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 calculations. Noise Rating (NR) curves. Sound transmission through walls. Calculate 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.
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Sound - Reverberation Time
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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.