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Acoustics Fundamentals

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Title: Acoustics Fundamentals


1
Acoustics Fundamentals
  • Environmental Technology IV
  • Professor Tango Parker Spring 2009

2
Acoustics is usually very broadly defined as
"the science of sound." Room Acoustics The
shaping and equipping of an enclosed space to
obtain the best possible conditions for faithful
hearing of wanted sound and the direction and the
reduction of unwanted sound. Room Acoustics
deal primarily with the control of sound which
originates within a single enclosure, rather than
its transmission between rooms.
3
The balance of keeping wanted sounds and
eliminating unwanted sounds
4
Sound WavesWhat is a wave?http//www.ketteri
ng.edu/drussell/Demos/waves-intro/waves-intro.htm
l
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frequency vibration cycles per second
amplitude
wave length distance between identical points on
a wave
8
http//www.surendranath.org/Applets.html
  • Amplitude and Frequency
  • Applet Menu gtWaves gt Transverse Waves
  • http//www.surendranath.org/Applets.html

9
Speaker diameter (cm) Frequencies (Hz) cutoff ka
Woofer 30 20-2,000 5.5
mid-range 12 2,000-5,000 5.5
tweeter 6 5,000-10,000 5.5
super-tweeter 3 10,000-20,000 5.5
The human ear can detect sounds between 20 HZ
and 20,000 HZ. Most sensitive in the range of
100HZ to 5000HZ Hear it http//www.surendranath.
org/Applets.html , then select menu/ new
applets/new menu/ waves/ hear the beats.
10
The length of a sound wave
20,000 HZ - 11/16
20 HZ 56 ½ feet
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15
Velocity Rate at which sound travels through a
conductor Air Wood Steel
16
Velocity Rate at which sound travels through a
conductor Air Wood Steel
1128 feet per second
11,700 feet per second
18,000 feet per second
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Sound Pressure/ Amplitude
19
Sound Pressure/Amplitude vs. Frequency
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22
Complex Waves
23
http//www.surendranath.org/Applets.html
  • Multiple Tones
  • Applet Menu gtWaves gt Transverse Waves gt Adding
    Transverse Waves (continuous)

24
The Mobility of Sound
25
Direct SoundSince sound travels in all
directions from the source, each listener will
hear just the segment if the overall sound wave
that is traveling in a direct line to his hear
(in a space free from reflecting surfaces). As
the distance from the source increases, the sound
pressure at the listener's ear will decrease
proportionately.(Example good Headphones)
26
Reflection
27
Diffusion
28
Diffraction The Sound Squeezes ThroughSound
waves are not always reflected or absorbed. When
an obstacle is the same size as the wavelength or
less, the sound can bend around obstacles or flow
through small openings, and continue onward. This
is called diffraction. This action is more likely
for deeper sounds (of low frequency, and this
with longer waveforms).
29
ReverberationThe perpetuation of reflected sound
within a space after the source has ceased is
called reverberation. The time interval between
reflections is usually so short that distinct
echoes are not heard. Instead, this series of
reflections will blend with the direct sound to
add "depth". Reverberation is a basic acoustic
property of a room. It can enrich speech and
music in all areas -- or it can slur speech and
generate higher noise levels throughout a room,
depending upon the room volume, timing, and
absorption.
30
Volume
Room Acoustics
Shape
Materials
Room Acoustics
31
Reflect
Room Acoustics
Absorb
Sound re-enforcement
32
The shape of a space determines the sound path
within the space
33
Room Acoustics
C
B
A
A
A
Reverberation
34
Parallel reflective surfaces generates unwanted
reverberation
35
  • Reverberation time must match room function
  • Pure speech requires short reverberation time
  • Symphony blends notes with long reverberation time

36
The lower part of the band is best for rooms
intended primarily for speech, the upper part is
better for music rooms, and the middle portion is
recommended for general purpose rooms.
37
Studies based on the audibility of speech and
music reveal that the most desirable
reverberation times generally fall within the
ranges shown below. These values are based on a
sound frequency of 500 Hz (approximate pitch of
male speech). Reverberation time in
secondsSpeech Small offices 0.50 to
0.75Classrooms/lecture rooms 0.75 to 1.00Work
rooms 1.00 to 2.00MusicRehearsal rooms
0.80 to 1.00Chamber music 1.00 to
1.50Orchestral/Choral/Average church
music  1.50 to 2.00Large organ/liturgical choir
2.00 to 2.25
38
Live!DEAD
39
A classification of typical rooms by acoustical
environments "Dead" Very Absorptive
"Live Highly Reflective
40
  • Absorbing Materials
  • Carpet
  • Soft ceiling tile
  • Rigid foam
  • people

41
  • Reflecting Materials
  • Masonry
  • Wood smooth panels
  • Smooth concrete
  • Glass

