Empirical measurements of vocal fold viscoelasticity at relatively high frequencies

Abstract

Viscoelastic shear properties of human vocal fold tissues have been quantified in details in a series of previous experiments [see, e.g., Chan and Titze, J. Acoust. Soc. Am. 106, 2008–2021 (1999)]. However, due to mechanical limitations of the rheometer used for empirical viscoelastic measurements, data have only been obtained at a relatively low frequency (up to 15 Hz). These low-frequency data are an order of magnitude below the physiological frequency range of phonation (on the order of 100–1000 Hz), requiring data extrapolation based on various theoretical approaches. The only truly valid approach, however, is direct empirical measurement of viscoelastic data at high enough frequency. Using a controlled strain rotational rheometer free of the inertial problems present in controlled stress rheometers, this paper reports preliminary measurements of dynamic shear data made at relatively high frequencies (up to 80 Hz), close to the frequency range of phonation in male speech.