Davies, P.O.A.L., Barney, A. and Shadle, C.H.
Aeroacoustic Sources in a Vocal Tract Model.
Proc. 15th Int. Cong. on Acoustics
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Predictive models of phonation appropriate for inclusion in articulatory synthesis include a relatively slowly time varying part, or acoustic filter, this is acoustically excited by a relatively rapidly time varying source. An investigation of the characteristic aeroacoustic sources associated with the voicing of open vowels was carried out on a simplified dynamic mechanical model with leading dimensions corresponding to those of an adult male. This consisted of a cylindrical tube open at one end and supplied at the other with a metered flow modulated by opening and closing of a pair of electromechanically driven shutters. The flow distribution measured with calibrated hot wires provided clear evidence of periodic vortical flow synchronised with the shuttered motion that travelled from its origin near the shutters to the open end, convecting at the mean flow speed. A similar flow structure has been observed in subjects voicing open vowels. Simultaneous calibrated pairs of wall pressure time histories defined the associated pressure field throughout the tract. Established techniques were then adopted to process the measurements and estimate the strength of the aeroacoustic sources associated with the potential (acoustic) and the rotational components of the flow in the tract and thus predict the sound radiated from the open end. The results were generally in close agreement with the corresponding free field measurements of the radiated sound spectrum at three representative mean flow speeds.
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