Directivity control using a structural actuator array

Directional sound fields can be generated by arrays of multiple sound sources, with the most common and straightforward method being an array of loudspeaker drivers. Although such a system, when appropriately designed, is capable of high levels of directivity control over a broad bandwidth and with good audio quality, it can be prohibitively expensive and too fragile in certain applications. This work presents and investigates the idea of using an array of actuators mounted to a structure to generate a directional sound field. Structural actuators have previously been used as an affordable and robust alternative to conventional loudspeakers, particularly in applications where the actuators can be used to drive a structure that would already be in place to radiate the desired sound field and where the required audio quality is lower. By distributing a number of actuators on a structure, and controlling the relative amplitudes and phases with which they are driven, it is possible to manipulate the structural vibration such that it generates a controlled directional sound field, similar to that resulting from an array of individual sound sources. In this work, an analytical model is first formulated of a rectangular panel excited by an array of structural actuators, which are approximated as point forces acting perpendicularly to the surface of the panel. This model is used to perform a simulation based parametric study, which provides insights into the design trade-offs for a structural actuator array based system. In particular, this considers how the number of actuators, their geometry and the dimensions of the structure influence the directivity control and achievable bandwidth. Based on this parametric study, a structural actuator array is assembled using a rectangular aluminium panel and six actuators. The system is tested and evaluated through measurements in an anechoic chamber