Mechanisms of active control for active acoustic structure based on mode theory

Active acoustic structure proposed in recent years has been viewed as an encouraging approach to actively reduce the sound radiation from vibrating structures. In this study, the mechanism of active control, which is one of the key problems in the study of such a structure, is investigated based on the theories of acoustic radiation mode and structural vibration mode. It is shown that the optimum reduction in the radiated sound power would be arrived, if the amplitude of the dominant radiation mode decrease and meanwhile other lower-rank radiation modes do not go up high. If the amplitude of the high-order radiation mode is decreased, so will also be done for the lower-order radiation modes. Four secondary panels can reduce the dominant radiation modes, that correspond to all the structural modes, and can guarantee a considerable reduction of the total sound power over the entire frequency range of interest.