A physical model of sound diffraction and reflections in the human concha.

An approximated physical model of the frequency transfer function of the human concha is developed in this paper. This formulation includes diffraction, reflection, and interference phenomena in the concha cavity. The performance of the proposed diffraction/ reflection model is compared with that of the single-delay-and-add approximation by checking their predictions against the experimental transfer function of a metal spiral-shaped diffracting/reflecting system. Results show that the diffraction/reflection model performs considerably better at predicting both the absolute center frequency of spectral minima and the relative frequency spacing between them. The diffraction/reflection model is then applied to a realistic concha shape and its predictions are compared with experimental head-related transfer functions for azimuth- and elevation-varying sound sources. In this case, the model predicts the elevation-dependent spectral features related to the transverse dimensions of the concha. Additionally, the diffraction/reflection model predicts that, because of sound diffraction, similar spectral features must be generated in the concha for sources at all azimuths within the frontal part of the ipsilateral hemisphere. Experimental and theoretical evidence supporting this prediction is presented.