The Role of Ear Canal Sound Pressure in Bone Conduction Across Different Bone Conduction Devices

Conflicting findings exist regarding the contribution of the outer ear canal pathway to bone conduction (BC) hearing perception. This pathway, represented by the ear canal sound pressure (EC SP ) generated under BC stimulation, may vary in significance depending on the type and position of bone conduction devices (BCDs). This study aimed to investigate the relationship between EC SP , cochlear promontory motion (V PROM ), and intracochlear pressure in the scala vestibuli (P SV ) across different BCD coupling types to evaluate the ear canal's contribution to BC hearing.

Measurements were conducted on 5 human cadaver heads using 4 types of BCD coupling conditions: an adhesive BCD, an active transcutaneous BCD at 2 positions, and a percutaneous BCD. ECSP was recorded in an open ear canal during BC stimulation, while 3-dimensional cochlear promontory motion was captured through laser Doppler vibrometry, and intracochlear pressure was measured using a custom pressure sensor. Frequency-dependent relationships among EC SP , V PROM , and P SV were analyzed and compared across coupling types.

Frequency-dependent differences were observed in the relationships between EC SP , V PROM , and P SV . Below 2 kHz, all devices exhibited a relatively flat relationship, with the adhesive BCD producing 10 to 15 dB higher EC SP relative to promontory motion compared with both the active transcutaneous and percutaneous BCDs. Around the ear canal resonance between 2 kHz and 3 kHz, EC SP increased by 10 to 20 dB relative to both V PROM and P SV . For the adhesive BCD, the resulting P SV -to-EC SP relationship was comparable to that observed under air conduction stimulation. Above the bony ear canal resonance, the relative contribution of EC SP declined.

This study demonstrates frequency-dependent and coupling-dependent relationships among EC SP , V PROM , and P SV , highlighting the contribution of the outer ear canal to bone conduction hearing. While this pathway is unlikely to substantially influence perception in conductive hearing loss, it may affect bone conduction hearing assessments in normal-hearing subjects.