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408 views30 pagesBU 3 Notes
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Ern NievaCopyright
© © All Rights Reserved
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/ 30
Pontifical and Royal
University of Santo Tomas
The Catholic Univers of the Philippines
CoueGe OF ARCHITECTURE
Building Utilities 3
Acoustics and Lighting
ARCH. RAFAEL C. ALLI, msarch 2019 Ezsion
Pontifical and Royal
University of Santo Tomas
‘The Catto Unversiy ofthe Philppines
span, Meni
v
Glossary of Acoustical Terms
‘Arch, Ratfy Cueva All, mearch
Acoustics (uh K00S this)
The science of sound, including its generation,
transmission and effects of sound waves; the
technology of designing spaces, structures and
mechanical systems to meet hearing needs; the
study of how sounds are created, transmitted and
received
‘Sound
An oscillation in pressure of the atmosphere which
is capable of being detected by the human ear.
Acoustical Environment
The overall environment, interior to exterior, that
affects the acoustic condition of the space or
structure under consideration.
Acoustical Treatment
The use of acoustical absorbing or reflecting
‘materials or sound-isolating structures to improve or
modify the acoustical environment.
Acoustical Analysis
‘The detailed study of all pertinent sound sources,
sound transmission paths and sound receptors in
the context of particular acoustical problem,
Acoustical Impedance
The resistance to the flow of acoustical energy,
measured in rayls at specific frequencies, affected
by density and fiber diameter
Architectural Acoustics
The science and technology of controling sound in
and around buildings.
Absorption, Sound
The ability of a material to absorb acoustical
energy. Measured in sabins. The product of area (s)
‘and absorption coefficient (a). The process of
dissipating sound energy by converting it to heat
The reciprocal of sound reflection.
Absorption Coefficient
The faction of sound energy impinging on a
surface that is absorbed by that surface; the ratio of
the sound absorbed to the sound incident on the
‘material, usually denoted by a.
Absorbing Materials
Materials that dissipate acoustic energy within their
structure as heat andfor mechanical energy of
vibration. Usually building materials designed
specifically for the purpose of absorbing acoustic
energy on the boundary surfaces of rooms or in the
cavities of structures
Airborne Sound
‘Sound that is transmitted through air by a series of
oscillating pressure fluctuations.
Ambient
‘The existing surrounding conditions such as air or
surface.
‘Amplification
Increase in intensity level of an audible signal
Produced by means of loud speakers and
‘associated electronic amplification apparatus.
Anechoic Room
‘An anechoic room is a specially designed chamber
where all sound emanating from a source is
essentially absorbed at the surfaces of the room.
Attenuation, Sound Attenuation
Lessening or reduction of sound intensity, e.g, from
80 db to 70 ab.
Background Sound
Noise from all sources in an environment, exclusive
of a specific sound of interest.
Baffle or Barrier, Sound
AA shielding structure or partition used to increase
the effective length of a sound transmission path
between two locations.
‘Complex Tone
‘Sound sensation characterized by more than one
frequency.
Compression
In sound, the concentration of the conductor
‘molecules to produce a high pitch layer of sound,
Fundamentals of Acoustics [IN Conductor, Sound
Material that carries or transmits energy from one
location to another; sound conductor must be an
elastic material,
Creep
Transmission of sound along curve surface
cycle
‘One complete displacement,
Cycles per second (CPS)
Unit of frequency; St unit (hertz)
Damping
Damping refers to energy dissipation in an
‘oscillating system. A damped system cannot
oscillate freely.
Decay Rate
The rate at which sound pressure level (in db)
decreases when the source of sound is eliminated
Decibel
The basic metric unit for describing the magnitude
of sound. Its 20 times the logarithm to the base 10
of the ratio of the sound pressure to a reference
Pressure of 0.0002 dyne/om*. This reference
pressure is considered the lowest value that the ear
can detect
Diaphragm
A thin body that separates two areas. In sound, the
skin of a partition or ceiling which separates the
room from the structural space in the center of the
partition or ceiling assembly,
juse Sound Field
‘A sound field in which the intensity of the sound is
independent of its direction; an area over which the
average rate of sound energy flow is equal in all
directions,
Direct Sound Field
‘A sound field in which the energy arrives at the
receiver in a direct path from the source, without
any contribution from reflections.
Distortion
‘Any change in the transmitted sound signal such
that the sound recsived is not a faithful replica of
the original source sound.
Echo
‘Sound waves which have been reflected back to a
listener with sufficient magnitude and time delay.
Focusing
Concentration of reflected acoustic energy within a
limited location in a room as the result of reflections
from concave surfaces,
Free Field or Free Sound Field
‘A field free from boundaries that would otherwise
tend to reflect sound.
Frequency
Number of complete oscillation cycles per unit of
time, A unit of frequency often used is the hertz
Fundamental Frequency
The lowest frequency present in a complex tone.
Flutter Echo
‘A rapid succession of echoes caused by reflection
Of sound back and forth between two parallel walls.
Geometric Acoustics
Behaviour of sound waves likened to that of light
rays and the law that apply.
Harmonics
‘A component of sound containing more than one
frequency which is an integral multiple of the lowest
frequency.
Hearing
The subjective response to sound, including the
entite mechanism of the extemal, middle and
intemal ear system and the nervous and cerebral
operations that translate the physical stimuli into
meaningful signals.
Hertz (Hz, SI unit), Cycles per second
A measure of frequency
Infrasound
Noise of the frequency less tha 20 cycles per
‘second, below the normal lower audible limit of the
human ear.
