Possibly the most exotic of the DIY's to date! Not sure if this even belongs on these boards, but of course I wanted you all to share in and enjoy the madness:
Using a plasma discharge to produce sound without moving parts. Apparently the idea is old as dirt, and several systems have been produced with it over the years. Ok, this will make it relevant to Klipsch: since the efficiency is rather low (~80dB), I would certainly like to try putting a horn onto it and see how that affects the SPL.
I haven't built electronics for quite a long time, and this seems to be rather more dangerous than anything I've ever done. Also not sure if I can get all the parts from a minimal number of dealers (ah, when I lived in Boston there was always the MIT flea every month!)
Actually, the valve is quite common, and most of the rest. Just not sure about the RF coil, and also would be nice to find a transformer that outputs both the 230V and the 6.3V (which I think is quasi-standard for building some tube amps anyway?)
If anyone else is interested, I'd be glad to hear about it. Esp. advice from tube-amp building type peoples, I know you're out there...
The page: http://members.aol.com/uhaumann2/plasma/plasma.htm
Here's the page in English, but a little less information and not quite as understandable as the German: http://members.aol.com/uhaumann2/plasma/eplasma.htm