Panasonic Electret Capsule WM-61A

This is an inexpensive and tiny microphone electret (6mm Dia. x 4mm) with a flat frequency response ideal for measuring loudspeakers.

The availability of these capsules in the U.K is poor and I eventually ordered them from Digikey (shipped from the U.S).

Housing the Mic

I used a 12" brass wand just over 6mm ID (K&S 9/32" OD) which I got from a local hobby/model shop. The alternative was a much prettier alumiunium tube (6mm ID from B&Q) but since I was going to solder a connector onto the end, I had to settle for the brass.

Two wires soldered to the back of the electret and twisted together. The black wire is soldered to the tab which has a trace connecting it to the capsule housing.

The other end of the wand slots comfortably into a standard RCA connector and is soldered on. An inline RCA connector would have been better but I had a good quality standard connector lying around...

To pretty things up, I used some heat shrink tubing (applied with a hairdryer) to cover up some of the brass. A few turns of insulation tape is put around the capsule so that it can be push fit into the housing snugly.

Electret Modification

I followed the modifcation suggested by Linkwitz and explained clearly on The modification increases the mic's SPL capability and reduces distortion. The modification is not neccessary, but since it's simple to do (in concept) it's probably worth the fiddly work if you can afford to waste a few capsules in the process.

Scape out the trace that is connected from one of the terminals to the capsule housing using a sharp knife (I used a scalpal), and connect the other terminal to the small tab (opposite the green dot) with some solder. Connect the wires to the termials (now they are reversed) and that's it.

The soldering is fidly so you may go through a couple of capsules getting it right. As you can see, my soldering is not up to scratch, but a quick check with the multimeter shows the old trace has been etched away properly and the new connection is good.

After a quick test (connected to a sound card), I applied some epoxy to the back of the electret to ensure the connections aren't distubed when fitting the capsule to the housing.

Other Mics

Here are some useful links to other similar DIY mics:

Copyright © 2006 Vikash Chauhan. All rights reserved.