A Hybrid Method for Acoustic Analysis of the Vocal Tract During Vowel Production

A hybrid method for vocal-tract acoustic simulation is proposed to handle the complex and moving geometries during speech production by combining the finite-difference time-domain (FDTD) method and the immersed boundary method (IBM). In this method, two distinct discrete point systems are employed for discretization. The fluid field is discretized by regular Eulerian grid points, while the wall boundary is represented by a series of Lagrangian points. A direct body force is calculated on the Lagrangian points and then interpolated to the neighboring Eulerian points. To validate the proposed hybrid method, a 2D vocal tract model was set by extracting area function from MRI data obtained for the Mandarin vowel /a/. By simulating acoustic wave in this model, the synthesized vowel was analyzed and the obtained formant frequencies were compared to those of real speech sounds. It is found that the mean absolute error of formant frequencies was 8.17% and better than the result in Literature. To show the ability of the hybrid method for solving acoustic problems with moving geometry, a pseudo moving boundary problem was designed and the results agree well with the acoustic theory.