Intensity (1)
The average rate of sound energy flow per unit area
in a direction perpendicular to the area.
Intensity Level (IL)
Ten times the logarithm of the ratio of sound
intensity to a reference sound intensity,
Inverse Square Law
‘At a distance from a source, under free-field
conditions, sound intensity varies inversely with the
‘square of the distance from the source, resulting in
a decrease in sound pressure level of 6 db for each
doubling of distance.
Fundarerias of Acosics ESA Liquidborne Sound
‘Sound caused by pulsations of liquid pressure
about the mean static pressure.
Loudness
‘The subjective attribute of an auditory sensation.
Masking
‘The obscuring or covering up of one sound by
another,
Noise
‘Any unwanted sound, usually of different
frequencies, annoying and interferes with speech
and hearing, or intense enough to cause hearing
damage.
Noise Isolation Class (NIC)
A single number rating derived in the same manner
as Sound Transmission Coefficient (STC) based on
Noise Reduction (NR)
Noise Reduction
‘The reduction in level of unwanted sound by any
several means (¢.g. distance in outdoor space, by
boundary surface absorption, by isolating barriers of
enclosures, etc.)
Octave
AA frequency band whose upper limit is twice the
lower limit; a division of the audible frequency
range, the center frequency of which is twice that of
the preceding band center frequency. The standard
acoustical octave bands are centered at 16, 31.5,
63, 125, 250, 500, 1000, 2000, 4000 and 8000 hz
Partials
‘Component of high frequencies,
Phon
A.unit of loudness level
Pink Noise
Wide frequency spectrum noise, whose amplitude
drops 3 dB per octave with increasing frequency
(equal energy per octave), useful for masking,
Pitch
Attribute of an auditory sensation which enables us
to order sound on a scale extending from low to
high frequency.
Pure Tone
Vibration produced at a single frequency.
Rayls
Unit of specific acoustic impedance or equivalent
characteristic acoustic impedance,
Reflected Sound
‘The resultant sound energy returned from a surface
(8) that is not absorbed or otherwise dissipated
upon contact with the surface (s).
Resonance
A state in which the forces of oscillation of a system
‘occur at or near a natural frequency of a system,
Reverberation
‘The persistence of sound in an enclosed space as
a result of repeated reflection or scattering of
sound,
Reverberation Sound Field
‘Sound that is reflected from the boundaries of and
furnishings within an enclosed space.
Reverberation Time
‘The time in seconds required for a sound to decay,
roughly speaking, to inaudibilty after the source
ceases. (Strictly, the time in seconds for the sound
level at specific frequency to decrease 60 db in
level after the source stops.)
Sabin
‘The measure of sound absorption of @ surface
equivalent to a square foot of perfectly absorptive
material; unit of measure of acoustical absorption,
Named after Wallace Clement Sabine, @ pioneer in
architectural acoustics,
Sone
A unit of how loud sound is perceived; it is a non-St
unit; proposed by Stanley Smith Steven in 1936,
‘Sound Absorber
Materials that have the capacity to absorb sound,
such as acoustical tile and panels, carpets,
0.50) ae refered to
as sound-absorbing; those with low coeficient (usually <
0.20) are sound reflecting.
Table 6
[Dif in coeticient eds formost
Situations
= 010 | Ue (usually not notceabe)
1000.40 Noticeable
> 00 Considerable
Room Noise Reduction
The buildup of sound levels in a room is due to the
repeated reflections of sound from its enclosing surfaces.
This buildup is affected by the size of the room and the
‘amount of absorption within the room. Noise reduction can
be found using theft. formula:
NR
0 fog (aafax)
Where: NR = room noise reduction (8)
4, = total room absorption from
treatment (sabins)
a, = total room absorption before
treatment (sabins)
‘Sample Problem
‘A small room 10 ft by 10 ft by 10 ft has all walls and floor
finished in exposed concrete, The ceiling is completely
covered with sound-absorbing spray-on material. Sound
absorption coefficient a's are 0.02 for concrete and 0.70
for spray-on material, both at 500 Hz.
a. Find the noise reduction NR in this room if
sound-absorbing panels are added to two
adjacent walls. The _sound-absorption
Coefficient «cis 0.85 for panels at 500 Hz
. Find the noise reduction NR if all four wall
surfaces are treated with sound-absorbing
panels and the floor is carpeted. The sound
absorption coefficient ofthe carpet is 0.50 at
500 He
Solution:
a. For Noise Reduction (NR)
— compute the surface area s
8, = 5x 10x10 = 500 ft? (concrete area)
Sj. = 10x10 = 100 ft? (spray-on material)
—scompute the total room absorption a, with spray-on
material onthe ceiling
a,=2ser=(500 x0.02) +(100 x0.70)= 80 sabins
> compute the total room absorption a, with sound-
absorbing panels covering two walls and. spray-on
materials on ceiling.
Eso. (300 x 0.02) +(200 x 0.85) + (100 x 0.70)
46 sabins
> compute the noise reduction NR
NR=10 log (@y/a;) =10 (log 246/80)= 4.87~5 dB
Without treatment
s; = 6x 10x10 = 6001"
2, = 600(0.020) + 100 (0.70) = 80
Fundamentals of Acoustics [IN NR=10 log (ay/a,)=10 (log 80/12)=8.2 ~ 8 dB
b. For Noise Reduction (NR)
—> Compute the total room absorption 23 with sound-
absorbing panels on all walls, spray-on material on ceiling
and carpet on foo
)=Esc.= (400x0.85) + (100x0.70) + (100x050)
460 sabins
> Compute the noise reduction NR for these
improvements compared to room conditions of spray-on
ceiling treatment alone.
