Calculation of sound radiation from an aperture of a building by means of Kirchhoff's diffraction formula

Abstract

When a noise source is located in a very large room as compared to the wavelength concerned, the integral equation method to calculate the sound field is not applicable because of limitations in computer capacity. In this case, an approximate approach based on Kirchhoff's diffraction formula becomes more practical. This formula requires the velocity potential and its normal derivative at the aperture, which are unknown. These unknowns may be assumed to consist of the direct wave from the source and the diffused ones. The latter are assumed to be plane waves with the same amplitude but random phase. The relation between the amplitude of the direct wave and the reflected ones is determined by geometrical acoustics. Thus the radiated sound field can be readily evaluated from the aperture by Kirchhoff's formula. The numerical results for a scale model of a reverberation chamber with a rectangular aperture are shown with measurements. The agreement between the calculations and the measurements is satisfactory.