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Bone Conducting Helmet System
By: Dannik
Published : October 7th, 2004
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Bone Conducting Helmet System

Bone conduction, as a method to facilitate hearing in people with outer ear or conductive hearing loss, was discovered in the 16th century. At that time, it was considered a novelty, of little worth. A century later, two deafness specialists started using this technique to assist patients, and in 1879, the Rhodes Audiophone, which used a vulcanite fan to pick up air vibrations and transmit them to the teeth, was patented. One of the first real commercial hearing aids, the Audiphone was the essential tool for the hard of hearing, until the modern carbon electric devices were developed.

But what is bone conduction? Simply put, it's the reason a person's own voice sounds different to them when they hear a recording of them speaking. Their vocal chords, when vibrating, cause the bones they are connected to to vibrate, which expands through your skull to the small bones in your ears. Since standard hearing works by the eardrums being vibrated by audio pressure waves which in turn shake these tiny bones, bone conduction bypasses the need for sound waves to create something audible.

Many theatres have removed the massive subwoofers from their sound systems and replaced them with resonators. These are basically low frequency drivers with no cone, but bolted to the floor so that as long as you are in contact with the floor, you will 'hear' and 'feel' the bass, but without the ear-damaging sound pressure waves normal subs create.

It's actually safer than normal speakers. Since there is no physical vibration hitting a person's eardrums, there is less chance of exposure damage.

So, why are the military and police in the world so excited?

Combine a subvocalization-ready microphone with a bone conduction speaker in a headset, and the person in the field can have a full, realtime communication system that, to them, is normal speech and hearing, but it makes virtually no sound. In a tactical situation, operating in a sensitive environment, communication is usually handled by whisper or hand signals for most operators across the various groups that work in tactical operations. This is a limited level of communication, as careful audio pickups will catch whispers, and hand signals, while very effective, are also very limited in the level of complexity expressable.

Another advantage of bone conduction as a speaker replacement is that since it does not use your outer ear, the conductor can be placed on the cheekbone near the ear, leaving the wearer's ears able to hear normal, ambient sound with no interference from the headset.

In civilian circles, bone conduction is used for everything from coin-sized cellular telephones, which operate by merely holding next to your cheekbone and voice dialing, to dentist's chairs that conduct soothing music into patients. A company in Sydney, Australia uses bone conduction headsets from a supplier to US special forces teams, in their operation of climbs up the Sydney harbour bridge. The headsets allow for instruction by the climb leaders to the climbers, but does not interfere with the natural sounds and conversation inherent to a tour trip.

This is just one more fantastic example of an old idea being reworked to keep operators, whether civilian, police or military, safer and more effective in the field.


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