NR=10 log (ay/a,)=10 log (460/80)=7.59~8 dB
Summary of Results
‘Surfaces Treated {in addition to | Room NR (at 500 Hz)
ceiling)
Two walls 5 0B
[Four walls & floor 8 0B
Noise Reduction Coefficient
The noise reduction coeticient NRC is arithmetic average
of the sound absorption coefficient, a's at 250, 500, 1000
and 2000 Hz for a specific material and mounting
condition. Given by the formula
NRC= (org + c1s0) + chaos + zon) / 4
‘Where: NRC = noise reduction coefficient
(decimal percent)
a. = sound absorption coefficient
(decimal percent)
‘Sample Problem
Find the NAC for a carpet with the following sound
absorption coefficient: 0.20 at 250 Hz, 0.35 at 500 Hz,
0.45 at 1000 Hz and 0.85 at 2000 He.
NRC = (0.20 + 0.35 + 0.45 + 0.55)/4 = 1.55/4
= 039 ~ 0.40
Reverberation Time
Reverberation Time is the time required for the sound to
decay in an enclosed space. When sound bounces off
from reflective surfaces such as walls, floor, ceiling,
furniture and even people it creates reverberation. The
reverberation time of a room or space may be defined as
the time it takes for sound to decay by 60 db. This can be
itten as the Tztime or simply T, sometimes Ris used.
Reverberation Time
‘The equation which Sabine defined and proved empirically
is:
Imperial Formula
Te= 0.08 wa - imperial Formula
where: T- reverberation time or time required for sound to
decay (seo)
¥- room volume (t")
2 total room absorption (Sabin)
Metric Formula
Tao= 0.161 Wa — Metric Formula
where: T- reverberation time or te required for sound to
decay (sec)
vv- room volume (m°)
2: total room absorption (metic sabin)
Illustrative Problem
AA classroom 60 ft. long by 35 ft wide by 15 ft high has
sound coefficient c's of 0.30 for walls, 0.04 for ceiling and
0.10 for floor. All c's are at 500 hz
a. Find the reverberation time T at 500 he in this
space wih no occupants and no sound-absorbing
treatment,
b. Find the reverberation time T if §0 percent of the
ceiling surface (along the perimeter of the room) is
treated with acoustical panels al «of 0.85.
Solution
a. Compute the room volume v.
v= 60x 35x 15 = 31,5001
~ Compute the surface area S
Ceiling= 60x 35 = 2100 2
Walls = 2x35 15 = 1050?
2x 60x15 = 1800 ft?
Floor = 60x25 = 2100?
> Compute the total room absorption a, using a
= Xsa
S a (SAC) | asa
[Ceiling 2100, 0.04 84
Walls 2850 [0.30 as
Floor Fa 210
a=Isa 1149
‘sabins > Compute the reverberation time T using T:
0.05 va
T= 0.05 (31500/1149)= 1.37 seconds at 500
he
b.— Compute the total om absorption using a =
Esc.
S| a (SA) a=sa.
Bae Toso | 008 |
ceiling
Treated | 1050 | 08s | 82
ceiling
Walis | 2850 | 0.35 5
Floor | 2100 04 210
‘a=Esa | 1989 sabins
— Compute new reverberation time T.
T= 0.05 wa= 0.05 (31500/1999)= 0.79
second
Therefore 1.37 - 0.79/ 1.37 = 42x 100 = 42%
reduction therefore, significant,
‘Dead spaces (sound decays rap)
eee nar
Increasing Reverberance
Recording & Broadcasting
‘Sudos
0aiy a4 wR BMW Oay Sy Mtoe o 12itr iam MOST ats eo le eer ani mee,
Reverberation Time (sec) Sound Reflection
The return of sound waves from surfaces on which they are
incident. Suppose a sound wave strikes a smooth surface
that is large compared tothe wavelength of the sound and
suppose that the path of this sound wave is represented by
a ray, that is, by a line perpendicular to the advancing
wavefront By the law of reflection, the angle of reflection 1
for this ray equals the angle of incidence |, and the
‘eflected ray lies in the plane of incidence.
The geometrical laws for reflection of sound waves are the
same as those for light waves. The apparent differences
involve only questions of scale, because the average
wavelength of sound is 100,000 times that flight.
A concave surface tends to concentrate the reflected
sound waves. Such surfaces are used to advantage as
reflectors, but if used indiscriminately they may lead to
oor acoustics asa result of undesirable focusing effects
Convex reflectors tend to spread the reflected waves.
Therefore, when placed atthe boundaries ofa room, they
tend to diffuse the sound throughout the room.
For this reason, some radio- broadcasting studios employ
cylindrical convex panels as part of ther wall construction
to promote difusion
The law of reflection is often used to investigate the etfects
cof various shapes of a proposed room on the distribution
cof sound in that room. Such studies can lead to the design
of interior surfaces that will give beneficial reflection, or to
the elimination or modification of surfaces that otherwise
would give rise to echoes. However, caution must be
exercised in such applications of the law of reflection,
because the wave properties of sound are neglected in this
simplification of the behavior of sound,
Acoustical Treatment
When sound impinges on the boundary surfaces of a
room, part ofits energy is absorbed and transmitted, and
part is rellected back into the room. Sound levels in
room can be reduced by effective use of sound-absorbing
treatment, such as fibrous ceiling boards, curtains and
carpets.
