Subband optimization for acoustic contrast control

Abstract

Multichannel filters to synthesize a personal sound zone are often designed in frequency domain. The frequency domain design assumes a circular convolution between impulse responses of loudspeakers and filter coefficients, and hence, the actual sound pressure field produced by the linear convolution with the impulse responses differs from the sound field predicted at the design stage. The circular convolution issue can be resolved by the time domain filter coefficient design, but in this case the uneven spectral energy across different frequencies is troublesome. A subband processing, which finds the optimal filter coefficients of loudspeakers at a single frequency based on the average responses over a frequency band of finite bandwidth, can be utilized to mitigate the circular convolution problem. The concept and design of the optimal subband are explained with impulse responses measured in a highly reflective condition, and the difference in performances with and without subband processing is demonstrated