The change of fundamental frequency of phonation (F0) per unit change of transglottal pressure (dF/dP) is known to vary depending on F0. In the coordinates with dF/dP as the y-axis and F0 as x-axis, dF/dP-F0 characteristic takes a shape like a letter V. The reason for this non-linear relation, is investigated with the rubber model of the vocal folds. The length and mass of the vibrating portion of this model are designed to vary in order to test the effects of these parameters on the values of dF/dP. The results suggest : 1) The F0-region lower than 200-250 Hz is mainly controlled by the elongation of the vocal folds. 2) The F0-region higher than these frequencies is mainly controlled by the mass-reduction of the vibrating portion. 3) This allotment in F0 control could be responsible for V shaped characteristic between dF /dP and F0. 4) The pathological lesions of the vocal folds alter this allotment.
