Handbook for Sound Engineers

84 Chapter 4

4.3.10 Windows

Occasionally sound rooms require windows. The obser-
vation window between control room and studio is an

example. It can very easily have a weakening effect on

the overall TL of the partition between the two rooms.

(See Section 3.3.11.) A wall with a rating of STC-60

alone might very well be reduced to STC-50 with even

one of the more carefully designed and built windows

installed. Just how much the window degrades the

overall TL depends on the original loss of the partition,

the TL of the window alone, the relative areas of the

two, and of course, the care with which the window is

installed. To understand the factors going into the

design of an effective observation window, a good place

to start is to study the effectiveness of glass as a

barrier.^15

Transmission Loss of Single Glass Plates. The mea-

sured transmission loss of ¼ inin, ½ inch, and ¾ inch

single-glass plates (or float) 52 inch × 76 inch is shown

in Fig. 4-35. As expected, the thicker the glass plate, the

higher the general TL except for a coincidence dip in

Figure 4-32. Numerous types of weather stripping can be
used for sealing doors to audio rooms. Courtesy Tab
Books, Inc.

C. Wiping rubber seal.

D. Drop bar.

B. Magnetic.

A. Foam or felt strips.

Figure 4-33. Sealing systems from Zero Mfg.

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770

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