‘Application for Sound-Absorbing Materials
‘© Reverberation Control
‘Sound-Absorbing materials can be used to control
reverberation so speech will not be garbled, The larger the
room volume, the longer reverberation time because
sound waves wil encounter room surfaces less often than
in small rooms, Each doubling the total amount of
absorption in a room reduces reverberation time by one —
half.
‘+ Noise Reduction in rooms
When correctly used, sound ~ absorbing materials can be
effective in controlling noise build-up within a room. in
large open — plan rooms, sound ~ absorbing materials can
contribute to speech privacy by causing sound energy to
decrease with distance
© Echo Control
Sound ~ absorbing materials can be used to control
echoes (usually simultaneously with controlling
reverberation). Echoes are long — delayed, distinct
reflections of sound.
‘Acoustical Materals- Sound Absorbing Materials
All building surtace treatments used in construction and
used in creating spaces have the capacity to absorb sound
to a certain degree. Under special conditions many of the
sound-absorpive materials ae also being used in sound
insulation. On any surface, sound is either absorbed or
reflected by the material. The sound energy adsorbed is
partially converted to heat but most energy is transmitted
to the other side of the material, unless such transmission
is retained by a mote impervious barter. A good sound
absorber is an efficient transmitter and an efficient sound
insulator. An effective sound insulator enclosure, on the
other hand will prevent the transmission of sound from one
side tothe other.
Common Building Materials
Brick
Bik is modular building block made from clay. It is used
to build load bearing and non-load bearing walls, as a
facing (brick veneer), and as paving material. Brick has
‘mass approximately 130 Ibs per cubic ft, brick attenuates
sound very wel. Exceptionally high orders of attenuation
can be achieved with two side-by-side but unconnected
brick walls. Joints must be fully mortared or otherwise
sealed. Absorption is negligible since there is little or no
porosity and the material is rigid. Consequently, brick is a
good all-requency sound reflector.
Fundamentals of Acoustics [I Concrete
Concrete is a mixture of Portland cement, stone and sand
aggregates, and water, cured into a hard mass of superior
compressive strengih. It is often reinforced with stee! and
used for structural member. Normal weight conorete has a
density of 144 pounds per cubic foot. Lightweight
concrete is less effective, unless of equal mass per unit
area, Like any hard material, concrete readily accepts and
‘transmits impact sounds. Concrete provides virtually no
absorption. There are, however, aerated conoretes that are
intentionally porous. These are fairly absorptive.
Masonry
Masonry is any of a large variety of stone-like materials,
‘Acoustical properties vary, but in general are comparable
to thase of brick, concrete, and concrete masonry units.
Concrete Masonry Units
Concrete masonry units are modular building blocks made
of concrete. They ate usually manufactured with hollow
‘cores. Normal-weight units can support considerable
loads. Lightweight units are generally used to build non-
load bearing pation.
The attenuation provided by concrete masonry units
depends mainly on their weight. Lightweight units may be
adequate in non-critical cases. Normal-weight units,
especially if solid or if their cores ae filled with sand or
mortar, attenuate sound very well. Two unconnected
‘concrete masonry walls can provide exceptionally high
‘orders of sound attenuation. Since its surface is somewhat
Porous, concrete masonry is slightly absorptive, unless
painted o° otherwise sealed. I well sealed, it becomes
good all-fequency reflector.
Glass
Glass is generally a light-transparent material made of a
mixture of silicates. It is used principally to glaze windows
and other openings that need to be closed, but without
excluding light,
Despite its mass (approximately 156 pounds per cubic
foot), glass is a marginal sound attenuator because it is
thin and the mass per unit area is quite small. Superior
performance is provided by well-separated double-glazing
and by certain types of laminated glass. Almost totaly
reflective in the higher frequencies, glass resonates and,
through this mechanism, can absorb appreciable amounts
of low-frequency sound,
Laminated Glass
Laminated glass is a sandwich of two or more sheets of
lass with viscoelastic interlayers that provide damping as
the sandwich is flexed. Certain types of laminated glass
offer substantially better sound attenuation than an equal
than an equal thickness of monolithic glass,
Wood Decking
Wood decking is one of the several structural materials
supported by beams or trusses to form flors and roofs. it
is often exposed as finished ceiling, Owing to its relatively
low mass (as compared to concrete), wood decking
provides only nominal attenuation untess ballsted with
‘heavier materials. Wood decks are generally reflective, but
unsealed cracks between the boards have been known to
contribute a fair amount of absorption.
Wood Paneling
Wood paneling means a relatively thin finish made of
‘wooden boards and panels. These are usually attached to
furring and thus kept clear ofthe wall behind the paneling,
Wood paneling on a wall generally results in negligible
improvement over the attenuation provided by basic wall
Wood absorbs low-frequency sound by resonance and
may lead to serious bass deficiency in music rooms
unless it is thick and or wel restrained.
Plywood
Plywood is a laminate of several layers of wood venest. It
is used in wood construction as an underlayment for
floors, as sheathing on studs or rafters or as finished
paneling on walls.
Mainly because of its density (36 pounds per cubic foot),
plywood is relatively ineffective as a sound attenuator.
