Measurement and compensation of discrepancy in sound source direction perceived through bone-conduction headphones for audible pure tones

Bone conduction (BC) headphones are reportedly more centered in the perceived direction of the sound source than air conduction (AC) headphones [Autumn Mtg Acoust. Soc. Japan, 3-1-18, pp. 865–866, 2013; IEEE Int’l Conf. GCCE, pp. 887–888, 2021], thereby undermining the advantages of BC headphones as hearing aids. However, the prior reports were limited to pure tones between 500 and 4,000 Hz. In the present study, we newly report the directional differences in sound stimulation by BC headphones over a wide frequency range of 125–16 000 Hz and propose a compensation method that emphasizes ILD. In the listening experiment, sound stimuli were presented separately with AC and BC headphones (SONY MDR-1R and TEAC Filltune HP-F200) with the sound pressure level (SPL) of 60 dB SPL. Appropriate ILD and ITD were added for each stimuli. SPL through the BC headphone was adjusted to have the same loudness for each participant, and participants then judged the direction of the sound. Although the direction perceived through the BC headphones was still closer to the center, even over a wide frequency range, our proposed compensation method could effectively mitigate this problem. [Work supported by JSPS KAKENHI grant no. JP23K11180.]