Reproduction of nearby sound sources using higher-order ambisonics with practical loudspeaker arrays

In order to reproduce nearby sound sources with distant loudspeakers to a single listener, the near field compensated (NFC) method for higher-order Ambisonics (HOA) has been previously proposed. In practical realization, this method requires the use of regularization functions. This study analyzes the impact of two existing and a new proposed regularization function on the reproduced sound fields and on the main auditory cue for nearby sound sources outside the median plane, i.e, low-frequencies interaural level differences (ILDs). The proposed regularization function led to a better reproduction of point source sound fields compared to existing regularization functions for NFC-HOA. Measurements in realistic playback environments showed that, for very close sources, significant ILDs for frequencies above about 250 Hz can be reproduced with NFC-HOA and the proposed regularization function whereas the existing regularization functions failed to provide ILDs below 500 Hz. A listening test showed that these lower-frequency ILDs provided by the proposed regularization function lead to a significantly improved distance perception performance. This test also showed that the distance of virtual sources are perceived less accurately than corresponding physical sources when amplitude cues are not available.