Aero-acoustics of silicone rubber lip reeds for alternative voice production in laryngectomees.
To improve voice quality after laryngectomy, a small pneumatic sound source to be incorporated in a regular tracheoesophageal shunt valve was designed. This artificial voice source consists of a single floppy lip reed, which performs self-sustaining flutter-type oscillations driven by the expired pulmonary air that flows through the tracheoesophageal shunt valve along the outward-striking lip reed. In this in vitro study, aero-acoustic data and detailed high-speed digital image sequences of lip reed behavior are obtained for 10 lip configurations. The high-speed visualizations provide a more explicit understanding and reveal details of lip reed behavior, such as the onset of vibration, beating of the lip against the walls of its housing, and chaotic behavior at high volume flow. We discuss several aspects of lip reed behavior in general and implications for its application as an artificial voice source. For pressures above the sounding threshold, volume flow, fundamental frequency and sound pressure level generated by the floppy lip reed are almost linear functions of the driving force, static pressure difference across the lip. Observed irregularities in these relations are mainly caused by transitions from one type of beating behavior of the lip against the walls of its housing to another. This beating explains the wide range and the driving force dependence of fundamental frequency, and seems to have a strong effect on the spectral content. The thickness of the lip base is linearly related to the fundamental frequency of lip reed oscillation.