42
LiveAuditoriums, theaters(for music)Obtain
proper reverberation time to enhance musical
quality.Provide reflective surfaces near source
to reinforce sound absorptive surfaces toward
rear.Medium LiveConference and board
roomsNormal speech must be heard over distances
up to about 35 ft.Allow middle section of
ceiling to act as a reinforcing sound-reflector.
Apply absorbent to periphery of ceiling or to
wall surfaces (not both). Additional treatment
will contribute little to noise reduction.
43
MediumCafeterias (school or office)Reduce
overall noise level.Use highly sound-absorptive
ceiling also use quiet equipment such as
rubberized dish trays.GymnasiumsInstructor
must be heard over background noiseUse
acoustical material over entire ceiling to reduce
noise walls remain untreated to permit some
reflected sound.
44
Medium DeadElementary-grade classroomsTeacher
must be heard distinctly reduce noise level
produced by children.Acoustical ceiling
essential. Supplementary acoustical space units
on upper rear and side walls are
desirable.Music rehearsal roomsUnlike music
hall, instructor must hear individual notes
distinctly minimum reverberation desired.Entire
ceiling, sidewalls, and wall facing musicians
would be treated wall behind musicians may be
left sound-reflective for proper hearing. Room
should be located away from normal use rooms.
45
DeadKindergartenMaximum noise
reduction.Maximum acoustical treatment on
ceiling space units on available wall
surfaces.Vocational classrooms and
shopsMaximum noise reduction.Acoustical tile or
lay-in panel ceiling, plus acoustical treatment
of available upper wall areas locate away from
normal use rooms.
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Reverberation time (in seconds) .05 x volume
of room ______________________________ sabins
48
SabinThe amount of sound absorbed is measured
in sabins. One sabin is equal to the sound
absorption of one square foot of perfectly
absorptive surface. The sound absorption
equivalent to an open window of one square foot.
(theoretical, since no such surface exists).
49
Measuring AbsorptionSound Absorption
Coefficient The fraction of the energy absorbed
(at a specific frequency) during each reflection
is represented by the sound absorption
coefficient of the reflecting/absorbing surface.
In the building industry, this is a meaningful
and widely accepted quantitative measuring of
sound absorption, and applies to all surfaces --
whether they be of reflective or absorptive
materials.
50
Reflective SurfacesHard, massive, non-porous
surfaces, such as plaster, masonry, glass and
concrete, absorb generally less than 5 of the
energy of striking sound waves and reflect the
rest. Such materials heaver absorption
coefficients of .05 or less.
51
Absorptive SurfacesPorous materials such as
acoustical tile, carpets, draperies and furniture
are primarily absorptive. They permit the
penetration of sound waves and are capable of
absorbing most of the sound energy. These
materials may have absorption coefficients
approaching 1.00 (one sabin per sq. ft.).
52
Poor acoustical characteristics in this lecture
room.
53
Reflective surfaces near the speaker. In
lecture rooms more than 40 feet long, the rear
wall should be absorptive to prevent echoes.
54

