Mitigation of Nonlinear Distortion in Sound Zone Control by Constraining Individual Loudspeaker Driver Amplitudes

Loudspeaker drivers are subject to nonlinear distortion in the low frequency range at high input levels. In sound zone control, distortion not only reduces the acoustic contrast between zones, but also gives perceived artefacts. Standard sound zone methods, such as acoustic contrast control, apply a constraint to the overall input power, but individual loudspeaker drivers are not controlled and the nonlinear distortion is mainly produced by the loudspeaker drivers with the highest input power. We investigate a sound zone control algorithm where amplitude limits are applied on a per-loudspeaker-driver basis, and its effect on the mitigation of nonlinear distortion. Experiments with pure-tone signals show that this approach improves the contrast for the pure tone component by 7.6 dB. Second order harmonic distortion in the dark zone is suppressed by 8.4 dB and third order harmonic distortion by 4.4 dB, compared to acoustic contrast control.