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8/16/2019 Lecture-01 Acoustical Terminology
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Building Services- V
Acoustical Terminology
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ACOUSTICS:
The scientific study of sound, its production, transmission, and effects.
ACOUSTICALThe properties of a material to absorb or reflect sound (adjective),
Acoustically (adverb).
ACOUSTICAL ANALYSIS
A review of a space to determine the level of reverberation or reflectedsound in the space (in seconds) influenced by the building materials used to
construct the space. Also the amount of acoustical absorption required to
reduce reverberation and noise.
ACOUSTICAL CONSULTANTA professional who is experienced in providing advice on acoustical
requirements, and noise control in a variety of situations.
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ACOUSTICAL NVI!ON"NT
The acoustical characteristics of a space or room influenced by the amount
of acoustical absorption, or lac of it in the space.
AI!BO!N SOUN#!ound that reaches the point of interest by traveling through the air.
A"BINT NOIS$SOUN#
All noise level present in a given environment, usually being a composite
of sounds from many sources far and near. Traffic, "#A$, masing sound
or even low%level bacground music can contribute to ambient level ofnoise or sound.
A"%LITU#
The nonnegative scaler measurement of a sound wave&s pea magnitude
during a frequency cycle or pea pressure variation.
A!C&ITCTU!AL ACOUSTICSThe control of noise in a building space to adequately support the
communications function within the space and its effect on the occupants.
The qualities of the building materials used to determine its character with
respect to distinct hearing.
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A!TICULATION CLASS 'AC(:
A measure of rating building elements such as acoustical ceilings and acoustical
screens for speech privacy purposes. A$ values increase with increasing privacy. A$
has replaced 'oise solation $lass ('$) as the accepted industry standard
performance value. '$ is based on hearing sensitivity rather than discernment ofactual speech, which is the primary concern in open office layouts prevalent in
acoustical design wor.
A!TICULATION IN#):
A measure of speech intelligibility influenced by an acoustical environment, and
rated from .* to *.. The higher the number, the higher the intelligibility of the
spoen word in a sentence from to *+.
A!A **CT:
Acoustical materials spaced apart can have greater absorption than the same amount
of materials butted together. The increase in efficiency is due to absorption is due tomore surface area on an acoustical panel, diffraction around the panels, and air space.
AST":
Acronym for American !ociety of Testing and aterials
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A-+I,&TIN,
A measure of sound pressure level designed to reflect the response of the
human ear, which does not respond equally to all frequencies. To describe
sound in a manner representative of the human ear&s response it is necessary
to reduce the effects of the low and high frequencies with respect to
medium frequencies. The resultant sound level is said to be A%weighted,
and the units are in decibels (d-A). The A%weighted sound level is also
called the noise level.
A-+I,&T# SOUN# LVL
The sound level measured with a sound level meter using A%weighting,
which alters the sensitivity of the sound level meter with respect to
frequency so that the sound level meter is less sensitive is less sensitive at
frequencies where the ear is less sensitive usually used in specifying
permissible sound levels in buildings.
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BAC,!OUN# NOIS
The sum total of all unwanted residual noise generated from all direct and reflected
sound sources in a space that can represent an interface to, or interfere with good
listening and speech intelligibility. ("earing impaired persons are especially victimi/ed
by bacground noise)
BA**L
An acoustical sound absorbing unit. 'ormally suspended vertically in a variety of
patterns to introduce absorption into a space to reduce reverberation and noise levels.
BA!!I! Anything physical or an environment that interferes with communication or listening.
BASS T!A%
An acoustic absorber or sound baffle used mainly in sound%recording studios and home
theaters to absorb sound at low frequencies less that about * hert/ ("/). -ass traps,
lie all acoustically absorptive materials, function by turning sound energy within theroom into minute amounts of heat through friction.
BOO"INSS
0ow frequency reflections. n small rooms, acoustical panels with air space behind can
better help control low frequency reflectivity.
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CLOU#
n acoustical industry terms, an acoustical panel suspended in a hori/ontal position from a
ceiling or roof structure. !imilar to a baffle, but in a hori/ontal position
.
COCTAIL %A!TY **CT
The $octail 1arty effect describes the ability to focus one&s listening attention on a singletaler among a mixture of conversations and bacground noises, ignoring other conversations.
This effect reveals one of the surprising abilities of our auditory system, which allows us to
communicate in a noisy place, such as a coctail party.
COINCI#NC !,ION
The typically high frequency at which sound can pass directly through a partition due to the partition resonating at that same frequency. !peed of wave traveling through the material
equals the speed if the sound (incident) wave in air.
