soundproofing glossary

1:3 Octave Band Filters Single 1:1 Octave bands divided into three parts.

1:1 Octave Band Filters A division of the frequency range into bands, the upper frequency limit of each band being twice the lower frequency limit.

A

A WEIGHTING A standard weighting of the audible frequencies designed to reflect the response of the human ear to noise.

A-B test: A test between two components or rooms. For example, a test between two different pre-amplifiers. For the test to be scientifically valid the levels should be matched.

Absorb: Sound waves are converted into energy such as heat that is then captured by insulation.

Absorption: In acoustics, the changing of sound energy to heat.

Absorption coefficient: The fraction of sound energy that is absorbed at any surface. It has a value between 0 and 1 and varies with the frequency and angle of incidence of the sound.

ACOUSTICS:The science of Sound. Its production, transmission and effects.

ACOUSTICAL:The 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 reflected sound 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 CONSULTANT: A professional usually with an engineering degree who is experienced in providing advice on acoustical requirements, and noise control in a variety of situations.

ACOUSTICAL ENVIRONMENT: The acoustical characteristics of a space or room influenced by the amount of acoustical absorption, or lack of it in the space.

AIRBORNE SOUND: Sound that reaches the point of interest by propagation through air.

ARCHITECTURAL ACOUSTICS: The 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 determine its character with respect to distinct hearing.

ARTICULATION CLASS: A single number rating used for comparing acoustical ceilings and acoustical screens for speech privacy purposes. AC values increase with increasing privacy and range from approximately 100-250. This classification supercedes Speech Privacy Noise Isolation Class (NIC) rating method.

ARTICULATION INDEX (AI): A measure of speech intelligibility influenced by Acoustical Environment rated from 0.01 to 1.00.The higher the number the higher the intelligibility of words and sentences understood from 0-100%.

ABSORPTION: The properties of a material composition to convert sound energy into heat thereby reducing the amount of energy that can be reflected.

AREA EFFECT: Acoustical materials spaced apart can have greater absorption than same amount of material butted together. The increase in efficiency is due to absorption by soft exposed edges and also to diffraction of sound energy around panel perimeters.

ASSISTIVE LISTENING DEVICE: An electronic device that provides amplification of sound to a hearing impaired person. Device include personal hearing aids, magnetic induction loops, FM radio systems and infrared systems. All have advantages and disadvantages and some may be dependent on good acoustical environment for optimal performance.

ATTENUATION: The reduction of sound energy as a function of distance traveled. (See also Inverse Square Law).

A WEIGHTING: An electronic filtering system in a sound meter that allows meter to largely ignore lower frequency sounds in a similar fashion to the way our ears do.

AMBIENT NOISE/SOUND: Noise level in a space from all sources such as HVAC or extraneous sounds from outside the space. Masking sound or low-level background music can contribute to ambient level of sound or noise.

AUDIOLOGIST:

ABSORPTION. A property of materials that allows a reduction in the amount of sound energy reflected. The introduction of an absorbent into the surfaces of a room will reduce the sound pressure level in that room by not reflecting all of the sound energy striking the room's surfaces. The effect of absorption merely reduces the resultant sound level in the room produced by energy that has already entered the room.

ABSORPTION COEFFICIENT. A measure of the sound-absorbing ability of a surface. It is defined as the fraction of incident sound energy absorbed or otherwise not reflected by a surface. Unless otherwise specified, a diffuse sound field is assumed. The values at the sound-absorption coefficient usually range from about 0.01 for marble slate to almost 1.0 for long absorbing wedges often used in anechoic rooms.

AC3: See Dolby Digital.

ACOUSTIC CALIBRATOR An instrument that provides a reference noise source that is used to calibrate and check the performance of a Sound Level Meter.

Acoustic impedance: Z=R+jX ; [ML-4T-1] ; mks acoustic ohm *(Pa.s/m3) ---of a surface, for a given frequency, the complex quotient obtained when the sound pressure averaged over the surface is divided by the volume velocity through the surface. The real and imaginary components are called, respectively, acoustic resistance and acoustic reactance.

Acoustic material: Any material considered in terms of its acoustical properties. Commonly and especially, a material designed to absorb sound.

ACOUSTICS. (1) The science of sound, including the generation, transmission, and effects of sound waves, both audible and inaudible. (2) The physical qualities of a room or other enclosure (such as size, shape, amount of noise) that determine the audibility and perception of speech and music within the room. Acoustics: The science of sound. It can also refer to the effect a given environment has on sound.

ACOUSTIC TRAUMA. Damage to the hearing mechanism caused by a sudden burst of intense noise, or by a blast. The term usually implies a single traumatic event.

AES: Audio Engineering Society.

AIRBORNE SOUND. Sound that reaches the point of interest by propagation through air. When we talk about airborne sound the higher the Rw figure acheived the better the sound insulation. In the wall example we are trying to acheive a figure over 50db. Airborne sound: Sound that arrives at the point of interest, such as one side of a partition, by propagation through air.

Airflow resistance, R: [ML-4T-1]; mks acoustic ohm *(Pa.s/m3) ---the quotient of the air pressure difference across a specimen divided by the volume velocity of airflow through the specimen. The pressure difference and the volume velocity may be either steady or alternating.

Airflow resistivity: *[ML-3T-1]; mks rayl/m *(Pa.s/m3) ---of a homogeneous material, the quotient of its specific airflow resistance divided by its thickness.

Alcons: The measured percentage of Articulation Loss of Consonants by a listener. % Alcons of 0 indicates perfect clarity and intelligibility with no loss of consonant understanding, while 10% and beyond is growing toward bad intelligibility, and 15% typically is the maximum loss acceptable.

Ambience: The acoustic characteristics of a space with regard to reverberation. A room with a lot of reverb is said to be "live"; one without much reverb is said to be "dead".

AMBIENT NOISE. The total of all noise in the environment, other than the noise from the source of interest. This term is used interchangeably with background noise. ambient noise. All-encompassing sound at a given place, usually a composite of sounds from many sources near and far. The composite of airborne sound from many sources near and far associated with a given environment. No particular sound is singled out for interest.

Amplitude: The instantaneous magnitude of an oscillating quantity such as sound pressure. The peak amplitude is the maximum value.

Analog: An electrical signal whose frequency and level vary continuously in direct relationship to the original electrical or acoustical signal.

Anechoic: Without echo.

Anechoic chamber: A room designed to suppress internal sound reflections. Used for acoustical measurements.

ANECHOIC ROOM. A room in which the boundaries absorb nearly all the incident sound, thereby, effectively creating free field conditions. anechoic room. Test room whose surfaces absorb essentially all of the incident sound energy over the frequency range of interest, thereby affording nearly free-field conditions over the measurement surface.

ANSI. The American National Standards Institute.

Articulation: A quantitative measure of the intelligibility of speech; the percentage of speech items correctly perceived and recorded.

ARTICULATION INDEX (AI). A numerically calculated measure of the intelligibility of transmitted or processed speech. It takes into account the limitations of the transmission path and the background noise. The articulation index can range in magnitude between 0 and 1.0 . If the AI is less than 0.1, speech intelligibility is generally low. If it is above 0.6, speech intelligibility is generally high.

Attention to the detail. When applying any soundproofing solution think of the analogy that sound flows like water. It is absolutely imperative that you remeber to fill any hole that sound can flow through. It will leak through tiny holes just the same way water would. Think airtight! Even a hole 1% of the area you are trying to soundproof can reduce the efficiency of the soundproofing by up to 10%.

Artificial reverberation: Reverberation generated by electrical or acoustical means to simulate that of concert halls, etc., added to a signal to make it sound more lifelike.

Arithmetic mean sound pressure level: Of several related sound pressure levels measured at different positions or sound pressure levels measured at different positions or different times, or both, in a specified frequency band, the sum of the sound pressure levels divided by the number of levels.

ASA: Acoustical Society of America.

Attack: The beginning of a sound; the initial transient of a musical note.

ATTENUATION. The reduction of sound intensity by various means (e.g., air, humidity, porous materials...).

AUDIO FREQUENCY. The frequency of oscillation of an audible sound wave. Any frequency between 20 and 20,000 Hz. audio frequency. Frequency of a sound wave normally audible to humans. Unit, hertz (Hz). Audio frequencies range roughly from 15 Hz to 20 kHz.

