Page 267 - Master Handbook of Acoustics

FIGURE 12-19 A comparison of the sound-absorption characteristics of three different types of

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carpet. (A) Wilton, pile height 0.29 in, 92.6 oz/yd . (B) Velvet, latex backed, pile height 0.25 in, 76.2
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oz/yd . (C) The same velvet without latex backing, 37.3 oz/yd , all with 40-oz hair felt underlay.
(Harris.)

Effect of Carpet Underlay on Absorbance

Foam rubber, sponge rubber, felts, polyurethane, or combinations are often used as the padding under
a carpet. Foam rubber is made by whipping a latex water dispersion, adding a gelling agent, and
pouring into molds. The result is always open-celled. Sponge rubber, on the other hand, formed by
chemically generated gas bubbles, can yield either open or closed cells. Open cells provide the
interstices required for good sound absorption while closed cells do not.

The influence of underlay on carpet absorption is significant. Figure 12-20 shows reverberation-