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Acceleration of gravity |
| (see g) |
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Addition |
| (see Decibel addition) |
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Articulation index |
| A measure of the intelligibility of speech. The AI is determined by understanding correctly spoken words; the scale ranges from 0.0 (completely unintelligible) to 1.0 (fully intelligible). The articulation index can be used to estimate sentence intelligibility. |
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Air-borne sound |
| Sound which reaches the receiver (listener) by traveling mainly through the air. |
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Ambient sound |
| The all-encompassing sound associated with a given environment. This is usually a composite of sounds from many sources, near and far. No particular sound is dominant. |
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Amplitude |
| the magnitude of the pressure of a sound wave or a vibrating surface. The amplitude is usually expressed in linear units. |
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American National Standards Institute |
| A standards setting body which involves a large number of technical and professional societies. The Acoustical Society of America is responsible for the acoustical standards activity. |
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ANSI |
| (see American National Standards Institute) |
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Acoustical Society of America |
| A professional society covering all aspects of acoustics including noise, vibration, psychoacoustics, musical acoustics, ultrasonics, etc. The society is also responsible for preparation of acoustical standards. |
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ASA |
| (see Acoustical Society of America) |
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American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) |
| A technical society for the heating, refrigerating and air-conditioning industry which published the ASHRAE Guide and Data Book and technical standards for the industry. |
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ASHRAE |
| (see American Society of Heating, Refrigerating and Air-Conditioning Engineers) |
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American Society for Testing and Materials |
| A professional society which prepares standards. One of the committees of the society is responsible for the standards, recommendations and procedures in the area of acoustics. |
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ASTM |
| (see American Society for Testing and Materials) |
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Attenuation (dB or dB/m[ft]) |
| The reduction of sound with distance. It is often used to describe the change in sound level as one moves toward or away from a sound source, i.e., a 6 dB change (for a point source) with halving or doubling of distance out-of-doors. A 3 dB change with halving or doubling of distance will occur with a line source, i.e., a highway. However, attenuation can also describe the reduction of sound per unit distance. |
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Audiologist |
| A health professional specializing in testing, evaluation, and protection of hearing. |
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Audiogram |
| A written record showing the results of a hearing test. The record contains the hearing level at each of the test frequencies. It may contain more than one years' testin |
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Audiometer |
| An instrument used to perform a hearing test. It permits testing at various frequencies at a wide range of hearing levels. Some audiometers are operated by the tester; some are operated by the one being tested; and some are controlled by a integrated circuit. |
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Average |
| The "energy" average of a series of discrete levels obtained by taking the sum of the anti-logs of one-tenth of the levels, dividing by the number of discrete levels and taking 10 times the logarithm of the result. This average is used for sound levels, sound pressure levels and sound power levels. |
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A-weighting |
| A frequency network which reduces the importance of low frequencies in a manner similar to the human hearing mechanism. The network is standardized and is contained in sound level meters and other acoustical instruments. |
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A-weighted sound level |
| The sound level which is measured using the A-weighting network of a sound level meter or other acoustical instrument. It can also be computed from octave or 1/3-octave band sound pressure levels that have been adjusted for A-weighting. |
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