23.4. The equivalent electrical circuit of the simulated glottis

The pressure relations presented in eq. (33) allow the formulate an equivalent electric circuit of the glottis, assuming continuous glottal flow Ug. The circuit is shown in Fig. 41.

Figure 41. The electrical equivalent of the glottis in the two mass model.

The values of the impedance elements are as follows (Ishizaka & Flanagan, 1972:1241):

(34)                                

This enables us to express the glottis impedance of the two mass model:

(35)                                  

Usually, the inductance Lc is neglected (because Lc << (Lg1 + Lg2)).

Almost all parameters of eq.(33) depend on the time and the opening areas Ag1 and Ag2. The changes in these cross-sectional areas are the consequence of the motion of the m1, m2 masses of both folds. The displacement amplitude of the masses is effected by the subglottal pressure Ps, the initial configuration of the folds described by cross-sectional areas Ag01, Ag02 at the rest position, the masses m1, m2 and the airflow velocity Ug. The driving pressure also depends on the supraglottal pressures. Thus, the effect of the glottis-vocal tract interaction has to be modelled. In order to achieve this, it is necessary to model the vocal tract.