Tadashi Nishimura1, Hiroshi Hosoi2, Osamu Saito3, Ryosuke Miyamae3, Ryota Shimokura3, Toshie Matsui4, Toshiaki Yamanaka3, Tadashi Kitahara3, Harry Levitt5. 1. Department of Otolaryngology-Head and Neck Surgery, Nara Medical University, 840 Shijo-cho, Kashihara, Nara 634-8522, Japan. Electronic address: t-nishim@naramed-u.ac.jp. 2. Nara Medical University, 840 Shijo-cho, Kashihara, Nara 634-8522, Japan. 3. Department of Otolaryngology-Head and Neck Surgery, Nara Medical University, 840 Shijo-cho, Kashihara, Nara 634-8522, Japan. 4. Department of Life Science Center of Tsukuba Advanced Research Alliance, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaragi 305-8577, Japan. 5. Professor Emeritus, The City University of New York, United States.
Abstract
OBJECTIVE: By attaching a transducer to the aural cartilage, a relatively loud sound is audible even with a negligibly small fixation force. Previous study has identified several pathways for sound transmission by means of cartilage conduction. This investigation focused on the relative contribution of direct vibration of the aural cartilage to sound transmission in an open and in an occluded ear. METHODS: Thresholds with and without an earplug were compared for three experimental conditions: the transducer being placed on the tragus, pretragus, and mastoid. Eight volunteers with normal hearing participated. RESULTS: The thresholds increased with distance of the transducer from the ear canal (tragus, pretragus, mastoid, in that order). The differences were statistically significant for all conditions except for the occluded ear at 4 kHz. With the earplug inserted, the thresholds for the tragus condition were most sensitive below 2 kHz, indicating a significant contribution of direct vibration of the aural cartilage. CONCLUSION: Direct vibration of the aural cartilage can enhance sound transmission. At low frequencies, cartilage conduction can deliver sound efficiently across a blockage in the ear canal. Stray airborne sound radiating from the transducer dominates cartilage conduction in the open ear at high frequencies.
OBJECTIVE: By attaching a transducer to the aural cartilage, a relatively loud sound is audible even with a negligibly small fixation force. Previous study has identified several pathways for sound transmission by means of cartilage conduction. This investigation focused on the relative contribution of direct vibration of the aural cartilage to sound transmission in an open and in an occluded ear. METHODS: Thresholds with and without an earplug were compared for three experimental conditions: the transducer being placed on the tragus, pretragus, and mastoid. Eight volunteers with normal hearing participated. RESULTS: The thresholds increased with distance of the transducer from the ear canal (tragus, pretragus, mastoid, in that order). The differences were statistically significant for all conditions except for the occluded ear at 4 kHz. With the earplug inserted, the thresholds for the tragus condition were most sensitive below 2 kHz, indicating a significant contribution of direct vibration of the aural cartilage. CONCLUSION: Direct vibration of the aural cartilage can enhance sound transmission. At low frequencies, cartilage conduction can deliver sound efficiently across a blockage in the ear canal. Stray airborne sound radiating from the transducer dominates cartilage conduction in the open ear at high frequencies.