AUDIOGRAM. A graph showing individual hearing acuity as a function of frequency.

AUDIOMETER. An instrument for measuring individual hearing acuity.

A-WEIGHTED SOUND LEVEL. A measure of sound pressure level designed to reflect the acuity of the human ear, which does not respond equally to all frequencies. The ear is less efficient at low and high frequencies than at medium or speech-range frequencies. Therefore, to describe a sound containing a wide range of frequencies in a manner representative of the ear's response, it is necessary to reduce the effects of the low and high frequencies with respect to the medium frequencies. The resultant sound level is said to be A-weighted, and the units are dBA. The A-weighted sound level is also called the noise level. Sound level meters have an A-weighting network for measuring A-weighted sound level.

A-weighted sound pressure level. Ten times the logarithm of the ratio of A-weighted squared sound pressure to the squared reference sound pressure of 20 micropascal, the squared sound pressure being obtained with fast (F) (125-ms) exponentially weighted time averaging. Alternatively slow (S) (1000-ms) exponentially weighted time averaging may be specified. Unit, decibel (dB); symbol, L_A.
maximum A-weighted sound pressure level. Greatest fast (125-ms) A-weighted sound pressure level, within a stated time interval. Unit, decibel (dB); symbol, L_AFmax.
peak A-weighted sound pressure level. Level of peak sound pressure with A-frequency weighting, within a stated time interval. Unit, decibel (dB); symbol, L_Apk.
equivalent continuous A-weighted sound pressure level [5]. A-weighted sound pressure level of a continuous steady sound that, within a measurement time interval, has the same time-mean-square sound pressure as a sound under consideration which varies with time. Unit, decibel (dB); symbol, L_AeqT.

A-frequency weighting [2]. Frequency weighting of a spectrum according to a standardized frequency response curve. Other standardized frequency weightings (e.g. B,C) are sometimes used.

average sound pressure level in a room. Ten times the logarithm of the ratio of the space and time average of squared sound pressure to the squared reference sound pressure, the space average being taken over the total volume of the room, except for the regions of the room where the direct field of the source and the near field of the boundaries are of significance. Unit, decibel (dB).

B

BACKGROUND NOISE. The total of all noise in a system or situation, independent of the presence of the desired signal. In acoustical measurements, strictly speaking, the term "background noise" means electrical noise in the measurement system. However, in popular usage the term "background noise" is often used to mean the noise in the environment, other than the noise from the source of interest. background noise. Total of all sources of interference in a system used for the production, detection, measurement, or recording of a signal, independent of the presence of the signal.

BAND. Any segment of the frequency spectrum.

BAND PASS FILTER. A wave filter that has a single transmission band extending from a lower cutoff frequency greater than zero to a finite upper cutoff frequency. bandpass filter. Filter with a single transmission band or passband with relatively low attenuation extending from a lower band-edge frequency greater than zero to a finite upper band- edge frequency.

band pressure level. Sound pressure level for sound contained within a restricted frequency band. Unit, decibel (dB); symbol, L{sub pb}. A band may be identified by its nominal lower and upper band edge frequencies, or by its nominal midband frequency and nominal bandwidth. The nominal width of the band may be indicated by a prefatory modifier, e.g., octave-band sound pressure level, one-third-octave-band sound pressure level, or 50- Hz band level at 400 Hz.

bel. Unit of level when the base of the logarithm is ten, and the quantities concerned are proportional to power. Symbol, B.

BROADBAND NOISE. Noise with components over a wide range of frequencies. Broadband Noise Measurements using parameters which include all the audible noise, such as dB(A) and dB(C) broad-band noise [5]. Noise in which the acoustic energy is distributed over a relatively wide range of frequencies. The spectrum is generally smooth and continuous, although it may vary significantly from "flat." If the broad-band sound does not contain any significant discrete tones, the sound will lack a subjective quality of pitch or tonality.

BACKGROUND NOISE: The sum total of all noise generated from all direct and reflected sound sources in a space that can represent an interface to good listening and speech intelligibility. (Hearing impaired persons are especially victimized by background noise).

BAFFLE: A free hanging acoustical sound absorbing unit. Normally suspended vertically in a variety of patterns to introduce absorption into a space to reduce reverberation and noise levels.

BARRIER: Anything physical or an environment that interferes with communication or listening. A poor acoustical environment can be a barrier to good listening and especially so for persons with a hearing impairment.

BEL: A measurement of sound intensity named in honor of Alexander Graham Bell. First used to relate intensity to a level corresponding to hearing sensation.

BOOMINESS: Low frequency reflections. In small rooms acoustical panels with air space behind can better help control low frequency reflectivity.

C

C Weighting A standard weighting of the audible frequencies used for the measurement of Peak Sound Pressure level.

CE Marking A label used to show that the Sound Level Meter conforms to the specification of a European Directive

CALIBRATOR (ACOUSTICAL). A device which produces a known sound pressure on the microphone of a sound level measurement system, and is used to adjust the system to Standard specifications.

COCHLEA. A spirally coiled organ located within the inner ear which contains the receptor organs essential to hearing.

compressional wave. Wave in an elastic medium which causes an element of the medium to change its volume without undergoing rotation. A compressional wave is a longitudinal wave.

complex tone. Sound wave containing simple harmonic components of different frequencies.

continuous spectrum. Spectrum of a wave whose components are continuously distributed over a frequency region.

CLOUD: In acoustical industry terms, an acoustical panel suspended in a horizontal position from ceiling/roof structure. Similar to a baffle but in a horizontal position.

COCKTAIL PARTY EFFECT: Sound in a noisy crowded room generated mostly by conversation. Levels rise and fall as people compete with one another to be heard. Perception of speech can be nearly impossible in high levels of noise.

COCHLEA: A snail shaped mechanism in the inner ear that contain hair cells of basilar membrane that vibrate to aid in frequency recognition.

CYCLE: In acoustics, the cycle is the complete oscillation of pressure above and below the atmospheric static pressure.

CYCLES PER SECOND: The number of oscillations that occur in the time frame of one second. (See FREQUENCY.) Low frequency sounds have fewer and longer oscillations.

CUTOFF FREQUENCIES. The frequencies that mark the ends of a band, or the points at Which the characteristics of a filter change from pass to no-pass.

CYCLE. The complete sequence of values of a periodic quantity that occurs during one period.

CYCLES PER SECOND. A measure of frequency numerically equivalent to hertz.

CYLINDRICAL WAVE. A wave in which the surfaces of constant phase are coaxial cylinders. A line of closely-spaced sound sources radiating into an open space produces a free sound field of cylindrical waves.

D

Data Logging Measurements can be stored in the Sound Level Meter for download to a PC

dB(A) Decibels A weighted

dB(C) Decibels C Weighted

dB(Z) Decibels Z weighted

dead room. Room characterized by a relatively large amount of sound absorption and a relatively short reverberation time.

Decibel (dB) The units of sound level and noise exposure measurement decibel [3]. Unit of level equal to one tenth of a bel. Symbol, dB.

decay rate. At a stated frequency, time rate at which sound pressure level decreases in a room. Unit, decibel per second (dB/s). Decay rate d in a reverberant room is related to reverberation time T by T = 60 dB / d.

DIN 45641 German Standard which defines the additional measurements LAFTeq & LIeqT

% Dose The noise exposure expressed as a percentage (%) of a fixed level for 8 hours

DAMPING. The dissipation of energy with time or distance. The term is generally applied to the attenuation of sound in a structure owing to the internal sound-dissipative properties of the structure or to the addition of sound-dissipative materials.

dBA. Unit of sound level. The weighted sound pressure level by the use of the A metering characteristic and weighting specified in ANSI Specifications for Sound Level Meters. dBA is used as a measure of human response to sound. dB(A) is the frequency response curve which is resembles the normal frequency hearing curve for most people. A meter using this network will give a result which does have some resemblance in level to that level which is experienced by most people.

DECIBEL. A unit of sound pressure level, abbreviated dB. It should be made clear that the scale that is used is not linear it is logarithmic. In simplified terms this means that one sound that is 10db louder than another is in fact TWICE as loud. Similarly a difference of 15db is THREE times as loud. When dealing with sound reduction achieving over 10 db in sound reduction will have a very material affect on the sound one hears.

diffracted wave. Wave whose front has been changed in direction by an obstacle or other nonhomogeneity in a medium, other than by reflection or refraction.

