Bone conduction Microphone:

...Doing the impossible.
Have you ever wanted to hold a conversation in a very noisy environment while wearing a set of grade 5 ear defenders and find this so difficult as to be almost impossible? You have to shout to try to make yourself heard and spend most of the time with hand signals, attempted lip reading and constant repeating. This method of communication can usually only be done when you are in close proximity to the other party.
What would you say to a method of wireless communication that would enable you, wearing good quality grade 5 ear defenders, and with absolutely no modification to the ear defenders, to have a conversation with another party or parties at up to a kilometer away whilst using a small petrol chainsaw ! didn't think it possible ?? well now it is! With a revolutionary electronic device called a bone conduction earphone/microphone Vox unit.

How does bone conduction work?
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
                                     bone conduction vox unit.JPG (13450 bytes)
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.       
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.

The vox sensitivity can be set to "low" for noisy environments and thus you have to talk louder to trigger the vox unit..There is a PTT button on the front of the unit that enables manual operation if desired     (unit is switched off to put it into manual mode)    For effective use, the earphone needs to be inserted firmly into the ear to seal out extraneous sounds . For long term use it may be advantageous for the user to go to an Audiology dept where they fit hearing aids, to have a very comfortable custom fitted ear piece made.


Power  1.5 v "AAA" battery ,    Vox operation 0.5 mA   PTT operation 6.6 mA (no drain in receive mode) battery life about 180 hrs average.   Vox sensitivity  high: -89dB and low -76 dB . Vox activation time 1 millisecond ,   Vox hold  delay is 1 second . Speaker/Microphone is 600 ohms impedance and a sensitivity of 113 dB SPL at 1kHz with 1mWpower.

It is recommended to use an alkaline battery with this unit as this will give a much greater battery life than common zinc carbon cells.                                                                                                                                                                 

The bone conduction unit costs only $150 plus gst .  unmodified fits Motorola gp300, Tait Orcha                To fit Uniden UHX-040 and 042         $220 plus gst             

The suitable Uniden 040  PRS radio cost an extra $130 plus gst

Available from
Pinfold Health Services Ltd.,1172 Arawa st,Rotorua 3201,New Zealand. ph +64-7-3488850 fax +64-7-3486555

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