Abstract:

Since the work of D. W. Warren and A. B. Dubois [Cleft Palate J. 1, 52--71 (1964)] was published, the ``pressure-flow technique'' has been widely used to estimate constriction areas within the vocal tract. However, two fundamental questions regarding this technique have not been clearly addressed: (1) What is exactly measured (minimum, maximum, or ``mean'' areas)? (2) Which accuracy can be expected from this technique? A theoretical and experimental study based on a vocal tract mechanical model, including various constriction shapes, is presented. Compared with much more complex viscous flow solutions, a simple one-dimensional flow model is shown to yield fair estimates of the areas (within 10%), except for low Reynolds numbers. The empirical head-loss factor K=0.67, sometimes used, appears meaningless and is probably due to an experimental artefact. The pressure-flow technique is shown to be relatively insensitive to the exact constriction shape (converging, straight, or diverging), and the estimated area to be close to the minimum area of the constriction. This result can be theoretically rationalized by considering that in all cases studied here the flow separation point is always close to the minimum constriction. Extensions and limits of these conclusions for unsteady flows will also be discussed.