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Sound - Room Absorption Coefficients

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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:

Sound - Room Absorption Coefficients
MaterialSound 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

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Sound - Room Absorption Characteristics

Mean absorption coefficients and reverberation times in typical rooms.

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Room size, absorption characteristics - and attenuation in direct sound fields.

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