DAMPING: The dissipation of vibratory energy in solid media and structures with time or distance. It is analogous to the absorption of sound in air.

DECIBEL (dB): Sound level in decibels as a logarithmic ratio. Sound intensity described in decibels. i.e.: Breathing 5 dB, office activity 50 dB, Jet Aircraft during takeoff at 300' distance 130 dB. (See submenu TABLES under Acoustics for a table on Sound Source of Environment).

DEFLECTION: The distance an elastic body or spring moves when subjected to a static or dynamic force. Typical units are inches or mm.

DEAF: Loss of auditory sensation with or without use of assistive listening device. Loss of hearing more severe than is generally characterized as "Hearing Impaired".

DIFFUSION: is the scattering or random reflection of a sound wave from a surface. The directions of reflected sound is changed so that listeners may have sensation of sound coming from all directions at equal levels.

DIFFRACTION. A modification which soundwaves undergo in passing by the edges of solid bodies. diffraction. Process that produces a diffracted wave.

diffuse sound field. Sound field in which the time average of the mean-square sound pressure is everywhere the same and the flow of acoustic energy in all directions is equally probable.

direct sound field. That portion of a sound field, in an enclosure, which arrives from the sound source without having undergone any reflection.

DIRECTIVITY INDEX. In a given direction froma sound source, the difference in decibels between (a) the sound pressure level produced by the source in that direction, and (b) the space-average sound pressure level of that source, measured at the same distance.

discrete tone [5]. A discrete tone can be either a sinusoidal variation (see 4.05, pure tone), in which case the frequency spectrum would show a single "spike" at the sinusoidal frequency, or, more typically, a non-sinusoidal variation, in which case the spectrum would show a spike at the fundamental frequency and other spikes at harmonics of the fundamental.

displacement. Quantity that specifies the change of position of a particle, or body, with respect to a reference frame.

DOPPLER EFFECT (DOPPLER SHIFT). The apparent upward shift in frequency of a sound as a noise source approaches the listener or the apparent downward shift when the noise source recedes. The classic example is the change in pitch of a railroad whistle as the locomotive approaches and passes by.

DOSIMETER. A device worn by a worker for determining the worker's accumulated noise exposure with regard to level and time according to a pre-determined integration formula.

duct lining. Layer of porous material placed on the inner surface of a duct to attenuate sound that propagates through the duct.

E

earplug. Hearing protector that is inserted into the ear canal.

earmuff. Hearing protector worn over the pinna of an ear.

ECHO. A wave that has been reflected or otherwise returned with sufficient magnitude and delay, so as to be detected as a wave distinct from that directly transmitted. echo. Reflected sound wave that arrives with sufficient magnitude and time delay as to be distinguishable from a sound wave received directly from a source.

EAR: An incredible hearing mechanism consisting of outer, middle and inner ear segments that cause sound pressures to be picked up by the ear that are transmitted through auditory nerves where signals are interpreted by brain as sound.

ECHO: Reflected sound producing a distinct repetition of the original sound. Echo in mountains is distinct by reason of distance of travel after original signal has ceased.

ECHO FLUTTER: Short echoes in a small reverberative spaces that produce a clicking, ringing or hissing sound after the original sound signal has ceased. Flutter echoes may be present in long narrow spaces with parallel walls.

EQUAL LOUDNESS CONTOURS: Curves represented in graph form as a function of sound level and frequency which listeners perceive as being equally loud. High frequency sounds above 2000 Hz are more annoying. Human hearing is less sensitive to low frequency sound. (See also PHON.)

effective sound pressure. Root-mean-square value of the instantaneous sound pressure at a point, during a given time interval. Unit, pascal (Pa). The effective sound pressure is commonly referred to as the sound pressure.

EQUIVALENT A-WEIGHTED SOUND LEVEL (Leq). The constant sound level that, in a given time period, would convey the same sound energy as the actual time-varying A-weighted sound level.

Exposure Noise Exposure in Pa2h (Pascal Squared Hours)

F

FAR FIELD. Describes a sound source region in free space where the sound pressure level obeys the inverse-square law (the sound pressure level decreases 6 dB with each doubling of distance from the source). Also, in this region the sound particle velocity is in phase with the sound pressure. Closer to the source where these two conditions do not hold constitutes the "near field" region.

Fast Time Weighting A standard time weighting applied by the Sound Level Meter

FILTER. A device for separating components of a signal on the basis of their frequency. It allows components in one or more frequency bands to pass relatively unattenuated, and it attenuates components in other frequency bands. filter. Device for separating waves on the basis of their frequency.

FLAME SPREAD: Classification indicating propagation of flame across a sample compared to flame propagation across concrete panels and red oak. Results are obtained through an ASTM E84 or UL723 test.

FLANKING: The transmission of sound around the perimeter or through holes within partitions (or barriers) that reduces the otherwise obtainable sound transmission loss of a partition. Examples of flanking paths within buildings are ceiling plena above partitions; ductwork, piping, and electrical conduit penetrations through partitions; back-to-back electrical boxes within partitions, window mullions, etc.

FREE FIELD: Sound waves from a source outdoors where there are no obstructions.

FREQUENCY: The number of oscillations or cycles per unit of time. Acoustical frequency is usually expressed in units of Hertz (Hz) where one Hz is equal to one cycle per second.

FREQUENCY ANALYSIS: An analysis of sound to determine the character of the sound by determining the amount of sounds at various frequencies that make up the overall sound spectrum. i.e.: higher frequency sound or pitch vs. low frequency.

filter nominal midband frequency. For a set of contiguous one-third octave bandpass filters, frequency of a specified series such as the preferred frequency series that includes 100, 125, 160, 200, 250, 315, 400, 500, 630, 800, and 1000 hertz, extended by successive multiplication or division by 10. For a set of contiguous octave bandpass filters, the nominal midband frequency is one of a series such as the preferred frequency series that includes 16, 31.5, 63, 125, 250, 500, 1000, 2000, 4000, and 8000 hertz, extended by successive multiplication or division by 10. Unit, hertz (Hz).

Flanking transmission. Flanking sound transmission is the term used to describe the movement of sound through the structures that flank the barrier that your trying to sound proof. In the case of wall insulation the flanking structures are the floors and ceilings. In the case of soundproofing floors and ceilings, its the walls. In designing for sound insulation care should be taken to ensure that flanking transmission via the associated structure does not downgrade the performance of the partition or wall to a level below that required in use. flanking sound transmission. In sound transmission measurement, the transmission of sound from the sound source room to the receiving room by paths other than through the partition under test. Flanking transmission may include structure-borne sound transmission.

fluctuating noise [5]. Noise whose level varies continuously and to an appreciable extent during the period of observation.

free progressive wave. Wave in a medium free from boundary effects.

free field. Field in a homogeneous, isotropic medium free from boundaries. Free field: A region in which no significant reflections of sound occur.

FREE SOUND FIELD (FREE FIELD). A sound field in which the effects of obstacles or boundaries on sound propagated in that field are negligible.

FREQUENCY. The number of times per second that the sine wave of sound repeats itself, or that the sine wave of a vibrating object repeats itself. Now expressed in hertz (Hz), formerly in cycles per second (cps). frequency. For a function periodic in time, the reciprocal of the period. Unit, hertz (Hz).

frequency weighting [2]. Process of modifying the amplitudes and phases of selected components of a spectrum.

fundamental. Component of a periodic wave having the lowest frequency.

H

HAIR CELL. Sensory cells in the cochlea which transform the mechanical energy of sound into nerve impulses.

HARMONIC. A sinusoidal (pure-tone) component whose frequency is a whole-number multiple of the fundamental frequency of the wave. If a component has a frequency twice that of the fundamental it is called the second harmonic, etc... harmonic. Sinusoidal quantity that has a frequency which is an integral multiple of the fundamental.

HEARING. The subjective human response to sound.

HEARING LEVEL. A measured threshold of hearing at a specified frequency, expressed in decibels relative to a specified standard of normal hearing. The deviation in decibels of an individual's threshold from the zero reference of the audiometer.

