Influence of finite impedance walls on the sound field in an enclosure

A numerical technique is presented for computing the pressure distribution in the interior of a rectangular enclosure. The analysis models the effect of a nonuniform distribution of wall impedance. The normal modes for this problem are evaluated by solving Green’s integral equation. The wall admittance function is represented as the sum of a mean value superimposed by spatially varying fluctuations. An asymptotic series solution for the pressure about the mean value of the wall admittance is not guaranteed convergence for functions that exhibit large perturbations from the mean. The convergence of the series is shown to be improved by transforming the pressure to a rational functional representation. The superposition of normal modes determined by this technique serves as Green’s function that allows the acoustics of the enclosure to be modeled for a variety of sources. The effect of the wall impedance on the transient response and the reverberation time of the room is presented. [Work supported in part by DOE.]