Death Ray (automatic smoke ring cannon)

While working on senior project the other day, I decided I wanted to build a death ray. I'm not quite sure why exactly, but it seemed like a spectacular idea. I have built smoke ring launcher things in the past but they were always operated by hitting the back membrane or whatever. This time, I thought it would be cool to use a speaker cone as the back diaphragm instead of the bottom of a garbage can or something.

Lucky for me, back in high school I managed to obtain a couple busted old 15" PA drivers and had built a very rough prototype subwoofer enclosure for it. I was feeling adventurous at the time so I built it with a passive radiator. I built it like crap so it sounded about the same so it was sitting in my basement all alone. The hole where the passive radiator went was quite useful as no holes needed to be cut in the enclosure. I took out the driver and flipped it around to expose the full surface area of the cone to the working side.

With the driver mounted, all that was left was to cut a hole in a piece of cardboard on the front and to get some power to the driver. I started off with a hole the size of a masking tape roll cut centered in a square of cardboard. I generated some waveforms in audacity to feed the driver through an old amp I had laying around. I found that using the top half of a sine wave at a high amplitude worked best. Also, having a reasonable amount of space between pulses helped clean up the smoke rings. I finally settled on using a 40hz wave with spacing between 0.2 and 1 second.

After playing around with that a bit, I cut a final orifice in a piece of 1/2" ply the size of a Minwax can. In all it worked fairly well and shit smoke rings about 12'. It probably would shoot them farther, but it was somewhat windy out and there was a fence in the way. I thing it would be awesome to use propane instead of smoke and shoot flaming rings of fire, but it may not be the smartest thing to do.

Here is a quick video of it in action, it sounds funny, but my little camera just couldn't pick it up properly.

While I had the sub and tone generator out, I decided to test for the brown note. Overall, it didn't do much, but I really felt funny afterward