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This paper considers the higher-order scattered and transmitted wave fields that result when an acoustic wave from a point source impinges at an arbitrary angle on a rectangular aperture in a rigid, thick wall. In this analysis, it is assumed that free field conditions exist on both sides of the aperture. Although the full scattered and transmitted pressure fields contain both modal sum and modal coupling effects, the modal coupling effects of the higher-order modes are ignored such that an approximate analytical solution to the uncoupled analysis can be utilized. Experiments have been undertaken to measure the sound pressure levels in the transmitted field that result when sound from a point source impinges on the opposite side of a rectangular aperture. Measurements were made with the source located at the required position to drive a particular in-aperture higher-order mode. The source was also located at positions that did not directly excite any in-aperture higher-order mode at a cut-on frequency. These results indicate that the approximate analysis developed here gives accurate solutions whether or not any mode of the aperture is driven at cut-on. Thus, the method can be used for any relative location of a source from a rectangular aperture of any dimensions.

This paper considers the wave fields that result when a plane wave impinges at an arbitrary angle on a rectangular aperture in a rigid, thick wall. A nondimensional form of a prior Fourier transform solution of this problem is derived, from which it is more easy to appreciate the relationship between the physical attributes of the aperture and incoming wave and the resultant acoustic fields. The scattered field from the aperture is examined in detail, in particular the modal contributions to the driving function for the amplitude of the velocity potential. Although the full scattered field contains both modal sum and modal coupling effects, it is shown that neglect of the modal coupling effects introduces minimal error to the solution in certain situations. An approximate analytical solution to the uncoupled analysis is then developed, which is accurate provided that the aperture is acoustically large, such that there are several cut-on modes within the aperture. The full nature of the scattered field can be easily interpreted from the nondimensional, analytical solution. In particular, an error analysis is given from which one can determine the required number of modes in a solution for given accuracy. [ABSTRACT FROM AUTHOR]