ABSORPTION

The loss or dissipation of sound energy in passing through a material or on striking a surface, usually through conversion to heat energy. The term may also refer to the property of a medium, material or object to DAMP sound energy. That part of the sound striking a surface which is not absorbed is either reflected or transmitted.

See: INCIDENCE, REFLECTION, REVERBERATION, SOUND PROPAGATION, SOUND SHADOW, TRANSMISSION.

The absorption process can be measured quantitatively (see ABSORPTION COEFFICIENT) and is of importance in the interior design of concert halls and recording studios, etc. The unit used is the absorption power of 1 square foot of open window space, called the sabin, (which reflects no sound and therefore is a perfect unit of absorption). Some examples of absorption capability of various surfaces are:

ABSORPTION (in Sabins)

at frequency (Hz)

Individual object
128
256
512
1,024
2,048
4,096
Author

Audience, per person with coat
2.3
3.2
4.8
6.2
7.6
7.0
B.S.

Auditorium chairs, wood
0.15
0.22
0.25
0.28
0.50
----
P.S.

Auditorium chairs, upholstered
----
3.1
3.0
3.2
3.4
----
F.W.

B.S.: Bureau of Standards; P.S.: P.E. Sabine; F.W.: F.R. Watson

Absorption units of various objects as a function of frequency (after Olson, Music, Physics and Engineering, Dover, 1967, p. 271, used by permission).

 
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