line in table for concrete, loss factor = 0.005 - 0.02

p610, the last column of numbers is the density and the 2nd last column isYoung’s modulus.

p617, In figure captions, change "C.6" to "C.5" and "C.5" to "C.6".

p621, Change number of Eq. 1.36 to C.24.

p622, In Equation (C.29), replace ZN with ZN /Dc

p623, In Equation (C.30), replace 2 with $ in three places.

p645, Missing references.Allard, J.F. and Champoux, Y. (1989). In situ two-microphone techniquefor the measurement of acoustic surface impedance of materials. NoiseControl Engineering Journal , 32, 15-23.

Barron, M. (1993). Auditorium acoustics and architectural design. E&FNSpon: London.



p646, Missing references.Beranek, L. L. (ed.) (1988). Noise and Vibration Control. Revisededition. Washington D.C: Institute of Noise Control Engineering.

Beranek, L.L. (1996). Concert and Opera Halls. How They Sound.Acoustical Society of America: New York.

Berglund, B., Lindvall, T. and Schwela, D.H. (1995). Community Noise.Stockholm: Stockholm University and Karolinska Institute.

Berglund, B., Lindvall, T. and Schwela, D.H. Eds. (1999). Guidelines forCommunity Noise. Geneva: World Health Organization.

p647, Missing references.Bragg, S.L. (1963). Combustion noise. Journal of the Institute of Fuel,Jan., 12B16.

Broner, N. and Leventhall, H.G. (1983). A criterion for predicting theannoyance due to lower level low frequency noise. Journal of LowFrequency Noise and Vibration, 2, 160B168.

p648, Missing references.Cazzolato, B.S. (1999). Sensing systems for active control of soundtransmission into cavities. PhD thesis, Adelaide University, SouthAustralia.

Cazzolato, B.S. and Hansen, C.H. (1999). Structural radiation modesensing for active control of sound radiation into enclosed spaces. Journalof the Acoustical Society of America, 106, 3732B3735.

Chapkis, R.L. (1980). Impact of technical differences between methodsof INM and NOISEMAP. In Proceedings of Internoise '80, pp. 831B834.

Chapkis, R.L., Blankenship, G.L. and Marsh, A.H. (1981). Comparisonof aircraft noise-contour prediction programs. Journal of Aircraft. 18, 926B 933.

p649, Missing references.Davy, J.L. (1993). The sound transmission of cavity walls due to studs. InProceedings of Internoise '93, pp. 975B978.

Davy, J.L. (1998). Problems in the theoretical prediction of soundinsulation. In Proceedings of Internoise '98, Paper #44.

Davy, J.L. (2000). The regulation of sound insulation in Australia. InProceedings of Acoustics 2000. Australian Acoustical SocietyConference, Western Australia, November 15-17, pp. 155-160.

Delaney, M.E., Harland, D.G., Hood, R.A. and Scholes, W.E. (1976). The



prediction of noise levels L10 due to road traffic. Journal of Sound andVibration, 48, 305-25.

p650, Missing references.Dutilleaux, G., Vigran, T.E. and Kristiansen, U.R. (2001). An in situtransfer function technique for the assessment of acoustic absorption ofmaterials in buildings. Applied Acoustics, 62, 555-572.

Edge, P.M. Jr. and Cawthorn, J.M. (1976). Selected methods forquantification of community exposure to aircraft noise, NASA TN D-7977.

Fahy, F.J. (2001). Foundations of Engineering Acoustics. London:Academic Press.

Fahy, F.J. and Walker, J.G. (1998). Fundamentals of Noise and Vibration.London: E&FN Spon.

FHWA (1995). Highway Traffic Noise Analysis and Abatement Guide.U.S. Dept. of Transportation, Federal Highway Administration,Washington, D.C.

Fitzroy, D. (1959). Reverberation formula which seems to be moreaccurate with nonuniform distribution of absorption. Journal of theAcoustical Society of America, 31, 893-97.

