Notes on glottal flow and acoustic inertial effects

Abstract

This text is a compilation of some of the notes that the author has written during the development of the low-order model "DICO" [2, 8, 10, 11] for vowel phonation and the even more rudimentary glottal flow model [9] for processing high-speed glottal video data. The following subject matters are covered: (i) Incompressible, laminar, lossless flow models for idealised rectangular and wedge shape vocal fold geometries. Equations of motion and the pressure distribution are computed in a closed form for each model using the unsteady Bernoulli's theorem; (ii) The assumption of incompressibility and energy loss (i.e., irrecoverable pressure drop) of the airflow in airways (including the glottis) is discussed using steady compressible Bernoulli theorem as the main tool; (iii) Inertia of an uniform waveguide is studied in terms of the low-frequency limit of the the (acoustic) impedance transfer function. It is observed that the inductive loading in the boundary condition sums up with the waveguide inertance in an expected way; (iv) It is shown that an acoustic waveguide, modelled by Webster's lossless equation with Dirichlet boundary condition at the far end, will produce the expected mass inertance of the fluid column as the low-frequency limit of the impedance transfer function.