The effect of hair on auditory localization cues

Abstract

Previous empirical and analytical investigations into human sound localization have illustrated that the head-related transfer function (HRTF) and interaural cues are affected by the acoustic material properties of the head. This study utilizes a recent analytical treatment of the sphere scattering problem (which accounts for a hemispherically divided surface boundary) to investigate the contribution of hair to the auditory cues below 5 kHz. The hair is modeled using a locally reactive equivalent impedance parameter, and cue changes are discussed for several cases of measured hair impedance. The hair is shown to produce asymmetric perturbations to the HRTF and the interaural time and level differences. The changes in the azimuth plane are explicated via analytical examination of the surface pressure variations with source angle. Experimental HRTFs obtained using a sphere with and without a hemispherical covering of synthetic hair show a good agreement with analytical results. Additional experimental and analytical investigations illustrate that the relative contribution of the hair remains robust, regardless of the placement of the pinnas, or inclusion of a cylindrical neck.

Acoustic Impulse Responses for Wearable Audio Devices

“…In many wearable-audio applications, microphones might be worn in, on, or under clothing. In the HRTF literature, it has been shown that hair, eyeglasses, and hats have small but measurable effects on acoustic transfer functions to the ear [25][26][27] but do not significantly affect human localization performance [26,28]. The strongest effects are from curly hairstyles that cover the pinna and wide-brimmed hats that reflect sounds from below into the ear and sounds from above away from the ear [26].…”

Auditory Spatial Perception: Auditory Localization

“…Even the presence (or lack) of hair and hair arrangement may affect monaural cues (Treeby et al, 2007). All these physical effects result in spectral changes in the sounds arriving at the ears and are, therefore, often referred to as monaural spectral cues.…”

An Overview of the Major Phenomena of the Localization of Sound Sources by Normal-Hearing, Hearing-Impaired, and Aided Listeners

“…Woodworth’s formula rθ + r sinθ accounts very well for measurements of the ITDs of clicks from loudspeakers ( Feddersen, Sandel, Teas, & Jeffress, 1957 ) and of high-frequency pure tones, but it fails for low-frequency pure tones ( Kuhn, 1977 ), in that the measured ITDs are larger than the formula predicts by a few hundred microseconds ( Aaronson & Hartmann, 2014 ). Empirical observations also show that the presence of the torso and any clothing on the subject can affect the values of ITD ( Kuhn, 1977 ; Treeby, Pan, & Paurobally, 2007 ). These effects are relatively small though, generally no more than a hundred microseconds, and so, given its simplicity, Woodworth’s formula is commonly used to convert azimuths to ITDs and vice versa in experimental work.…”