Influence of the Lip Horn on Acoustic Pressure Distribution Pattern of Sibilant /s/

Influence of the lip horn on the acoustic pressure distribution of the sibilant /s/ was experimentally studied using a vocal tract replica to which a rectangular baffle was added to represent a human face. The sound was generated by a sweep sound source (Frequency: 2–15 kHz) positioned at the inlet of the pharynx or by air flowing through the replica. The sound generated by the sweep source was measured along two semi-circles of radius 4 cm every 2° (near-field) and radius 48 cm every 15° (far-field), where as the sound generated by the flow was measured along semi-circles of radius 10 cm every 2°. From the normalized pressure distributions, it was observed that the lip horn enhances the pressure amplitude up to 15 dB at the center of the lips in both transverse and sagittal plane in the frequency range above 5 kHz. The pressure distribution patterns measured with the acoustic source were similar to those measured with the flow supply. This indicates that the pressure pattern of sibilant /s/ is affected by the vocal tract geometry rather than by the source characteristics.