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Terminologies in Acoustics. Building Utilities 3 M.S.Chua. Terminologies. Absorption The changing of sound energy to heat. Terminologies. Absorption coefficient - PowerPoint PPT Presentation
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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.
Image Source: http://www9.dw-world.de/rtc/infotheque/sound_processors/REVERB1.gif
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
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