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Engineering ToolBox > Sound Absorption Coefficients for some common Materials
The sound absorption coefficient indicates how much of the sound is absorbed in the actual material. The absorption coefficient can be expressed as:
α = Ia / Ii (1)
where
Ia = sound intensity absorbed (W/m2)
Ii = incident sound intensity (W/m2)
Absorption coefficient - α - for some common materials can be found in the table below:
| Material | Sound Absorption Coefficient - α |
| Plaster walls | 0.01 - 0.03 |
| Unpainted brickwork | 0.02 - 0.05 |
| Painted brickwork | 0.01 - 0.02 |
| 3 mm plywood panel | 0.01 - 0.02 |
| 6 mm cork sheet | 0.1 - 0.2 |
| 6 mm porous rubber sheet | 0.1 - 0.2 |
| 12 mm fiberboard on battens | 0.3 - 0.4 |
| 25 mm wood wool cement on battens | 0.6 - 0.07 |
| 50 mm slag wool or glass silk | 0.8 - 0.9 |
| 12 mm acoustic belt | 0.5 - 0.5 |
| Hardwood | 0.3 |
| 25 mm sprayed asbestos | 0.6 - 0.7 |
| Persons, each | 2.0 - 5.0 |
| Acoustic tiles | 0.4 - 0.8 |
Note! The absorption coefficient varies with the frequency of sound.
The total sound absorption in a room can be expressed as:
A = S1 α1 + S2 α2 + .. + Sn αn = ∑ Si αi (2)
where
A = the absorption of the room (m2 sabine)
Sn = area of the actual surface (m2)
αn = absorption coefficient of the actual surface
The mean absorption coefficient for the room can be expressed as:
am = A / S (3)
where
am = mean absorption coefficient
A = the absorption of the room (m2 sabine)
S = total surface in the room (m2)
A rooms acoustic characteristics can be calculated with the formulas above, or estimated for typical rooms.