Put your fingers in you ears and block them. Go on, I'm not joking. You now can hear next to nothing of the sounds around you ! While you have your fingers in your ears, talk, sing or say something, you can hear yourself! The sound of you speech is coming through your skull bones tissues and into your ear!
The bone conduction principle uses a very sensitive microphone/earphone to detect that sound that travels through your head when you speak. The sound is picked up from within the ear canal.
This is how the system enables you to hold a conversation with someone in a very noisy environment i.e. a Sawmill, factory ,Steel mill or even when using a small petrol two-stroke chainsaw! . When you talk, the earphone /microphone picks up the speech travelling through your head into your ear canal. It cannot hear the external sound because of the good quality ear defenders. The system will only work if you wear good quality ear defenders to exclude all outside noise while the earphone is firmly in the users ear canal or have a precise fitting and sealing custom moulded earpiece made by an audiologist at your nearest hearing clinic
The bone conduction vox unit has a small battery powered electronic control box the size of a box of matches and contains tone and frequency shaping electronics to improve speech intelligibility. The device has two speech sensitivity settings, off and a volume control for received Audio. From this unit runs a wire to an earphone, worn firmly inserted into ones ear underneath the ear defenders. The module plugs into the radio transceiver via a 2.5 mm mic jack plug and a 3.5 mm speaker jack which plug into the transceiver. The unit works on radios such as the Tait Orca or Motorola GP300 . The above bone conduction unit can also be supplied with a small inexpensive 40 Channel Uniden PRS two way radio at an extra cost. This set-up would enable those users within a line of sight range of up to one Km (or more) to keep in touch. I.e. forestry workers on a skid pad, log loaders, tree fellers etc enhancing the safety aspect of the industry.
The Bone conduction microphone unit has two types of operation.
Automatic transmit (Vox) , this has a high and low sensitivity setting, so as soon as you speak. the radio goes to transmit and those around on your same radio channel can hear you talk. When you stop talking,and after a delay of about 1.5 seconds, it allows the radio to go back to receive mode so you can then listen for someone else, a reply maybe?.
Manual mode, You can select the radio to go to transmit by pressing a PTT button on the front of the small control box, when you let this button go the radio returns to receive mode.
The Radio conversation is also heard through the same earphone that acts as a microphone.
Simple, but very effective, in fact it is the few systems that will work reliably in noisy environments.
OPERATION OF THE UNIT:
The earphone is placed firmly in the ear canal , and the unit switched on and plugged into the handheld radio transceiver i.e. Tait Orca or Motorola GP300 , the Vox sensitivity is set to high, as soon as you speak the speech vibrations are picked up through the skull by the sensitive earphone acting as a microphone . The detected speech is amplified and modified in tonal quality , pre emphisised and the vox unit switches the transceiver to transmit , There is a 1.5 second "Hold" or tail where the vox unit stays in transmit mode before dropping back to receive this is to allow for the pauses in your speech . In receive mode the audio from the speaker jack is routed via the volume control straight to the earpeice and heard as per normal.