Acoustics

Fundamentals of Architectural Acoustics

Sound is a longitudinal wave. Remember that longitudinal waves are

made up of areas where the wave is compressed together, and other areas where it is expanded.

Sound can be vibration which is pressure – felt but not heard.

We will look in detail at three fundamental characteristics of sound: Speed, Frequency, and Loudness. *

Speed The speed of sound in air actually

depends on the temperature of the air. The sound travels faster through media

with higher elasticity and/or lower density. Speed of sound is 1130 feet per second or

344 m/s Light is 186,000 miles per second

Frequency Most often we will be looking at sound

waves that humans can actually hear, which are frequencies from 20 – 20,000 Hz.

Infrasonics -20 Hz - Ultrasound 20,000Hz Frequency is sometimes referred to as

pitch.

Loudness The loudness of a sound depends on the

wave’s amplitude. This is why a stereo system has an

“amplifier”, a device that increases the amplitude of sound waves.

The louder a sound, the bigger the amplitude.

This is also a way of measuring the amount of energy the wave has.

Loudness The system used to measure the loudness

of sounds is the decibel system, given the unit dB.

The decibel system is based on logarithms, which means for every step up by one, the sound is actually ten times louder. For example, a 15dB sound is ten times louder than a 14dB sound.

* Lesson 49: Properties of Sound by Mr. Clintberg’s Study Physics

One of the loudest man-made sounds 215 dB

That much sound energy creates heat.

Water is used to absorb the energy

That’s steam you see. It’s not all smoke.

If they did not use water to absorb the sound, the shuttle and tower would fail due to the energy generated from 215 dB.

Noise pollution is huge especially in our cities

Inverse Square Law Not in textbook

Chapter 18

Sound in Enclosed Spaces

Sound Absorption Noise Reduction Coefficient (NRC)

Verses Sound Transmission Coefficient (STC) (textbook class it Sound Transmission

Class)

STC

NRC

Review Specification CSI Division 09511 – Acoustical Panel

Ceilings See Handout in class

Also available on line at Arch 433 - Web Site

Review Specification CSI Division 09511 – Acoustical Panel

Ceilings Submittals

Ceiling Samples – tile and grid Tile 6 inch square samples Grid boxes – 3 samples each Follow directions in section 01330 – Submittal

Procedures Ceiling layout – drawings – 3 sets Attachment methods

Review Specification CSI Division 09511 – Acoustical Panel

Ceilings Quality Assurance

Class “A” Coordination – Anything above the ceiling Extra Material

Review Specification CSI Division 09511 – Acoustical Panel Ceilings Manufactures - Panels

Mineral Base Type III (see slide 24) Pattern EI (see your handout for “E”+ “I” STC -35 Tegular Edge Size 24”x 24” Manufacture – Armstrong – Cirrus 584 (or equal)

“by” Celotex or USG

Review Specification CSI Division 09511 – Acoustical Panel Ceilings Manufactures – Grid

Direct Hung Powdered-Actuated Fasteners in Concrete - OK

Wire – 12 gauge Hold Down Clips – Yes Grid – 15/16” Manufactures – Armstrong, Chicago, Interiors Inc.

Review Specification CSI Division 09511 – Acoustical Panel Ceilings Acoustical Sealant

At perimeter joints and openings Flame spread & smoke development < 25 per ASTM E84

Exposed At perimeter joints and openings Flame spread & smoke development < 25 per ASTM E84

Concealed BA-98 Pecora or Tremco Act. Sealant AC-20 FTR or Sheetrock Act. Sealant, USG

Review Specification CSI Division 09511 – Acoustical Panel

Ceilings Execution

Balance boarders Splay hangers Sealant @ wall angle Screw attach wall angle Cleaning

Let’s do a sound absorption problem!!!!

Carpenter Hall Room 102 Foot print of Carpenter Room 102

32’ x 98’ Ceiling Ht.

14’ to 10’ average 12’ Sound Absorption @ 500Hz

The Formula T = .05 V/a 

and

NR = 10log (a2/a1)

We’ll get to the formulas later

I can explain everything

Walls Plaster, gypsum or lime on brick = ά

.02Floor

Wood = ά .10Ceiling

Plaster, gypsum or lime = ά .06(See handout) ά = Noise Reduction Coefficient (NRC) or

Sound Absorption Coefficient This is similar to the example on page 791

What is the reverberation time with no finishes? Walls

ά SabinsBack 10’x 32’= 320 sf

Front 14’x 32’= 448 sf

Sides (12’ave. x 98’) x 2 = 2,352 sf

3,120 sf x ά .02 = 62.4

Floor31 x 98 3,038 sf x ά .10 =

303.8Ceiling

31 x 98 3,038 sf x ά .06 = 182.3

Total 548.5

Wallace Clement Sabine

Father of Architectural

Acoustics

T = .05 V/a

The Formula T = .05 V/a

 T = Time of ReverberationV = Volumea = Sabins 

The Formula T = .05 V/a

V = Volume of room 31’x 98’x 12a = sabins of = 548.5T= .05(31’x 98’x 12’)/ 548.5T= .05(36,456)/548.5

T= 3.32 seconds

With acoustical tile & carpet,what would be

the reverberation time?

