Microphone array techniques for surround sound recording can be broadly classified into two groups: those that attempt to produce the continuous phantom imaging around 360° in the horizontal plane and those that treat the front and rear channels separately. The equal segment microphone array (ESMA) is a multichannel microphone technique that attempts to capture a sound field in 360° without any overlap between the stereophonic recording angle of each pair of adjacent microphones. This study investigated the optimal microphone spacing for a quadraphonic ESMA using cardioid microphones. Recordings of a speech source were made using the ESMAs with four different microphone spacings of 0 cm, 24 cm, 30 cm, and 50 cm, based on different psychoacoustic models for microphone array design. Multichannel and binaural stimuli were created with the reproduced sound field rotated over 45° intervals. Listening tests were conducted to examine the accuracy of phantom image localization for each microphone spacing, in both loudspeaker and binaural headphone reproductions. The results generally indicated that the 50-cm spacing, which was derived from an interchannel time and level trade-off model that is perceptually optimized for 90° loudspeaker base angle, produced more accurate localization results than the 24-cm and 30-cm ones, which were based on conventional models derived from the standard 60° loudspeaker setup. The 0-cm spacing produced the worst accuracy with the most frequent bimodal distributions of responses between the front and back regions. Findings from this study are expected to be useful for acoustic recording for virtual reality applications as well as for multichannel surround sound.
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