However, it is often adequate in combination with other
materials or where high performance is not required, Thin
plywood, if fured out from a solid wall, is @ potent low-
frequency absorber. At higher frequencies, plywood is
cuit reflective
Metal
Metals are any ofthe family of aloys, but especially steel,
\which is commonly used to provide structural support.
Sound Absorbing Materials and Construction
All materials have some absorbing properties. Incident
sound energy which is not absorbed must be reflected,
transmitted oF dissipated. A material's sound absorbing
Fundamentals of Acoustics INN Properties can be described as sound absorption
coefficient in a particular frequency range. The coefficient
can be viewed as a percentage of sound being absorbed,
where 1.0 is complete absorption (100%0 and 0.01 being
minimal absorption (1%)
There ate three basic categories of sound absorbers,
namely: Porous materials commonly formed of matted or
spun fibers, Panel (Membrane) absorbers having an
impervious. suface mounted over an ait space, and
Resonators created by holes connected to an enclosed
volume of tapped air, The absorptance of each type of
‘sound absorber is dramatically, in some cases, influenced
by the mounting method employed
+ Porous materials
The basic acoustical characteristic of all porous
materials, such as fiberboards, soft plasters, mineral
‘wools and isolation blankets, is a cellular network of
interlocking pores. Sound absorption in porous
materials is more efficient at high than at low
frequencies but thet acoustical efficiency improves in
‘the low frequency range with increased thickness and
with distance from ther solid backing.
* — Pretabricated acoustical units
(wallboard and tile board)
These include various types of perforated,
‘unperforated, fissured or textured cellulose and
‘mineral fiber tle, lay-in panels and perforated
metal pans with absorbent pads constitute
typical units in this group.
Most sound- absorbing tiles and panels are not
sufficiently durable for wall application. For
walls, use fibrous materials with protective
open facings (e.g. perforated or expanded
metal, perforated hardwood, metal. sia,
fabric-covered panels or shredded formboard,
Use membrane-faced or ceramic tile materials
for humid environment such as swimming pool
areas, kitchen and locker rooms.
= Acoustical plaster and sprayed-on
materials (fibrous material w/ binder)
Acoustical plaster is a plaster-ike product,
distinguished by its porosity after it dries. It
was originally intended to create jointless
surfaces (like those of ordinary plaster) that
absorb sound, which ordinary plaster does not.
The performance of acoustical tile is highly
dependent on the correct mix and application
technique. Noise reduction coetficient in the
order of 0.60 have been obtained under
controlled conditions, but field installations
usually yield much less. Acoustical plaster is
‘nat a reliable sound absorber.
These acoustical finishes are used mostly for
noise in auditoriums where any other
acoustical treatment would be impractical
because of curved or irregular shape of the
surface. They are applied in a semi-plastic
consistency, either by spray gun or by hand
troweling,
Their acoustical efficiency, usualy best at the
higher frequencies, depends largely on such
job condition as the thickness and composition
of the plaster mixture, the amount of binder,
the state of undercoat at the time of
application, and the manner in which the finish
is applied
= Acoustical Tile
‘Acoustical tle is @ widely used ceiling material
made of mineral or cellulose fibers or of
fiberglass. Itis available in a variety of modular
sizes from approximately 300 x 300 mm (12
in, x 12 in) to 610 mm x 1220 mm (24 in. x
48 in.) and larger. Acoustical tile is usually
suspended in a metal grid, but some types of
tile can be glued or otherwise attached to solid
surfaces. Its prone to damage when contacted
and is therefore not recommended for surfaces,
especially walls that are within human reach,
Suspended tile provides more low frequency
absorption than glued-on tile. Membrane-faced
tiles provide less high-frequency absorption
than those whose faces are porous.
= Acoustical Foam
Acoustical foam is one of a variety of celular
materials, usually made of polyurethane.
Foams are manufactured either with open cells
Gir can be blown in and through the material
or with closed cells (each cell is sealed; the
material is airtight)
Fundamentals of Acoustics [I Open-cell foams are excellent sound
absorbers, provided they are suficiently thick
Theit uses include padding for upholstered
theater seats to stabilize reverberation
regardless of occupancy.
Close-cell foams absorbs sound, but less
efficiently and less precictably. They are more
often applied to ringing surfaces, such as large
‘metal plate to provide damping,
= Acoustical (isolation) blankets (wool,
lass fiber)
Acoustical blankets are manufactured from
Fock wool, glass fibers, wood fibers, tair fet,
etc. generally installed on @ wood or meta
framing system. These blankets are used for
acoustical purposes in varying thicknesses
between 1 and & inches (25 and 125 mm).
‘Their absorption increases with thickness,
particularly at low frequencies. Acoustical
blankets do not constitute an aesthetically
satisfying finish, they are normally covered
with suitable type of perforated boards, wood
slats, flying soreen, e., placed and fastened
to the framing system,
= Fiberglass
Fiberglass, which is available in the form of
batts, blankets and boards, is an excellent
sound absorber. The manufacturing process
ensures consistent porosity at a very fine
scale, Applications include a great many
sound-absorbing treatments, insulation as in
stud walls and ducts, and various application
in industrial noise control. Compressed blocks
or sheets of fiberglass are also used to form
resilient supports/ hangers or as joint filler
where rigid tes are to be avoided,
The absorptivity of fiberglass depends on flow
resistance, which, in turn, is affected by the
materials thickness, its density, and the
diameter of the fibers. In most applications, the
thickness of the board or blanket is the most
important consideration in its selection.
