Page 223 - The Master Handbook Of Acoustics

198 CHAPTER NINE

1.0
3 5 7
20 cm 4 4 4 4
spacing

0.8 3
4 4
10 cm
spacing
Absorption coefficient 0.4 from wall
0.6

20 cm

10 cm from wall

0.2 Free space

0
125 250 500 1 kHz 2 kHz 4 kHz
Frequency - Hz
FIGURE 9-16

Actual measurements of sound-absorption coefficients of a velvet material (19
oz/sq yd) in free space and 10 cm and 20 cm from a solid wall. The point at which
the increase in absorption due to wall reflection is to be expected are indicated.
9
(After Mankovsky. )

can be compensated in other ways, principally with resonant-type,
low-frequency absorbers.
To compound the problem of unbalanced absorption of carpet,
dependable absorption coefficients are hard to come by. A bewildering
assortment of types of carpet and variables in underlay add to the
uncertainty. Unfortunately, reverberation chamber measurements of
random-incidence absorption coefficients for specific samples of car-
pet are involved and expensive, and generally unavailable to the
acoustical designer. Therefore, it is well to be informed on the factors