On the numerical modelling of interior sound fields by the modal function expansion approach

Much attention has been paid to sound absorption by active or semi-active means in recent years. Such absorbing treatments are usually applied at the boundaries of the controlled acoustic domain. A study of the impedance at the vibrating boundaries of an actively controlled interior sound field may shed some light on the design of semi-active absorption systems. A popular approach to modelling the interior sound field is to use a Green's function in terms of the acoustic eigenfunctions for the rigid enclosure. It is known that the pressure distribution obtained by this approach is accurate in the interior of the domain, and is inaccurate for modelling impedance on the vibrating boundary. This paper studies this inaccuracy quantitatively and its effect on the optimal control of the interior sound field, and also describes a particular solution approach for determining the interior pressure when a model of the sound field is used. (C) 1998 Academic Press Limited.