[Collins] Re: {Collins] Low impeadance headsets

[Dr.Gerald Johnson]

http://www.sportys.com/acb/showdetl.cfm?&did=19&product_id=5617&fromgoogle=yes 
says the M-1/DC is an amplified microphone needing a DC supply. Doesn't say the 
impedance.

http://www.aircraftspruce.com/menus/av/microphone.html says the M-4 is an electret 
microphone. So it also needs DC power.

Electret microphones tend to be low impedance and low output.

The noise reduction virtues of these microphones tends to work only over a narrow 
frequency range so their response curve is limited and peaked for voice recognition, not 
fidelity.

The impedance step up can come from a transformer for low impedance microphones 
to high impedance amplifiers. Radio Shack used to carry such a thing. I don't know if 
they do now. Some like a 200 ohm to 50,000 ohm transformer, about the size of a sugar 
cube if uncased. There's one like it in Shure switchable impedance microphones and 
Shure probably sells one yet.

Do a google search on "David Clark" (as a phrase) headsets with your headset model 
numbers. Some vendor might accidentally admit impedance.

-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.