Abstract

The vocal folds are essential for speech production, and a better understanding of vocal fold vibration characteristics may help improve treatments of voice disorders. However, studying real vocal folds presents significant challenges. In-vivo studies are limited by access and safety issues. Excised larynges have a short useable lifetime (on the order of minutes) and are difficult to parameterize. In contrast, synthetic vocal fold models have long useable lifetimes and can be easily parameterized. In this thesis, a series of tests performed on recently developed synthetic, self-oscillating models of the human vocal folds are discussed. These tests include measurements of vibration frequency, sub-glottal pressure, and time-averaged flow rate. The differences between one-layer and two-layer synthetic models are evaluated. Comparisons are made between synthetic model and real vocal fold behavior. The synthetic model is shown to have vibrated at frequencies, pressures, and flow rates consistent with human phonation. The influence of sub-glottal tube length on model vibration frequency is examined. Motion is observed using high-speed imaging. Velocity measurements of the glottal jet using particle image velocitmetry (PIV) were performed with and without an idealized vocal tract, including the effects of the false folds, for various cases of vocal tract asymmetry. Glottal jet velocities measured using PIV were consistent with velocities measured using excised larynges. A starting vortex was observed in all test cases. The presence of the false folds acted to restrain the sides of the starting vortex, and in some cases created new vortical structures shed from the false folds. An algorithm was created to calculate and visualize the jet core centerline. In the vocal tract cases, the glottal jet tended to skew toward the nearest wall; in the false fold cases, the opposite trend was observed as the jet skewed away from the nearest wall (towards the midplane). Plots of RMS velocity showed distinct regions of shear layer and jet core. Vocal tract cases at pressures much greater than phonation onset pressure showed significant increases in RMS velocities compared to open jet and false fold cases.

Degree

MS

College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering

Rights

http://lib.byu.edu/about/copyright/

Date Submitted

2008-03-21

Document Type

Thesis

Handle

http://hdl.lib.byu.edu/1877/etd2339

Keywords

PIV, synthetic model, vocal folds, false folds, glottal jet

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