Sound - Room Absorption Coefficients
The sound absorption coefficient is the ratio of absorbed sound intensity in an actual material to the incident sound intensity and can be expressed as
α = Ia / Ii (1)
where
α = sound absorption coefficient
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 1) - α - |
|---|---|
| Acoustic belt, 12 mm | 0.5 |
| Acoustic tiles | 0.4 - 0.8 |
| Asbestos, sprayed 25 mm | 0.6 - 0.7 |
| Brickwork, painted | 0.01 - 0.02 |
| Brickwork, unpainted | 0.02 - 0.05 |
| Carpet, heavy on concrete | 0.3 - 0.6 |
| Carpe, heavy on foam rubber | 0.5 - 0.7 |
| Concrete block, coarse | 0.3 - 0.4 |
| Concrete block, painted | 0.05 - 0.07 |
| Cork sheet, 6 mm | 0.1 - 0.2 |
| Fiberboard on battens, 12 mm | 0.3 - 0.4 |
| Floor, concrete or terrazzo | 0.02 |
| Floor, linoleum, asphalt, rubber or cork tiles on concrete | 0.03 |
| Floor, wood | 0.06 - 0.1 |
| Hardwood | 0.3 |
| Glass, large panes heavy plate | 0.03 - 0.05 |
| Glass, ordinary windows | 0.1 - 0.2 |
| Gypsum board, 12 mm | 0.04 - 0.07 |
| Mineral wool, 100 mm | 0.65 |
| Persons, each | 0.2 - 0.5 |
| Plaster walls | 0.01 - 0.03 |
| Plywood panel, 3 mm | 0.01 - 0.02 |
| Polystyrene, expanded on 50mm battens | 0.35 |
| Polystyrene, expanded rigid backing | 0.15 |
| Polyurethane foam, flexible | 0.95 |
| Rubber sheet, 6 mm porous | 0.1 - 0.2 |
| Slag wool or glass silk, 50 mm | 0.8 - 0.9 |
| Snow | 0.75 |
| Wood wool cement on battens, 25 mm | 0.6 - 0.07 |
1) Note! - the sound absorption coefficient varies with frequency.
Download and print Room Sound Absorption Coefficient chart
Total Room Sound Absorption
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)
Si = area of the actual surface (m2)
αi = absorption coefficient of the actual surface
Mean Absorption Coefficient
The mean absorption coefficient for the room can be expressed as:
αm = A / S (3)
where
αm = mean absorption coefficient
S = total surface in the room (m2)
The acoustic characteristics of a room can be calculated with the formulas above, or estimated for typical rooms.
Example - Room Acoustic Absorption
The total sound absorption in a room with
- 10 m2 concrete floor with absorption coefficient 0.02
- 10 m2 concrete roof with absorption coefficient 0.02
- 40 m2 fiberboard walls with absorption coefficient 0.3
can be calculated as
A = (10 m2) (0.02) + (10 m2) (0.02) + (40 m2) (0.3)
= 12.2 m2 Sabine
The mean absorption coefficient can be calculated as
αm = (12.2 m2 Sabine) / ((10 m2) + (10 m2) + (40 m2))
= 0.2
Related Topics
• Acoustics
Room acoustics and acoustic properties, decibel A, B and C, Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity and sound attenuation.
• Noise and Attenuation
Noise is usually defined as unwanted sound - noise, noise generation, silencers and attenuation in HVAC systems.
Related Documents
Maximum Sound Pressure Levels in Rooms
Maximum recommended sound pressure levels in rooms like kindergartens, auditoriums, libraries, cinemas and more.
Propagation of Sound Indoors - the Room Constant
In a room the sound or noise will reach the receiver as direct and reverberant sound.
Sound - Reverberation Time
The sound reverberation time indicates how long it takes until the sound pressure level in a room is decreased with 60 dB.
Sound - Room Absorption Characteristics
Mean absorption coefficients and reverberation times in typical rooms.
Sound - Room Attenuation in Direct Sound Fields
Room size, absorption characteristics - and attenuation in direct sound fields.