= Fibrous Batts and Blankets
Usually made of fiberglass or mineral fiber,
fibrous batts and blankets are among the most
common forms acoustical (also thermal)
insulation in use today. They serve two distinct
acoustical purposes. It exposed to the room, as
‘a wall finish (behind fabric or an open grillage)
of a8 a ceiling finish (behind perforated open
pans or spaced slats), they absorb sound and
thus reduce noise and reverberation in the
room. Performance depends on thickness and
‘on the properties of the facing,
It used between two faces of a parton
(typically in the stud space, but also above
suspended ceilings where the ceiling and the
floor above form the patttion), batts and
blankets improve attenuation. They do it by
absorbing sound that is in transit through the
partitions cavity. IF cavity is braced by rigid
ties (@9., wood studs), there is. litle
improvement.
+ Fibrous Boards
Fibrous board works much like batts and
blankets but is of higher density- up to
approximately 20 pounds per square foot but
more usually near 6 pounds per square foot
Such rigid or semi-tigid boards, especially
those made of fiberglass, are excellent sound
absorbers. They are available with a variety of
‘sound-transparent (usually fabric) facings, for
use as walls or ceiling panels. Less porous or
thinner boards, such as those made of mineral
fiber, are somewhat less absorptive.
= Fibrous Plank
Fibrous plank is a rigid (often structural)
material, usually made of coarse fiers, such
as wood fibers, embedded in a cementitious
mix. The fibrous surface absorbs sound. If
exposed 10 the room, fibrous planks reduces
noise and reverberation in the room.
= Fibrous Spray
Fibrous spray is any ofa variety of sprayed-on
insulating material, often specified for
fireproofing application. Previously made of
asbestos fibers, which are known to be health
hazard, mast contemporary sprays contain
cellulose or mineral fibers of various
descriptions. Fibrous spray is. inherently
Porous and therefore absorptive. However,
Fundamentals of Acoustics (II performance is highly dependent on thickness
and application technique.
+ Insulation (Loose)
Loose insulation is similar to fibrous batts and
blankets, except that it can be blown or
dumped in place. It serves much the same
purpose as batts within a partition; that is, it
improves attenuation through th partition.
= Carpets
Carpe is any of a variety of soft floor finishes
made of synthetic materials such as nylon or
natural materials such as wool. It is either
Glued directly to the floor or installed over an
‘underlayment of hairfelt or foam rubber.
In addition to their application as flooring,
carpets are being used as versatile acoustical
material because airbome sound and noise
within a room, it reduces in some cases almost
completely eliminate impact noises trom
above, and they eliminate surface noises
{shuttling of feet, clicking of heels, moving of
fumiture). The use of carpet as sound-
absorbing material contributes tothe following:
1. The fiber type has practically no effect on
sound absorption. 2. Cut piles provide more
absorption than loop piles under otherwise
identical conditions 3. With increased pile
height and weight, in cut-pile fabrics, the
sound absorption increases 4. In loop pile
fabrics when pile weight inoreases, with the
density held constant, sound absorption
improves; when pile weight increases, with the
pile constant, sound absorption increases to a
certain level 5. The more permeable backing,
the higher the sound absorption 6. Hair, hair
jute ad foam rubber pads contribute to higher
sound absorption than the less permeable
rubber and urethane-foam pads.
= Curtains and Fabrics
Curtains and fabrics include a range of textiles
that are used on their own (as curtains) or as
Covering for other materials that may or may
not be sound absorbing. Curtains absorb
sound if they are reasonably heavy (at least
500 grams per square meter) and, more
importantly, if their flow resistance is
sulficietly high- to the point of severely
impeding, but not stopping, airflow through the
material
Fabvies attached directly to hard surfaces do
not absorb sound. However, if stretched over
‘materials such as fiberglass, and provided they
are not airtight, they make an acoustically
excellent finish that fully preserves. the
substrate's absorptivity
= Panel or Membrane Absorbers
The non-perforated panel, or membrane absorbers
represent the second group of sound absorbing
materials. Impervious material installed on a solid
backing but separated from it by airspace will act as
panel absorber and wil vibrate when struck by sound
waves. The incident sound energy is then converted to
heat. Panels of this sort are efficient low frequency
absorbers. When selected properly, panel absorbers
balance the somewhat excessive medium and high
frequency absorption of porous absorbers and room
contents
Panel resonators are built with a membrane such as
thin plywood or linoleum infront ofa sealed air space
generally containing absorbent material. The panel is
‘set in motion by the alternating pressure of the
impinging sound wave.
Wood and hardwood panels, gypsum boards,
suspended plaster celling, fured-out plasters, rigid
plastic boards, windows, glazing, wood floors and
platforms and metal plates are ofthis type of sound
absorption materials. Porous materials spaced away
from their solid backing also act as vibrating panel
absorbers, favorably contributing to absorption at low
frequencies.
Sound energy is converted into heat through internal
viscous damping. Panel absorbers are used where
low-frequency absorption is required and middle and
high frequency absoration is unwanted or provided by
‘another treatment. Panel absorbers are often used in
recording studios.
+ Volume or Cavity resonator (Hemhottz
resonators)
The cavity (oF Hemholt) resonators, the third andthe
last group of sound absorbers, consists of an
enclosed body of air conned walls and connected by
Fundamentals of Acoustics (III a narrow opening (called the nec) tothe surrounding
space, in which sound travels. The impinging sound
causes the air in the nec to vibrate, and the air mass
causes the entire construction to resonate at a
patiular frequency. By adjusting neck opening and
cavity dimensions, the unit can be tuned to resonate
ata desired frequency.
