Page 226 - The Master Handbook Of Acoustics

201
ABSORPTION OF SOUND

1.0

0.8

A
Absorption coefficient 0.4 B D C
0.6

0.2

0
125 250 500 1 kHz 2 kHz 4 kHz
Frequency - Hz
FIGURE 9-18
Sound-absorption characteristics of the same Axminster carpet with different underlay.
(A) 80-oz hair felt. (B) Hair felt and foam. (C) 40-oz hair felt. (D) No underlay, on bare
5
concrete. (After Harris. )
acoustical difference whether one or ten people are in a small moni-
toring room. The problem is how to rate human absorption and how to
involve it in calculations. The usual method of multiplying a human
absorption coefficient by the area of a human has its problems. The
easy way is to determine the absorption units (sabins) a human pre-
sents at each frequency and add them to the sabins of the carpet,
drapes, and other absorbers in the room at each frequency. Table 9-2
lists the absorption of informally dressed college students in a class-
room along with a range of absorption for more formally dressed peo-
ple in an auditorium environment.