Audio Engineering

Acoustic Environment 107

Table 3.4 : Continued

Materials Coeffi cient

125 Hz 250 Hz 500 Hz 1 kHz 2 kHz 4 kHz

Transite, 3/16-in. perforated,

cement–asbestos board, 11% open

area

Mounted against solid backing

Mounted over 1 in. air space

Mounted over 2 in. air space

Mounted over 4 in. air space

Paper-backed board, mounted over 4-in.

air space

0.01

0.02

0.02

0.02

0.34

0.02

0.05

0.03

0.05

0.57

0.02

0.06

0.12

0.17

0.77

0.05

0.16

0.27

0.17

0.79

0.03

0.19

0.06

0.11

0.43

0.08

0.12

0.09

0.17

0.45

Water surface, as in a swimming pool 0.008 0.008 0.013 0.015 0.02 0.025

Wood paneling, 3/8 in. to 1/2 in. thick,

mounted over 2-in. to 4-in. air space

0.30 0.25 0.20 0.17 0.15 0.10

Table 3.5 gives typical absorption units in sabins rather than percentage fi gures. Sabins
are either in per-unit fi gures or in units per length.

Finally, the room will possess a reverberation time, RT 60. This is the time in seconds that
it will take a steady-state sound, once its input power is terminated, to attenuate 60 dB.
For the sake of illustration, assume a room with the following characteristics:

V  500,000 ft^3 ,

s

a





42 500

0 128

,,

..

ft^2

Therefore the RT 60 is

RT

V

(^60) Sa

0 049

45





.

. s.