An in vitro setup to test the relevance and the accuracy of low-order vocal folds models

Abstract

An experimental setup and human vocal folds replica able to produce self-sustained oscillations are presented. The aim of the setup is to assess the relevance and the accuracy of theoretical vocal folds models. The applied reduced mechanical models are a variation of the classical two-mass model, and a simplification inspired on the delayed mass model for which the coupling between the masses is expressed as a fixed time delay. The airflow is described as a laminar flow with flow separation. The influence of a downstream resonator is taken into account. The oscillation pressure threshold and fundamental frequency are predicted by applying a stability analysis to the mechanical models. The measured frequency response of the mechanical replica together with the initial (rest) area allows us to determine the model parameters (spring stiffness, damping, geometry, masses). Validation of theoretical model predictions to experimental data shows the relevance of low-order models in gaining a qualitative understanding of phonation. However, quantitative discrepancies remain large due to an inaccurate estimation of the model parameters and the crudeness in either flow or mechanical model description. As an illustration it is shown that significant improvements can be made by accounting for viscous flow effects.

Mechanical response measurements of real and artificial brass players lips

“…14 This technique has been described previously 7 and has been widely used for experiments with musical valves. 10,15 An expanded laser beam was directed through the opening between a pair of artificial lips. The beam was then focused on to a photosensitive diode.…”

“…4,8,9 The results here could support such a motion, but could also be described by a simple two mass transverse model such as that frequently used for the human vocal folds. 10,11 The coupled nature of the resonances means that it is difficult to relate particular resonances to specific degrees of freedom.…”

“…10,11 Experiments using artificial lips 12 in combination with computational modeling have shown that an "outward-inward striking" resonance pair, in the terminology of classical reed physics, 1 can provide the necessary flexibility. The terms outward striking and inward striking here refer to the manner in which the aperture of a musical reed is expected to respond to a steady increase in supply pressure.…”

Vocal tract resonances in speech, singing, and playing musical instruments

“…Hardware (in vitro) models have the advantage that the properties may be measured in considerable detail (Titze et al, 1995;Kob, 2002;Ruty et al, 2007), but the disadvantage that we do not know how well the behavior of their valves resembles that of living, controlled, vocal folds.…”

Amplitude and frequency modulation control of sound production in a mechanical model of the avian syrinx

“…Ellington et al, 1996;Sane and Dickinson, 2002), human speech production (e.g. Ruty et al, 2007;Tack et al, 2006;Van Hirtum et al, 2007) and vocal fold prosthetics design (Tack et al, 2006;de Vries et al, 2000). The first mechanical model of the syrinx to our knowledge was developed by Dürrwang (Dürrwang, 1974), who used it to illustrate the concept of Bernoulli's principle during sound production by flow-induced oscillating structures and to study resonance properties of the trachea.…”