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Characteristics of a pulsating jet through a small modulated orifice, with application to voice production.

A detailed understanding of the aerodynamics of air flow in the larynx and the vocal tract is needed to refine physiological models of human voice production. This understanding can be applied in speech synthesis, voice diagnostics, and voice recognition. To date, most aeroacoustic models of phonation have been based on Bernoulli's orifice theory, i.e., the assumption that flow phenomena within the larynx are "quasi-steady." This assumption, however, has never been rigorously verified experimentally. In this study, detailed aerodynamic measurements were performed of a pulsating open jet through a modulated orifice with a time-varying area. Orifice geometry and characteristic Reynolds numbers and Strouhal numbers of the pulsating jet flow were representative of speech production. Simple source-filter models based on the quasi-steady flow assumption and an ideal one-dimensional monopole source model were found to yield satisfactory velocity, flow rate, and dynamic pressure predictions for most of the duty cycle. Significant deviations from quasi-steady behavior were observed only during the early part of the duty cycle, where the flow velocity in the center core rapidly reached a peak value immediately after release of the false folds. This acoustic near-field phenomenon did not affect the pressure waves generated by the pulsating jet through the orifice, propagated in the long rigid tube upstream of the orifice. The impact on this phenomenon on actual sound generation within the larynx, and wall pressures on the vocal folds, is not clear.