Page 222 - The Master Handbook Of Acoustics

197
ABSORPTION OF SOUND

Porous Solid
materials wall
1
4 2
Absorption coefficient Freq. = 1,000 Hz

0
0 2 4 6 8 d
d = Distance from wall-inches Variable
A

Porous Solid
materials wall
1
3 5 7
4 4 4 4
Absorption coefficient

0
100 1 kHz 2 kHz 3 kHz 12"
Frequency - Hz Fixed
B
FIGURE 9-15

(A) The sound absorption of porous material such as a drape varies with the distance from
a hard wall. The maximum absorption is achieved when the drape is one-quarter wave-
length from the wall, the minimum at a half wavelength. (B) The sound absorption of
porous material hung at a fixed distance from a wall will show maxima at spacings of a
quarter wavelength and odd multiples of a quarter wavelength as the frequency is varied.