Numerical analysis of the acoustic role of vocal tract in the horseshoe bat

The sound field distribution and effects for sound pressure in vocal tract of the horseshoe bat, Rhinolophus ferrumequinum, have been obtained using FEM technique. The models of vocal tracts used for FEM calculation are constructed by tomography scanning. These models are used to set up finite element model for calculating the sound field distribution by loading the unit sound source in glottis. By change the frequency of the unit sound source the frequency response was figured out and the acoustic role of vocal tract chambers was examined by obtaining the transfer function and sound pressure distribution before and after filling the chambers using voxels. Sound pressures in the trachea and nostrils are recorded and some analysis of the acoustics of subglottal and vocal tract was made to find the function of the construction in vocal tract and subglottal parts. The results show nasal chambers can effectively improve the Q (quality factor) value near the second harmonic, and alternate the sound distribution in the supraglottal part. whereas the tracheal chambers can reduce the amplitude of the sound pressure in the subglottal part, their function is like a band block filter which can block the second harmonic component of the back propagation sound under the glottis.