The larynx and lower pharynx contain at least three pairs of soft tissues that can in theory be set into flow-induced oscillation and act as sound sources: the true vocal folds, the ventricular (false) folds, and the aryepiglottic folds. The hypothesis was that they can be controlled to produce somewhat independent frequency contours (intonations or melodies). Computer simulation with a simplified Navier-Stokes solution for convective and compressible air movement was used. It was found that true folds, false folds, and aryepiglottic folds can all be dominant with variable adduction if they have similar structure and biomechanical properties. Downstream sources tend to have an advantage because they can benefit from favorable driving pressures associated with an acoustically inertive vocal tract. Strong interaction with neighboring sources tends to result in subharmonic bifurcations and chaotic segments. So far, it has not been demonstrated that simultaneous independent tones can be produced with the current simulations. Entrainment and roughness (distortion) predominate due to strong interaction. Proximity of the sources may prevent independence, even if muscular control would allow it.
Ingo R. Titze (Wed,) studied this question.