Parametric study in the formation of a virtual speaker and baffle on a thin panel

Abstract

Any thin panel structure can be converted into a speaker and baffle system, if the actuator array surrounding the structure is properly tuned. Different from the sound radiation from a plate excited by an actuator attached to the structure, the sound quality and radiation efficiency become similar to the actual loudspeaker system. Limitations in the location and space of conventional speaker systems can be also avoided. To this end, the concept of acoustical holography can be adopted so as to realize a rendered vibration field, i.e., speaker and baffle, on a panel by using the inverse determination of magnitude and phase weightings for the array actuators. With the proper weightings of the control actuators, the bending wave generated from each actuator can create the rendered vibration field with the interaction of the other waves. Considering the eventual sound radiation, the rendering parameters like speaker size, location, included number of modes, actuator number, and actuator spacing affect the end result. To validate the present control method, numerical simulation is performed on a thin, simply-supported, rectangular plate. Relationships between rendering parameters and radiation performance are studied. When the speaker zone size becomes small, the number of high order modes should be increased to accomplish the control. It is seen that the typical radiated sound has two dip patterns in its spectrum. One is related to the speaker size: dips appear when the Helmholtz number, determined by bending wavenumber and speaker diameter, becomes 7.6, 13.6, and 20. The other dip pattern is not much related to the speaker size, but is mostly affected by the speaker location. It is also shown that the redundancy of actuators due to their relative positions can be eliminated by assuring the independency among actuator positions.