Why Sound Conditioning?? The objective of
sound-conditioning is to create a haven for the
occupant, shielded from annoyance and
distractions. With such an environment,
individuals show increased productivity, tenants
complain less, turnovers and vacancies are
reduced, and property values rise.
55
Structure borne sound Steel Frame
Plumbing Pipe
56
Source
Path
Receiver
57
Isolation Of Equipment
58
Isolation Of Equipment
Low-end RTUs (roof top units) are typically loud
. No isolation springs / poorly balanced
59
Background Noise
60
Acceptable Background Noise LevelsAs a rule, we
can tolerate, and even welcome, a certain amount
of continuous sound before it becomes noise. An
"acceptable" level neither disturbs room
occupants nor interferes with the communication
of wanted sound. Recommended category
classification and suggested noise criteria range
for steady background noise as heard in various
indoor functional activity areas as indicated in
the Preferred Noise Criterion (PNC)Curves.
61
Type of Space (and acoustical requirements)PNC
curveConcert halls, opera houses, and recital
halls (for listening to faint musical sounds)10
to 20 dbLarge auditoriums, large drama theaters,
and churches (for excellent listening
conditions)Not to exceed 20 db Broadcast,
television, and recording studios (close
microphone pickup only)Not to exceed 25 db
Small auditoriums, small theaters, small
churches, musical rehearsal rooms, large meeting
and conference rooms (for good listening), or
executive offices and conference rooms for 50
people (no amplification)Not to exceed 35 db
Bedrooms, sleeping quarters, hospitals,
residences, apartments, hotels, motels, etc. (for
sleeping resting, relaxing)25 to 40 db Private
or semiprivate offices, small conference rooms,
classrooms, libraries, etc. (for good listening
conditions)30 to 40 db
62
Type of Space (and acoustical requirements)PNC
curveLiving rooms and similar spaces in
dwellings (for conversing or listening to radio
and TV)30 to 40 db Large offices, reception
areas, retail shops and stores, cafeterias,
restaurants, etc. (for moderately good listening
conditions)35 to 45 db Lobbies, laboratory work
spaces, drafting and engineering rooms, general
secretarial areas (for fair listening
conditions)40 to 50 db Light maintenance shops,
office and computer equipment rooms, kitchens and
laundries (for moderately fair listening
conditions)45 to 55 db Levels above PNC-60 are
not recommended for any office or communication
situation.
63
Minimize Background Noise Level - Overall noise
levels which may interfere with wanted
communication should always be anticipated and
corrected. To provide maximum quiet, typical
methods include the following 1. Elimination
of outside noise by sound attenuation in walls,
ceilings, and floor2. Use of quiet
mechanical equipment wherever possible.3
.Control of remaining noise by absorption --
carpeting, upholstery, and acoustical treatment
placed above and behind audience.4. Individual
handling of unusual noise sources -- for example,
isolation of a noisy movie projector.5.
Electronic amplification of the wanted sound
level above the background noise level -- usually
done as a last resort.
64
Masking Creating Background
"NoiseWhen an undesirable background sound
can't be reduced or eliminated, it can sometimes
be masked (made less objectionable by introducing
a different sound). For example, piped-in music
in restaurants can mask the din of dish clatter
and multiple conversation.At the other extreme,
a masking sound may be introduced to correct an
oppressively quiet room. For example, a telephone
ring or a slight cough can be distracting in a
very "dead" room, and speech privacy would be
impossible. In many cases the heating and air
conditioning systems will provide a sufficient
amount of masking noise.
65
white noisepink noise
66
Sound Isolation
67
  • The control of intruding sound ideally begins
    with the initial building concept and continues
    to be a consideration through the life of the
    building. Total sound conditioning affects
  • site selection
  • building orientation on the site
  • room orientation within the building
  • design, detailing, specification
  • construction
  • inspection.
  • Predictable sound attenuation can be achieved by
    careful attention to detail during all phases of
    planning and construction.

