Page 199 - The Master Handbook Of Acoustics

174 CHAPTER EIGHT

A double window is most certainly
indicated; a triple window adds little
more. The mounting must minimize cou-
pling from one wall to the other. One
source of coupling is the window frame,
another is the stiffness of the air between
the glass panels. The plan of Fig. 8-9 is a
practical solution to the double-window
problem for concrete block walls. Fig-
ure 8-9B is an adaptation to the staggered
5 /8" Gypsum bd.
stud construction. In the latter there are,
2 4 in effect, two entirely separate frames—
2 4
one fixed to the inner and the other to the
outer staggered stud walls. A felt strip
may be inserted between them to ensure
16" against accidental contact.
Heavy plate glass should be used, the
Construction - Standard stud partition heavier the better. There is a slight advantage
in having two panes of different thickness. If
Weight - 7.3 lb/sq ft
desired, one glass can be inclined to the
Sound transmission class other to control light or external sound
STC 34 dB without fiberglass
STC 36 dB with 3 1 /2" fiberglass reflections, but this will have negligible
effect on the transmission loss of the win-
(Owens-Corning Fiberglas Corporation)
dow itself. The glass should be isolated from
FIGURE 8-6 the frame by rubber or other pliable strips.
Standard stud partition. The spacing between the two glass panels
has its effect—the greater the spacing the
greater the loss—but there is little gain in going beyond 8 inches, nor seri-
ous loss in dropping down to 4 or 5 inches.
The absorbent material between the panes in the design of Fig. 8-9
discourages resonances in the air space. This adds significantly to the
overall insulation efficiency of the double window, and it should
extend completely around the periphery of the window. If the double
window of Fig. 8-9 is carefully constructed, sound insulation should
approach that of an STC 50 wall but will probably not quite reach it.
For the staggered stud wall in which a double window is to be placed,
the use of a 2 × 8 plate instead of the 2 × 6 plate will simplify mount-
ing of the inner and outer window frames.