Acoustics
OR HOW TO MAKE A CLIENT HAPPY
ACOUSTICS
Fundamentals of Architectural
Acoustics
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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. *

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
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
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
Frequency
 Most
often we will be looking at sound waves that
humans can actually hear, which are frequencies
from 20 – 20,000 Hz.
 Infrasonics
 Frequency
-20 Hz - Ultrasound 20,000Hz
is sometimes referred to as pitch.
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
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.

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
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
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
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
One of the loudest manmade 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.
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Noise pollution is huge especially in our cities
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
Inverse Square Law
 Not
in textbook
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
Chapter 18
Sound in Enclosed Spaces
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
Sound Absorption
 Noise
Reduction Coefficient (NRC)
Verses
 Sound Transmission Coefficient (STC)
(textbook class it Sound Transmission Class)
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STC
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NRC
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
Review Specification
 CSI
Division 09511 – Acoustical Panel Ceilings
 See
Handout in class
 Also available on line at Arch 433 - Web Site
ACOUSTICS

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

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
Review Specification
 CSI
Division 09511 – Acoustical Panel Ceilings
 Quality Assurance
 Class
“A”
 Coordination
– Anything above the ceiling
 Extra Material
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
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
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
Review Specification
CSI Division 09511 – Acoustical Panel Ceilings
 Types of Material

There
are 20 types
A Type III
 Mineral
base with painted finish;
 Type includes:
 Form 1 Nodulated, cast, or molded
 Form 2 Water felted
 Form 3 Dry felted
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
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.
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
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
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
Review Specification
 CSI
Division 09511 – Acoustical Panel Ceilings
 Execution
 Balance
boarders
 Splay hangers
 Sealant @ wall angle
 Screw attach wall angle
 Cleaning
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
Let’s do a sound absorption problem!!!!
SOUND ABSORPTION
 Carpenter
Hall Room 102
Foot print of Carpenter Room 102
32’ x 98’
 Ceiling Ht.
14’ to 10’ average 12’


Sound Absorption @ 500Hz
SOUND ABSORPTION
The Formula T = .05 V/a
and
NR = 10log (a2/a1)
We’ll get to the formulas later
I can explain
everything
SOUND ABSORPTION
Walls
Plaster, gypsum or lime on brick = ά .02
Floor
Wood
= ά .10
Ceiling
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
SOUND ABSORPTION
What is the reverberation time with no finishes?
Walls
ά
Sabins
Back 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
Floor
31 x 98
3,038 sf x ά .10 =
303.8
31 x 98
3,038 sf x ά .06 =
182.3
Ceiling
Total
548.5
SOUND ABSORPTION
Wallace Clement
Sabine
Father of
Architectural
Acoustics
T = .05 V/a
SOUND ABSORPTION
The Formula T = .05 V/a
T = Time of Reverberation
V = Volume
a = Sabins
SOUND ABSORPTION
The Formula T = .05 V/a
V = Volume of room 31’x 98’x 12
a = sabins of = 548.5
T= .05(31’x 98’x 12’)/ 548.5
T= .05(36,456)/548.5
T= 3.32 seconds
SOUND ABSORPTION
With acoustical tile & carpet,
what would be
the reverberation time?
SOUND ABSORPTION
Walls
Sabins
ά
Back
Front
Sides
10’x 32’=
320
14’x 32’=
448
(12’ave. x 98’) x 2 = 2,352
3,120 sf x ά .02
=
31 x 98 3,038 sf x ά .14
=
Floor with Carpet
Ceiling
62.4
425.32
- 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
SOUND ABSORPTION
The Formula T = .05 V/a
V = Volume of room 31’x 98’x 12
a = sabins of 891.22
T= .05(31’x 98’x 12’)/ 891.225
T= .05(36,456)/ 891.22
T= 2.04 seconds
SOUND ABSORPTION
3.32 seconds vs. 2.04 seconds
What! 2.04 vs.
3.32 seconds
Is this a big enough
difference?
SOUND ABSORPTION
NR = 10log (a2/a1)
NR = Noise reduction
a2 = 2.04 seconds
a1 = 3.32 seconds
SOUND ABSORPTION
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.
SOUND ABSORPTION
Change in Intensity Level,
db
1
3
5
10
18
Change in Apparent
Loudness
Almost imperceptible
Just perceptible
Clearly noticeable
Twice as loud
Very much louder
SOUND ABSORPTION
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 Tile
280 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
THINK ABOUT IT!?
ENCORE
SOUND ABSORPTION

Seating 110 seats
Fabric Seats = ά .56
Audience
= ά .80
SOUND ABSORPTION
Floor
3,038 sf
x ά
.10 =
Floor area
(5 x 98)x 2 = 980 sf
(32 -10) x 8 = 176 sf
(32–10) x 5 = 11o sf
1, 266 sf
3,038 sf – 1,266 sf = 1,776 sf seating area
303.8
SOUND ABSORPTION
Walls
3,120 sf x ά .02
=
47.04
1,266 sf x ά .14
=
177.24
1,776 sf x ά .80
=1,402.8
Floor with Carpet
With students
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
SOUND ABSORPTION
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.
SOUND ABSORPTION
YEAH!
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How to reduce the noise sooooo…..
Let’s cut to the chase. We’ll use a bathroom wall to
begin with.
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The goal is to design and construct walls, ceilings
and floors that reduce or eliminate unwanted
noise or sound.
Sound that we find in ……..
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Bathrooms!
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
Lets start with the floor.
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
Now the walls
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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.
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Metal Studs
STC 37 to 41
w/ insulation
STC 44 to 48
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Wood Stager Studs
Common plate
STC 46 to 48
Without insulation
STC 38 to 42
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Wood Stager Studs
Common plate
w/ insulation
STC 46 to 50
Without sound bd.
and insulation
STC 38 to 42
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Dual plates and studs
STC 42 to 44
W/ insulation
STC 50 to 53
Make sure the joist are
parallel to wall and
all flooring and ceiling
material divided.
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Stud wall 2 x 4 with resilient
channel and insulation
STC 40 to 42
w/ insulation STC 47 to 51
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Metal studs w/
sound deadening board
one side STC 52
Sound deadening board
both sides STC 54
w/ insulation and sound
deadening board both sides
STC 57
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ARCH 433

Mid Term Exam
 March
6th
What does it cover ?
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
Other Stuff
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Other than walls, ceilings and floors , how can we
design and build spaces to reduce unwanted sound.
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Because Mom and Dad do not want to
wake-up baby……when …well .. you…..know!
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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.

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Always have gypsum bd.
cut tight and sealed around
Receptacle boxes. Use sound
deadening products behind
the boxes.
Never place boxes back to
back or in the same stud
cavity.
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Always run
gypsum bd.
behind soffits.
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If you are creeping home
late, never nail the stair
stringers to wall studs.
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Cast Iron
Verses
Plastic Pipe
Nothing worst than hearing someone flush
the toilet or wash their hands.
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Cast Iron
The use of
neoprene
gaskets and
hubless
coupling with
cast iron pipe
and fittings
significantly
reduces noise
and vibration..
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
What about fine tuning for Commercial
Buildings
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"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!!!! "
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I call this the Die Hard Ceiling System Lecture
Let me show you a much better systemSee lecture i.e. white board
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Let me show you a much better systemSee lecture i.e. white board
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Thank
you for
being a
great
class