Multipoint linearization of parametric loudspeakers using volterra filters

Parametric loudspeakers have attracted intensive interest due to its application in directional sound reproduction. Recently, Volterra filters have been adopted for compensating the nonlinear distortions in the parametric loudspeaker. The harmonic distortions are effectively reduced at one single control point using a pth-order inverse filter. However, in practical use, a lower total harmonic distortion (THD) level over a larger geometrical area using multiple control points can be more interesting. In this study, an exact linearization method using Volterra filters for two positions based on the multiple-input/multiple output inverse theorem (MINT) is proposed with one parametric loudspeaker and one moving coil loudspeaker. Two inverse filters based on the established Volterra filter models are designed by which input signals are pre-distorted before being fed to those two loudspeakers respectively. To validate this proposed approach, experiments have been conducted. The experimental results show that with these two inverse Volterra filters, THD levels of the parametric loudspeaker over an area defined by at least two points can be reduced.