On the meaning and accuracy of the pressure–flow technique to determine constriction areas within the vocal tract

Abstract

Since Warren and DuBois (D.W. Warren, A.B. DuBois, Cleft Palate Journal 1 (1964) 52–71), the “Pressure–Flow technique” has been widely used to estimate constriction areas within the vocal tract. In this paper, three fundamental questions regarding this technique are addressed: (1) What exactly is measured (minimum, maximum or “mean” areas)? (2) What degree of accuracy can be expected from this technique? (3) To what extent can this method be applied to unsteady flow conditions? A theoretical and experimental study based on a mechanical vocal tract model, including various constriction shapes, is presented. The pressure–flow technique is shown to be relatively insensitive to the exact constriction shape (circular, uniform or diverging), and the estimated area to be close to the minimum area of the constriction. This result can be theoretically rationalised by considering that in all cases studied here, the flow separation point is always close to the minimum constriction. Compared with much more complex viscous flow solutions, a simple one-dimensional flow model is shown to yield fair estimates of the areas (within 20%), except for low Reynolds numbers flows. The empirical head-loss factor, or flow coefficient, k=0.65, sometimes used, appears to be disputable and is probably due to an experimental artefact. Lastly these results are extended to the case of unsteady flow.