A parametric loudspeaker uses the effects of self-modulation in air to generate audible sound, which has drawn much attention recently owing to its attractive and promising feature of sharp directivity. For a parametric loudspeaker, Berktay's solution is often adopted to analyze the performance of different modulation techniques. However, most techniques assume that the ultrasound transducer is ideal. So WU Ming, YE Chao, WU Shuaibin, HUANG Chenxi and YANG Jun of Institute of Acoustics, Chinese Academy of Sciences carried out a series of studies and discussed the effects of the nonideal ultrasound transducer on the performance of the parametric loudspeaker, which may provide a guide to the design of a distortion–reduction preprocessing technique for given ultra-sound transducers.

In the study, the researchers first derive the frequency contents of self-demodulated secondary wave pressure for the nonideal ultrasound transducer on the basis of Berktay's solution. Then, according to the relationship between the input signal and the envelope of primary wave pressure, they obtain the harmonic distortion and intermodulation distortion for different modulation techniques. The following simulation experiments results show that in the case of using the double-sideband amplitude modulation (DSB-AM) technique, the amplitudes of the fundamental frequency and intermodulation distortion components are affected by both the phase and magnitude response of the ultrasound transducer, whereas the harmonic distortion component is only affected by the phase response. In the case of using the single-sideband amplitude modulation (SSB-AM) technique, the amplitudes of the fundamental frequency component and intermodulation distortion components are only affected by the magnitude response of the transducer and the harmonic distortion component remains zero.

This research result was published on the recently issued journal of JAPANESE JOURNAL Of APPLIED PHYSICS (49, 2010).