Effects of the Position of Tongue on the Sound Generation of Sibilant/S/

Abstract

The sibilant /s/ is one of the fricative sounds produced by raising the tongue against the frontal palate of the mouth to form a constriction of the airflow. Thus, the movement of the tongue plays important roles in the sound generation of sibilant /s/. In this study, we investigated the effect of the tongue positions on the airflow and generation of the sibilant /s/ using an in vitro vocal tract model implementing a movable tongue. A replica model of vocal tract was produced by a 3D printer from the CT images of a subject who pronounced sibilant /s/. Steady airflow was given to the vocal tract model by compressor and the sound generated was measured with a microphone. The time variations of airflow velocity in the vocal tract were also measured with a hot wire anemometer. Our results showed that the power spectrum density of the sound generated by the vocal tract model quantitatively agreed with that of the sibilant /s/ from the subject by adjusting the position of the tongue. The flow measurements revealed that the flow fluctuation increased in the vicinity of the incisors rather than the constriction where the flow velocity was the highest. We found that the sound source of sibilant /s/ was produced by turbulence enhanced by the impingement of the airstream emerging from the constriction on the downstream incisors.