Acoustic absorption is 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. The absorption process can be measured quantitatively and is of importance in the interior design of concert halls (see acoustics of buildings) and recording studios, etc. The unit used is the sabin: the metric sabin is the absorption power of 1 square meter of open window space (which reflects no sound and therefore is a perfect unit of absorption), the imperial unit is the absorption power of 1 square foot of open window space. The sabin is named after the American physicist William Clement Sabine who founded the field of architectural acoustics.
The absorption coefficient is the fraction of energy which is absorbed on striking any surface. It therefore takes values between 0 and 1, and is usually depends on the frequency. In room acoustics, this coefficient, given the symbol a, is expressed as a fraction of the perfect absorption at an open window of equal area.
See also attenuation.