Emphasizing interaural level difference corrects the shift of perceived direction of sound for consumer-grade bone-conduction headphones

Abstract

Sounds are perceived not only in air-conduction (AC) manner but also in bone-conduction (BC) one. According to our investigation [Autumn Mtg Acoust. Soc. Japan, 3-1-18, pp. 865-866, 2013; IEEE Int’l Conf. GCCE, pp. 194-197, 2014] about the discrepancy of perceived directions of sound through a BC headphone (TEAC Filltune HP-F200) and an AC headphone (SONY MDR-Z900), the perceived direction through a BC headphone inclined toward the center. In this report, we examined a correction of the shift of perceived direction of sound by emphasizing interaural level difference (ILD). Seven students with normal audibility participated in our experiment. It was carried out in a sound proof room. Sound stimuli were pure-tones of 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz, with 11 different directions for each stimulus. The sound level through AC headphone was 70 dB. That through BC headphone was adjusted to have the same loudness, for each participant. As a result, the perceived direction through BC headphones was improved. Although the BC headphone used in our experiment produced about 20 dB of ILD in the external auditory meatus, it is difficult to explain that in terms of cross hearing and trans-cranial attenuation, but cartilage conduction hearing. Emphasizing ITD had little improvement of perceived direction.