Page 197 - The Master Handbook Of Acoustics

172 CHAPTER EIGHT

4"

16"

8"

Construction - 4" concrete block
Weight - 18 lb/sq ft (plain)
30 lb/sq ft (plastered both sides)

Sound transmission class -
STC 40 dB plain
STC 48 dB plastered both sides

(Solite Corporation)
FIGURE 8-4
Four-inch concrete block construction.

It was stated earlier that porous sound absorbing materials are
of limited value in insulating against sound. This is true when nor-
mal transmission loss is considered, but in structures as those in
Figs. 8-7 and 8-8, such porous materials have a new contribution to
make in absorbing sound energy in the cavity. This can improve
the transmission loss in some wall structures by as much as 15 dB,
principally by reducing resonances in the space between the walls,
while in others the effect is negligible. The low-density mineral
fiber batts commonly used in building construction are as effective
as the high-density boards, and they are much cheaper. Mineral
fiber batts within a wall may also meet certain fire-blocking
requirements in building codes.