Building Acoustics

Sound absorbers 173

Figure 5.12 Absorption factor at normal incidence. Hole-perforated plate backed by a cavity of depth 100 mm.
For further specifications, see text.

100 1000

200 400 600 800 2000 4000

Frequency (Hz)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

A

bso

rption

facto

r

25 Pa.s/m

10 Pa.s/m

5 Pa.s/m

125 250 500 1000 2000 4000

Frequency (Hz)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

A

bsorption factor

1

2

3

3 4

14

7.5

Fabric

Figure 5.13 Absorption factor measured in a reverberation chamber. 14 mm perforated panel, perforation rate
12%, with a layer of fabric backed by a cavity of depth 50 mm. Curve no. 1 – cylindrical holes, empty cavity.
Curve no. 2 – cylindrical holes, cavity filled with mineral wool. Curve no. 3 – conical holes, cavity filled with
mineral wool.