lecture-01 acoustical terminology

8/16/2019 Lecture-01 Acoustical Terminology

1/22

Building Services- V

Acoustical Terminology


2/22

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.


3/22

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.


4/22

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


5/22

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.


6/22

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.


7/22

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.


8/22

#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 *


9/22

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


10/22

*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.


11/22

&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 *=%


12/22

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.


13/22

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


14/22

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 "/, *


15/22

%&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


16/22

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


17/22

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!


18/22

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


19/22

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 *


20/22

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


21/22

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.


22/22

+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.

lecture-01 acoustical terminology

Documents