Modulation Methods and Beamforming Techniques on a Steerable Parametric Acoustic Array Loudspeaker

Sammanfattning

Directional sound have many use cases in today’s society. By targeting specific users with directional instead of wide-spreading sound, amplitude can be reduced for unintended listeners. A Parametric Acoustic Array loudspeaker transmits hearable sound in an ultrasonic beam by utilizing a nonlinear acoustic phenomenon called Parametric Acoustic Array. The shorter wavelengths of the ultrasonic frequencies makes it easier to design loudspeakers with higher directivity compared to using conventional methods. The same nonlinear process that give rise to this phenomenon also induce severe distortion to the signal. Several modulation methods have been proposed to mitigate this problem. This thesis evaluates several commonly used modulation methods and how they affect the distortion. The thesis also evaluates steering of a parametric array loudspeaker by utilizing a phased array. The evaluation is done in an empirical, experimental way by measuring the sound generated by a Parametric Acoustic Array loudspeaker. Results show that the sound beam can be steered by only applying phase shift on the carrier wave, and that different modulation methods impose different amount of distortion.