Sunday, July 09, 2006

Dynamic MIcs



Dynamic mics used to be the most common type of mic available until electret condensers were produced in huge quantities for cellphones and other consumer gadgets. I like this image because you can see right in to the ring magnet and part of the moving coil attached to the tympanic diaphragm. You can also see the cylindrical magnet that is in the center however there isn't much to look at. That spiral turbine pleated arrangement must have been designed to keep the coil centered in the gap while allowing adequate in and out movement. It also might be responsible for suppression of lateral modes.

One thing that limits the dynamic is that the diaphragm and coil tend to have a lot of mass. Also, the need to keep the coil, which is made of very fine wire, centered in the gap requires a reasonably stiff drumhead. Yet they work fairly well and are reliable.

The dynamic loudspeaker is exactly the same, just larger. The typical cheap headphone transducer is also the same and in fact you can make a very serviceable stereo recording mic out of ordinary headphones and use it to record concerts. It's done all the time.

Just look for the person in the crowd facing the band who is trying not to move.

I find that a larger speaker such as a paper cone automotive speaker makes a very good communications mic for ham radio applications and very often people prefer it over the EV635 for voice. I send that into either a Collins 32V2 or a Johnson Valiant that has been greatly modified. These are both high fidelity transmitters with over 20 Khz of transmit bandwidth, if needed.

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