Measurement and calculation of individual head-related transfer functions using a boundary element model including the measurement and effect of skin and hair impedance

This research investigates various aspects of the Head-Related Transfer Function (HRTF), which is a description of the acoustic frequency filtering performed by the geometry of the head as a function of incident angle. The effects of this filtering are used in the brain to determine the location of sound sources in space. Initially, various methods for measuring the HRTF are examined, as well as several means of normalizing or equalizing the data. One method is chosen which best represents the informational content of the measured data for comparisons between experimental methods. The question as to whether the acoustic properties of skin and hair contribute to the HRTF is also examined. Measurements are made of the acoustic absorption and impedance of various skin and hair samples using a plane wave tube and two microphones. The limitations of this technique and published standards are also included. Finally, an individual HRTF is calculated using an optically generated surface mesh and a numerical boundary element (BEM) solution. The results of the impedance measurements are included in the calculations. Final analysis consists of comparing the various calculated HRTFs and measured HRTFs. Geometric variations in the head mesh such as removal of the pinna are also included. Good agreement is found given the assumptions made in the generation of the computational model (i.e. lack of torso) throughout the frequency range of the model, which extends from 1-6 kHz. Computational speed and size of the numerical problem limit the work to this region.