Yes, what you hear in that video is only coming from the scorching hot, high voltage plasma arc. It is vibrating the surrounding air similar to a regular speaker but it does so but sending electrons across the spark gap at the same frequency of the music. It's a great conversation starter to keep in your office!
Plasma speakers make amazing tweeters because they can reproduce high frequency sounds better than regular speakers due to the lack of a heavy diaphragm to move. From an audiophiles perspective, plasma tweeters are as good as it gets for high frequency sounds. For low frequency sounds, larger speakers perform much better.
Warning! This is not a beginner project and has the potential to kill you if you are not careful. Please do not attempt this instructable unless you are aware of all the risks involved and have experience with high power, high voltage applications. The speaker can also generate dangerous levels of ozone if left on for too long in confined spaces. Use in a large room and don't use it for long periods of time(More than a few songs at a time).
Step 1: What You Will Need
1. 12V 50A Power Supply: http://amzn.to/1SqM8qd
2. Flyback Transformer: http://amzn.to/1NiRWkc
3. Stainless steel electrodes(or tungsten). You can make them from rods found in printers. The larger, the better because small electrodes will melt.
4. Copper Grounding lugs: http://amzn.to/1Sawjdq
5. Block of wood to mount the grounding lugs. http://amzn.to/1Sawjdq
6. At least 2 Logic Level MOSFETs- http://amzn.to/1Sawjdq The STP40NF10L I used are great because they have a super low Rdson at 5V and even lower at higher voltages.
7. Heatsinks - http://amzn.to/1Sawjdq Preferrably with a fan to further cool them down.
8. Heatsink compound: http://amzn.to/1Sawjdq
9. NE555 Timer - http://amzn.to/1Sawjdq Be wary of using other 555 variants as some are not capable of driving the MOSFETS directly.
10. 3.5mm audio cable: http://amzn.to/1Sawjdq
11. Other components shown in the schematic.
Step 2: Schematic and Optimizing Setup
As noted in the schematic, the power supply is very important here. I suggest using the same 12V 50A power supply that I used in order to have a very reliable supply and the ability to upgrade your speaker if needed. Yes, a 12V 12A power supply will work but it will not be nearly as loud.
The capacitor labeled 10nF in my schematic will need to be changed to suit your flyback transformer's resonant frequency along with the two potentiometers. If you wire yours up exactly as I have do, be sure not to turn the potentiometers to either of their extremes. This is because most potentiometers are poor made and turning all the way clockwise or all the way counterclockwise can result in opening up the circuit at that point. To avoid this limitation, just add a small resistor in series with each potentiometer. Using the two MOSFETs in parallel is a great way to keep the temperature of the MOSFETs from getting too hot. You can even add a third MOSFET in parallel to handle even more power without overheating. The max temperature my MOSFETs get are about 70C which is just fine seeing the max that can handle is 175C.
Instead of the paralleled MOSFETs, you can opt for much more expensive alternatives that can handle high voltages across the drain and source with a low Rds ON and a low voltage threshold.
The RC snubber found across the primary is a great way to dissipate the flyback transformer's inductive spike when the MOSFETs turn off as well as the ringing associated with the leakage inductance of the flyback transformer. The capacitor you use needs to be able to handle the current you are operating at. The resistor should also be free of an inductive components. Be sure to measure the inductance of the resistor you use to make sure is isn't inductive. Carbon film resistors are ideal and you can always use small resistors in series to evenly distribute the power dissipation.
Start with 8 windings on your flyback transformer primary and monitor your MOSFETs temperatures. Remove one winding at a time to increase the power. You can add an audio jack or hard wire in an audio cable for your audio input.
Step 3: Enjoy!
I hope you found this instructable helpful. Feel free to ask any questions you might have and please vote for me for the Circuits contest and the Amps & Speakers contest.