Sound - Room Absorption Coefficients | MEPKit Engineering Tools

Material	Sound Absorption Coefficient (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
Carpet, 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 50 mm 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 - 0.7

Material

Sound Absorption Coefficient (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

Carpet, 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 50 mm 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 - 0.7

Overview

The sound absorption coefficient (α) is the ratio of absorbed sound intensity to incident sound intensity:

α = I_a / I_i

Where:

α = sound absorption coefficient
I_a = sound intensity absorbed (W/m²)
I_i = incident sound intensity (W/m²)

Note: The sound absorption coefficient varies with frequency.

Total Room Sound Absorption

The total sound absorption in a room can be expressed as:

A = ∑(S_i × α_i)

Where:

A = the absorption of the room (m² Sabine)
S_i = area of the actual surface (m²)
α_i = absorption coefficient of the actual surface

Mean Absorption Coefficient

The mean absorption coefficient for the room:

α_m = A / S

Where:

α_m = mean absorption coefficient
S = total surface in the room (m²)

Example - Room Acoustic Absorption

For a room with:

10 m² concrete floor (α = 0.02)
10 m² concrete roof (α = 0.02)
40 m² fiberboard walls (α = 0.3)

Total absorption: A = (10)(0.02) + (10)(0.02) + (40)(0.3) = 12.2 m² Sabine

Mean absorption coefficient: α_m = 12.2 / 60 = 0.2