CONICET | Buscador de Institutos y Recursos Humanos

In this work, a directional loudspeaker, also known as a parametric array loudspeaker (PAL), is designed and constructed. The operation is based on the phenomenon called self-modulation that happens when two high-frequency collimated beams interact in a viscous medium, due to its non-linear properties. The sound obtained after the self-modulation is formed in the beam of the ultrasonic carrier signal propagating beyond the absorption distance in which the carrier has been sufficiently attenuated. This allows to achieve a focused audible signal and therefore a directional polar pattern of narrow angle. To compensate for non-linearity of the auto-modulation, a predistortion is introduced with two modulation methods, in double-sideband amplitude (AM-DBL) and pulse-width modulation (PWM). Its effect on directionality, sound pressure level and harmonic distortion is experimentally analyzed.