"By treating the vocal tract as a series of cylindrical sections, or acoustic lines, it is possible to use transmission line theory" ... to find the resonances of the tract. The schematic circuit of such a model is shown below.
Schematic circuit of Dunn's electrical vocal tract
Dunn said of his model
"The use of transmission line theory in calculating vowel resonances has led naturally to the setting up of a transmission line vocal tract model in the laboratory. A line with distributed constants is approximated through the use of 25 lumped sections, each representing a cylinder 0.5 cm long and 6 cm**2 in cross section. The whole is then divided into two 'cavities' by the use of a lumped, but variable, inductance which can be inserted between any two sections of the line. This represents the 'tongue hump' constriction. Another variable inductance at the end of the line represents the constriction at the lips. A high impedance complex-wave generator is applied to the input."
"A photograph of the EVT is shown above. The coils and condensers of the line are mounted in the rear. The panel in the center carries the tongue hump inductance and a control for its magnitude. Its position in the tract is changed by sliding the whole panel back and forth. A fixed panel at the right carries a control for the magnitude of the lip constriction. Either cavity can be shortened by cutting out sections at the ends, by means of the sliders at the upper corners."
"The whole series of English vowels can be produced by this apparatus -- not perfectly, but distinctly better than we were able to make with three independent tuned circuits without suppression between and above the resonances. A series of spectrograms of vowels made by the EVT is reproduced below."
H. K. Dunn, "The calculation of vowel resonances, and an electrical
vocal tract",
Journal of the Acoustical Society of America, 1950, vol. 22, p. 740-753.