Walls ά SabinsBack 10’x 32’= 320Front 14’x 32’= 448Sides (12’ave. x 98’) x 2 = 2,352

3,120 sf x ά .02 = 62.4Floor with Carpet

31 x 98 3,038 sf x ά .14 = 425.32Ceiling - Acoustical tile

(5x7) 8 each 280 sf x ά .85 = 238 3,038 sf – 280 sf 2,758 sf x ά .06 = 165.5

w/o carpet (769.7) Total 891.22

The Formula T = .05 V/a

V = Volume of room 31’x 98’x 12a = sabins of 891.22

T= .05(31’x 98’x 12’)/ 891.225

T= .05(36,456)/ 891.22

T= 2.04 seconds

3.32 seconds vs. 2.04 seconds

What! 2.04 vs. 3.32 seconds

Is this a big enough difference?

NR = 10log (a2/a1)

NR = Noise reduction a2 = 2.04 seconds

a1 = 3.32 seconds

NR = 10log (a2/a1)

NR = 10 log (2.04 / 3.32)

NR = 10 log (.614) NR = 2.11

Noise Reduction of = 2.11 db Acoustical tile alone = 1.48 db

WHAT!

Sound Absorption

Is this enough?

Let’s look at a rule of thumb.

Change in Intensity Level, db

1351018

Change in Apparent Loudness

Almost imperceptibleJust perceptibleClearly noticeableTwice as loudVery much louder

For a noise reduction of 2.11! Carpet

3,136 sf of carpet or 348 sy at $22.00 sy = $7,666.00

Acoustical Ceiling Tile280 sf x $2.25 = $630.00

Total cost furnished and installed $8,296.00$8,296.00 for an imperceptible noise

reduction!

(For 1.48 db reduction just for the acoustical tile)

Doesn’t make a lot of sense

Seating 110 seats Fabric Seats = ά .56

Audience = ά .80

Floor 3,038 sf x ά .10 =

303.8Floor area (5 x 98)x 2 = 980 sf(32 -10) x 8 = 176 sf(32–10) x 5 = 11o sf 1, 266 sf3,038 sf – 1,266 sf = 1,776 sf seating area

Walls

3,120 sf x ά .02 = 47.04Floor with Carpet

1,266 sf x ά .14 = 177.24With students

1,776 sf x ά .80 =1,402.8

Ceiling - Acoustical tile

(5x7) 8 each 280 sf x ά .85 = 238 3,038 sf – 280 sf 2 758 sf x ά .06 = 165.5

Total 2,030.58

T= .05(36,456)/ 2,030.58

T= .90 seconds

The seating alone with or without students has much more value than either the ACT or the Carpet.

YEAH!

How to reduce the noise sooooo….. Let’s cut to the chase. We’ll use a bathroom wall to begin with.

The goal is to design and construct walls, ceilings and floors that reduce or eliminate unwanted noise or sound.

Sound that we find in ……..

Bathrooms!

Lets start with the floor.

Now the walls

A standard wall 2x4 studs and plates with ½” gypsum board on both sides has a STC of 32 to 36.

Add insulation STC 35 to 39.

STC 37 to 41w/ insulationSTC 44 to 48

Metal Studs

STC 46 to 48

Without insulationSTC 38 to 42

Wood Stager StudsCommon plate

Wood Stager StudsCommon platew/ insulation STC 46 to 50

Without sound bd. and insulationSTC 38 to 42

Dual plates and studsSTC 42 to 44

W/ insulationSTC 50 to 53

Make sure the joist areparallel to wall and all flooring and ceilingmaterial divided.

Stud wall 2 x 4 with resilientchannel and insulation

STC 40 to 42w/ insulation STC 47 to 51

Metal studs w/sound deadening boardone side STC 52

Sound deadening boardboth sides STC 54

w/ insulation and sounddeadening board both sidesSTC 57

Mid Term Exam March 6th

What does it cover ?

Other Stuff

Other than walls, ceilings and floors , how can we design and build spaces to reduce unwanted sound.

Because Mom and Dad do not want to wake-up baby……when …well .. you…..know!

In rooms where you do not want sound to travel through HVAC ductwork, install separate supply and return systems.

Air ducts are great for carrying sound.

Always have gypsum bd.cut tight and sealed aroundReceptacle boxes. Use sounddeadening products behind the boxes.

Never place boxes back to back or in the same stud cavity.

Always run gypsum bd. behind soffits.

If you are creeping home late, never nail the stairstringers to wall studs.

Cast Iron Verses

Plastic Pipe

Nothing worst than hearing someone flush the toilet or wash their hands.

Cast IronThe use of neoprene gaskets and hubless coupling with cast iron pipe and fittings significantly reduces noise and vibration..

What about fine tuning for Commercial Buildings

"Come out to the coast, we'll get together, have a few laughs... Hold it… Hold it…. Max said this ductwork wouldn’t hold me up!!!! "

Let me show you a much better system- See lecture i.e. white board

I call this the Die Hard Ceiling System Lecture

Let me show you a much better system- See lecture i.e. white board

Thank you for

being a

great class