ON THE METHOD FOR ESTIMATING THE VOLUME VELOCITY OF AN ACOUSTIC SOURCE IN A CHAMBER

Abstract

The volume velocity of an acoustic source is important in determining acoustic parameters such as the source strength and the acoustic transfer impedance, in the areas of transfer function analysis by using vibro-acoustic reciprocity, and in radiated power estimation. Measurement of volume velocity in ideal environments is often not available, so that simple and cheap estimation methods have been sought. One of the suggested techniques is the internal pressure method incorporating a loudspeaker attached to a chamber wall and a microphone inserted into the cavity. Although the method is easy to handle with a simple measurement set-up, the coupling effect between the dynamic system of the loudspeaker and acoustic field, and the effects of higher order modes introduced by the discontinuities in the acoustic held should be considered for precise results. In this study, an analytical and an experimental method are proposed to obtain the volume velocity in the chamber. In the analytical model, higher order modes due to the discontinuities of loudspeaker and microphone boundaries are included and the effects of these higher order modes are investigated by varying the non-dimensionalized geometrical parameters. Coupling effects are compensated for by using the results for two cylinders with different lengths. The volume velocity of a loudspeaker thus obtained agrees very well with that measured by a laser sensor.