On the frequency-independence of interior radiation modes using coupled modes theory

Active structural acoustic control systems rely on the exact knowledge of the sound radiation properties. For the sound radiation into cavities these are commonly derived from the uncoupled, rigid-walled cavity modes. There is an ongoing debate about the validity of such an approach, since the velocity continuity along the structure is violated. In this paper the sound radiation properties are evaluated using the coupled acoustic modes, taking into account the real boundary conditions of the structural velocity. With this approach the acoustic energy in the cavity can be estimated at the structural surface and recent activities in the field of active control of interior sound radiation are validated.