On the Alignment of Acoustic and Coupled Mechanic-Acoustic Eigenmodes in Phonation by Supraglottal Duct Variations

Abstract

Sound generation in human phonation and the underlying fluid–structure–acoustic interaction that describes the sound production mechanism are not fully understood. A previous experimental study, with a silicone made vocal fold model connected to a straight vocal tract pipe of fixed length, showed that vibroacoustic coupling can cause a deviation in the vocal fold vibration frequency. This occurred when the fundamental frequency of the vocal fold motion was close to the lowest acoustic resonance frequency of the pipe. What is not fully understood is how the vibroacoustic coupling is influenced by a varying vocal tract length. Presuming that this effect is a pure coupling of the acoustical effects, a numerical simulation model is established based on the computation of the mechanical-acoustic eigenvalue. With varying pipe lengths, the lowest acoustic resonance frequency was adjusted in the experiments and so in the simulation setup. In doing so, the evolution of the vocal folds’ coupled eigenvalues and eigenmodes is investigated, which confirms the experimental findings. Finally, it was shown that for normal phonation conditions, the mechanical mode is the most efficient vibration pattern whenever the acoustic resonance of the pipe (lowest formant) is far away from the vocal folds’ vibration frequency. Whenever the lowest formant is slightly lower than the mechanical vocal fold eigenfrequency, the coupled vocal fold motion pattern at the formant frequency dominates.

Restraining vocal fold vertical motion reduces source-filter interaction in a two-mass model

“…In normal phonation, the vocal folds generally vibrate in an aerodynamically driven mode, in which vocal fold vibration is sustained by a near field interaction between the vocal folds and glottal airflow. However, vocal fold vibration may also be influenced by sub- and supra-glottal acoustic resonances ( Ishizaka and Flanagan, 1972 ; Rothenberg, 1981 ; Fant, 1982 ; Zhang et al , 2006a , b ; Zañartu et al , 2007 ; Titze, 2008 ; Lucero et al , 2012 ; Kraxberger et al , 2023 ; Zhang, 2023 ). This is particularly the case when the fundamental frequency F 0 approaches the first resonance of either the subglottal or supraglottal tract.…”

Sound generation mechanisms in a collapsible tube

“…The current computational power allows to study cardiovascular (Itatani et al, 2022) and respiratory (Lasota et al, 2023;Schoder et al, 2020) diseases in both patientspecific (Kraxberger et al, 2023;Mylavarapu et al, 2013) and idealized geometries (Li et al, 2023;Shabbir et al, 2023). One remarkable example of an idealized geometry model of a human vessel is a collapsible tube.…”