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Perceptual Aspects of Hearing
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Hearing
Sound Pressure Level
Sound Power
Sound Intensity
Multiple Sources
Sound Pressure Level and Power
Sound Pressure Level
``Threshold of audibility'' or the minimum pressure fluctuation detected by the ear is less than
of atmospheric pressure or about
N/m
at 1000 Hz.
``Threshold of pain'' corresponds to a pressure
times greater, but still less than 1/1000 of atmospheric pressure.
Because of the wide range, sound pressure measurements are made on a logarithmic scale (decibel scale).
Sound Pressure Level (SPL)
, where
N/m
.
SPL is proportional to the average squared amplitude.
Sound Power
Total sound power emitted by a source in all directions.
Measured in watts (joules / second).
Sound Power Level (PWL) =
, where
watts.
Sound Intensity
Rate of energy flow across a unit area.
Sound Intensity Level (IL) =
, where
watts/meter
.
Multiple Sources
Two equal sources produce a 3 dB increase in sound power level.
Two equal sources produce a 3 dB increase in sound pressure level, assuming no interference.
Two 80 dB sources add to produce an 83 dB SPL.
©1999 CCRMA, Stanford University. All Rights Reserved.
Maintained by
Gary P. Scavone
,
gary@ccrma.stanford.edu
.