Hearing Health Guide
Definition
Bone conduction is the process by which sound reaches the cochlea through vibrations transmitted directly through the bones of the skull, bypassing the outer ear canal, eardrum, and middle ear ossicles. In audiology, bone conduction testing is used to determine whether hearing loss originates in the inner ear (sensorineural) or the outer/middle ear (conductive).
In normal hearing, sound travels through the air, enters the ear canal, vibrates the eardrum, is amplified by the three ossicles of the middle ear, and then enters the fluid-filled cochlea. Bone conduction bypasses all of these steps: a vibrating device placed on the skull transmits vibrations directly to the cochlear fluid.
Everyone hears through bone conduction to some extent. It's why your voice sounds different in recordings than it does to you in person. The bone-conducted version of your voice includes lower frequencies that aren't captured by microphones.
During a hearing evaluation, audiologists test both air conduction (through headphones) and bone conduction (using a vibrator placed behind the ear on the mastoid bone). Comparing the two reveals the type of hearing loss.
If air conduction thresholds are elevated but bone conduction is normal, the cochlea is working but sound is being blocked before it arrives: this indicates conductive hearing loss. If both are equally elevated, the cochlea itself is damaged: sensorineural hearing loss. A combination is mixed hearing loss.
Bone-anchored hearing aids (BAHAs) use bone conduction to deliver sound directly to the cochlea, bypassing a damaged or absent outer or middle ear. They are surgically implanted or worn with a soft band headband, and are indicated for conductive hearing loss, single-sided deafness, or mixed hearing loss where conventional aids are not appropriate.
Consumer bone conduction headphones (Shokz, AfterShokz) use the same principle to deliver audio while leaving the ear canal open. They're popular for running and cycling because they allow ambient awareness. These are consumer devices, not medical hearing aids.
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