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The following HTML text is provided to enhance online readability. Many aspects of typography translate only awkwardly to HTML. Please use the page image as the authoritative form to ensure accuracy. 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. Please note: No rights are granted to use content that appears in the work with credit to another source.
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