Effects of the Epilarynx Area on Vocal Fold Dynamics and the Primary Voice Signal

For the analysis of vocal fold dynamics, sub- and supraglottal influences must be taken into account, as recent studies have shown. In this work, we analyze the influence of changes in the epilaryngeal area on vocal fold dynamics. We investigate two excised female larynges in a hemilarynx setup combined with a synthetic vocal tract consisting of hard plastic and simulating the vowel /a/. Eigenmodes, amplitudes, and velocities of the oscillations, the subglottal pressures (Psub), and sound pressure levels (SPLs) of the generated signal are investigated as a function of three distinctive epilaryngeal areas (28.4آ mm2, 71.0آ mm2, and 205.9آ mm2). The results showed that the SPL is independent of the epilarynx cross section and exhibits a nonlinear relation to the insufflated airflow. The Psub decreased with an increase in the epilaryngeal area and displayed linear relations to the airflow. The principal eigenfunctions (EEFs) from the vocal fold dynamics exhibited lateral movement for the first EEF and rotational motion for the second EEF. In total, the first two EEFs covered a minimum of 60% of the energy, with an average of more than 50% for the first EEF. Correlations to the epilarynx areas were not found. Maximal values for amplitudes (up to 2.5آ mm) and velocities (up to 1.57آ mm/ms) changed with varying epilaryngeal area but did not show consistent behavior for both larynges. We conclude that the size of the epilaryngeal area has significant influence on vocal fold dynamics but does not significantly affect the resultant SPL.