Recently I was working on a hydrophone project and I needed to figure out how to disassemble an electret capsule and put it back together without ruining it. Robin Whittle has great photos, explanations, and specs concerning some specific capsules on his page “Dismantling four Transound electret microphones” and Open Music Labs has a thorough explanation of the parts and theory, so I jumped in and started hacking:
There are two capsules covered in this guide: The Panasonic WM-61a and the Primo EM172.
Taking Apart a Panasonic WM-61a
These steps don’t really cover re-assembly but I think you could just epoxy it back together afterward. I haven’t tried because I wanted to disassemble a WM-61a to harvest the internal impedance-converter FET so I could use it in other applications.
Remove the FET if you need to. The long lead is the Gate, which makes contact with the electret backplate when assembled. The Drain and Source leads are soldered through the PCB to the contacts on the other side.
Taking Apart a Primo EM172 (and widening front opening)
I needed to enlarge the front opening of this capsule so I could encapsulate it in silicone and use it as a hydrophone. This mod makes the mic sound terrible in air, but it allows the silicone to more completely contact the diaphragm, which is crucial underwater.
Snip around the rolled edge but leave some sections intact so you can crimp these “fingers” back down later when you re-assemble the mic.
Re-assemble everything and crimp the leftover “fingers” over the PCB. Seal the edges with epoxy so it’s air-tight.