The role of talker sex and physical dimensions in horizontal speech directivity

Human speech directivity plays a role in speech perception, including for speech recognition in multi-talker environments. Individual variability in speech directivity patterns arises in part because of differences in physical attributes across talkers. Here, individual variability in horizontal speech directivity using anechoic, multi-channel, high-fidelity recordings of the Bamford-Kowal-Bench sentences produced by 15 female and 15 male talkers were examined. The frequency-dependent directivity index (DI) for each talker was calculated and the effects of frequency, sex, and body mass index (BMI) on directivity indices were tested. Minimum radiation toward 0° and maximum radiation toward 90° occurred at 700-850 Hz, resulting in an increase in spectral level at 90° compared to 0° for this frequency range. There was some evidence for sex differences in directivity at a limited set of frequencies (1 and 6-7 kHz). BMI predicted the minimum DI magnitude and frequency locus of the minimum directionality at 0°, where higher BMI is associated with a higher frequency locus. These findings highlight how individual physical characteristics shape speech radiation patterns, which could influence the availability of head orientation and level cues for target talker segregation and, thus, may have implications for speech perception in multi-talker environments.