ACTIVE CONTROL OF SOUND RADIATION USING VOLUME VELOCITY CANCELLATION

The active control of sound transmission through a panel has been form ulated using a near-field approach. The effects of minimizing the soun d power radiated by the panel and of canceling the net volume velocity of the panel are compared not only in terms of the reduction in sound radiation but also in terms of the change in the space average mean-s quared velocity of the panel and the space average mean-squared pressu re at its surface. Simulations of a thin panel excited by an incident acoustic plane wave and a piezoelectric control actuator show that vol ume velocity cancellation gives similar reductions in the transmitted sound power to the minimization of sound power radiation up to frequen cies at which the size of the plate is about half an acoustic waveleng th. The acoustic radiation is analyzed in terms of the radiation modes of the panel which are also used to explain spillover effects. Spillo ver, which leads to increases in the mean-squared velocity of the pane l and to increases in near-held pressure levels when using a piezoelec tric patch as a secondary actuator can be removed by using an actuator which generates a uniform force over the surface of the panel. Such a n actuator is the reciprocal of the volume velocity sensor and could b e fabricated in the same way. The transfer function between such a mat ched actuator/sensor pair is shown to be minimum phase, so that the pe rformance of a feedback control system should be as good as a feedforw ard one, which would allow control of arbitrary broadband excitation o f the panel. (C) 1995 Acoustical Society of America.