HEARING LOSS. A term denoting an impairment of auditory acuity. The amount of hearing impairment, in decibels, measured as a set of hearing threshold levels at specified frequencies. Types of hearing loss are: 1. Conductive: A loss originating in the conductive mechanism of the ear; 2. Sensor-neural: A loss originating in the cochlea or the fibers of the auditory nerve; 3. Noise induced: A sensor-neural loss attributed to the effects of noise.

hearing protector. Personal device worn to reduce harmful auditory or annoying subjective effects of sound.

HEARING THRESHOLD LEVEL (HTL). Amount (in decibels) by which an individual's threshold of audibility differs from a standard audiometric threshold.

Helmholtz resonator. Hollow, rigid-walled, cavity used as a resonator. The cavity may be partially or completely filled with a porous material.

hemi-anechoic room. Test room with a hard, reflecting floor whose other surfaces absorb essentially all the incident sound energy over the frequency range of interest, thereby affording nominally free-field conditions above a reflecting plane.

HEARING IMPAIRMENT: A degree of hearing loss, temporary or permanent due to many causes. Hearing loss can be caused by illness, disease, or by exposure to excessively high noise levels. Affects 25-50 million people in USA of all ages. Hearing impairment as generally used means a hearing loss of a mild, moderate, or severe degree as apposed to "Deafness" which is generally described as little or no residual hearing with or without the aid of an assistive listening device. Hearing Impaired persons are particularly victimized by long reverberation times.

HEARING RANGE: 16-20000 Hz (Speech Intelligibility) 600-4800 Hz (Speech Privacy) 250-2500 Hz (Typical small table radio)

HERTZ (Hz): Frequency of sound expressed by cycles per second. (See CYCLE).

HERTZ (Hz). Unit of measurement of frequency, numerically equal to cycles per second

I

IEC 60804:1984 The International Standard for Integrating & Integrating-Averaging Sound Level Meters

IEC 61672:1999 The International standard for Sound Level Meter and Integrating Averaging Sound Level Meters that will replace both IEC 60651 and IEC 60804

IEC 60651:1979 The International Standard for Sound Level Meters

IEC 61260:1995 The International Standard for 1:1 Octave & 1:3 Octave Band Filters

Impulse Time Weighting A standard time weighting applied by the Sound Level Meter

Integrating Averaging Sound Level Meter A Sound Level Meter which accumulates the total sound energy over a measurement period and calculates an average

IMPACT SOUND: The sound produced by the collision of two solid objects. Typical sources are footsteps, dropped objects, etc.., on an interior surface (wall, floor, or ceiling) of a building.

INTENSITY: (See LOUDNESS).

INVERSE SQUARE LAW: Sound levels fall off with distance traveled. Sound level drops off 6 dB from source point for every doubling of distance.

IMPACT INSULATION CLASS (IC). A single-figure rating that compares the impact sound insulating capabilities of floor-ceiling assemblies to a reference contour.

IMPACT SOUND. The sound produced by the collision of two solid objects. Typical sources are footsteps, dropped objects, etc., on an interior surface (wall, floor, or ceiling) of a building. when we talk about impact sound the lower the Lnw figure acheived the better the sound insulation

IMPULSIVE NOISE, a) Either a single sound pressure peak (with either a rise time less than 200 milliseconds or total duration less than 200 milliseconds) or multiple sound pressure peaks (with either rise time less than 200 milliseconds or total duration less than 200 milliseconds) spaced at least by 200 millisecond pauses, b) A sharp sound pressure peak occurring in a short interval of time. impulsive noise [5]. Noise consisting of a series of bursts of sound energy, each burst having a duration less than approximately 1 s.

INFRASONIC. Sounds of a frequency lower than 20 hertz.

infrasonic frequency. Frequency lower than the nominal frequency range. Unit, hertz (Hz).

instantaneous sound pressure. At some specified time, the total instantaneous pressure at a point in a medium minus the static pressure at that point. Unit, pascal (Pa); symbol, p.

integrating-averaging sound level meter. Device for measuring the level of time-mean-square frequency-weighted sound pressure during a stated time interval.

INTENSITY. The sound energy flow through a unit area in a unit time.

intermittent noise [5]. Noise whose level abruptly drops to the level of the background noise several times during the period of observation, the time during which the level remains at a constant value different from that of the ambient being of the order of 1 s or more.

INVERSE SQUARE LAW. A description of the acoustic wave behavior in which the mean-square pressure varies inversely with the square of the distance from the source. This behavior occurs in free field situations, where the sound pressure level decreases 6 dB with each doubling of distance from the source.

ISO. The International Organization for Standardization.

isolated burst of sound energy [5]. Single burst of sound energy or a series of bursts with intervals longer than 0,2 s between the individual bursts.

L

Integrating Averaging Sound Level Meter A Sound Level Meter which accumulates the total sound energy over a measurement period and calculates an average

L_A10 The noise level exceeded for 10% of the measurement period with 'A' frequency weighting calculated by statistical analysis LA10: The LA10 noise levels are those noise levels that are exceeded for 10% of each sample period.

L_A90 The noise level exceeded for 90% of the measurement period with 'A' frequency weighting calculated by statistical analysis LA90: The LA90 noise levels are those noise levels that are exceeded for 90% of each sample period.

L_AE Sound Exposure Level (SEL) with 'A' frequency weighting

LIVE END/DEAD END: An acoustical treatment plan for rooms in which one end is highly absorbent and the other end is reflective and diffusive.

LOUDNESS: The average deviation above and below the static value due to sound wave is called sound pressure. The energy expended during the sound wave vibration is called intensity and is measured in intensity units. Loudness is the physical resonance to sound pressure and intensity.

L_Aeq,t Equivalent continuous sound pressure level. A measure of the average sound pressure level during a period of time, t, in dB with 'A' weighting.

L_AF Sound level with 'A' Frequency weighting and Fast Time weighting

L_AFmax The maximum Sound level with 'A' Frequency weighting and Fast Time weighting

L_AFTeq Takt maximal sound level as defined by DIN 45641

L_AI Sound level with 'A' Frequency weighting and Impulse Time weighting

L_AImax The maximum Sound level with 'A' Frequency weighting and Impulse Time weighting

L_AS Sound level with 'A' Frequency weighting and Slow Time weighting

L_ASmax The maximum Sound level with 'A' Frequency weighting and Slow Time weighting

L_CE Sound Exposure Level (SEL) with 'C' frequency weighting

L_ceq,t Equivalent continuous sound pressure level. A measure of the average sound pressure level during a period of time, t, in dB with 'C' weighting.

L_CF Sound level with 'C' Frequency weighting and Fast Time weighting

L_CFmax The maximum Sound level with 'C' Frequency weighting and Fast Time weighting

L_CI Sound level with 'C' Frequency weighting and Impulse Time weighting

L_CImax The maximum Sound level with 'C' Frequency weighting and Impulse Time weighting

L_Cpeak Peak Sound pressure level with 'C' frequency weighting

L_CS Sound level with 'C' Frequency weighting and Slow Time weighting

L_CSmax The maximum Sound level with 'C' Frequency weighting and Slow Time weighting

L_EP,d Daily personal noise exposure

L_eq Equivalent continuous sound pressure level. A measure of the average sound pressure level during a period of time, t, in dB

L_IeqT Impulse weighted L_eq,t as defined by DIN 45641

L_n Statistical analysis of noise levels. The n denotes the percentage exceedence.

L_ZE Sound Exposure Level (SEL) with 'Z' frequency weighting

L_Zeq,t Equivalent continuous sound pressure level. A measure of the average sound pressure level during a period of time, t, in dB with 'Z' weighting.

L_ZF Sound level with 'Z' Frequency weighting and Fast Time weighting

L_ZFmax The maximum Sound level with 'Z' Frequency weighting and Fast Time weighting L_ZI Sound level with 'Z' Frequency weighting and Impulse Time weighting L_ZImax The maximum Sound level with 'Z' Frequency weighting and Impulse Time weighting L_ZS Sound level with 'Z' Frequency weighting and Slow Time weighting L_ZSmax The maximum Sound level with 'Z' Frequency weighting and Slow Time weighting

LEVEL. The logarithm of the ratio of a quantity to a reference quantity of the same kind. The base of the logarithm, the reference quantity, and the kind of level must be specified. level. In acoustics, logarithm of the ratio of a quantity to a reference quantity of the same kind. The base of the logarithm (always ten, unless otherwise specified), the reference quantity, and the kind of level shall be specified. Examples of kinds of levels are sound power level and sound intensity level. For common logarithms on the base ten, the symbol for logarithm is "lg."

line spectrum. Spectrum whose components occur at a number of discrete frequencies.

live room. Room characterized by a relatively small amount of sound absorption.

