An Attempt to Calibrate Headphones for Reproduction of Sound Pressure at the Eardrum

This paper provides an analysis of headphone calibration for reproduction of sound pressure at the eardrums of the listener. If the vibrations of the listener's eardrums are reproduced, the listener would perceive an auditory sensation as if he/she were in the original sound scene. The visual and other sensations also affect sound impressions, but they are not always available, e.g., when the sound sources are out of sight. Moreover, reproduction of stimuli as faithfully as possible on each modality is a reasonable approach to produce a solid impression of the sense of presence. For reproduction of vibrations at the eardrums, calibration functions for individual characteristics of ear-canal transfer functions and eardrum impedance are required because they are generally different from person to person. Sound pressure at the entrance to the ear canal observed with and without headphones, with the ear canal blocked and open, and at the eardrum was investigated through equivalent circuits based on electrical circuit theory, and a new headphone calibration function was derived. The effects of calibration functions were then quantitatively evaluated in experiments using a head and torso simulator (HATS), revealing that sound pressure can be reproduced at the eardrums in a wide frequency range such as 100 Hz to 10 kHz. Relations of the relevant impedance were also investigated.