alk509

A question about edge-terminated capsules...
« on: January 19, 2005, 04:31:48 PM »
Hey guys,

Having never messed with mic capsules, I've been wondering this lately:

The way i understand it, you got your backplate, with a thin (~30 to 50 microns) ring on top, then the diaphragm with the metallized side facing out, and a metal ring on top that holds everything together and provides electrical contact with the diaphragm, with screws that go through it and screw into the backlate, correct? Now, what do they do to prevent the screws from shorting the diaphragm and the backplate they screw into?

Is it clear? I'm I getting this all wrong?

Thanks!

Peace,
Al.

Lest laziness get the best of you!


PRR

A question about edge-terminated capsules...
« Reply #1 on: January 19, 2005, 07:13:22 PM »
On a classic Omni, the shell and diaphragm are ground, the backplate is live. No problem.

On a dual-diaphragm you need two or three terminals. One way is to float both diaphragms and the back electrode. Here, it seems convenient to not-metalize the rim of the diaphragm (it contributes nothing anyway) so it is isolated from the shell. Another way is to ground both diaphragms and use a split backplate: acoustically one unit but electrically two units. That has the advantage that there is no exposed voltage to attract dust, the disadvantage that a good backplate is hard enough to do without the added complication of split electrical sides.

A question about edge-terminated capsules...
« Reply #2 on: January 19, 2005, 07:39:22 PM »
I also don't know how this is easily done. If the outer metal ring is in contact with the diaphram, the metal screws going through this into the backplate make continuity throughout. How exactly is it insulated?

PRR

A question about edge-terminated capsules...
« Reply #3 on: January 19, 2005, 08:19:30 PM »
The backplate has to be supported on glass or top-quality plastic.

Someone here please point to pictures for these guys? 1,000 words and all that jazz.

dale116dot7

A question about edge-terminated capsules...
« Reply #4 on: January 19, 2005, 08:45:49 PM »
Look at the Debenham article, it shows one way to do it. Basically, the 'backplate' is made in two parts - a plastic outside bit where the screws holding the diaphragm go, and a metal inner bit which is the brass (or aluminum) piece that is the backplate proper. An alternate is to use two brass pieces - one disk and one ring - separated by a piece of plastic. Really, do look at the drawings of that article, it's pretty clear how to do it.

gyraf

A question about edge-terminated capsules...
« Reply #5 on: January 20, 2005, 05:24:38 AM »
Quote
what do they do to prevent the screws from shorting the diaphragm and the backplate they screw into?


You don't screw the membrane retaining ring into the backplate, but into an isolating area surrounding the backplate:



On edge-terminated capsules, you have to have this isolation between backplate and screw-mounts for the membranes, so you need a plastic or acrylic surrounding around the backplate.

For centre-terminated capsules, you can make them all-metal, like the KK67..:



When you DIY a center-terminated capsule, and you don't have access to a centre-only-goldsputtered membrane, you will need to isolate the membrane retaining ring from the surrounding material also. Here's how Tim C. did that on one of his first capsules:



Jakob E.
..note to self: don't let Harman run your company..

alk509

A question about edge-terminated capsules...
« Reply #6 on: January 20, 2005, 09:51:31 AM »
Ooohhh... I get it now! You guys are a legend! Thanks! :thumb:

Peace,
Al.

Lest laziness get the best of you!


 

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