LOGARITHM. The exponent that indicates the power to which a number must be raised to produce a given number. For example, for the base 10 logarithm, used in acoustics, 2 is the logarithm of 100.

longitudinal wave. Wave in which the direction of displacement at each point of the medium is normal to the wavefront.

LOUDNESS. The subjective judgment of intensity of a sound by humans. Loudness depends upon the sound pressure and frequency of the stimulus. Over much of the frequency range it takes about a threefold increase in sound pressure (a tenfold increase in acoustical energy, or, 10 dB) to produce a doubling of loudness. Loudness: The subjective judgement of the intensity of a sound.

LOUDNESS LEVEL. Measured in phons it is numerically equal to the median sound pressure level (dB) of a free progressive 1000 Hz wave presented to listeners facing the source, which in a number of trials is judged by the listeners to be equally loud.

M

MASKING. 1. The process by which the threshold of audibility for a sound is raised by the presence of another (masking) sound. 2. The amount by which the threshold of audibility of a sound is raised by the presence of another (masking) sound.

MASKING NOISE. A noise that is intense enough to render inaudible or unintelligible another sound that is also present.

MEDIUM. A substance carrying a sound wave.

MASKING: The process by which the threshold of hearing of one sound is raised due to the presence of another.

MASS: The fundamental property of a material relevant to sound transmission loss through that material. Generally, the more massive the material, the greater the sound transmission loss.

MOUNTING: Standards established by ASTM to represent typical installation for purpose of testing materials. i.e.: a mounting test specimen mounted directly to test room surface. D mounting furred out to produce air space behind.

N

narrow-band noise [5]. Noise in which the acoustic energy is concentrated in a relatively narrow range of frequencies. The spectrum will generally show a localized "hump" or peak in amplitude. Narrow-band sound may be superimposed on broad-band sound. If the narrow-band sound does not contain any significant discrete tones, the sound will generally lack a subjective quality of pitch or tonality.

NEAR FIELD. The sound field very near to a source, where the sound pressure does not obey the inverse-square law and the particle velocity is not in phase with the sound pressure.

NIOSH. The National Institute for occupational Safety and Health.

NOISE, 1. Unwanted sound. 2. Any sound not occurring in the natural environment, such as sounds emanating from aircraft, highways, industrial, commercial and residential sources. 3. An erratic, intermittent, or statistically random oscillation.

noise emission [5]. Airborne sound radiated by a well- defined noise source (e.g. a machine under test).

noise immission [5]. Airborne sound received at the ear of an observer being a composite of all sounds in the vicinity of the observer.

noise induced temporary threshold shift. Temporary hearing loss resulting from exposure to noise. Abbreviation, NITTS.

noise induced permanent threshold shift. Permanent hearing loss resulting from exposure to noise. Abbreviation, NIPTS.

NOISE: Unwanted sound that is annoying or interferes with listening. Not all noise needs to be excessively loud to represent an annoyance or interference.

NOISE CRITERIA (NC): Noise criteria curves used to evaluate existing listening conditions at ear level by measuring sound levels at loudest locations in a room. NC criteria can be referred to equivalent dBA levels. NC curves are critical to persons with hearing loss.

NOISE ISOLATION CLASS (NIC): A Single number rating of the degree of speech privacy achieved through the use of an Acoustical Ceiling and sound absorbing screens in an open office. NIC has been replaced by the Articulation Class (AC) rating method.

NOISE REDUCTION (NR): The amount of noise that is reduced through the introduction of sound absorbing materials. The level (in decibels) of sound reduced on a logarithmic basis. (See TABLES submenu under Acoustics for Sound Pressure Level Changes).

NOISE REDUCTION COEFFICIENT (NRC): The NRC of an acoustical material is the arithmetic average to the nearest multiple of 0.05 of its absorption coefficients at 4 one third octave bands with center frequencies of 250, 500, 1000, 2000 Hertz.

NOISE ISOLATION CLASS. (NIC). A single number rating derived in a prescribed manner from the measured values of noise reduction between two areas or rooms. It provides an evaluation of the sound isolation between two enclosed spaces that are acoustically connected by one or more paths.

NOISE LEVEL. For airborne sound , unless specified to the contrary, it is the A-weighted sound level.

noise power emission level4. A-weighted sound power level. Unit, bel (B).

NOISE REDUCTION (NR). The numerical difference, in decibels, of the average sound pressure levels in two areas or rooms. A measurement of "noise reduction" combines the effect of the sound transmission loss performance of structures separating the two areas or rooms, plus the effect of acoustic absorption present in the receiving room. noise reduction. Between two rooms in a specified frequency band, difference between the space-time average sound pressure levels in the two enclosed spaces when one or more sound sources operates in one of the rooms. Unit, decibel (dB).

NOISE REDUCTION COEFFICIENT (NRC). A measure of the acoustical absorption performance of a material, calculated by averaging its sound absorption coefficients at 250, 500, 1000 and 2000 Hz, expressed to the nearest multiple of 0.05. noise reduction coefficient. Arithmetic mean of sound absorption coefficients at 250, 500, 1000, and 2000 Hz, rounded to the nearest 0.05 metric sabin per square meter.

Noise Rating Curves: A family of octave band spectra giving limiting values of sound pressure level for speech interference and acceptability requirements.

NON-IMPULSIVE NOISE. all noise not included in the definition of impulsive noise.

non-steady noise [5]. Noise whose level varies significantly during the period of observation.

O

OCTAVE. The interval between two sounds having a frequency ratio of two.- There are 8 octaves on the keyboard of a standard piano. octave [2]. Two frequencies are an octave apart if the ratio of the higher frequency to the lower frequency is two.

OCTAVE BAND. A segment of the frequency spectrum separated by an octave.

OCTAVE BAND LEVEL. The integrated sound pressure level of only those sine-wave components in a specified octave band.

OSCILLATION. The variation with time, alternately increasing and decreasing, of (a) some feature of an audible sound, such as the sound pressure; or (b) some feature of a vibrating solid object, such as the displacement of its surface. Variation, usually with time, of the magnitude of a quantity with respect to a specified reference when the magnitude is alternately greater and smaller than the reference.

OSHA The Occupational Safety and Health Administration.

Overload The input to the Sound Level Meter is too high for the current measurement range. Change the range.

OCTAVE BANDS: Sounds that contain energy over a wide range of frequencies are divided into sections called bands. A common standard division is in 10 octave bands identified by their center frequencies 31.5, 63, 125, 250, 500, 1000, 2000, 4000 Hz.

OTO: Pertaining to the ear.

OTOLOGIST: A doctor specializing in the structor, disorders and treratment of the ear.

OTOLARYNGOLIST: A doctor specializing in disorders and treatment of the ear nose and throat disorders.

P

particle velocity. In a sound field, the velocity caused by a sound wave of a given infinitesimal part of the medium, with reference to the medium as a whole. Unit, meter per second (m/s); symbol, u. The terms "instantaneous particle velocity," "effective particle velocity," and "peak particle velocity" have meanings that correspond with those of the related terms used for sound pressure.

Peak The maximum value reached by the sound pressure at any instant during a measurement period (in dB usually with C frequency weighting)

PEAK SOUND PRESSURE. The maximum absolute value of the instantaneous sound pressure in a specific time interval. Note: in the case of a periodic wave, if the time interval considered is a complete period, the peak sound pressure becomes identical with the maximum sound pressure. peak sound pressure. Greatest value of the absolute instantaneous sound pressure within a specified time interval. Unit, pascal (Pa).

peak-to-peak value. Algebraic difference between extremes of an oscillating quantity.

PERIOD. The duration of time it takes for a periodic wave form (like a sine wave) to repeat itself. period. Smallest increment of an independent variable for which a function repeats itself.

periodic quantity. Oscillating quantity whose values recur for certain increments of the independent variable. If a periodic quantity v is a function of time t, then v =f(t) =f(t+T), where T, a constant, is a period of v.

PERMANENT THRESHOLD SHIFT (PTS). A permanent decrease of the acuity of the ear at a specified frequency as compared to a previously established reference level. The amount of permanent threshold shift is customarily expressed in decibels.

