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Science > Acoustics 
speed of sound (c)
Science; Acoustics
At a temperature of 20 °C, the speed of sound in air at sea level is approximately 343 m/s - not to be confused with sound particle velocity. In air the decrease of the sound ...
free field microphone
Science; Acoustics
At frequencies above 1 kHz the wavelength of sound is small enough for a half-inch microphone to 'disturb' or affect the sound field you are trying to measure. Free field ...
standard atmospheric pressure (atm)
Science; Acoustics
Atmospheric pressure is the force per unit area exerted on a surface by the weight of air above that surface. Standard atmospheric pressure is equal to 101.325 kPa the preferred ...
day-evening-night equivalent level (Lden)
Science; Acoustics
A-weighted, Leq. noise level, measured over the 24 hour period, with a 10 dB penalty added to the levels between 23.00 and 07.00 hours and a 5 dB penalty added to the levels ...
evening equivalent level (Levening)
Science; Acoustics
A-weighted, Leq. Sound level, measured during the evening period 19.00 - 23.00 hours. Also known as the evening noise indicator and other terms.
day equivalent level (Lday)
Science; Acoustics
A-weighted, Leq. Sound level, measured over the 12-hour period 07.00 - 19.00 hours. Also known as day noise indicator and other terms.
day-night equivalent level (Ldn)
Science; Acoustics
A-weighted, Leq. Sound level, measured over the 24 hour period, with a 10 dB penalty added to the levels between 23.00 and 07.00 hours. Also known as the day-night noise indicator ...
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