A Preliminary Study of Pitch Matching between 40-kHz Air-conducted Ultrasonic Wave and Air-conducted Audible Sound 40 kHz 気導超音波と気導可聴音のピッチマッチングの試み

It has generally been believed that humans can not perceive high-frequency soundwave higher than about 20 kHz as a normal auditory sound. However, it is reported that some of the younger group whose age was between 18 and 33 could hear 24-kHz pure tone at more than 88 dB sound pressure level (SPL) [2]. In case of bone conduction, clear perception of the ultrasound up to 100 kHz is also reported [2,3]. A measurement of the hearing threshold of air-conducted 40 kHz ultrasound is also reported: the mean threshold was around 133.3 dB SPL [4]. In addition, several investigations pointed that the perveived bone-conducted ultrasound derived a high-frequency pitch, which was approximately from 8 kHz to 16 kHz [5-7]. These findings implies that the human inner ear has certain sensitivity to ultrasound. However, the perveived pitch of the air-conducted ultrasound has not been investigated. In this study, therefore, we performed a pitch-matching experiment between the normal audible sound and the 40-kHz air-conducted ultrasound which is widely used in our daily lives.