Bone conduction: why your own voice sounds different to you
Bone conduction is the transmission of sound to the inner ear through bone, rather than air. The bone conducts vibration well and can transmit sound to bone tissue as well as fluids inside the skull which then transfer vibrations to the inner ear. You can still hear what's going on around you but there may be a muffled quality. Bone conduction is often used with hearing aids and cochlear implants. Low frequency sounds are better transmitted through bone than high frequency sounds. This is why people tend to feel the low bass notes in music more than the higher pitched notes. This is also why your own voice sounds different to you than it does to other people. When someone else speaks, the sound of their voice is transmitted through air conduction. Your own voice on the other hand , is transmitted through bone and skull conduction. This is why it often sounds higher pitched or louder to you than it does to other people.
Bone anchored hearing aids, or BAHA's, are devices that help people with conductive hearing loss. They work by transmitting sound vibrations directly to the cochlea through the skull. This is done by implanting a small titanium abutment in the bone behind the ear. A sound processor is then attached to the abutment. This sends sound vibrations directly to the cochlea, bypassing the outer and middle ear.
The first device to use bone conduction to transmit sound was "Osophone", which was described and patented by Hugo Gernsback in in 1924. The Osophone consisted of two parts: a vibrating speaker with bits that are ipped between the teeth, and a microphone or any other suitable sound producing mechanism connected to the speaker. Osophone could be used with all radio receivers since it does not require any electric current. It was advertised as a replacement for headphones.
The Osophone was never put into production, but the idea of using bone conduction to transmit sound has been revisited many times over the years. The first bone anchored hearing aid was implanted in 1977. This technology became available to general public only in 1987.
But more than a century before the technology was described, Ludwig van Beethoven was already using bone conduction. He started to lose his hearing in 1801, and by 1812 he was almost completely deaf. In order to continue composing music, he had to find a way to hear the notes without relying on external sound sources.
Beethoven came up with a very special way to hear the music that he composed. He would place one end of rod in his mouth and another on piano, with which he could feel vibrations from sound waves. In this way, Beethoven was able to "hear" whether or not the composition is correct: if it sounded right when transmitted through bone conduction, he knew it was good.
Bone conduction technology has come a long way since Beethoven's time, but the principle is still the same. Bone conduction headphones are now available to general public and are often used by athletes, because they do not obstruct hearing and allow you to stay aware of your surroundings. They are also popular with people who work in noisy environments, because you can use them along with earplugs. The use of bone conduction technology is becoming more and more common, and with good reason. It is a safe, efficient way to transmit sound directly to the inner ear.