Subglottal pressure oscillations in anechoic and resonant conditions and their influence on excised larynx phonations

Abstract

Excised larynges serve as natural models for studying behavior of the voice source. Acoustic resonances inside the air-supplying tubes below the larynx (i.e., subglottal space), however, interact with the vibratory behavior of the larynges and obscure their inherent vibration properties. Here, we explore a newly designed anechoic subglottal space which allows removing its acoustic resonances. We performed excised larynx experiments using both anechoic and resonant subglottal spaces in order to analyze and compare, for the very first time, the corresponding subglottal pressures, electroglottographic and radiated acoustic waveforms. In contrast to the resonant conditions, the anechoic subglottal pressure waveforms showed negligible oscillations during the vocal fold contact phase, as expected. When inverted, these waveforms closely matched the inverse filtered radiated sound waveforms. Subglottal resonances modified also the radiated sound pressures (Level 1 interactions). Furthermore, they changed the fundamental frequency (fo) of the vocal fold oscillations and offset phonation threshold pressures (Level 2 interactions), even for subglottal resonance frequencies 4–10 times higher than fo. The obtained data offer the basis for better understanding the inherent vibratory properties of the vocal folds, for studying the impact of structure-acoustic interactions on voice, and for validation of computational models of voice production.

Flow-induced oscillations of vocal-fold replicas with tuned extensibility and material properties

“…It increased slightly with increasing pre-strain. Subglottal pressure for hydrogel and sound pressure level for all materials are comparable with previous research based on artificial vocal folds 11 as well as excised larynges 2 , 92 , 95 , 97 .…”

“…The first resonance frequency of the subglottal tract in our experiment was estimated around 14 Hz (the open-closed tube between the settling chamber and the vocal folds being 6.2 m long). Hence, harmonics of subglottal tract resonances might appear in the range of the present study, and possible interactions are not totally excluded 97 . However, their influence would certainly be minimal given the high length of the subglottal tract.…”

“…One can note that this low frequency range is found in laryngeal mechanism M0 or vocal fry 93 , 94 for which the folds are very thick and passive, with limited contraction of thyro-arytenoid muscles. To better understand such global low-pitch measurements on the replicas, we first investigated possible acoustic coupling with the subglottal tract, likely to drive the vibration frequency of artificial vocal folds in some cases 17 , 96 , 97 . The first resonance frequency of the subglottal tract in our experiment was estimated around 14 Hz (the open-closed tube between the settling chamber and the vocal folds being 6.2 m long).…”