CONST!AIN# LAY! #A"%IN, 'CL#(
#ibrational energy is dissipated and converted into small amounts of heat as a result of the
extension and compression, or shearing of a damping layer. A viscoelastic damping compound between two stiff or rigid constraining layers such as drywall or plywood. This conversion of
vibration to heat reduces the resonance of the stiff layers much lie placing a hand on a drum
head to stop it from resonating.
CYCL
n acoustics, the cycle is the complete oscillation of a sound wave&s pressure above and below
the atmospheric static pressure.
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#A"%IN,
The process by which vibrations are converted into heat over time and distance.
#CIBL 'dB(
A logarithmic unit used to express the difference or magnitude of the level or power of
sound intensity. t is equal to ten times the common logarithm of the ratio of the two
levels. 894$ : -40; A whisper is about
d-, and the threshold of pain for the human ear is around *
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C&O
A reflected sound producing a distinct repetition of the original sound that
reaches the listener when the delay is ? .* sec after the direct sound. The
reflecting object must be at an average of about = ft in order for an echo to
be heard.
C&O *LUTT!
An echo flutter can be heard as a ringing effect caused when a sound
rapidly bounces bac and forth between two hard, flat parallel surfaces
within a room. 4cho flutters can be controlled with diffusers and sound
absorbing products. Also nown as a 2lutter 4cho.
.UAL LOU#NSS CONTOU!S
A measure of sound pressure over the frequency spectrum represented bycurves on a graph for which a listener perceives the different frequencies to
be at equal volumes. "uman hearing is less sensitive at low frequencies
whereas high frequencies above
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*LANIN,
An indirect path of sound transmission traveling around a partition or
barrier within a building reducing the !T$ significantly. !ome examples of
flaning paths are noise under doors, electrical conduit penetrations in the
partition, window mullions, bac to bac electrical boxes, ductwor and
ceiling plenums, as well as shares walls, floors, and ceilings
*! *IL#
!ound waves not varying in magnitude according to direction of
measurement in a sound environment that is free from all bounding surfaces
or obstructions.
*!.UNCY
The number of cycles per second of a given tone. Acoustical frequency is
normally measured in units called "ert/ ("/). @ne "/ is * cycle per second,
two "/ is < cycles per second, and so on.
*!.UNCY ANALYSIS
An analysis of a sound to determine the character (the volume of sounds at
various frequencies) that mae up the overall sound&s spectrum. i.e.
higher frequency sound or pitch vs, low frequency sound or pitch. A sound
is rarely composed of a single pure frequency.
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&A!IN, I"%AI!"NT '&A!IN, LOSS(
Any degree, full or partial, of impairment of the ability to apprehend sound.
!ound waves vary in frequency and amplitude. "earing loss can be caused
by age, illness, or by exposure to excessively high noise levels.
4nvironments with longer reverberation times mae it harder for those with
hearing loss to understand conversation.
&A!IN, !AN,
An average young person&s hearing range is from as low as *=%
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LIV N# $ #A# N#
An acoustical treatment plan usually for performance purposes, where one end of the performance
space is highly absorbent, and the other end is more reflective or diffused. As an example, in a good
theater the stage would be the 94A9 4'9 so that the performer could hear the purest sound
produced. The audience would be in the 0#4 4'9 of the theater and able to enjoy the warm sound
produced by the reverberation and diffusion of the performance as its sound wors with the room&s
acoustic treatments.LOU#NSS
A subjective measurement of the perception of a sound&s intensity, and duration and can be raned
from soft to loud. 0oudness depends on sound pressure, intensity, and frequency. 4very * d- is
roughly a doubling or halving of loudness. Also nown as ntensity.
"ASIN,
The ability or process in which one sound maes the ear incapable of hearing another sound. ostcommonly used in open office environments to help speech privacy and are more commonly and
less accurately nown as Ewhite noiseF or Epin noiseF.
"ASS
The weight of a given material in a given volume. Generally the heavier or denser a material is, the
more sound it will stop and the higher the Transmission 0oss (T0) will be. t is harder for a sound
wave to move a heavy (high mass) wall than a light (lower mass) wall.
"ASS LA+
2or every doubling of mass there is a =d- improvement of transmission loss. 2or example, if you
were to measure a stand alone single layer of HIDF drywall (not attached to a wall of any ind)
compared to < layers of HIDF drywall wall, a T0 gain of :=d- would be seen. f you were to double
the mass again, going from < to C layers of HIDF drywall (again, not an actual wall, just drywall), the
T0 would again improve :=d-.'ote that this 9@4! '@T mean that adding another sheet of
drywall to an existing wall gives you :=d-. 7ou would have to double the weight of the entire wall,which includes studs and insulation.
