Active control of noise in a strongly coupled rectangular cavity

This paper deals with a strongly coupled rectangular cavity in which both acoustic field and vibration field strongly couple with each other, hence its fundamental characteristics significantly differ from in vacuo structural modes and rigid wall acoustic modes. First, the eigenpairs of a rectangular cavity comprising a flexible panel placed on top and five rigid walls are derived, its fundamental properties being investigated. It is revealed that there exist two kinds of acoustic mode; standing wave acoustic mode and evanescent mode. The former is generated as a result of sound reflection in the cavity, whereas the latter is produced by coupling effect between structure and sound, and is characterized as the sound pressure localization in the vicinity of a panel. This paper therefore elaborates the intriguing properties the evanescent mode possesses. Furthermore, modal orthogonality equations in terms of compliance and density of a panel are obtained. The modal equations, in case of a forced response, of the cavity are then derived. Using the eigenpairs obtained, acoustic potential energy inside the cavity is described, and the optimal feedforward control law for minimizing the energy is derived. Finally control effect for suppressing strongly coupled acoustic modes of the cavity is shown.