INSITU ESTIMATION OF AN ACOUSTIC SOURCE IN AN ENCLOSURE AND PREDICTION OF INTERIOR NOISE BY USING THE PRINCIPLE OF VIBROACOUSTIC RECIPROCITY

Abstract

The volume velocity of an acoustic source can be widely used in determining the vibroacoustic transfer functions, in measuring the acoustic transfer impedances, and in finding the generated power of an acoustic source. Several techniques utilizing special experimental devices have been proposed for this purpose, including the laser velocimetry, the internal pressure measurement, and the face-to-face electroacoustic measurement. However, for a source in an enclosure with flexible walls, the vibroacoustic coupling should be considered, especially in the case of a loudspeaker source that has low internal mechanical impedance. The present method, which uses the principle of vibroacoustic reciprocity, can give a reasonable estimation of the transfer functions and can be used in determining the volume velocity of a source in situ. Because the present method does not require a special facility or the information on the source surface vibration, the method can be applied to any irregularly shaped source in a flexible enclosure. With the obtained vibroacoustic transfer functions, the interior noise field in an enclosure can be predicted by vectorial summation when the boundary points are excited by uncorrelated dynamic forces. The predicted internal pressure in an enclosure is in good agreement with the measured internal pressure even in the presence of sound absorbers inside the enclosure.