Leafcutter John shares the steps he took to build a phantom-powered underwater mic from a steel can (looks pretty classy!) –

I decided to house the pre-amp in the same enclosure as piezo elements (to avoid noise entering the circuit). The challenge here is to find a decent enclosure. As the piezo’s and the pre-amp will be underwater they need to be inside something water-tight.
After a few experiments, I found you can quite easily solder steel food cans together using a regular soldering iron and electrical solder. It works for water pipes so It should be water-tight in this case.  NOTE: aluminum cans will not work at all well!!! Get out your magnet and find some steel ones!

The resulting audio samples sound quite good, justifying the gobs hotglue sealer and onboard preamp. Get started building your own over at Leafcutter’s site. [via Hack a Day]