Bone conduction

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Bone conduction is the conduction of sound to the inner ear through the bones of the skull.

Some hearing aids employ bone conduction, achieving an effect equivalent to hearing directly by means of the ears. A headset is ergonomically positioned on the temple and cheek and the electromechanical transducer, which converts electric signals into mechanical vibrations, sends sound to the internal ear through the cranial bones. Likewise, a microphone can be used to record spoken sounds via bone conduction.

Bone conduction products are usually catergorized into three groups

• Ordinary products such as EARS-FREE headset or headphone
• Hearing Aids and Assistive listening devices
• Specalized communication products (i.e. underwater & high-noise environments)

Bone conduction products have following advantages over traditional headphones:

• Ears-free, thus providing extended use comfort and safety
• No electromagnetic waves (EMW), eliminating the potential effect of EMW on cerebrum (if any)
• High sound clarity in very noisy environment
• Protecting hearing from loss due to extended use of conventional headsets and earpieces.

There are some disadvantages:

• No stereo sound, as all sound seems to come from inside your head
• Some implementations require more power than headphones
• Less clear recording & playback than traditional headphones and microphone

One example of a bone conduction speaker is a rubber over-moulded piezo-electric flexing disc about 40mm across and 6mm thick used by SCUBA divers. The connecting cable is moulded into the disc, resulting in a tough, water-proof assembly. In use the speaker is strapped against one of the dome-shaped bone protrusion behind the ear. As would be expected, the sound produced seems to come from inside the user's head, but can be surprisingly clear and crisp.

See also: hearing test