Fleming, G.G., Burstein, J., Rapoza, A.S., Senzig, D.A. and Gulding, J.M.(2000). Ground effects in FAA's integrated noise model. Noise ControlEngineering Journal, 48, 16B24.

p652, Missing references.Hidaka, T., Nishihara, N. and Beranek, L.L. (2001). Relation of acousticalparameters with and without audiences in concert halls and a simplemethod for simulating the occupied state. Journal of the AcousticalSociety of America, 109, 1028B1041.

Add Nosal, E-M. to the authors of the Hodgson (2002) paper.

Howard, C.Q., Cazzolato, B.S. and Hansen, C.H. (2000). Exhaust stacksilencer design using finite element analysis. Noise Control EngineeringJournal, 48, 113-120.

p653, Missing referenceJean, Ph., Rondeau, J.-F. and van Maercke, D. (2001). Numerical modelsfor noise prediction near airports. In Proceedings of the 8th InternationalCongress on Sound and Vibration, Hong Kong, 2-6 July, pp. 2929B2936.

p654, the reference, "Landau, L.D. and Lifsltitz, E.W." should be "Landau, L.D.



and Lifshitz, E.W."

p654, Missing references.Kuo, S.M. and Morgan, D.R. (1996). Active noise control systems. NewYork: John Wiley.

Kurze, U.J. and Anderson, G.S. (1971). Sound attenuation by barriers.Applied Acoustics, 4, 35B53.

Larson, K.M.S. (1994). The present and future of aircraft noise models:a user's perspective. In Proceedings of Noise-Con '94, pp969 B 974.

Lee, J-W., Hansen, C.H., Cazzolato, B. and Li, X. (2001). Activevibration control to reduce the low frequency vibration transmissionthrough an existing passive isolation system. In Proceedings of the 8th

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Li, K.M. (1993). On the validity of the heuristic rayBtraceBbasedmodification to the WeylBVan der Pol formula. Journal of the AcousticalSociety of America, 93, 1727B1735.

Li, K.M. (1994). A high frequency approximation of sound propagationin a stratified moving atmosphere above a porous ground surface. Journalof the Acoustical Society of America, 95, 1840B1852.

Li, K.M., Taherzadeh, S. and Attenborough, K. (1998). An improvedrayBtracing algorithm for predicting sound propagation outdoors. Journalof the Acoustical Society of America, 104, 2077B2083.

p655, Missing references.Maidanik, G. (1962). Response of ribbed panels to reverberant acousticfields. Journal of the Acoustical Society of America, 34, 809B826.

Menge, C.W., Rossano, C.F., Anderson, G.S. and Bajdek, C.J. (1998).FHWA Traffic Noise Model, Version 1.0, Technical Manual. U.S. Dept.Transportation, Washington, D.C.

p656, Missing references.Neubauer, R.O. (2000). Estimation of reverberation times in non-rectangular rooms with non-uniformly distributed absorption using amodified Fitzroy equation. 7th International Congress on Sound andVibration, Garmisch-Partenkirchen, Germany, July, pp. 1709B1716.

Neubauer, R.O. (2001). Existing reverberation time formulae - acomparison with computer simulated reverberation times. In Proceedingsof the 8th International Congress on Sound and Vibration, Hong Kong,July, 805-812.



Nilsson, A. (2001). Wave propagation and sound transmission insandwich composite plates. In Proceedings of the Eighth InternationalCongress on Sound and Vibration , Hong Kong, July, pp. 61B70.

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Passchier-Vermeer, W. (1968). Hearing Loss Due to Exposure to SteadyState Broadband Noise. Report No. 36. Institute for Public Health Eng.,The Netherlands.

Passchier-Vermeer, W. (1977). Hearing Levels of Non-Noise ExposedSubjects and of Subjects Exposed to Constant Noise During WorkingHours. Report B367, Research Institute for Environmental Hygiene, TheNetherlands.

Plovsing, B. (1999). Outdoor sound propagation over complex ground. InProceedings of the Sixth International Congress on Sound and Vibration,Copenhagen, Denmark, 685B694.

p658, Missing references.Price, A.J. and Crocker, M.J. (1969). Sound transmission through doublepanels using Statistical energy analysis. Journal of the Acoustical Societyof America, 47, 154B158.

