Project Design
Acoustics
Sound pressure level
Sound occurs when air vibrates. This vibration propagates in air as
pressure waves and reaches the ear drum of the human ear. Independent
of the type of noise (speech or motor noise) the sound can be measured
as sound pressure. The larger the sound pressure, the louder the noise
is perceived. The human ear can perceive a range from 20 × 10
-6
P a
(hearing threshold) up to 20 Pa (threshold of pain). This range that
corresponds to a ratio of 1:1,000,000 is not perceived by the human ear
linearly, but rather logarithmically. For this reason the sound pressure is
not specied as pressure, but rather as sound pressure level in decibel
(dB). Values of sound pressure level for typical situations are:
Noise Sound pressure
level in dB(A)
Sound pressure
in μPa
Perception
Forest 20 100 very quiet
Library 40 1,000 quiet
Speech 55 10,000 normal
Street 80 100,000 loud
Pneumatic hammer 100 1,000,000 very loud
Typical noise situations and occurring sound pressure levels and sound pressures
The non-linear perception of sound pressure leads to a state where two
equally loud sound sources are not perceived as double as loud as one
sound source but only 3 dB louder. Doubling of the volume of a noise
source is associated with a sound pressure level increase by 10 dB.
5.10 Acoustics
5.10.1 Sound
pressure level
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