Page 251 - Master Handbook of Acoustics

FIGURE 12-7 Sound absorption coefficients of typical porous materials A, B, and C show a

similarity in general shape. Good high-frequency absorption and poor low-frequency absorption
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characterize porous absorbers. (A) High-grade acoustical tile. (B) Medium-weight (14 oz/yd )
velour draped to half area. (C) Heavy carpet on concrete without padding. (D) Coarse concrete
blocks, unpainted. (E) Coarse concrete blocks, painted.

Glass-Fiber Low-Density Materials

Great quantities of glass-fiber materials are used in the acoustical treatment of recording studios,
control rooms, and public spaces. These glass fibers can consist of both special, high-density
materials, and ordinary, low-density building insulation. There is evidence that thicker panels with a

rear air cavity are preferred over thin panels, and low density is also preferred over high density. In
wood or steel stud single-frame walls, staggered stud walls, and double walls, thermal insulating
batts are commonly used.
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This material usually has a density of about 1 lb/ft . Such material is often identified as R-11, R-
19, or other such numbers. These R-prefix designations describe thermal insulating qualities, but are

related to thickness. The thickness of R-8 is 2.5 in, R-11 is 3.5 in, and R-19 is 6 in.