noise barrier

Noise Attenuation Provided by Highway Noise Barriers Email: [email protected]

Lecture 10: Noise Attenuation Provided by Highway Noise Barriers

Noise Attenuation Provided by Highway Noise Barriers Email: [email protected] 2

Presentation Overview

n Definitions of barrier attenuation

n Performance of noise barriers

n Design considerations and materials

n Examples of noise barriers


What is a noise barrier?

- Any form of solid obstacle between source and receiver can comprise a noise barrier

- Unlike building insulation, noise barriers are designed to protect the external as well as the internal environment at a dwelling

- The majority of barriers are installed in the vicinity of transportation and industrial noise sources to shield nearby residential properties

- Noise barriers are cost effective only for the protection of large areas including several buildings and are rarely used for the protection of individual properties

- Noise barriers of usual height are generally ineffective in protecting the upper levels of multistorey dwellings


What these barriers look like?

Absorbing lining


Are noise barriers subjectively effective?

0

1

2

3

4

5

6

7

8

9

54 64 74 84

A-weighted SPL (LAeq dBA)

Ave

rag

e n

ois

ines

s ra

ting

Barrier No barrier


Objective Performance of Noise Barriers


Definition

2

10 20

10log ,bpIL dB

p

= −

sound pressure at a receiver in absence of the barrier

sound pressure at a receiver behind the barrier


Basic Prediction Method

A common prediction method of noise barrier performance is outlined in ISO 9613-2

12 2

3

5 1 51

3C

w wλ λ

− = + +

double diffraction term

receiversource

rr

w

d 0r

sr

receiversource

rrsr

0r

3 1C = single noise barrier

insertion loss

10 310log 3 20 metIL C Kδλ

= +


Other Prediction Methods

Theoreticaln Keller J. B. J. Opt. Soc. Am., 1962n Embleton T.F.W., J. Acoust. Soc. Am. 1980n Hadden W.J. and Pierce A.D., J. Acoust. Soc. Am. 1981

Empiricaln Maekawa Z., Appl. Acoust. 1968n Tatge R. B., J. Acoust. Soc. Am. 1973

Numericaln Hothersall D.C. and Chandler-Wilde S. N., J. Sound Vib. 1991n Duhamel D., J. Sound Vib. 1996


Boundary Element Method

Requires the discretization of the boundary, Γ, with the step / 5s λ∆ <

r0r

acoustic surface admittanceGreen's function


Nomograms: single barrier

receiversource

noise barrier

rrsr

0r

01 rrr rs −+=δPath difference,

H

practical limit


Nomograms: double or wide barrier

01 rwrr rs −++=δPath difference,

receiversource

rr

mw 0.1=

d0r

sr

practical limit


Propagation effects


Maximum performance: 20 dB (single), 25dB (double)

Turbulence scattering effect


Refraction

Atmospheric refraction effect

wind speed

heig

ht

wind direction

shadow zone

ground

sound rays

Receiversource

NB


Combined atmospheric effects: light wind

Measured and predicted excess attenuation at a receiver 18m from 2.44m wide, 2.55m high barrier showing the effect of atmospheric turbulence.

Source is 8m from barrier (by J. Forssen, Appl. Acoust. 2002)


Measured and predicted excess attenuation at a receiver 18m from 2.44m wide, 2.55m high barrier showing the effect of atmospheric turbulence.

Source is 8m from barrier (by J. Forssen, Appl. Acoust. 2002)

Combined atmospheric effects: strong wind


Ground effect


Ground effect

piknp

β=∂∂

' ' '( , )d dx y=dr


Effect of foliage

Scattering by branchesImproved flow stability and reduced turbulence


Noise Barrier Design


Barrier Placement


Barrier Length

The length of a noise barrier should considerably exceed the barrier height.

LR80θ ≥ o

L4

R≥

NB


Transmission of Sound through Barrier

Noise contribution transmitted through the barrier material should be insignificant in comparison with the diffracted sound, i.e.

According to the ISO 9613-2

Range of materials from 4.5 kg/m2 to 244 kg/m2

10 dBd tL L− ≥

210 kg/msρ >


Categories for airborne sound insulation (EN 1793-3:1997)

Category DLR , dB

B0 Not determined

B1 < 15

B2 15 to 24

B3 > 25


Material Absorption


Categories of absorptive performance defined in EN 1793-1

Category DLa , dB

A0 Not determined

A1 <4

A2 4 to 7

A3 8 – 11

A4 > 11

It is generally accepted that noise barriers with high surface absorption offer superior performance only when the distance between a noise barrier and the source is less or comparable to the barrier height.


Effect of barrier shape


Modification to barrier top edge

Noise Attenuation Provided by Highway Noise Barriers Email: [email protected] 31∆L (dB) is given here relative to a 3m high plane screen NB

Ishi

zuka

and

Fuj

iwar

a, A

ppl.

Acou

st. 20

04


Modification to Barrier Profile


Noise barrier materials


Concrete noise barriers

Concrete wall with transparent elementsSolid concrete wall

Concrete barrier blended with plants


Timber noise barriers


Transparent noise barriers

acrylic panes

glass panes

composite barrier


Barrier with absorbing lining

Transparent barrier

Transparent noise barriers


Metal sheet noise barriersMetal barrier with aestheticstructural elements

Perforated absorbing panels


Other types of noise barriers


Earth berms


Earth berms vs Noise barriers


Eco-designs

Based on the combination of a structural frame, earth wall and living plants

Height limited to 4-6m

Fit well into urban, sub-urban or rural areas

Most of bio-barriers require irrigation and general maintenance


Eco-designs


Eco-designs - Examples

Wooven-willowPlanting in coated steel pockets

Planting over concrete pipes


Eco-designs – Wooven-willow


How barriers are installedEarth work

Concrete work


Good reference

Kotzen, B. and English C., (1999)Environmental Noise Barriers – A Guide to their Acoustic and Visual Design, E&Fn Spon, London and New York.


Any Questions

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