Air Raid Siren

(MakeItLoud submittal is 'r3' versions)

Too loud for iPhone microphone--over 94dB at 2 meters. (also measures 94dB at 1m, so I'm sure the microphone is swamped.) You can add any number of sirens, so you can double to quadruple the sound level easily (3dB or 6dB more). But it gets harder to crank without binding up.

It's a little picky on printing. I suggest 0.3 mm layers, and medium quality. I've built in some compensation for inaccurate printing (I use Afinia, which commonly prints 0.07mm too large). It might take a few tries to get it just right. If the .STL files make the crank too sloppy, let me know, and I'll make some with lower 'undercut' (when I can).

I had misread the due date (thought it was Dec 16 till today), so I'll be a few try/fix iterations short of what I'd like. My first misprint had the siren 16mm smaller than the crank, so I had to drill new holes for it to attach. My second rev was too large for the contest rules (by the same 16mm).

Theory of o