High frequency ray acoustics models for duct silencers

Hybrid modal/ray acoustics models for high frequency multimode sound propag ation through finite-length dissipative duct silencers are being investigat ed and in this paper, the very simplest of these-involving no mean fluid fl ow, two-dimensional sound propagation, a locally reacting duct liner and no area change in the silencer-is described. A mode-matching scheme is also p resented. Numerical predictions of silencer attenuation from the hybrid mod el and the mode-matching model are compared to experimental data taken from a two-dimensional silencer apparatus, and favourable agreement is noted. A bove a certain lower frequency limit, the hybrid mode/ray model gives a goo d approximation for the silencer attenuation: in comparison to mode-matchin g predictions. Wave diffraction effects at the silencer terminations are al so discussed. (C) Academic Press.