Raney, J.P. and Cawthorn, J.M. (1998). Aircraft noise, Chapter 47 inHandbook of Acoustical Measurements and Noise Control, 3rd edn.reprint, edited by C.M. Harris, Acoustical Society of America, New York.

Raspet, R., L'Esperance, A. and Daigle, G.A. (1995). The effect ofrealistic ground impedance on the accuracy of ray tracing. Journal of theAcoustical Society of America, 97, 683B693.

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Saunders, R.E., Samuels, S.E., Leach, R. and Hall, A. (1983). AnEvaluation of the U.K. DoE Traffic Noise Prediction Method. ResearchReport ARR No. 122. Australian Road Research Board, Vermont South,VIC., Australia.

Sendra, J.J. (1999). Computational Acoustics in Architecture.



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p659, In the Shepherd reference, change "1985" to "1986"

p660, Missing references.Soom, A. and Lee, M. (1983). Optimal design of linear and nonlinearvibration absorbers for damped systems. Journal of Vibration, Acoustics,Stress and Reliability in Design, 105, 112B119.

Steele, C. (2001). A critical review of some traffic noise predictionmodels. Applied Acoustics, 62, 271-287.

Sutton, O.G. (1953). Micrometeorology. New York: MGraw-Hill.

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Takagi, K. and Yamamoto, K. Calculation methods for road traffic noisepropagation proposed by ASJ. In Proceedings of Internoise ‘94.Yokohama, Japan, pp.289B294.

p660, Tse reference, change "1979" to "1978".

p661, Missing references.U.K. DOT (1988). Calculation of Road Traffic Noise. Department ofTransport. London: HMSO.

U.K. DOT (1995a). Calculation of Railway Noise. Department ofTransport. London: HMSO.

U.K. DOT (1995b). Calculation of Railway Noise. Supplement 1.Department of Transport. London: HMSO.

Watters, B.G., Labate, S. and Beranek, L.L. (1955). Acoustical behaviorof some engine test cell structures. Journal of the Acoustical Society ofAmerica, 27, 449B456.

Wiener, F.M. and Keast, D.D. (1959). Experimental study of thepropagation of sound over ground. Journal of the Acoustical Society ofAmerica, 31, 724.

Yoshioka, H. (2000). Evaluation and prediction of airport noise in Japan.Journal of the Acoustical Society of Japan (E), 21, 341B344.

Zaporozhets, O.I. and Tokarev, V.I. (1998). Aircraft noise modelling forenvironmental assessment around airports. Applied Acoustics, 55, 99B127.

p661, In the Zinoviev reference, replace "In print" with " 269, 535-548."



p663, after last line, add, "ANSI S3.6 B 1997. Specification for Audiometers."

p667, line 1, replace "E90-99" with "E90-02".

p715, Change "Noise Reduction Index" to "Noise Reduction Coefficient".


INDEXA, B or C weighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15, 18absorber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164absorption coefficient

analytical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77, 79empirical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79sabine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

add sound waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10coherent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10incoherent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

air compressor noise prediction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12, 33, 104

double diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34, 106indoor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111outdoor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104overall noise reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34, 106

boiler noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183break in noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152break out noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151characteristic impedance

complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42combine level reductions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12compressor

air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171refrigeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

control valve noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175-177liquid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179steam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

cooling tower noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173CoRTN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15critical damping ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156Curle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Cylindrical room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57daily noise dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14impulsive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

damping measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156diesel and gas engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

casing noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

Index 224


exhaust noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184inlet noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

dipole source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23directivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

exhaust stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147directivity index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30dissipative mufflers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136, 145

exit loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140expansion loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140flow noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146flow resistivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139impervious membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138, 139inlet attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140lined duct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137, 138liner attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

ductphase speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116break-in noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152breakout noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151cut on frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116cylindrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116higher order mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116rectangular . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116unlined . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117unlined duct attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