AA cavity resonator absorbs the maximum energy in a
rnatraw region of low frequency band. An empty jar or
bottie, also act as a cavity resonator; however, it
maximum absorption is confined to a narrow
frequency band; that is extremely selective in its
absorption.
Types of Volume or Cavity Resonators
‘= Individual resonator
Individual cavity resonators are made of
empty clay vessels of different sizes. Their
effective absorption spread between 100 and
400 hertz
Standard concrete block using a regular
concrete mixture but with slotted cavities
called soundbox units consitute
contemporary design of the cavity resonator.
The blocks cast into two series, called Type
A and Type B. Type A units have
approximately 1/4 in. (6 mm) slots and non-
‘combustible filler materials in their cavities
with slots at the top. Thicknesses vary from 4
to 8 inches.
Perforated resonator
Perforated panels, spaced away from a solid
backing, provide a widely used practical
application of the cavity resonator principle.
They contain a large umber of necks,
constituting the perforations of the panel
thus functioning as an array of cavity
resonators. The perforations are circular
(sometimes slotted). The airspace behind
the perforations form the undivided body of
the resonator, separated into ays. by
horizontal and vertical elements of the
framing system,
* Slit resonators
in auditorium design, acoustical effect can
be accomplished by using relatively
inexpensive blankets along the room
surfaces. However, due to their porosity,
isolation blankets need protection against
abrasion. The protective screen consists of a
system of wood, metal or rigid plastic slats
with @ series of openings, gaps or exposed
slots. The protective screen, with its
adequately spaced elements andthe
isolation blanket behind it constitute a sit
resonator.
Prefabricated Sound Absorbing Materials
Most sound — absorbing ttles and panels are not
sufficiently durable for wall application. For walls, use
fibrous materials with protective open facings (e9
perforated or expanded metal, perforated hardboard, metal
slats), fabric covered panels, or shredded-wood form
board. Use membrane — faced or ceramic tile materials for
humid environment such as swimming pool, kitchens &
locker rooms.
Prefabricated Acoustical Units
= Regular pertorated tle Suspended Sound — Absorbing Panels and Units
These units are installed with all edges and sides exposed,
they can provide extremely high absorption per ft, of
material because at six surface will be exposed to sound
waves.
Types of suspended sound-absorbing panels
* Parallel
Textured and/ or patterned tile or pane!
renee oat ug
Slotted tile or panel
Ved
TANI
HLT
Membrane- faced or ceramic tile materials
Transondent Facings
Sound transparent facings (called tansondent) may range
SS from 5 to 50 percent or more open area. Facings tend to
reduce the effectiveness of sound ~ absorbing materials,
by reflecting high ~ frequency sound waves. In genera,
the lower the % of open area in the facing, the less
absorption of high frequency sound energy.
Smooth spray-on materials (mineral or cellulose
fibers)
Bieri oy
Relative Efficiency of Sound Absorbers
‘+ Thin porous materials
(convert sound energy into heat by triction)
| Material
Patten
Features
Applications
Material
Patter
‘Applications
* Vibrating Panels (Resonant Panels)
(convert sound energy into vibrational energy
which is dissipated by intemal damping and
fadiation)
= Volume resonators:
( also called Hemholt, reduce soundenergy by
friction at opening and by inter reflections within
cavity
Table 7
Commercial Type Acoustical Materials for Various
Building Applications
Polyurethane Foam Sound Absorber
Open call Polyrethane Acoustical Foam
Scientifically engineered pattem designed to
absorb the widest range of frequencies
Effectively reduces reflecled noise and
reverberation time to produce safe and
enjoyable suroundings
Industial, commercial, audio room, residential,
sound recording studios, radio stations, band
rooms, swimming pons, churches, schools,
‘gun ranges, equipment enclosures.
Melamine Foam aie
Open cell melamine or polyurethane
The linear wedge pattem offers excellent
absorption and. allows you to create many
diferent designs. Install vertically, horizontal,
diagonally, checkerboard as well as create your
design
For use in industial, commercial, audio rooms
and. esidential martets. Ceilings, walls,
patttions, sound studio, radio rooms, band
rooms, gyms, swimming pools, gun ranges,
mechanical rooms. and. enclosures. Thicker
Material
Patten
‘Applications
Materia
Pattem
Features
Applications
Material
Patter
Features
Applications:
wedges are designed for use in anechoic
chambers and test cells
Melamine Foam Linear Wedges
Open cell melamine or polyurethane
The linear wedge pattem offers excelent
absorption and. allows you to create many
diferent designs. Install vertically, horizontally,
‘agonaly, checkerboard as well as create your
design
For use in industal, commercial, audio rooms
and residential markets,
‘Melamine Foam Sound Absorber
(Open Cell Melamine Acoustica Foam
Convotuted Double Hump Anechoic Wedges.
Designed for sound absorption in a wide range
‘of frequencies. increased surace absorption
aa
Industial, commercial, audio, residental,
ceilings, wals, patton. Sopund/ recording
studios, aio stations, board rooms, swimming
Pools, churches, schools, gun ranges,
enclosures.
