A personal sound zone system renders different audio contents to multiple listening groups within the same physical space. Such zones are called bright zones. Personal sound zone systems provide concurrent, interference-free listening experiences to multiple listeners using loudspeaker arrays. Nonlinear distortion in loudspeaker drivers can cause audible artifacts, and the acoustic contrast can be degraded especially at high driving levels. The distortion can be reduced by constraining the total control effort, but artifacts can still be present due to one or several loudspeaker drivers having high control effort. To reduce nonlinear distortion the researcher applied individual control effort constrained acoustic contrast control (ICECACC), where control effort constraints are imposed for each individual loudspeaker driver. Simulations and experiments were performed on a two-sound-zone setup, with one bright and one dark zone using individually control effort constrained acoustic contrast control (ICECACC) or acoustic contrast control (ACC) and a two-tone stimulus generating both harmonic and intermodulation distortion. Frequency resolved measurements show that ICECACC and ACC give nearly identical acoustic contrast at the two fundamental frequencies, but ICECACC has less nonlinear distortion than ACC. Experiments using a multitone stimulus and identical total control efforts also gave reduced nonlinear distortion with ICECACC over ACC, however this was achieved at the expense of contrast. The results show that a compromise can be made between acoustic contrast and nonlinear distortion.
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