Performance of Low Frequency Sound Zones Based on Truncated Room Impulse Responses

Abstract

Using spatially distributed loudspeakers and properly designed control filters, it is possible to generate sound zones that play different audio contents in different regions of the same room. For low frequency content, the design of control filters relies on the room impulse responses (RIRs) between each loudspeaker and the desired listening positions. Estimates of the RIRs can be obtained by distributing wireless microphones within the sound zones and thereby systematically acquiring sufficient knowledge about the acoustical characteristics of the room and loudspeakers. Longer acquisition times would generally lead to better estimates of the RIRs but would also introduce processing delays, which is undesirable in cases where time-varying RIRs are to be compensated. In addition, shorter RIRs may imply lower computational complexity.In this work, control filters were calculated using truncated versions of the RIRs in order to simulate the effect of a reduced acquisition time. The performance was evaluated in terms of the acoustic contrast ratio (ACR) and it was seen that within a certain limit, doubling the acquisition time increases the ACR around 4 dB or more. Moreover, to keep the sound pressure low in the dark zone, only a limited part of the reverberation tail is required.