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

The volume velocity of an acoustic source is important in determining acoustic parameters such as the source strength and the acoustic trans fer impedance, in the areas of transfer function analysis by using vib ro-acoustic reciprocity, and in radiated power estimation. Measurement of volume velocity in ideal environments is often not available, so t hat simple and cheap estimation methods have been sought. One of the s uggested techniques is the internal pressure method incorporating a lo udspeaker attached to a chamber wall and a microphone inserted into th e cavity. Although the method is easy to handle with a simple measurem ent set-up, the coupling effect between the dynamic system of the loud speaker and acoustic field, and the effects of higher order modes intr oduced by the discontinuities in the acoustic held should be considere d for precise results. In this study, an analytical and an experimenta l method are proposed to obtain the volume velocity in the chamber. In the analytical model, higher order modes due to the discontinuities o f loudspeaker and microphone boundaries are included and the effects o f these higher order modes are investigated by varying the non-dimensi onalized geometrical parameters. Coupling effects are compensated for by using the results for two cylinders with different lengths. The vol ume velocity of a loudspeaker thus obtained agrees very well with that measured by a laser sensor.