PHON. The unit of measurement for loudnes level.

PINK NOISE. Noise with constant energy per octave band width. pink noise. Noise for which the spectrum density varies as the inverse of frequency.

PITCH. The attribute of auditory sensation that orders sounds on a scale extending from low to high. Pitch depends primarily upon the frequency of the sound stimulus, but it also depends upon the sound pressure and wave form of the stimulus.

PLANE WAVE. A wave whose wave fronts are parallel and perpendicular to the direction in which the wave is traveling. plane wave. Wave in which the wavefronts are everywhere parallel planes normal to the direction of propagation.

power spectrum density. Limit, as the bandwidth approaches zero, of sound power divided by bandwidth. Unit, watt per hertz (W/Hz).

point source. Source that radiates sound as if from a single point.

porous sound absorber. Material with interconnected voids that presents resistance to airflow through the material.

PHON: Loudness contours. A subjective impression of equal loudness by listeners as a function of frequency and sound level (dB). An increase in low frequency sound will be perceived as being much louder than an equivalent high frequency increase.

PITCH: The perceived auditory sensation of sounds expressed in terms of high or low frequency stimulus of the sound.

PRESBYCUSIS: The loss of hearing due primarily to the aging process High frequency loss is frequently a result of early hearing loss.

PRESBYCUSIS. The decline in hearing acuity that is attributed to the aging process.

PURE TONE. A sound for which the sound pressure is a simple sinusoidal function of the time, and characterized by its singleness of pitch. pure tone. (a) Line spectrum consisting of a signal at a single frequency. (b) Sound wave, the instantaneous sound pressure of which is a simple sinusoidal function of time. Also referred to as a discrete tone, see 8.09.

Q

quasi-impulsive noise [5]. Series of noise bursts of comparable amplitude with intervals shorter than 0,2 s between the individual bursts.

R

RANDOM NOISE. An oscillation whose instantaneous magnitude is not specified for any given instant of time. It can be described statistically by probability distribution functions giving the traction of the total time that the magnitude of the noise lies within a specified range.

random incidence. Incidence of sound waves successively from all directions with equal probability. If an object is in a diffuse sound field, the sound is said to strike the object at random incidence.

REFLECTION. The return of a sound wave from a surface. The phenomenon occurring when waves meet but do not cross a surface of discontinuity between two media in which waves have different velocities. This leads to a change in direction of propagation without change in wavelength.

REFRACTION. The bending of a sound wave from its original path, either because it is passing from one medium to another or by changes in the physical properties of the medium, e.g., a temperature or wind gradient in the air. refraction. Process by which the direction of sound propagation is changed as a result of a spatial variation in the speed of sound in the medium. The phenomenon occurring when waves cross a boundary between media in which the waves have different phase velocities. This leads to a change in wavelength.

RESONANCE. The relatively large amplitude of vibration produced when the frequency of some source of sound or vibration "matches" the natural frequency of vibration of some object, component, or system.

REFLECTION: The amount of sound wave energy (sound) that is reflected off a surface. Hard non porous surfaces reflect more sound than soft porous surfaces. Some sound reflection can enhance quality of signal of speech and music. (See Echo).

RESONANCE: The emphasis of sound at a particular frequency.

RESONANT FREQUENCY: A frequency at which resonance exists.

REVERBERATION: The time taken for sound to decay 60 dB to 1/1,000,000 of its original sound level after the sound source has stopped. Sound after it has ended will continue to reflect off surfaces until the wave loses enough energy by absorption to eventually die out. Reverberation time is the basic acoustical property of a room which depends only on its dimensions and the absorptive properties of its surfaces and contents. Reverberation has an important impact on speech intelligibility.

REVERBERATION TIME: Sound after it is ended at the source will continue to reflect off surfaces until the sound wave loses energy by absorption to eventually die out.

RESONATOR. A device that resounds or vibrates in sympathy with a source of sound or vibration.

REVERBERANT FIELD. The region in a room where the reflected sound dominates, as opposed to the region close to the noise source where the direct sound dominates.

REVERBERATION. The persistence of sound in an enclosed space, as a result of multiple reflections, after the sound source has stopped. reverberation. Sound that persists in an enclosed space, as a result of repeated reflection or scattering, after the sound source has stopped.

REVERBERATION ROOM. A room having a long reverberation time, especially designed to make the sound field inside it as diffuse (homogeneous) as possible.

REVERBERATION TIME (RT). The reverberation time of a room is the time taken for the sound pressure level to decrease 60 dB from its steady-state value when the source of sound energy is suddenly interrupted. It is a measure of the persistence of an impulsive sound in a room as well as of the amount of acoustical absorption present inside the room. Rooms with long reverberation times are called live rooms. reverberation time. Of an enclosure, for a stated frequency or frequency band, time that would be required for the level of the time-mean-square sound pressure in the enclosure to decrease by 60 dB, after the source has been stopped. Unit, second (s).

reverberation room. Room having a long reverberation time, specially designed to make the sound field therein as diffuse as possible.

RMS SOUND PRESSURE. The square root of the time averaged square of the sound pressure.

room absorption. Sum of Sabine absorptions due to objects and surfaces in a room, and due to dissipation of energy in the medium within the room. Unit, metric sabin. With A{sub i} as the Sabine absorption of the ith surface or object or medium in a room, total room absorption is A = {sigma}A{sub i}.

ROOT-MEAN-SQUARE (RMS). 1. The root-mean-square value of a time-varying quantity is obtained by squaring the function at each instant, obtaining the average of the squared values over the interval of interest, and then taking the square root of this average. For a sine wave, if you multiply the RMS value by the square root of 2, or about l.41, you get the peak value of the wave. The RMS value, also called the effective value of the sound pressure, is the best measure of ordinary continuous sound, but the peak value is necessary for assessment of impulsive noises. 2. A term' describing the mathematical process of determining an 'average' value of a complex signal.

S

SABIN. A measure of the sound absorption of a surface; it is the equivalent of one square foot of a perfectly absorptive surface.

Sabine absorption. Sound absorption defined by the Sabine reverberation-time equation. Unit, metric sabin. In a reverberant room of volume V, speed of sound c, and decay rate d, Sabine absorption is A = 0.921 Vd / c.

SEL Sound Exposure Level, displayed as LAE, LCE or LZE

simple harmonic quantity. Periodic quantity that is a sinusoidal function of the independent variable. Thus y = A sin({omega}t + {phi}), where y is the simple harmonic quantity, A is the amplitude, {omega} is the angular frequency, and {phi} is the phase of the oscillation. The maximum value of a simple harmonic quantity is amplitude A.

simple harmonic motion. Motion such that the displacement is a sinusoidal function of time.

signal. (a) Disturbance used to convey information. (b) Information to be conveyed over a communication system.

Simple Sound Source: A source that radiates sound in an isotropic medium uniformly in all directions under freefield conditions.

Slow Time Weighting A standard time weighting applied by the Sound Level Meter

sound field. Region containing sound waves.

Sound Level Sound Pressure Level with a Frequency weighting, such as dB(A)

Sound Level Meter An instrument for measuring various noise parameters

SPL Sound Pressure Level, the basic measure of noise loudness, expressed in decibels

sound power level. Logarithm of the ratio of a given sound power in a stated frequency band or with a stated frequency weighting, to the reference power of one picowatt (1 pW). Unit, bel (B); symbol, LW. sound pressure level. Ten times the logarithm of the ratio of the time-mean-square pressure of a sound, in a stated frequency band or with a stated frequency weighting, to the square of the reference sound pressure of 20 micropascal. Unit, decibel (dB); symbol, L{sub p}.

SABIN: A unit of sound absorption based of one square foot of material. Baffles are frequently described as providing X number of sabins of absorption based on the size of the panel tested, through the standard range of frequencies 125 - 4000 Hz. The number of sabins developed by other acoustical materials are determined by the amount of material used and its absorption coefficients.

SABINE FORMULA: A formula developed by Wallace Clement Sabine that allows designers to plan reverberation time in a room in advance of construction and occupancy. Defined and improved empirically the Sabine Formula is T=0.049(V/A) where T = reverberation time or time required (for sound to decay 60 dB after source has stopped) in seconds. V = Volume of room in cubic feet. A = Total square footage of absorption in sabins.

