Is cartilage conduction classified into air or bone conduction?

Abstract

Objectives/Hypothesis: The aim of this study was to establish the sound transmission characteristics of cartilage conduction proposed by Hosoi (2004), which is available by a vibration signal delivered to the aural cartilage from a transducer.Study Design: Experimental study. Method: Eight volunteers with normal hearing participated. Thresholds at frequencies of 0.5, 1, 2, and 4 kHz for air conduction, bone, and cartilage conductions were measured with and without an earplug. The sound pressure levels on the eardrum at the threshold estimated with a Head and Torso Simulator were compared between air and cartilage conductions. The force levels calibrated with an artificial mastoid at the threshold were compared between bone and cartilage conductions.Results: The difference in the estimated sound pressure levels on the eardrum at the thresholds between air and cartilage conductions were within 10 dB. In contrast, the force levels at the thresholds for cartilage conduction were remarkably lower than those for bone conduction. These findings suggested that sounds were probably transmitted via the eardrum for cartilage conduction. The threshold shifts by an earplug showed no significant difference between bone and cartilage conductions at 0.5 kHz. At 1 and 2 kHz, the threshold-shifts increased significantly in the order of bone, cartilage, and air conductions. These results suggested that airborne sound induced by the vibration of the cartilaginous portion of the ear canal played a significant role in sound transmission for cartilage conduction.Conclusions: Cartilage conduction has different characteristics from conventional air and bone conductions.

Cartilage conduction efficiently generates airborne sound in the ear canal

“…In an occluded ear canal, the intensity of the radiated airborne sound increases to decrease the thresholds in low frequency range [3]. Our previous study found the threshold decrease at 0.5 kHz for CC when the transducer was placed on the cavity of the ear canal [4]. The current results will reveal the difference in the contribution of Direct-AC and Cartilage-AC to the sound transmission among the locations.…”

“…Fig. 2 shows the transducer whose property is described in the previous study [4]. The tragus (aural cartilage), pretragus (soft tissue), and mastoid (bone) locations for transducer placement are shown in Fig.…”

“…The contribution of the other two pathways (Cartilage-AC, in particular) to the sound transmission is important to distinguish CC from AC and BC. In our previous study, the output levels at the threshold of audibility were compared among AC, BC, and CC using a Head and Torso Simulator and an artificial mastoid [4]. The results showed that the Direct-AC and Cartilage-AC were the dominant sound transmission paths.…”

“…1 shows three possible sound transmission pathways when the transducer is attached to the aural cartilage. These pathways are referred to as Direct-AC, Cartilage-AC and Cartilage-BC [4,8]. The Direct-AC should not include the components of CC because its pathway does not involve the aural cartilage.…”

“…In this condition, the airborne sound influences BC thresholds at the frequency of 0.4-1.2 kHz [3]. When the transducer is directly placed on the aural cartilage, the airborne sound significantly influences the thresholds even in an open ear [4]. This form of sound transmission to the cochlea is referred to as cartilage conduction (CC) [5][6][7].…”