Terminologies in Terminologies in AcousticsAcoustics

Building Utilities 3

M.S.Chua

Terminologies

Absorption The changing of sound energy to heat.

Terminologies

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.

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Terminologies

Acoustic barrier Solid walls or partitions, solid

fences, earth mounds, earth berms, buildings, etc used to reduce noise, without eliminating it.

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Terminologies

Air-borne noise This refers to noise which is fundamentally transmitted by way of the

air and can be attenuated by the use of barriers and walls placed physically between the noise and the receiver.

Terminologies

Ambient noise The composite of airborne sound from many sources near and far

associated with a given environment. No particular sound is singled out for interest.

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Terminologies

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

acoustical measurements.

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Terminologies

Attenuate To reduce the level of an electrical or acoustical signal.

Terminologies

Audible range The limits of frequency which are audible or heard as sound. The

normal ear in young adults detects sound having frequencies in the region 20Hz to 20kHz, although it is possible for some people to detect frequencies outside these limits.

Terminologies

Background noise Background noise is the term used to describe the noise measured in

the absence of the noise under investigation. It is described as the average of the minimum noise levels measured on a sound level meter and is measured statistically as the A-weighted noise level exceeded for ninety percent of a sample period. This is represented as the L90 noise level

Noise from all sources unrelated to a particular sound that is the object of interest. Background noise may include airborne, structureborne, and instrument noise.

Terminologies

Baffle A movable barrier used to

achieve separation of signals from different sources. The surface or board upon which a loudspeaker is mounted.

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Terminologies

Damp To cause a loss or dissipation of the oscillatory or vibrational energy

of an electrical or mechanical system.

Terminologies

Decibel [dB] The term used to identify ten times the common logarithm of the

ratio of two like quantities proportional to power or energy. (See level, sound transmission loss.) Thus, one decibel corresponds to a power ratio of 100.1.

Terminologies

Decibel [dB] The range of pressure variations associated with everyday living may

span over a range of a million to one. On the top range, may be the sound of a jet engine and on the bottom of the range may be the sound of a pin dropping.

Instead of expressing pressure in units ranging from a million to one, it is found convenient to condense this range to a scale 0 to 20 and give it the units of decibels. The following are examples of the decibel readings of every day sounds;

Terminologies

Decibel [dB] 0dB the faintest sound we can hear 30dB a quiet library or in a quiet location in the country 45dB typical office space. Ambience in the city at night 60dB Martin Place at lunch time 70dB the sound of a car passing on the street 80dB loud music played at home 90dB the sound of a truck passing on the street 100dB the sound of a rock band 115dB limit of sound permitted in industry 120dB deafening

Terminologies

Diffraction The distortion around solid obstacles of waves travelling past.

Terminologies

Far Field That part of the sound field in which sound pressure decreases

inversely with distance from the source. This corresponds to a reduction of approximately 6 dB in level for each doubling distance.

Terminologies

Fluctuating noise Noise that varies continuously and to an appreciable extent over the

period of observation. It can also include intermittent noise. As a guide, when the level varies noticeably by more than 5 dB over a period of less than one minute, the noise is considered to be fluctuating.

Terminologies

Free field An environment in which a sound wave may propagate in all

directions without obstructions or reflections. Anechoic rooms can produce such an environment under controlled conditions.

Terminologies

Frequency Frequency is synonymous to pitch. Sounds have a pitch which is

peculiar to the nature of the sound generator. For example, the sound of a tiny bell has a high pitch and the sound of a bass drum has a low pitch. Frequency or pitch can be measured on a scale in units of Hertz or Hz.

The measure of the rapidity of alterations of a periodic signal, expressed in cycles per second or Hz.

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Terminologies

Hertz the unit of frequency, abbreviated Hz. The same as cycles per

second. The name is in honor of Heinrich Hertz, an early German investigator of radio wave transmission.

Terminologies

Impulsive noise Having a high peak of short duration or a sequence of such peaks. A

sequence of impulses in rapid succession is termed repetitive impulsive noise.

Terminologies

Intermittent noise The level suddenly drops to that of the background noise several

times during the period of observation. The time during which the noise remains at levels different from that of the ambient is one second or more.

Terminologies

Loudness A rise of 0 dB in sound level corresponds approximately to a

doubling of subjective loudness. That is, a sound of 85 dB is twice as loud as a sound of 75 dB which is twice as loud as a sound of 65 dB and so on. That is, the sound of 85 dB is 400% times the loudness of a sound of 65 dB.

Terminologies

Low-frequency noise Containing major components within the low frequency range (20Hz

- 250Hz) of the frequency spectrum.

Terminologies

Near field Locations close to the sound source between the source and the far

field. The near field is typically characterized by large sound pressure level variations with small changes in measurement position from the source.

Terminologies

Noise Sound which a listener does not wish to hear.

Terminologies

Octave An octave is a doubling or halving of frequency. 20Hz-40Hz is often

considered the bottom octave. Each octave you add on the bottom requires that your speakers move four times as much air!

Terminologies

Periodic A signal that repeats the same pattern over time is called periodic,

and the period is defined as the length of time encompassed by one cycle, or repetition. The period of a periodic waveform is the inverse of its fundamental frequency.

Terminologies

Quality, acoustic An attribute, characteristic or property of the noise, its duration, its

time-varying characteristics or its frequency content. Examples are the "screech" of screaming, the "rumble" of an air conditioner, the "dripping" of a tap.

Terminologies

Reverberation The persistence of sound in an enclosed or partially enclosed space

after the source of sound has stopped; by extension, in some contexts, the sound that so persists.

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Terminologies

Reflection Sound wave changed in

direction of propagation due to a solid object obscuring its path.

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Terminologies

Sabin The unit of measure of sound absorption in the inch-pound system.

Terminologies

Sound A fluctuation of air pressure which is propagated as a wave through

air.

Terminologies

Sound absorption The ability of a material to absorb sound energy through its

conversion into thermal energy.

Terminologies

Sound level meter An instrument consisting of a microphone, amplifier and indicating

device, having a declared performance and designed to measure sound pressure levels.

Terminologies

Sound pressure level The level of noise, usually expressed in decibels, as measured by a

standard sound level meter with a microphone.

Terminologies

Sound power level Ten times the logarithm to the base 0 of the ratio of the sound power

of the source to the reference sound power.

Terminologies

Structure-borne noise This refers to noise which is generated by vibrations induced in the

ground and/or structure. These vibrations excite walls and slabs in buildings and cause them to radiate noise. This type of noise can not be attenuated by barriers or walls but requires the interposition of a resilient (neoprene, springs etc.) break between the source and the receiver.

Terminologies

Timbre The quality of a sound that distinguishes it from other sounds of the

same pitch and volume. The distinctive tone of an instrument or a singing voice.

Terminologies

Tonal noise Containing a prominent frequency and characterized by a definite

pitch.

Terminologies

Wavelength The distance the sound wave

travels to complete one cycle. The distance between one peak or crest of a sine wave and the next corresponding peak or crest. The wavelength of any frequency may be found by dividing the speed of sound by the frequency. (speed of sound at sea level is 331.4 meters/second or 1087.42 feet/second).

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References

http://www.renzotonin.com.au/wizardsPDF/acousticTerminology.pdf

http://www.csupomona.edu/~dmgrasmick/mu108/acousticterms.pdf