Measurement of the glottal impedance with a mechanical model

An approximate but realistic model of the human larynx was constructed to gain better knowledge of the complex glottal impedance and its dependence on glottal width, flow, and frequency. The glottal width was adjustable from 0 to 3 mm, the flow from 0 to 500 cm3/s. The model was fitted into a system of tubes, through which compressed air could be conducted. Supraglottally, a broadband signal was fed into the tube, and, with a two-microphone directional coupler, the complex glottal impedance at a given reference plane was directly determined as a function of frequency. Since the calculated impedance is sensitively dependent on the definition of the position of the reference plane, it is difficult to obtain quantitative statements about the frequency dependence. Nevertheless, in the presence of flow, it is possible to achieve reliable results by analysis of the relative position of the measured curves. On the one hand, the glottal inductance decreases linearly with increasing flow velocity; on the other hand, it diminishes nonlinearly with decreasing frequency. Finally, some difficulties in the definition of glottal impedance are pointed out.