Elimination of bending wave reflection from the boundary of a panel speaker using an actuator array

The panel speaker, excited by an actuator at the center of the panel, has an inherent sound quality problem due to the irregular spectral characteristic, in particular at low- and mid-frequencies. It is because the cylindrical bending wave generated from the driving point is reflected from the boundary of the panel, and the standing wave field is quickly formed to exhibit the multi-modal behaver. In this study, to avoid the formation of such undesired structural modes, several control actuators are positioned at the periphery of the panel to eliminate the reflected wave from the boundaries. To this end, the vibration field is decomposed into the traveling and evanescent wave components, and then a matrix equation is derived to relate the input force of the actuators with the complex amplitude of each wave component. The gain of the control actuators is obtained by solving the inverse problem. Simulation and experiment are conducted to validate the proposed control method. The result reveals that the driving-point mobility of the main actuator on the controlled field exhibits a dynamic behaviour as like an infinite plate. A nearly flat spectrum of the radiated sound is achieved too.