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:
- 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|
|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|
|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
The total sound absorption in a room can be expressed as
A = S1 α1 + S2 α2 + .. + Sn αn
= ∑ Si αi (2)
A = the absorption of the room (m2 Sabine)
Si = area of the actual surface (m2)
αi = absorption coefficient of the actual surface
The mean absorption coefficient for the room can be expressed as:
αm = A / S (3)
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.
The total sound absorption in a room with
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))
Room acoustics and acoustic properties, decibel A, B and C, Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity and sound attenuation.
Noise is usually defined as unwanted sound - noise, noise generation, silencers and attenuation in HVAC systems.
Maximum recommended sound pressure levels in rooms like kindergartens, auditoriums, libraries, cinemas and more.
In a room the sound or noise will reach the receiver as direct and reverberant sound.
The sound reverberation time indicates how long it takes until the sound pressure level in a room is decreased with 60 dB.
Mean absorption coefficients and reverberation times in typical rooms.
Room size, absorption characteristics - and attenuation in direct sound fields.
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