About a month ago, my partner suggested a new project: Let’s turn their found-in-an-abandoned-hospital second world war gas mask into a microphone… Sure! Their idea was pretty straight forward: Dissesamble a Sure SM58 microphone. Open and empty out the filter cartridge of the mask. Somehow install the SM58 internals inside the canister. Oh, and make sure whatever we do looks nice enough for live performances.

Step 1 - Dissasemble an SM58 microphone

The SM58 is surprisingly easy to disassemble, as almost everything is screwed together. This is pretty cool from a repairability perspective, but also makes our life pretty easy. One thing to note is that the SM58 has a potted transformer. Luckily as documented by White Noise Studio, the potting compound appears to just be hot glue, so the transformer can be pulled out with a bit of heat.

The SM58 microphone capsule in front of the gas mask.

Pulling the shock mount apart, the microphone becomes a lot more fragile, exposing tiny wires that are luckily taped down. Also, doing this loses all indication of polarity on the two internal contacts, so remember to mark one first if not having inverse phases is something you care about.

(Also yes I forgot to photograph this process and most of the rest, so the images will be a bit wonky.)

Step 2 - Empty out a filter cartridge

First things first, (some) old gas canisters contain asbestos. Which ones and how old? From a cursory search, that information is fraught and not readily available. The Helsinki University Museum has a pretty nice writeup on a concrete case with context, but is in no way comprehensive.
In my read, asbestos seems primarily to be a feature of WW2 cartridges, and this one from the 80s should probably be fine, but as the blog post highlights, there are no guarantees.
Really if we were smart people, this project would have pivoted to designing and 3d printing a model cartridge, but no luck. We proceeded outside on a trash-able surface with gloves, manual tools and water for dousing anything vaguely fibrous to avoid particulates.

The lid of the canister has been removed, revealing a tightly folded paper filter.
The canister has been opened further, revealing large pile of activated charcoal granules.

Opening up the cartridge we found a bunch of activated charcoal sandwiched between folded paper filters. Comparing to the images of the cottonous contents of the asbestos containing cartridges it seems that we got lucky, though we took no chances emptying and washing the cartridge thoroughly before proceeding. Sharp metal edges everywhere did not make any of that easier, though in the end we had an empty filter cartridge. In summary, don’t do this, there are better ways.

Step 3 - Fit an SM58 inside a gas canister

With a disassembled microphone and an emptied out filter cartridge, the last step was to put one inside the other, and wire it up in a reasonable way. I approached this through incrementally drawing and printing parts as necessary. I first started out printing a simple locking mechanism for the lid, assembled with hot glue. Then I proceeded with mounting the microphone. For this i reused the bolt on the back of the mic cartridge to tension it against the filter canister opening. To cover the sticking out bolt, I printed a small hat for the inlet hole of the cartridge. Finally, we soldered and glued down the microphone transformer, fed a cable back out the side of the cartridge, and mounted an XLR connector at the back of the mask.

Various 3d printed parts alongside the open canister with locking print glued on.
The open canister, microphone bolt tensioned against a circular 3d print on the inside.
The assembled canister, microphone tensioned against its inner wall.
XLR connector mounted on the back canvas flap of the mask.

Results

The modified gas mask.

Well, it’s a gas mask microphone. While I am overall happy with the aesthetic results, the mask itself has some practical issues. Even without the filter, the mask is not exactly easy to breathe in, and the glass fogs up almost immediately. Also, no stepping away from the microphone to breathe, that’s just a feature of your recording now, and its pretty loud as the air has to pass around it.
My partner produced a horror-piece for an indie movie using the microphone. It’s pretty neat: