Fiber movements and sound attenuation in glass wool

Propagation of a plane harmonic sound wave in fiber materials such as glass wool is studied theoretically and experimentally. Wave equations are set u p that take into account the movement of the fiber skeleton. The attenuatio n of the sound wave in slabs of glass wool was calculated and measured. The main new result is that the experimental attenuation of a low-frequency pr opagating wave is lower when the fibers move. For a wave with frequency 100 Hz in glass wool of density 30 kg/m(3) the attenuation of a layer of thick ness 0.20 m is 4 dB if the fibers move, and 12 dB if they do not move. The attenuation was computed from the fiber diameters and their density, which was found from the mass density. Measured attenuation is lower than the val ues calculated. Nevertheless, if the density is adjusted, a complete fit is obtained between experimental and theoretical values for frequencies 50-50 00 Hz. (C) 1999 Acoustical Society of America. [S0001-4966(99)02601-6].