In this paper, a simplified boundary element method (BEM) is proposed in order to extend the acceptable high frequency range of a conventional acoustic BEM. Because the third-octave band spectrum is usually used for a wide range spectral analysis, the formulation stemming from Kirchhoff-Helmholtz integral equation should be capable of calculating the band level representing the averaged characteristics in a band. For this purpose, the monopole and dipole source terms are transformed into auto- and cross-spectrum between two vibrating sources, in which the cross-spectra are eventually discarded based on the assumption of uncorrelated structural motion. In order to check the validity of the formulation, a comparison is made with the Rayleigh integration in evaluating the sound pressure radiated from the baffled beam. The condition rule for the cross-correlation limit is also shown for the proper use of this method. Application to test examples shows that the resultant trend agrees well with the analytic solution. In addition, it is found that the overdetermination technique to overcome the nonuniqueness in exterior problems is not required for the proposed method.
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