Development of an Acoustic Filter for Parametric Loudspeaker in Air

Parametric loudspeakers can generate a highly directional beam of sound, having applications in targeted audio delivery. Audible sound modulated into an ultrasonic carrier will get self-demodulated along the highly directive beam due to the non-linearity of air. This non-linear demodularization should be compensated to reduce audio distortion, different amplitude modulation techniques have been developed during the last years. However, some studies are only theoretical whereas others do not analyze the audio distortion in depth. Here, we present a detailed experimental evaluation of the frequency response, harmonic distortion and intermodulation distortion for various amplitude modulation techniques applied with different indices of modulation. We used a simple method to measure the audible signal that prevents the saturation of the microphones when the high levels of the ultrasonic carrier are present. This work could be useful for selecting predistortion techniques and indices of modulation for regular parametric arrays.whereand ω are the amplitude and the angular frequency of the carrier, and ( ) is the 4 This dependence implies that the self-demodulated wave ( ) is not linear to ( ) and that it will 5 suffer from high levels of distortion due to the generated harmonics and a strong low-pass 6 equalization. 7 Various preprocessing techniques have been developed to reduce distortion using different 8 modulations of the envelope ( ). Existing experimental measurements [8-10] are mostly based on 9 the total harmonic distortion or at certain representative frequencies, which may not completely 10 capture the non-linear response of the speakers. Here, we present an extensive comparison of the 11 different amplitude modulation techniques under various modulation indices in terms of frequency 12 response, harmonic distortion and intermodulation distortion. This study analyzes the 13 intermodulation distortion and the harmonics distortions of the different amplitude modulation 14 techniques for various modulation indices. Furthermore, the analysis is split by order. To avoid the 15 presence of spurious signal in the measurements, our method previously selects a dynamic 16 microphone with limited frequency response.

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Development of an Acoustic Filter for Parametric Loudspeaker in Air

Cited by 3 publications

References 12 publications

An alternative method to measure the on-axis difference-frequency sound in a parametric loudspeaker without using an acoustic filter

An alternative method to measure the on-axis difference-frequency sound in a parametric loudspeaker without using an acoustic filter

Multipoint linearization of parametric loudspeakers using volterra filters

Experimental Evaluation of Distortion in Amplitude Modulation Techniques for Parametric Loudspeakers

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