68
Site Selection for Sound Control
Orientation
69
Room Arrangement
1. What is the STC rating of the outside kitchen
exterior wall?
70
sound barrier
71
Sound BarriersIf the noise source is intense and
no natural sound barrier exists, a man-made sound
barrier should be considered as part of the
design. A solid fence-type barrier may remove
from 10 to 20 db from the noise level.
High-frequency sounds will be reduce more than
low frequency sounds. The cost of an outside
barrier may be less than the cost of reducing the
sound transmission in the construction.This type
of sound barrier must completely shield the
building from the noise source. It should be
placed as close to the sound source as possible
to obtain the greatest sound-shadow angle. If a
fence or wall is used, no louvers or openings
should be permitted.
72
Acoustical Zoning
73
Airborne Sound Airborne sound includes
conversation, outdoor noises, music and machine
noises (machines usually also produce impact
sound). It is the major source of intruding sound
from rooms on the same floor and from the
outdoors. It is controlled by1. Mass (weight),
2. Isolation (decoupling), 3. Absorption
4. Limpness of Construction. These must be
combined with airtight sealing and the
elimination of flanking paths (routes by which
the sound travels around a partition rather than
being stopped by it).
74
Mass
75
Impact Sound
Impact IsolationIf the surface receiving the
impact, such as a floor, can be isolated from the
structure, the impact sound will not be
transmitted. Likewise, if the structure can be
isolated from the ceiling below, the impact sound
will be restricted from traveling into the room
below. Isolation of the ceiling of the receiving
room can be accomplished with resilient mounting
of the drywall panels or lath. This still allows
some sound from above to enter the structure and
travel to other rooms. Resilient subflooring
materials such as insulation board and
underlayment compounds are effective, as is heavy
carpet over thick under pad. A combination of
these methods is necessary to produce ideal
attenuation of impact noise. Other sources of
structure-borne sound, such as motors, flushing
toilets, dishwashers, garbage disposals, blowers,
and plumbing, can be isolated from the structure
by resilient mounting procedures.
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Isolation (Decoupling)
78
staggered 2x3 studs on a single sill plate, with
alternate studs connected to opposite diaphragms
79
double row of studs on separate sill plates
80
2x4 studs with one diaphragm attached through
sound deadening board.
81
2x4 studs with one diaphragm attached by means of
resilient channels
82
Resilient Channel
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Absorption
The amount of sound energy dissipated depends on
the thickness of the material, its density (which
determines the amount of difficulty that the
sound encounters in traveling through), and it's
resiliency (flexibility with the ability to
spring back to its original shape). Mineral wool
insulation because of its porous yet dense
character, is highly effective in this
application. Sound attenuation blankets are
manufactured with higher density than thermal
insulating blankets to obtain optimum
attenuation. Mineral fiber sound attenuation
blankets, placed between the studs in a resilient
partition with resilient channels, retard
movement of the air column and convert
considerable sound energy into heat. However, if
the diaphragms are directly connected to rigid
studs, the partition will act as a single
diaphragm, rendering the wool ineffective in
dissipating sound energy.
85
www.usg.com search forSA 100 - Fire Resistant
Assemblies
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www.usg.com
SAFBsound attenuation fire blankets
88
Effective mass is contributed by the gypsum
panels or plaster. A common wood-stud partition
with 5/8-in. SHEETROCK FIRECODE "C" Gypsum Panels
on each side will test STC 34. Using double-layer
panels on each side will increase the rating to
STC 41,an improvement, but certainly not
optimum. Increasing the mass beyond this point
is of little value since other, less expensive
methods of achieving better performance are
available. Gypsum panels decoupled on one side
with RC-1 SHEETROCK Resilient Channels, will have
sound attenuation of STC 49 STC 59 with the
addition of 3-in. THERMAFIBER Insulating
Blankets.The performance of an assembly can vary
as much as 15 STC points with the quality of the
workmanship
89
The performance level being sought will usually
fall in the STC range of 45 to 60. The partitions
used in most single-family dwellings today would
test about STC 35 (although the actual
performance is often even less due to leaks and
flanking paths). On the other end of the scale,
STC-60 partitions are found increasingly in
luxury multi-family dwellings, and other quality
buildings. Partition performance of STC 60 will,
for practical purposes, reduce an 85 db noise
level (the maximum normally encountered in a
residence) to a 25 db background sound
(comparable to a night-time rural sound level) --
near ideal for sleeping rooms.
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Noise Reduction Coefficient (NRC)The average
amount of sound energy absorbed over a range of
frequencies between 250 Hz and 2,000 Hz.
NORMAL SPEECH RANGE
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What is CAC? A CAC, or Ceiling Attenuation
Class, is a measure of the sound transmission
loss as noise travels between rooms. Essentially,
it is the ability of a ceiling panel to block
sound between rooms. Q What spaces require CAC
values? A CAC values are essential in interior
spaces that require physical separation from
other areas such as conference and board rooms,
private offices, bathrooms, and corridors. Q
Is CAC important in open plan offices? A
Actually, CAC is important to assure privacy for
areas outside or adjoining an open plan such as
private offices or conference rooms.
94
Details, Specifications and Construction
95
Some of the most common flanking paths are
supplied by plumbing pipes, air ducts and
electrical conduit rigidly connected between the
floor and ceiling. Continuous walls between
floors, columns or any other continuous
structural elements will act as flanking paths
for impact sound. In fact, any rigid connection
between the two diaphragms will effectively
transmit impact sound.
Flanking Paths
96
Flanking Paths
97
Flanking Paths
HVAC
Good
98
Sound Control
  • Negative impacts
  • Flanking Paths
  • Electrical Boxes
  • Especially back-to-back
  • HVAC
  • Perimeter Seals
  • Doors
  • Other penetrations

Example Back-to-back electrical boxes
50 STC
99
Flanking Paths
100
Flanking Paths
CUTOUTS
101
Eliminating a flanking path with a non-resilent
material
102
Sound Seal
STC 53
103
Sound Seal
STC 53
Acoustical Sealant
104
Sound Seal
2 Layers 5/8 Gypsum Board
STC 53
Insulation
Acoustical Sealant
Sealed
105
Sealing
figure 50B. 53 STCBoth Base layers sealed.No
relief on face layers.
figure 50A. 29 STCUnsealed
figure 50C. 53 STCSealant applied to
runnertrack and board.
figure 50D. 53 STCSealant beneath and on edgeof
runner track. Base layer not relieved. Face
layer relieved and sealed.
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Sound Control
Usually the Dimension of the Framing 3 5/8
  • How to achieve Sound Attenuation
  • Increase STC by
  • Isolation
  • De-coupling

65 dB
15 dB
  • Absorption
  • Mass

Insulation either SAFB or fiberglass to
absorb sound energy
RC-1 or resilient channel
Drywall or engineered panel
50 STC
109
Improving Sound TransmissionLoss
Rules of Thumb ?
  • Doubling Partition Width
  • 5 dB Transmission Loss Improvement
  • Doubling MASS
  • 5 dB Transmission Loss Improvement

110
Improving STC
ISOLATION
STC 48
STC 43 - 25 ga. Steel stud STC 40 - 20 ga. Steel
stud
STC 54
STC 61
111
Doors Door Frames
High STC Partitions
Solid Core
112
Assignment 11
  • Room sabin absorption calculations and
  • reverberation

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