Figure 4.

Frequency (top) and growth rate (bottom) of the first four modes of the coupled system as a function of the subglottal pressure, for vocal folds with a straight glottis (left column) and a convergent glottis (right column). The vertical line indicates the point of onset. T=0.3, g₀=0.01, σ=0.4, and other parameters are given by Eq. 16. Equation 2 was solved with the first ten modes included. Interaction between the first three modes helped to lower the phonation threshold pressure in the straight-glottis case.