Bone conduction
Intentional transmission of sound through bone can be used with individuals with normal hearing—as with bone-conduction headphones—or as a treatment option for certain types of hearing impairment.
After the fork starts vibrating, placing it in the mouth with the stem between the back teeth ensures that one continues to hear the note via bone conduction, and both hands are free to do the tuning.
[10] In the 1820s, French physician Jean Marc Gaspard Itard improved on this device by attaching the other end of the rod not to a musical instrument but to the mouth of another speaker.
[8] In 1923, Hugo Gernsback created a new kind of bone conduction hearing aid called the "Osophone",[11] which he later elaborated on with his "Phonosone".
[17] There are many different types of bone conduction hearing aids but most of them work on the same principle and comprise necessary components like microphones, signal processing, energy supply and a transducer that generates vibrations.
Surgical bone conduction devices consist of an internal implant and an external audio processor used to transmit sound.
[25] A transcutaneous bone conduction device transmits sound signals, either electronic or mechanical, through the skin.
[31] Percutaneous devices have been associated with skin complications, ranging from slight redness to the formation of granulation tissue and recurring infection.
[33] In another study a meta-analysis of complications with osseointegrated hearing aids showed that revision surgery is required in up to 34.5% of cases.
[40] The BAHA Connect and Ponto are passive percutaneous devices, whereby the audio processor is fixed onto an abutment placed through the skin.
However, unlike with the percutaneous devices, the vibrations from the audio processor pass through the skin before they reach the internal implant.
[17] To counteract this, passive transcutaneous devices may require the use of strong magnets that squeeze the skin to achieve optimal conduction.
This can lead to pain and irritation of the skin and soft tissue between the two magnets, and in worst cases cause necrosis.
In use, the speaker is strapped against one of the dome-shaped bone protrusions behind the ear and the sound, which can be surprisingly clear and crisp, seems to come from inside the user's head.
The use of bone conduction means that any vocal content that is received by the Glass user is nearly inaudible to outsiders.
[44][45] Land Rover BAR employed 'military' bone conduction technology, designed by BAE Systems, within their helmets for use within the 2017 America's Cup.
[46] The helmets allowed the crews to communicate effectively with each other under race conditions and within the harsh, noisy environment; whilst maintaining situational awareness due to their ears being uncovered.
[47] In March 2019 at The National Maritime Museum, London, British composer Hollie Harding premiered the use of Bone Conduction Headphones as part of a musical performance.
[49] Because bone conduction headphones transmit sound to the inner ear through the bones of the skull, leaving the ears free to pick up sound from the environment, users can listen to audio while maintaining greater situational awareness than with acoustic in- or over-ear headphones.