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NOIS
n acoustics 'oise is described as any sound in the acoustic domain both wanted and unwanted. Bhile
music and birds chirping are examples of wanted sounds, noise is more commonly used in reference to
unwanted sounds such as traffic, airplane, industrial, and other annoying sounds. 'oise does not have to
be excessively loud to be annoying or cause interference.
NOIS C!IT!IA 'NC(
'$ is determined by '$ $urves which are a series of curves of octave%band spectra, used to provide asingle number rating of the noisiness of an indoor space. The room&s octave%band spectrum is compared
with this set of curves to determine the '$ level of the room and illustrates the extent to which unwanted
noise such as mechanical or "#A$ noise interferes with speech intelligibility.
NOIS ISOLATION CLASS 'NIC(
A single%number rating of building elements such as acoustical ceilings and acoustical screens for speech
privacy purposes derived from the measured values of noise reduction between two enclosed spaces thatare connected between one or more paths that can not be isolated such as open office environments. '$
has been replaced by Articulation $lass (A$).
NOIS "ITI,ATION
'oise mitigation is a set of strategies to reduce noise pollution.
NOIS !#UCTION 'N!(
The average amount of reduced sound pressure level (!10) measured in decibels (d-) on a logarithmic
basis between two rooms separated by a wall with a sound source in one room and the measurement taen
in the other room. '3 is also be used to determine the reduction of !10 caused by an absorbent material
before and after it is introduced into a room with a sound source.
NOIS !#UCTION CO**ICINT 'N!C(
An arithmetic average of an acoustic material to the nearest multiple of .H of four sound absorption
coefficients at frequencies of
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OCTAV BAN#S
!ounds that contain energy over a wide range of frequencies are divided into sections called
bands. An octave is the interval between two discrete frequencies having a frequency ratio
of two. 2or instance, frequencies of H "/ and * "/ are said to be separated by one
octave. The * most commonly used octave band are centered at the following frequencies
K*.H "/, =K "/, *
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%&ON
A unit measurement of perceived sound or loudness. * 1hon is equal to *
d-!10 at a frequency of * "/.
%IN NOIS
A random signal of every frequency in which each higher octave drops off K
d-. The lower octaves have more power, and the higher octaves have less
power. 1in noise is used to test loudspeaers and EtuneF a room for
optimum audio reproduction or masing systems.
%LNU"
An open cavity between a given space&s dec and dropped ceiling or an
enclosed space not for human occupancy purposes in buildings. ost open
office designs have open plenums for electrical and "#A$ purposes and area flaning path for sound transmission.
REFLECTION
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REFLECTION
Sound wave energy that strikes and bounces of a surace through which it cannotpass. Harder and non porous suraces, such as a painted concrete wall, are morereective than sot porous suraces, such as an acoustical panel. Sound reection canbe used to enhance the quality (intelligibility o music and speech.
RESONANCE
!very item has a natural requency o vibration, which is determined by a combinationo actors such as mass and stifness. "hanging a actor will change the resonancerequency. #t is much easier to get an ob$ect to vibrate at its resonance point. #nacoustics, an airborne requency can be ampli%ed due to the reinorcement o apartition vibrating at resonance. &lso as an e'ample, i a wall is resonating at ))H*,requencies around ))H* will pass much more readily through that wall.
RESONANCE REGION
+he requency at which the entire partition or wall assembly resonates. +his requencyis dependent on cavity depth, insulation, mass, etc.
RESONANT FREQUENCY
& requency at which a resonance e'ists.
REVERBERATION
+he perpetuation o sound wave energy in an enclosed space ater the original sound
source has stopped. &ter this original sound source has stopped the sound waveenergy will continue to be reected, and absorbed until it looses enough energy to dieout. ore reverberation can be good or music, but poor or speech intelligibility.
REVERBERATION TIME
+he time it takes in seconds or a sound to decay -) d or one/millionth o its originalsound level ater the source has stopped in an enclosed space. "ommonly reerred to
as 0+-).
SA
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SABIN
A measure or unit used to measure the amount of sound absorption of a room or acoustic
material. * metric !abin is equal to the value of * square meter of *+ absorbing material.
'amed in honor of Ballace $lement !abine (*D=D%*L*L) who developed the formula allowing
for the calculation of reverb time within a space prior to construction.
S%TU"n acoustics, a thin layer of material such as foil, steel, or lead that helps prevent sound waves
from passing through an absorptive material.
SI,NAL TO NOIS !ATIO
The comparison of the level of desired signal such as speech and music to the level of
bacground or unwanted noise. The higher the ratio the lower the bacground or unwanted
noise interferes with the desired signal.
