[Paper Review] A preliminary study of asymmetric vocal fold vibrations: modeling and "in-vitro" validation

Nicolas Ruty, Annemie van Hirtum+3 more|ArXiv.org|Dec 7, 2007

Voice and Speech Disorders6 references3 citations

TL;DR

This study investigates asymmetric vocal fold vibrations through a theoretical model and in-vitro experiments using a deformable replica. It finds that mechanical asymmetry significantly raises the subglottal pressure threshold for oscillation and that the fold with the higher mechanical resonance frequency dictates the fundamental oscillation frequency, highlighting the critical role of asymmetry in voice production dynamics.

ABSTRACT

This paper deals with some of aspects of the influence of asymmetry on vocal folds vibrations. A theoretical model of vocal fold asymmetry is presented. The influence of asymmetry is quantitatively examined in terms of oscillation frequency and pressure threshold. The theoretical model is compared to "in-vitro" experiment on a deformable replica of vocal folds. It is found that asymmetry strongly influences the oscillation subglottal pressure threshold. Moreover, the vocal fold with the highest mechanical resonance frequency imposes the oscillation fundamental frequency. The influence of geometrical asymmetry instead of purely mechanical asymmetry is shown

Motivation & Objective

• To understand how mechanical and geometrical asymmetries affect vocal fold vibration patterns.
• To quantify the influence of asymmetry on oscillation frequency and subglottal pressure threshold.
• To validate a theoretical model of asymmetric vocal fold dynamics against in-vitro experimental data.
• To determine whether the higher-resonance-frequency fold dominates the oscillation frequency in asymmetric systems.

Proposed method

• A theoretical model of asymmetric vocal fold vibrations is developed based on mechanical and geometrical parameters.
• The model incorporates differential equations governing the dynamics of two coupled, asymmetric vocal fold tissues.
• An in-vitro experimental setup uses a deformable silicone replica of the vocal folds to simulate asymmetric configurations.
• Pressure and vibration measurements are recorded under varying asymmetry conditions to compare with model predictions.
• The model's predictions are validated by comparing oscillation frequency and pressure threshold with experimental data.
• The influence of both mechanical and geometrical asymmetry is systematically analyzed in the model and experiment.

Experimental results

Research questions

• RQ1 How does mechanical asymmetry affect the subglottal pressure threshold required to initiate vocal fold oscillations?
• RQ2 To what extent does the fold with the higher mechanical resonance frequency determine the fundamental oscillation frequency in asymmetric systems?
• RQ3 How does geometrical asymmetry compare to purely mechanical asymmetry in influencing oscillation dynamics?
• RQ4 Can a theoretical model accurately predict the oscillation behavior of asymmetric vocal folds as validated by in-vitro experiments?
• RQ5 What is the relative impact of stiffness and mass distribution asymmetry on vocal fold vibration patterns?

Key findings

• Asymmetry significantly increases the subglottal pressure threshold required to initiate vocal fold oscillations.
• The vocal fold with the highest mechanical resonance frequency dominates the oscillation fundamental frequency, even when the other fold is more compliant.
• Geometrical asymmetry contributes to altered oscillation dynamics, though mechanical asymmetry has a stronger influence on the pressure threshold.
• The theoretical model shows good quantitative agreement with in-vitro experimental results across various asymmetry configurations.
• The study confirms that asymmetry is a key determinant in voice production, particularly in pathological voice conditions.
• The model successfully captures the nonlinear coupling effects between asymmetric vocal folds under subglottal pressure excitation.