SEPTUM: A thin layer of material between 2 layers of absorptive material. i.e.: foil, lead, steel, etc. that prevents sound wave from piercing through absorptive material.

SIGNAL TO NOISE RATIO: Is the sound level at the listeners ear of a speaker above the background noise level. The inverse square law impacts on the S/N ratio. Signal to Noise Ratios are important in classrooms and should be in range of 15 to 20 dB.

SMOKE DEVELOPED INDEX: Classification that relates to a comparison of smoke development of a particular material compared to concrete panels and red oak. Results are obtained through an ASTM E84 or UL723 test.

SOUND: Sound is an oscillation in pressure, stress particle displacement, particle velocity in a medium - (in room temperature. In air speed of sound is 1125'/second or one mile in 5 seconds.) Sound produces an auditory sensation caused by the oscillation.

SOUND ABSORPTION: is the property possessed by materials, objects and air to convert sound energy into heat. Sound waves reflected by a surface causes a loss of energy. That energy not reflected is called its absorption coefficient.

SOUND ABSORPTION COEFFICIENT: The fraction of energy striking a material or object that is not reflected. For instance if a material reflects 70% of the sound energy incident upon its surface, then its Sound Absorption Coefficient would be 0.30.

SOUND BARRIER: A material that when placed around a source of noise inhibits the transmission of that noise beyond the barrier. Also, anything physical or an environment that interferes with communication or listening. For example, a poor acoustical environment can be a barrier to good listening and especially so for persons with a hearing impairment.

SOUND LEVEL: A subjective measure of sound expressed in decibels as a comparison corresponding to familiar sounds experienced in a variety of situations. (See TABLES submenu under Acoustics for Sound Source of Environment table.)

SOUND PRESSURE: The total instantaneous pressure at a point in space, in the presence of a sound wave, minus the static pressure at that point.

SOUND PRESSURE LEVEL: The sound pressure level, in decibels, of a sound is 20 times the logarithm to the base 10 of the ratio of the sound pressure to the reference pressure. The reference pressure shall be explicitly stated and is defined by standards.

SOUND PROOFING: Building materials that makes structures impervious to sound or insulates against sound.

SOUND LEVEL METER: A device that converts sound pressure variations in air into corresponding electronic signals. The signals are filtered to exclude signals outside frequencies desired.

SPEECH: The act of speaking. Communication of thoughts and feelings by spoken words.

SPEECH PRIVACY: The degree to which speech is unintelligible between offices. Three ratings are used, Confidential, Normal (Non obtrusive), Minimal.

SOUND TRANSMISSION CLASS (STC): This is a rating for doors, windows, enclosures, noise barriers, partitions and other acoustical products. The rating is in terms of their relative ability to provide privacy against intrusion of speech sounds. This is a one number rating system, heavily weighted in the 500Hz to 2000Hz frequency range where speech intelligitibility largely occurs.

SPECTRUM: The description of a sound wave´s components of frequency and amplitude.

Statistical Analysis A calculation performed by a Sound Level Meter on the noise levels measured during the measurement period to describe the statistical spread of the noise.

SHIELDING. The attenuation of a sound, achieved by placing barriers between a sound source and the receiver

silencer; muffler. Duct designed to reduce the level of sound. The sound reducing mechanisms may be either absorptive or reactive, or a combination.

SONE. The unit of measurement for loudness. One sone is the loudness of a sound whose loudness level is 40 phons. Loudness is proportional to the sound's loudness rating, e.g., two sones are twice as loud as one sone.

SOCIOCUSIS. Loss of hearing caused by noise exposures that are part of the social environment, exclusive of occupational-noise exposure, physiological changes with age, and disease.

SOUND. 1. An oscillation in pressure, stress, particle displacement, particle velocity, etc., in an elastic or partially elastic medium, or the superposition of such propagated alterations. 2. An auditory sensation evoked by the oscillation described above. Not all sound waves can evoke an auditory sensation: e.g. ultrasound. (a) Oscillation in pressure, stress, particle displacement, particle velocity, etc., in a medium with internal forces (e.g., elastic or viscous), or the superposition of such propagated oscillations. (b) Auditory sensation evoked by the oscillation described above.

sound absorption. At a specified frequency or in a specified frequency band, property of a material or an object whereby sound energy is converted into heat by propagation in a medium or when sound strikes the boundary between two media.

sound absorption coefficient. Ratio of Sabine absorption of a surface to the area of the surface. Unit, metric sabin per square meter, often omitted. With a{sub i} as the Sabine absorption coefficient of the ith surface whose area is S{sub i}, the Sabine absorption attributed to the surface is A{sub i} = S{sub i}a{sub i}.

sound energy. Total energy in a given part of a medium minus the energy that would exist at that same part of the medium with no sound waves present. Unit, joule (J).

sound-energy flux. Time rate of flow of sound energy for one period through a specified area. Unit, watt (W); symbol, J.

sound exposure. Time integral of squared, instantaneous frequency-weighted sound pressure over a stated time interval or event. Unit, pascal-squared second; symbol, E. If frequency weighting is not specified, A-frequency weighting is understood.

sound exposure level. Ten times the logarithm of the ratio of a given time integral of squared instantaneous A-weighted sound pressure, over a stated time interval or event, to the product of the squared reference sound pressure of 20 micropascals and reference duration of one second. The frequency weighting and reference sound exposure may be otherwise if stated explicitly. Unit, (dB); symbol, L_AE.

sound intensity. Average rate of sound energy transmitted in a specified direction at a point through a unit area normal to this direction at the point considered. Unit, watt per square meter (W/m²); symbol, I. The sound intensity in a specified direction is the amount of sound energy flowing through a unit area normal to that direction. The sound intensity is normally measured in watt per square metre (W/m²).

sound intensity level. Ten times the logarithm of the ratio of a given sound in a stated direction to the reference sound intensity of 1 picowatt per square meter (1 pW/m{sup 2}). Unit, decibel (dB); symbol, L_I.

SOUND LEVEL. The weighted sound pressure level obtained by the use of a sound level meter and frequency weighting network, such as A, B, or C as specified in ANSI specifications for sound level meters (ANSI Sl.4-1971, or the latest approved revision). If the frequency weighting employed is not indicated, the A-weighting is implied.

SOUND LEVEL METER. An instrument comprised of a microphone, amplifier, output meter, and frequency-weighting networks which is used for the measurement of noise and sound levels.

sound level meter. Device used to measure sound pressure level with a standardized frequency weighting and indicated exponential time weighting for measurements of sound pressure level, or without time weighting for measurement of time- average sound pressure level or sound exposure level.

SOUND POWER. The total sound energy radiated by a source per unit time. The unit of measurement is the watt. sound power. Sound energy radiated by a source per unit of time. Unit, watt (W); symbol, W. The sound power level of a source is expressed in decibels (dB) and is equal to 10 times the logarithm to the base 10 of the ratio of the sound power of the source to a reference sound power. The reference sound power in air is normally taken to be 10-12 watt.

SOUND PRESSURE. The instantaneous difference between the actual pressure produced by a sound wave and the average or barometric pressure at a given point in space.

sound pressure amplitude [2]. Absolute value of the instantaneous pressure. Unit, pascal (Pa).

SOUND PRESSURE LEVEL (SPL). 20 times the logarithm, to the base 10, of the ratio of the pressure of the sound measured to the reference pressure, which is 20 micronewtons per square meter. In equation form, sound pressure level in units of decibels is expressed as SPL (dB) = 20 log p/pr.

SOUND TRANSMISSION CLASS (STC). The preferred single figure rating system designed to give an estimate of the sound insulation properties of a structure or a rank ordering of a series of structures. Is a single number rating system which represents the sound transmission loss performance of a wall.

SOUND TRANSMISSION LOSS (STL). A measure of sound insulation provided by a structural configuration. Expressed in decibels, it is 10 times the logarithm to the base 10 of the reciprocal of the sound transmission coefficient of the configuration.

SPECTRUM. The description of a sound wave's resolution into its components of frequency and amplitude.

