In acoustics, the sabin (or more precisely the square meter or foot sabin) is a unit of sound absorption, used for expressing the total effective absorption for the interior of a room. Sound absorption can be expressed in terms of the percentage of energy absorbed compared with the percentage reflected. It can also be expressed as a coefficient, with a value of 1.00 representing a material which absorbs 100% of the energy, and a value of 0.00 meaning all the sound is reflected.
The concept of a unit for absorption was first suggested by American physicist Wallace Clement Sabine, the founder of the field of architectural acoustics. He defined the "open-window unit" as the absorption of of open window. The unit was renamed the sabin after Sabine, and it is now defined as "the absorption due to unit area of a totally absorbent surface".
Sabins may be calculated with either imperial or metric units. One square foot of 100% absorbing material has a value of one imperial sabin, and 1 square metre of 100% absorbing material has a value of one metric sabin.
The total absorption in metric sabins for a room containing many types of surface is given by
where are the areas of the surfaces in the room (in m<sup>2</sup>), and are the absorption coefficients of the surfaces.
Sabins are used in calculating the reverberation time of concert halls, lecture theatres, and recording studios.