SIN +AV
A continuous uniform (sound) wave having a constant amplitude and frequency.
SOUN#
#ibrational mechanical energy that propagates as a wave through matter such as air and water
and is defined by the properties of sound waves which are frequency, amplitude, wavelength,intensity, period, speed and direction. The speed of sound depends on the temperature, and
medium it travels through. The average speed of sound through the air at sea level and at => mph).
SOUN# ABSO!%TION
The property of materials such as air, walls or acoustic panels that changes sound wave energy
into heat energy. Bhen a sound wave hits a surface, that which is not reflected is absorbed.
SOUN# BA!!I!
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SOUN# BA!!I!
n acoustics, a sound barrier is any material or structure that is placed around a sound
source to impede the transmission of the noise beyond the barrier. A poor acoustical
environment, such as a room with a long reverberation time, can be a EbarrierF to speech
intelligibility or good hearing.
SOUN# LVLA subjective measure of sound or !ound 1ressure 0evel (!10) expressed in decibels (db)
as a comparison corresponding to familiar sounds experienced in a variety of situations.
SOUN# LVL "T!
An instrument containing a microphone, amplifier, output meter, and various frequency%
weighting settings used to measure sound levels or noises at different frequencies.SOUN# %!SSU!
The varying difference between the instantaneous pressure of a sound wave at a point in
space and the static atmospheric pressure at that point.
SOUN# %!SSU! LVL 'S%L(
4xpresses in decibels (d-), !10 of a sound is
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SOUN# ATTNUATION
3educing the intensity or the sound pressure level of sound, which is transmitted from one point to
another.
SOUN# !"#IATION
1rocess of abatement, remedying, or other method to contain or remove sound or noise from an
environment.
SOUN# T!ANS"ISSION CLASS - STC
A method for a single number raning of walls, doors, windows, noise barriers, partitions, and other
acoustic products measured over *= different frequencies ranging from *
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TI" +I,&T# AV!A, 'T+A(
The guideline used by the @ccupational !afety and "ealth Administration
to measure noise levels in the worplace. 4xposure to loud noise over a
long time can cause hearing damage. f the TBA noise level, which is the
average sound level over D hours, is exceeding DH d-(A), a hearing
conservation program is required. The table below shows the equivalent
amount of noise and exposure time equal to D hours of exposure.
1SH& 2ermissible 3oise !'posure4) d(&5.) Hours46d(&-.) Hours47 d(&8.) Hours49 d(&:.) Hours))
d(&6.) Hours)6 d(&.7 Hours)7 d(&.) Hours)d(&:) inutes7 d(&7 inutes or less
ULT!ASOUN#
!ound pressures with frequencies greater than the upper limit of human
hearing which is approximately
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VIB!ATION
echanical periodic or random oscillations about some specified reference or
equilibrium point. #ibration is expressed in terms of frequency or number of
cycles that occur in a given time period such as "ert/ ("/), cycles per second
(cps), cycles per minute (cpm), rotations per minute (rpm), and stroes per minute(spm). A few examples are drums, tuning fors, engines, or the imbalance of a
rotating object lie in a washing machine.
VIB!ATION ISOLATO!
A resilient support which accomplishes the process of isolating an object from thesource of vibrations. An example would be the use of a #ibration solator to eep
the vibration of a roof top "#A$ unit from transferring to the building.
VOLU"
n acoustics, #olume is similar to 0oudness in that it is a subjective measurement
of the perception of a sound&s intensity, and duration and can be raned from soft
to loud. 0oudness depends on sound pressure, intensity, and frequency.
• n architecture, #olume is the cubic space of a given enclosed space by using the
calculation
#olume J !pace 0ength x !pace Bidth x !pace "eight.
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+AVLN,T&
The distance between two identical crests in a sound wave or cycle. Bavelength
can be easily pictured as the wave ripples in water from a tossed stone. !ound
wavelengths vary by frequency. The higher the sound frequency, the shorter the
wavelength These frequencies are more quicly dissipated and easier to controlwhereas lower end frequencies produce longer wavelengths which tae longer to
dissipate and are harder to control. 0ow end frequencies with long wavelengths
emanate from sound sources that cause most noise complaints such as traffic
noise, and many music systems lie those found in today&s home theaters.
+&IT NOIS
A random signal in which all frequencies in all bands have equal power.
mpact nsulation $lass ($) is a single number rating used to compare and
evaluate the performance of floorIceiling assemblies measured in an acoustic
laboratory. 2ield mpact nsulation $lass (2$) is a single number rating used to
compare and evaluate the performance of floorIceiling assemblies (and
associated structures) derived from field impact sound measurements in
accordance to A!T 4LDL.