Measuring the human head-related transfer functions: A novel method for the construction and calibration of a miniature ‘‘in-ear’’ recording system

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Abstract
A method for the construction of a small ‘‘in‐ear’’ system for recording the human‐free field‐to‐eardrum and headphone‐to‐eardrum transfer functions is described. Customized in‐ear inserts were obtained by a simple ear printing and electroplating method, resulting in a thin (<0.25 mm) outer shell that minimized obstruction of the entrance at the ear canal. The insert can be used to position a microphone probe tube deep within the auditory canal. The effects of this recording system on the sound field in the ear canal were calibrated using a model head equipped with a second internal microphone close to the eardrum. Transfer functions were recorded for 343 different stimulus locations in free space and for a headphone sound source. For the free‐field stimuli the presence of the recording system resulted in a small attenuation with maximum effects around 3.5 and 12.5 kHz (−1.5 and −2.0 dB, respectively). Passing the data through an auditory filter model reduced the averaged attenuation to less than −1.4 dB. Phase was undistorted up to 2.5 kHz. These results suggests that the perturbations produced by the insert are unlikely to be perceptually relevant.

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