Acoustical Baffles
oA
Porous Expanded Polypropylene
Fiberlass-ee
Soft textured Beaded Surtace
Economical, multi-purpose, moisture
resistant, durable, ightweight and cleznable
Gymnasiums, Aucitoria, Classrooms, Music
tooms, Arenas and Stadia, Churches, Ofices,
Computer rooms, Restaurants’ Cafeteria,
(PePP},
Concert Halls and Theaters, Gun Ranges,
Manvfacturing Plants, machine Enclosures,
Water Treatment Pants, Swimming Pools, Food ‘Absorptive/ Noise Barrier Quilted Curtains
Material Acoustical Foam or Fiberglass core, faced with
quilted aluminized fabric
Pattern Quilted pattem
Featues Effective Durable Absorber with mass loaded
vinyl barrier option,
Applications fective solution to a wide range of noise
contol problems, Machinery and. work area
enclosures, moisture or humid conditions and
‘outdoor noise contol. Silicone fabric available
for outdoors,
‘Melamine Foam Composite Sound Containment System
Saha
-
Material 1" Melamine Acoustical Foam, Bonded to 1/8"
tk, 1 Ih sq. mass loaded noise barrier with
1/4" melamine Foam Vibration Decoupler
Patter Convoluted or Flat Surface Patter
Applications Ideally suited to line equipment enclosures.
Commonly used 10 line walls and ceilings of
tly or mechanical rooms to absorb and
contain the noise source. Use where sound
absorption, noise reduction and vibration
contro ae needed
Hanging Acoustical Battles
{
|
Material Bonded Acoustical Pad (BAP), Recyclable
Fibergass- free,
Patter Soft- textured sutace
Features Economical, Mult- purpose, High Performance,
Durable, Lightweight
Applications Gymnasiums, Auditor, Classrooms, Music
rooms, Arenas and Stadia, Churches, Offices,
Computer rooms, Restaurants) Cafeteria,
Concert Halls and Theaters, Gun Ranges,
Manufacturing Plants, Machine Enclosures,
Water Treatment Pants.
Low Frequency Sound Absorber/ insulator
ay
Material 1.2 Ib. density, recycled bonded acoustical
cotton fiber.
Pattern Soft Gray. Ideal behind acoustical fabric,
perforated or sloted panel surfaces.
Featues Exceptionally good low frequency absorption,
Applications Industal, architectural or audio application,
machinery and mechanical roms. For hash
noisy environment that require high
perfomance low fequency reduction. Above
acoustical cling grid systems. User-friendly
altemative to glass fiber insulation
Sound Deadening, Sound Absorbing, insulating, Low Cost
Material ——_-Reoycled Wood Fiber Residue
Applications Acoustical board can be used as-tlooring
underlayment or as damping layer between
studs and gypsum boards to improve Sound
Transmission Class (STC)
Porous Expanded Polypropylene (PEPP) Acoustical Wall
Panels
Fundamentals of Acoustics SN Material
Pattern
Features
Applications
Semi- rigid Porous Expanded Polypropylene
Acoustical Bead Foam (PEPP)
Non- abrasive, slighty textured, porous.
Lightweight, impact-resistant, moist
bacteria and fungi- resistant. Tackable surtace,
UY stable
Gymnasiums, Auditoria, Swimming pools,
‘eras, Food Processing Pants, Food
Preparation areas, caeleias and Restaurants,
manufacturing Plants, Car washes, Rooftop and
Machine enclosures, Gun ranges, Dog kennels,
Locker rooms,
Sailcloth and Vinyl Encapsulated Acoustical Baffles
Material
Patter
Features
Applications
Fiberglass core encapsulated in Polyvinyl
Chloride Film or saicioth
Plain- Type Aor Type B mounting
Cost elective, lightweight, high acoustical
performance, moisture and chemical resistant.
Any large area where noise and reverberation
needs to be reduced, Gymnasiums, community
centers, sports arena, swimming pools,
factories, animal hosplals, food processing
plants, lage open areas.
Polyurethane Foam Composite Sound Containment
Material
Pattem
Applications
Polyurethane Acoustical Foam bonded to 1 10,
sq. fL_mass loaded vinyl noise barrier with
polyurethane foam vibration decouples.
Fiat Surface
Ideally suited to line equipment enclosures,
Commonly used to line walls and ceilings of
utility” oF mechanical rooms to absorb and
contain the noise source. Use where sound
absorption, noise reduction and vibration
contol are needed,
‘Applications
Bonded Acoustical Pad (BAP)
Bonded Acoustical Pad panels are ideally
suiled to schools, gymnasiums, cafeterias,
classrooms, churches, multi- purpose rooms,
‘community centers and more.
‘Acoustical Cotton Fiber Composite Panel- Sound
Material
Patten
Features
‘Applications
Absorber
Bonded Acoustical Pad (BAP), Recyclable,
Fiberglass te, High density fier
Soft textured sure, fl on oe sie.
Economical, multi- purpose, high performance
absorption combined with STC value.
Gymnasiums, Auditora, Classooms, Music
rooms, Arenas and Stadia, Churches, Offices,
Computer rooms, Restaurants/ Cafeteria,
Concert Halls and Theaters, Gun Ranges,
Manufatuing Plans, Machine. Enclosures,
‘Water Treatment Plants,
Ceiling Tiles
Melamine foam celing ties are excelent
choice for controling sound reverberation
within a varely of rooms, These are availble in
plain face or width a numberof bevels cut into
the panel. It can be used to form unique visual
patterns inthe ceting. Their sound absorption
is much greater than standard ceiling ties
Fundamentals of Acoustics (NN Gypsum Board
Gypsum board is the generic name for the
family of products comprised mainly of non-
combustible gypsum core and paper facings.
Gypsum board is commonly refered to as