ABSORBING READING: SOME USEFUL ABSORPTION COEFFICIENTS

Dimensions are given in imperial or metric, as originally published.

Material

125Hz

250Hz

500Hz

1kHz

2kHz

4kHz

50mm Acoustic Foam

0.08

0.25

0.6

0.9

0.95

0.9

100mm Acoustic Foam

0.2

0.7

0.99

0.99

0.99

0.99

50mm Mineral Wool (Med Density)

0.2

0.45

0.7

0.8

0.8

0.8

Plaster on brick

0.013

0.015

0.02

0.03

0.04

0.05

Cotton drapes draped to half area. 15oz/sq yd

0.07

0.37

0.49

0.81

0.65

0.54

Foam backed carpet on concrete

0.05

0.16

0.44

0.7

0.6

0.4

Heavy carpet + heavy foam underlay on concrete

0.15

0.25

0.5

0.6

0.7

0.8

Coarse concrete

0.36

0.44

0.31

0.29

0.39

0.25

Painted concrete

0.01

0.05

0.06

0.07

0.09

0.08

Wood floor

0.15

0.11

0.10

0.07

0.06

0.07

Window glass

0.35

0.25

0.18

0.12

0.07

0.04

Plate glass

0.18

0.06

0.04

0.03

0.02

0.02

6mm glass

0.1

0.06

0.04

0.03

0.02

0.02

Plaster on brick

0.013

0.015

0.02

0.03

0.04

0.05

9mm Plasterboard over 20mm air gap

0.3

0.2

0.15

0.05

0.05

0.05

Brickwork

0.05

0.04

0.02

0.04

0.05

0.05

Vinyl flooring

0.03

0.04

0.05

0.04

0.05

0.05

Breeze block

0.25

0.40

0.6

0.5

0.75

0.5

LF panel absorber

0.28

0.22

0.17

0.09

0.10

0.11

Perforated Helmholz absorber, 4-inch depth, mineral wool damping, 0.79% perforation.

0.4

0.84

0.4

0.16

0.14

0.12

Perforated Helmholz absorber,8-inch depth, mineral wool damping, 0.79% perforation.

0.98

0.88

0.52

0.21

0.16

0.14

Broad-band absorber, 1-inch fibreglass slab at mouth of 7-inch deep cavity

0.67

0.98

0.98

0.93

0.98

0.96

Padded seat (unoccupied)

0.1

0.2

0.25

0.3

0.4

0.3

To complicate the issue slightly, the absorption coefficient for a given material varies with frequency, but it isn’t practical to do a different set of calculations for every possible audio frequency.

via Practical Acoustic Treatment, Part 3.

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