What Is Bone Conduction?

Bone conduction is the transmission of sound to your inner ear through your jawbone instead of your eardrum.

I was running down the jogging track at my local park and chanced upon my friend Ron. I had seen Ron running the track a few times every week.

However, on that specific day, something about him caught my attention. Ron was wearing a pair of headphones, but the headphones didn’t go into his ears; instead, they just stuck to the part of his face right in front of his ears.

My first instinct was to laugh at his inability to wear headphones correctly, but I didn’t. He noticed me staring, so he took off his ‘headphones’ and stuck them onto my face, just over my jaw. To my surprise, I felt the music. I could hear every single beat as clear as day, but there was nothing plugged into my ears!

My entire body was confused. After two full verses of the song, I was convinced… this was some crazy future tech transmitting energy beams straight into my brain. Ron laughed at the look on my face and explained. “Don’t worry… nothing’s frying your brain. It’s just bone conduction!”




(Photo Credit : m*etamorworks/ Shutterstock)

“The sound waves are being transmitted through your jawbone, bypassing the eardrum and going straight to your hearing center. It the technology of the future!”
What is Bone Conduction?

We hear sound in two different ways: through our eardrums and through our bones. Most sounds from our external environment, from annoying car horns to sweet canary chirps, reach us by way of our eardrums. The eardrums convert the sound into vibrations and send them to the inner ear (cochlea). These vibrations resonate a different part of the cochlea, depending on their audio frequency. The resonant movements are then translated into neural signals, which are transmitted to the brain, thus completing the seemingly “simple” hearing process.









Hearing through the eardrums (air conduction) vs. hearing through the bones (Photo Credit : Msahid manik/Wikimedia Commons)

The most common sound we hear predominantly through bone conduction is our own voice! That’s right. The sound of our voice is transmitted via the jawbone to your cochlea, bypassing the eardrum, resonating the relevant parts b*ased on audio frequencies, and finally ending up as neural signals in the brain. Sounds transmitted through the eardrum and those transmitted via bone conduction tend to vary slightly. The most common implication of this is that your voice sounds very different in a recording than when you speak. The recorded voice is being transmitted through air conduction, while the latter reaches your brain via bone conduction.
History of Bone Conduction

While your own voice may be the most frequently heard sound through this m*ethod, hearing through bone conduction also has far wider applications. Contrary to what Ron said, bone conduction isn’t a new technology at all. In fact, the first patent for a device to transmit sound through bone conduction was filed in 1924. Moreover, the concept of bone conduction has played a significant role in the history of music.




Beethoven heard his piano through bone conduction (Photo Credit: Wikimedia Commons)

The renowned 18th century composer Ludwig van Beethoven, who was famously deaf, utilized bone conduction to hear what he played. Of course, his solution wasn’t nearly as elegant as some of the devices on the market today. Beethoven attached a rod to his piano and clenched the other end in his teeth so the vibrations from his piano would reach him via his jawbone.




Your voice sounds very different when you speak vs. when you hear it on a recording (Photo Credit : Syda Productions/ Shutterstock)

Bone conduction technology has come a long way today. In the last five years, bone conduction has found applications in a variety of fields, including the military, medicine and, of course, those swanky bone conduction headphones.
Applications of Bone Conduction

BAE Systems, a renowned manufacturer of defense systems, has created a special communication prototype for soldiers that leverages bone conduction technology to transmit sound through their helmet straight to the inner ear. Soldiers must strike a balance between being fully aware of their surroundings in harsh environments, while also being able to effectively communicate with their comrades. They built an audio transducer, no larger than a five-cent coin, and embedded it into the soldiers’ helmets. This allowed their ears to remain open and helped them remain aware of their immediate surroundings, all while maintaining an unbroken line of communication. The device is still in its prototype phase, but soon enough, we will see helmets shipping with integrated bone conduction communication transducers.




Soldier in a helmet with bone conduction capabilities (BAE Systems) (Photo Credit : PRESSLAB/ Shutterstock)

Commercial sunglasses can also double as music players thanks to bone conduction. Devices like Google Glass and Bose’s Frames have embedded small speakers into their sunglasses, conveniently located close to the jaw, which transmit sound via bone conduction.




Google Glass (Photo Credit : Peppinuzzo/Shutterstock)

Bone conduction technology is also helping to restore hearing for people challenged by deafness. Companies have created a specialized hearing device called Bone Anchored Hearing Aids (BAHA). These consist of two parts: an external processor and a fixture surgically implanted into the bone near the inner ear. The processor captures sound and artificially transmits it to the internal fixture, which vibrates the inner ear, thereby allowing the person to hear.




BAHA devices help restore hearing through bone conduction (Photo Credit : public domain/Wikimedia Commons)

Bone conduction is an age-old concept that has recently come back to the fore and found new applications in a wide variety of fields. However, most of the tech is either in the prototype or concept stages. Very few manufacturers have built commercially viable products using this exciting technology. It will be quite interesting to see how this technology evolves and finds mainstream appeal in products being developed by leading tech and industrial giants across the globe.
References
Stanford University
Notre Dame University
Linköping University
BAE Systems
Hearing Link