The absorption coefficient ‘α’ is defined as the ratio of the sound energy absorbed by the surface to the total sound energy incident on that surface.
\alpha=\frac{\text { sound energy absorbed by the surface }}{\text { Total sound energy incident on the surface }}
Definition (in terms of O.W.U) :
The absorption coefficient of a material is defined as the ratio of the sound energy absorbed by some area of the surface to that of the same amount of sound energy absorbed by the same area of an open window.
\alpha=\frac{\text { sound energy absorbed by } 1 \mathrm{~m}^2 \text { of the surface }}{\text { sound energy absorbed by } 1 \mathrm{~m}^2 \text { open window }}Hence, the value of α varies between 0 and 1, 1 being for open window.
Table Absorption coefficient of some materials
| S. No | Name of the material | Absorption Coefficient (O.W.U) |
| 1. | Marble | 0.01 |
| 2. | Glass | 0.02 |
| 3. | Brick wall | 0.03 |
| 4. | Wood | 0.06 |
| 5. | Carpet | 0.15-0.3 |
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