How does SD condensor mic work?

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crazydoc

crazydoc

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In a recent thread there was a question about the diaphragm size of the mxl603. I thought to myself, I'll just measure it. So I unscrewed the top part of the mic, thinking the diaphragm was the shiney doohicky I saw thru the end screen. There is a round plastic thing behind this with a brass stud attached, which impinges on and depresses a spring loaded plunger sticking out of a plastic dome in the body of the mic when the top is screwed on.
It looks like, if this is the diaphragm, that it makes a mechanical connection with the rest of the mic, rather than an electrical one as is my understanding with LD condensors.
Can someone explain how this works, or point me in the right direction? Thanks

BTW, the mxl603 measures 22x135mm outside dimensions, and the id of the tube is 20mm. It looks like the shiney thing I am assuming is the diaphragm would measure from 18 to 20mm in diameter (as the perimeter is covered by a retaining ring.)
 
It's a pretty standard design for all SD capsules.

Inside that capsule assembly is the diaphragm, the back plate, a ceramic spacer, a plastic cover and a spring-loaded, gold-plated plunger to make a solid connection to the microphone body.

The plunger is connected to the diaphragm and carries the needed 48 to 70 polarizing voltage to the diaphragm, and carries the signal the other way to the electronics in the mic body.

When the capsule is screwed into the body, it makes a tight seal to avoid cavity resonances and air leakage, while the mating plug in the microphone body makes a solid connection with the spring-loaded center pin.
 
Thanks, Harvey

In this case I guess the plunger and the plastic cover reside in the mic body, and the diaphragm, back plate and ceramic spacer screw off. My main question was the electrical connection, and you answered that.

Can you recommend a book or other source of information on the design and construction of mics? I have Tremaine's Audio Cyclopedia and Handbook for Sound Engineers, ed. Ballou, but they basically describe a limited number of commercial circuits. I'm particularly interested in modifying LD condensers, and have already seen the Royer and Dorsey mods. I would guess that a lot of this stuff is proprietary.

Thanks again for the help.
 
The Microphone Book by John Eargle is very good. The AES Journal has an older microphone collection that is still very relevant, and of course John Woram's The Recording Studio Handbook is a must read.

There's just not a whole lot out there about microphone design.
 
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