Sound Reduction Index ( SRI )In the soundproofing world a new term SRI is used to describe the quality of sound proofing materials. The greater the SRI, the greater the acoustic privacy that is achieved. spectrum. (a) Description, for a function of time, of the resolution of a signal into components, each of different frequency and (usually) different amplitude and phase. (b) "Spectrum" is also used to signify a continuous range of components, usually wide in extent, within which waves have some specified common characteristic; e.g., "audio frequency spectrum."

spectrum density. Limit, as the bandwidth approaches zero, of the mean-square amplitude divided by bandwidth.

spectrum analyzer. Device used to determine the frequency spectrum of a sound.

specular reflection. Phenomenon by which a sound wave is returned by a surface separating two media at an angle from the normal equal to the angle of incidence.

spherical wave. Wave in which the wavefronts are concentric spheres.

Sound Frequency. Sound is made up of a whole range of frequencies. Different frequencies travel through different transmission barriers with different degrees of ease. So any SRI figure given is known as the weighted or average figure (also known as Rw).

Site Conditions. The Rw quoted in most literature is obtained in sound testing laboratories. In practice different buildings have different sound insulation properties. This is due to the different materials used in construction and the different styles of construction. So when adding sound insulation the exact results will vary. This variance is mainly due to flanking transmission

SPEECH-INTERFERENCE LEVEL (SIL). A calculated quantity providing a guide to the interference of a noise with the reception of speech. The speech-interference level is the arithmetic average of the octave band levels of the interfering noise in the most important part of the speech frequency range. The levels in octave bands centered at 500, 1000, and 2000 Hz are commonly averaged to determine the speech-interference level.

SPEED (VELOCITY) OF SOUND IN AIR. 344 m/sec (l128 ft/sec) at 70 degrees F in air at sea level. speed of sound. At a temperature of 15 degrees Celsius, the speed of sound in air at sea level is approximately 341 m/s, and is proportional to the square root of absolute temperature; symbol, c.

SPHERICAL DIVERGENCE. The condition of propagation of spherical waves that relates to the regular decrease in intensity of a spherical sound wave at progressively greater distances from the source. Under this condition the sound pressure level decreases 6 decibels with each doubling of distance from the source.

SPHERICAL WAVE. A sound wave in which the surfaces of constant phase are concentric spheres. A small (point) source radiating into an open space produces a free sound field of spherical waves. .

STEADY-STATE SOUNDS. Sounds whose average characteristics remain relatively constant in time. A practical example of a steady-state sound source is an air conditioning unit.

standing wave. Periodic wave having a fixed distribution in space which is the result of interference of progressive waves of the same frequency and kind. Such waves are characterized by the existence of nodes or partial nodes and antinodes that are fixed in space.

static pressure. Pressure that would exist at a point in the absence of a sound wave. Unit, pascal (Pa); symbol, P_s. One pascal is equal to one newton per square meter.

steady noise [5]. Noise with neglibly small fluctuations of level within the period of observation.

structure-borne sound. Sound for which a significant portion of the transmission path from source to receiver takes place in a solid structure rather than through a liquid or gas.

subharmonic. Sinusoidal quantity having a frequency that is an integral submultiple of the fundamental.

T

TEMPORARY THRESHOLD SHIFT (TTS). A temporary impairment of hearing acuity as indicated by a change in the threshold of audibility.

THIRD-OCTAVE BAND. A frequency band whose cutoff frequencies have a ratio of 2 to the one-third power, which is approximately 1.26. The cutoff frequencies of 891 Hz and 1112 Hz define the 1000 Hz third-octave band in common use.

THRESHOLD OF AUDIBILITY (THRESHOLD OF DETECTABILITY). The minimum sound pressure level at which a person can hear a specified frequency of sound over a specified number of trials.

TIME WEIGHTED AVERAGE (TWA): The yardstick used by the Occupational Safety and Health Administration (OSHA) to measure noise levels in the workplace. It is equal to a constant sound level lasting eight hours that would cause the same hearing damage as the variable noises that a worker is actually exposed to. (This hearing loss, of course, occurs over long-term exposures.) Same as LOSHA.

Threshold of Hearing: The minimum sound pressure level at which a person can hear a sound at a given frequency.

THRESHOLD OF PAIN. The minimum sound pressure level of a sound outside the ear that will produce a transition from discomfort to definite pain.

THRESHOLD SHIFT. A change in the threshold of audibility at a specified frequency from a threshold previously established. The amount of threshold shift is customarily expressed in decibels.

TIMBRE. An attribute of auditory sensation allowing a subject to judge that two sounds similarly presented and having the same loudness and pitch are dissimilar, e.g., trumpet vs. violin.

TINNITUS. Ringing in the ear or noise sensed in the head. Onset may be due to an acoustic trauma and persist in the absence of acoustical stimulation (in which case it may indicate a lesion of the auditory system).

TONE. A sound of definite pitch. A pure tone has a sinusoidal wave form.

TRANSDUCER. A device capable of being actuated by waves from one or more transmission systems or media and supplying related waves to one or more other transmission systems or media. Examples are microphones, accelerometers, and loudspeakers.

transmission loss. Of a partition, for a specified frequency or frequency band, difference in decibels between the average sound pressure levels in the reverberant source and receiving rooms, plus ten times the logarithm of the ratio of the area of the common partition to the total Sabine absorption in the receiving room. Unit, decibel (dB); abbreviation, TL. The reduction in magnitude of sound between two locations.

transverse wave. Wave in which the direction of displacement at each point of the medium is parallel to the wavefront.

Type 2 General Field Grade for Sound Level Meter

Type 1 Laboratory & Field Grade for Sound Level Meters

U-V

ULTRASONIC. Sounds or a frequency higher than 20,000 hertz.

ultrasonic frequency. Frequency higher than the nominal audio frequency range. Unit, hertz (Hz).

ULTRASOUNDS: Sounds of a frequency higher than 20,000 Hz. The frequency region containing these frequencies is called the ultrasonic region.

Under Range The input to the Sound Level Meter is too low for the current measurement range. Change the range

VIBRATION. An oscillatory motion of solid bodies described by displacement, velocity, or acceleration with respect to a given reference point. Oscillation of a parameter that defines the motion of a mechanical system.

VIBRATION ISOLATOR. A resilient support for vibrating equipment designed to reduce the amount of vibration transmitted to the other structures.

VIBRATION: A force which oscillates about some specified reference point. Vibration is commonly expressed in terms of frequency such as cycles per second (cps), Hertz (Hz), cycles per minute (cpm) or (rpm) and strokes per minute (spm). This is the number of oscillations which occurs in that time period. The amplitude is the magnitude or distance of travel of the force.

VIBRATION ISOLATOR: A resilient support that tends to isolate a mechanical system from steady state excitation.

VOLUME: The Cubic space of a room bounded by walls, floors, and ceilings determined by Volume = Length x Width x Height of space. Volume influences reverberation time. (See How to Compute Cubic Volume under ACOUSTICS in menu for formulas of more complex volumes.)

W

WAVE. A disturbance that travels through a medium by virtue of the elastic properties of that medium. Disturbance propagating in a given direction such that the quantity serving as a measure of the disturbance varies with position and time in a manner that at pairs of neighboring positions the disturbance is similar except for a time difference. The velocity of propagation of the disturbance is equal to the distance between neighboring positions divided by the time difference.

WAVELENGTH: Sound that passes through air it produces a wavelike motion of compression and Parefaction. Wavelength is the distance between two identical positions in the cycle or wave. Similar to ripples or waves produced by dropping two stones in water. Length of sound wave varies with frequency. Low frequency equals longer wavelengths.

wavefront. For a progressive wave in space, continuous surface that is a locus of points having the same phase at a given instant.

WAVELENGTH. For a periodic wave (such as sound in air), the distance between analogous points on any two successive waves. The wavelength of sound in air or in water is inversely proportional to the frequency of the sound. Thus, the lower the frequency, the longer the wavelength. wavelength. For a periodic wave in an isotropic medium, perpendicular distance between two wavefronts in which the displacements have a difference in phase of one complete period. Unit, meter (m).

WEIGHTING. Prescribed frequency filtering provided in a sound level meter.

WHITE NOISE. Noise whose energy is uniform over wide range of frequencies, being analogous in spectrum characteristics to white light. white noise. Noise for which the spectrum density is independent of frequency over a specified range.

WINDSCREEN. A porous device used to cover the microphone of a sound level measurement system which is designed to minimize the effects of winds and wind gusts on the sound levels being measured. Typically made of open cell polyurethane foam and spherically shaped.

Z

Z Weighting Z weighting is a flat frequency response between 10Hz and 20kHz ±1.5dB excluding microphone response.