Effect of tongue position in the simplified vocal tract model of sibilant fricatives /s/ and /ʃ/

Abstract

In this study, a simplified vocal tract model which reproduces both sibilant fricatives /s/ and /ʃ/ is proposed to investigate the effect of tongue position on flow and sound generation in the vocal tract. The simplified model consists of a tongue with sibilant groove and upper and lower teeth in a rectangular channel. Dimensions of the model were determined based on CT images of the subject pronouncing sibilant /s/. The sound and flow fluctuation generated by the model were measured with a microphone and a hot-wire anemometer, respectively. In addition, the large-eddy simulation was conducted to reveal the characteristics of sound source generated by the turbulent flow in the vocal tract. The acoustic measurement showed that the backward shift of the tongue increased the spectral slope value, indicating that the acoustic characteristics were changed from /s/ to /ʃ/. The large-eddy simulation showed that the position of sound source downstream of teeth was shifted backward and the magnitude of the sound source was decreased by shifting the tongue backward. These results indicate that both the resonance characteristics and the position of the sound source were changed by shifting the tongue which causes the difference in acoustic characteristics between /s/ and /ʃ/.