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Technology for a Quieter America
sound pressure in gases of 20 μPa. Unit, decibel (dB); abbreviation, SPL; symbol, LP. (b) For sound in media other than gases, unless otherwise specified, reference sound pressure is one micropascal (1 μPa).
NOTE: A sound pressure level with reference to a pressure of 1 μPa is numerically 10 lg(202/12) = 26 decibels greater than the sound pressure level for the same sound pressure but with reference to 20 μPa.
†Speech interference level—One-fourth of the sum of the band sound pressure levels for octave bands with nominal midband frequencies of 500, 1,000, 2,000, and 4,000 Hz. Unit, decibel; abbreviation, SIL; symbol, LSI.
*Tire/road noise—Unwanted sound generated by the interaction between a rolling tire and the surface on which it is rolling. Also known as tire/pavement noise.
†Time-average sound level—See description for equivalent continuous sound level.
*Turbulence—A fluid mechanical phenomenon that causes fluctuation in the local sound speed relevant to sound generation in turbo machines (pumps, compressors, fans, and turbines), pumping and air-conditioning systems, or propagation from jets and through the atmosphere.
*Weighting network—Electronic filter in a sound-level meter that approximates, under defined conditions, the frequency response of the human ear. The A-weighting network is most commonly used. See frequency weighting.