Page 201 - The Master Handbook Of Acoustics

176 CHAPTER EIGHT

be embedded in the door jamb. Such a soft
trap could also be used in conjunction
with one of the several types of seals.
Figure 8-11 shows a do-it-yourself door
seal that has proved reasonably satisfac-
tory. The heart of this seal is a rubber or
plastic tubing an inch or less in outside
3
diameter with a wall thickness of about ⁄32
5 /8" Gypsum bd.
in. The wooden nailing strips hold the
2 4 tubing to the door frame by means of a
2 4 canvas wrapper. A raised sill is required
at the floor if the tubing method is to be
used all around the door (or another type
16" of seal such as weatherstripping could be
utilized at the bottom of the door). An
Construction - Double wall
advantage of tubing seal is that the degree
Weight - 7.1 lb/sq ft of compression of the tubing upon which
Sound transmission class the sealing properties depend is available
STC 43 dB without fiberglass for inspection.
STC 55 dB with 3 1 /2" fiberglass A complete door plan patterned after
STC 58 dB with 9" fiberglass
BBC practice is shown in Fig. 8-12. It is
(Owens-Corning Fiberglas Corporation) based upon a 2-in-thick solid slab door and
FIGURE 8-8 utilizes a magnetic seal such as used on
refrigerator doors. The magnetic material is
Double wall partition.
barium ferrite in a PVC (polyvinyl chloride)
rod. In pulling toward the mild steel strip, a
good seal is achieved. The aluminum strip “C” decreases sound leakage
around the periphery of the door.
It is possible to obtain a very slight acoustical improvement and, to
some at least, an improvement in appearance by padding both sides of
a door. A plastic fabric over 1-in foam rubber sheet can be “quilted”
with upholstery tacks.

Noise and Room Resonances
Room resonances can affect the problem of outside noise in a studio.
Any prominent modes persisting in spite of acoustic treatment make
a room very susceptible to interfering noises having appreciable
energy at these frequencies. In such a case a feeble interfering sound
could be augmented by the resonance effect to a very disturbing level.