Performance of parametric transducer arrays and its relationship with the carrier frequency

Abstract

Personal privacy is an imperative consideration, and this extends to listening privately via the ear speaker, earphone or headphones of electronic acoustical devices.

This thesis pertains to an electronic device that generates a private audio zone where only people who are located within the private audio zone are able to hear the sound projected to the said private audio zone. In this research project, we demonstrate the proof-of-concept private audio zone prototype where the private audio zone is generated by means of multiple directional parametric loudspeakers systems where each parametric loudspeaker system comprises a processor, an amplifier and an array of parametric transducers. Multiple directional parametric loudspeakers are required because each directional parametric loudspeaker generates a directional audio beam with very low sound pressure level. When these audio beams overlap, the loudness increases significantly. The overlapping area hence becomes a private audio zone.

In this thesis, the performance of private audio zone generated by multiple parametric transducer arrays and a single parametric transducer array are compared. Experimental results indicate that the multiple parametric loudspeakers create a private audio zone whose audio sound loudness is significantly higher than that generated by a single directional parametric loudspeaker. Specifically, one single parametric transducer array produces 71.5 dB SPL sound while the three single parametric transducer arrays produce 79.7 dB SPL sound.

Furthermore, the effects of the carrier frequency on parametric loudspeaker performance are investigated and discussed. Specifically, the 40 kHz carrier frequency is optimal for the single parametric transducer array, and for the multiple parametric transducer arrays, both 40kHz and 41kHz carrier frequencies are optimal.