Hearing Through Bone Conduction Headsets

Abstract

Bone conduction (BC) stimulation has mainly been used for clinical hearing assessment and hearing aids where stimulation is applied at the mastoid behind the ear. Recently, BC has become popular for communication headsets where the stimulation position often is close to the anterior part of the ear canal opening. The BC sound transmission for this stimulation position is here investigated in 21 participants by ear canal sound pressure measurements and hearing threshold assessment as well as simulations in the LiUHead. The results indicated that a stimulation position close to the ear canal opening improves the sensitivity for BC sound by around 20 dB but by up to 40 dB at some frequencies. The transcranial transmission ranges typically between −40 and −25 dB. This decreased transcranial transmission facilitates saliency of binaural cues and implies that BC headsets are suitable for virtual and augmented reality applications. The findings suggest that with BC stimulation close to the ear canal opening, the sound pressure in the ear canal dominates the perception of BC sound. With this stimulation, the ear canal pathway was estimated to be around 25 dB greater than other contributors, like skull bone vibrations, for hearing BC sound in a healthy ear. This increased contribution from the ear canal sound pressure to BC hearing means that a position close to the ear canal is not appropriate for clinical use since, in such case, a conductive hearing loss affects BC and air conduction thresholds by a similar amount.

Pinna hardness and vibrator placement: Their effects on bone conduction through the pinna

“…Despite their statistical significance, these minor differences suggest that both AC and BC are comparably effective in evoking auditory perception. This finding is consistent with Surendran and Stenfelt's conclusion [19,30] that ECSP significantly contributes to BC hearing, especially in a healthy ear. Shimokura's work [31] further confirms this, showing that direct contact of a vibrator with the pinna significantly increases sound pressure levels.…”

“…While BC is a widely accepted phenomenon, the concept of CC, particularly with vibrator placement on the pinna, has been suggested by Hosoi et al as a distinct pathway [3]. However, study led by Stenfelt et al supports the idea that even when sound transmission occurs through the soft tissues of the pinna, it ultimately results in the excitation of the inner ear through skull vibrations, aligning with the classical understanding of BC [19,23]. Given these diverse perspectives, and con-sidering cases of pathological ears that do not have a direct cartilage path to the inner ear, our study interprets CC not as a separate mechanism but as a subset or particular instance of BC.…”

“…Moving away from traditional sites like the mastoid, researchers have explored the placement of vibrators near the front of the ear canal. This placement enhances sound pressure within the ear canal and improves hearing thresholds in normal hearing [19]. However, with bony aural atresia, the thresholds remain similar regardless of the BC vibrator's location, except below 500 Hz, where positioning it in front of the ear canal yields better thresholds compared to the mastoid [20].…”

“…Advances in BC technology have prompted to a reevaluation of sound travels to the inner ear, particularly emphasizing the pinna's role beyond just sound collection and direction. Studies [17,18], including the work by Surendran et al [19], have explored alternative locations for BC vibrators. Moving away from traditional sites like the mastoid, researchers have explored the placement of vibrators near the front of the ear canal.…”

Exploring running-style modulation

“…As both user safety and user experience are highly important aspects of any new emerging technology, this concern should be addressed in the further development of the instrumented earbuds and the guided exploration training. Possible solutions could be to reduce the passive noise-cancelling effect of the earbuds, to implement technologies currently used in hearing aids (Vanitha Devi & Vasundhara, 2023), or to explore bone conduction headsets (Surendran, Prodanovic, & Stenfelt, 2023). Alternatively, other modalities, such as visual instructions and feedback using augmentedreality glasses could be explored.…”