85
Aquarea air / water heat pump – design handbook 07 / 2014
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
Pa
(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 specified 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
