Page 202 - The Master Handbook Of Acoustics

177
CONTROL OF INTERFERING NOISE

1/4" Rubber or neoprene strips

1/4" Polished plate glass 3/8" Polished plate glass

Cover cloth
Mineral fiber absorbent

A

B

FIGURE 8-9

Four-inch concrete block construction.

Active Noise Control
Framing
Many have had the idea of canceling Heavy plywood
noise by radiating a replica of the noise
in inverse phase. It sounds simple but is
very difficult to implement. It has been
Sand
made to work fairly well in the immedi-
ate vicinity of a telephone in an indus-
Perforated hardboard
trial area of heavy noise. Very serious
investigations are in progress to apply Mineral
fiber
the principle to automobiles and other
such controlled spaces. The prospects of 1 /16" lead
active noise control being applied in
sound-sensitive areas such as home lis- FIGURE 8-10
tening rooms, recording studios, or con- A reasonably effective and inexpensive “acoustic”
trol rooms are rather remote but new door. Dry sand between the plywood faces adds to the
mass and thus the transmission loss. Sound traveling
digital sound processing techniques between the door and jamb tends to be absorbed by
might change that. the absorbent door edge.