210 



BELL SYSTEM TECHNICAL JOURNAL 



The above material is a description of a simple model of two degrees 

 of freedom which simulates the principal characteristics from the 

 standpoint of performance of the more complex larynx which has 

 many degrees of freedom. It is this idealized model which will be 

 considered in the subsequent treatment. Such points of performance 

 of the actual larynx which may be due to the action of ignored and 



Fig. 2 — Schematic Larynx Model. 



presumably subsidiary modes of motion will, of course, not be pre- 

 dicted by the theory. These are assumed to be of minor importance. 

 The possible independence of motion of the two vocal cords will be 

 considered later, however. 



The contraction of the air stream at the glottis introduces a rela- 

 tively large concentrated kinetic energy in the air stream at this point 

 similar to that at the mouth of a Helmholtz resonator. The inertia 

 of a small plug of air between the vocal cords may then to a first 

 approximation be treated as a mass L\. A concentration of frictional 

 resistance also occurs at this point due to viscosity and to turbulence. 

 A positive displacement q-z (outward) of the vocal cords causes an 

 increase in the mass of the plug of air in the glottis and a change in 

 the effective resistance, R, encountered by it. The inertia Z-/ and 

 resistance R of the glottis are therefore both functions of q-i, the dis- 

 placement of the vocal cords from a mean position, and of the width 

 of the glottis. If further Q^ represent the average displacement of 