effective length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122electric motor noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

cooling air requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101, 103partial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

energy density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11kinetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

environmental noise descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20equivalent continuous noise level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13equivalent diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127excess attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30, 147

air absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41CONCAWE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36, 41, 108OCMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Index 225


turbulence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36, 42, 108exhaust noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184exhaust stack directivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

excess attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147, 149fan noise prediction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170FHWA-TNM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192, 195file menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3flat room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67flow noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146flow resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22flow resistivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22, 36, 41, 108forest attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10furnace noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

high pressure drop gas burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187low pressure gas burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186oil burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186primary and secondary air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186

gear noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191generator noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189graph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2, 8ground

characteristic impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42excess attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41flow resistivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41, 42ISO method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43reflection coefficient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41, 42spherical wave reflection coefficient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

ground effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1hearing damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14hearing damage risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13hissy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17housing

attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39IIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

1/4 wave tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122expansion chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123helmholtz resonator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124, 125orifice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119perforated sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

Index 226


resistive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119, 123tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118, 119volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

incoherent source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26insertion loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

constant pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1, 10, 55, 154, 167jet noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174, 214level reductions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12line source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24lined duct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

perforated facing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137logarithmic decrement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156long room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68loss factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156loudness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17main menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3meteorological effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43monopole source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23NC curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15NCB curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15noise criteria curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17noise exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13noise source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

constant pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128constant volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

normal impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73NR curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15, 97occupational noise descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20options menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4, 7particle velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11phons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17, 18pipe flow noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180-182pipe lagging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Hale method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114Michelson method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

plane piston source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26plane wave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11plenum chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141plotting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8process equipment

attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Index 227


pump noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174quadrupole source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23quality factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123radiation efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27radiation field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25radiation impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27RC curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17reactive muffler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

1/4 wave tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131duct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127expansion chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132Helmholtz resonator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130insertion loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133, 134low pass filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133quality factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

rectangular source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26reflecting surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29reflection coefficient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42reflection loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36, 108refrigeration compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172reverberation time

Fitzroy equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Fitzroy-Kuttruff equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Millington-Sette equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Neubauer equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Norris-Eyring equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Sabine equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

RNC curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17room acoustics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55room modal properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

cylindrical room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57rectangular room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

rumbly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17run menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4run symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Rw measure of TL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96sabine rooms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65save data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33small engine exhaust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134sones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17, 18

Index 228


sonic gradient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44, 45sound absorber

backing cavity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72impervious membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72, 73panel absorber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77perforated panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72, 74porous material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72, 73

sound absorptionapplications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80reverberation times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

sound intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10, 11sound intensity level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11sound power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10, 45

free field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45near field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50reverberant field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46semi free field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45surface vibration measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

sound power level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167sound propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26sound sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23, 26

dipole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24monopole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26quadrupole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

source type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29constant power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29constant pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29constant volume velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

speech interference criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18speech privacy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22speed of sound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12, 26

gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12liquids in a thin-walled tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12solids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

spherical waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11SPL Averager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54STC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83, 96subtract coherent SPL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Index 229


TNM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192, 195tools menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4, 5traffic noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192, 215train noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

track segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200transformer noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189transient response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69transmission loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

composite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98composite material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87, 94Davy (single wall) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85double wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91IIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96isotropic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85material properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86multi-leaf Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93multi-leaf walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87orthotropic panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85, 89Rw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96sharp (single) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85single wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85STC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

turbine noisegas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183steam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

turbulence parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42vibrating sphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24vibration

absorber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164vibration absorber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164

optimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164, 165specified . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164

vibration isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1544-isolator system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156, 158flexible support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158single degree of freedom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154transmitted force reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155, 158

vibration units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155vortex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24weighting networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18wind gradient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35, 107

· 2009. 5. 19. · enc software user’s guide revision 3.3, april, 2009 © causal systems table...

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