Low frequency radiation from a (compact) structure with and without sound holes.

Abstract

At long wavelengths, a force driven, closed elastic structure radiates as a dipole. However, this may or may not be the case in the presence of a sound hole. Radiation remains dipole-like when the interior volume behaves as an acoustic fluid coupled to the structure. This is commonly referred to as the sound hole sum rule in musical acoustics [Weinreich (1985)]. However, should the interior acoustic volume be uncoupled, or simply ignored, the radiated field is dominated by a monopole contribution. For example, this may occur with mechanically isolated, piping systems exposed to the exterior medium. In this situation, the monopole or dipole nature of the radiation depends on the effective number of sound holes, for example, whether the driven system is well connected to the exterior along both the inlet and outlet. Finite element structural-acoustic models are developed and exercised to investigate these systems and issues. In addition, a substructuring technique is utilized to account for the potential influences of interior structural complexity.