Physical acoustics and measurements pertaining to directional hearing
George F. Kuhn · The Journal of the Acoustical Society of America · 1983
The physical mechanisms of acoustic wave diffraction and scattering by the head and torso, as well as the resonances excited in the external ear produce interaural time differences, interaural pressure level differences, and direction-dependent pressure spectra at the eardrum. The frequency dispersion of the diffracted wave causes the phase-derived and envelope-derived interaural time differences to be frequency dependent and to differ from each other. However, at high frequencies these time differences converge to one common value which equals the delay of the leading edge of a pulse. Interaural pressure level differences at high frequencies result primarily from the frequency-dependent attenuation of the waves diffracted into the shadow region of the head and from the directivity of the pinna. Spectral localization cues which are usually associated with the localization in the vertical, median plane result from the interference of the wave scattered by the torso and the direct wave to the external ear, at low frequencies; transverse wave motion in the pinna appears to produce the direction-dependent high-frequency pressure spectra at the eardrum. Mathematical models which describe the wave motion about the head and in the external ear will be described and compared to physical measurements. Potential effects on the localization cues for aided listeners and associated difficulties of these acoustical measurements with real microphones in the external ear will also be discussed. [Portions of this work were supported by the National Science Foundation.]