A simulation study on the array control of a rectangular panel speaker for improving the sound radiation performance

Abstract

When a primary actuator excites the centre point of a rectangular panel speaker, the reflected bending waves at the edges of the plate are superposed with the incident wave and other reflected waves, and this results in a strong modal behaviour. Accordingly, the radiated sound spectrum possesses strong amplitude fluctuations, which results in a poor sound quality. This paper considers via simulations a rectangular panel speaker excited at its centre by a primary actuator and controlled by an edge-located array of control actuators to suppress the multi-modal behaviour of the panel. The basic concept is to eliminate the bending wave reflection from the panel boundary using the control actuator array; thus, only a freely travelling cylindrical wave generated by the main actuator remains. The input gain of the control actuators is obtained via the solution of the inverse problem derived using the transfer matrix between the actuator input and the velocity response on the plate. To ensure the economical use of the input energy required by the control actuators while maintaining the desired acoustic performance, regularisation is employed when solving the inverse problem. By assuming the linearity between the input voltage and the generated force of the actuator, the input efficiency of the control actuators is compared. The control performance is investigated by using a 2-mm thick aluminium panel with an area of 0.7 x 0.4 m(2). The controlled result shows that the driving-point mobility of the primary actuator approaches that of the infinite plate, which means that the boundary, now the connection line of the control actuators, is converted into an anechoic one. Elimination of the modal effect yields the smoothed spectrum of the radiated sound without severe peaks and troughs.