Homebrew plasma tweeter

Macadaciouse

Would it be possible to regulate the voltage going to a HV power supply (such as the ballast to a neon sign) with enough precision to use it as a plasma speaker? If output voltage is directly related to input, couldn't an amplifier sufficiently powerful to take line level audio to the minimum level of the transformer be sufficient? Just an idea

Mike Green

Sure it's possible. It's just not easy. People have made plasma speakers before. Commonly they use a transformer to produce the voltages needed. Most high voltage transformers are made to function at low frequencies (60Hz) and these work poorly at the higher frequencies. You have to design the transformer for audio spectrum use.

PJAllen

What does this have to do with the BASIC Stamp or Parallax products?

Jonathan

If you mean modulate the plasma arc, no, the Stamp aint gonna do that. If you mean regulate the b+ voltage you could, but there are many better ways to do it. You mention a neon sign xfrmr, I have never seen one used as a power source for a PT. My PT uses a B+ of about 400V and I used a tube to regulate it (I decided to keep silicon out of my design).

Jonathan

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www.madlabs.info - Home of the Hydrogen Fuel Cell Robot

Macadaciouse

I was wondering if the stamp could work between the mp3 player and the arc; I'm new here, no need for large fonts. Anyone have a wiring diagram I could study? The best resource I could find was this: http://www.instructables.com/id/Build-A-Plasma-Speaker/ and it is notoriously prone to overheating/death.

PJAllen

"...overheating/death."
Nothing to worry about then.· Banzai.

Tracy Allen

Hey Jonathan, How did your plasma tweeter work out? I see you have several interesting HV projects on your madLabs site.

This subject has been of interest to me for some time, mainly because we do a lot of work with ultrasonics and would like a really flat source of sound waves from 10 to 100 kHz, for test and calibration purposes. I'm attaching a DIY paper students wrote as a project, and in addition to their own efforts it has good historical background and references. Some of the inventions have made great efforts to stabilize and confine the plasma. As far as Parallax applicability, I could see a Stamp or Prop driving the flyback and also providing the modulation.

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Tracy Allen
www.emesystems.com

Beau Schwabe

Just another thought.... You don't need electricity to necessarily create a plasma.

When I was in high school I volunteered some of my time at the local science museum (It was a great experience BTW)
One of the projects I helped work on was a Standing wave flame tube. Because this was an interactive display, one of the problems that had to be overcome was that under certain musical situations, the flame could potentially cause itself to go out. Because the flame or 'plasma' is conductive (more conductive than a non-flame) if the flame went out it could be detected electrically and re-lit.

I wonder if the conductivity of this kind of plasma could be used to modulate the flame instead by either making an electrical shunt or introducing an electrical potential within the flame. .... Just a thought.


Here is a You-Tube Example of the Standing wave flame tube or 'Ruben's Tube'
www.youtube.com/watch?v=HpovwbPGEoo&feature=player_embedded

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Jonathan

Beu, Tracy,

Yeah, you can modulate non electrically generated plasma (flame based) look around, I think you will find some sources. The singing arc was discovered in London when they used arc lamps for street lighting. Some of them were noisy and someone took the time to find out why.

My plasma tweeter worked out great, but it was a journey to get it running. Waaaaay worth the effort though, it's one of the coolest things I have ever seen. The sound quality is incredible! I used tubes for mine, no sillycon except for a full wave bridge rectifier. I did have some tube rectifiers, but the thing was already drawing 1500 watts or so. Now that I live off grid, I can't easily play with tubes, they use too much juice. One of these days I'm going to build a IGBT driven solid state version.

Jonathan

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www.madlabs.info - Home of the Hydrogen Fuel Cell Robot

Jonathan

BTW, just glanced at your student's paper. Awesome! The tube schematic is very similar to mine, and it has some cool SS schematics for me to ponder. Give that student a pat on the back from me!

Jonathan

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www.madlabs.info - Home of the Hydrogen Fuel Cell Robot

Macadaciouse

How did the coronaphone turn out? Was the sound output comparable to traditional speakers?

Tracy Allen

Most of the reference links at the end of that student paper are broken, but this one, www.ee.vill.edu/ion/index.html is also an excellent student project. Especially the introduction, and for theory the subsections 6, "modeling corona", and then the final product and testing in sections 15, 16 and 17.

Beau, that Ruben's tube must be something in person, to see and hear.

The smoothest results seem to have come from corona discharge below the spark point, some 20kV and a frequency of at least 5 MHz better higher, 20 MHz or 35 MHz.

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Tracy Allen
www.emesystems.com

Beau Schwabe

Tracy Allen,

"Beau, that Ruben's tube must be something in person, to see and hear." - probably what got me interested early on in resonance.

One of the newer exhibits at the Oklahoma City Science Museum (formerly known as the Omniplex) that is very similar in concept to the Standing wave flame tube uses water instead of flames for the demonstration. (a bit safer)

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Tracy Allen

The sound output of the plasma tweeter claimed in the corona-phone article was something like 85 dB at 3 inches for a sine wave input. I assume they meant dBm ref 20 µPa. That is an okay sound level, comparable to a vacuum cleaner at 1 meter, but the authors were disappointed with the volume and suggested they needed a deeper modulation of the high voltage. They suggested that a PWM modulation scheme might be better than the linear. I don't know, the plasma might be able to reproduce the high frequency details of the PWM.

WRT the Ruben's tube, I was wondering about the sound level inside. Sound levels are typically far far less than atmospheric pressure, so even with a substantial sound input, how do you explain the strikingly different flame heights? In Ruben's original experiments, he had a rubber membrane stretched across one end of the tube and excited it with bells or organ pipes. Not painfully high sound levels! Lets say 94 dBm, roughly 1 Pa. That is a pressure fluctuation in the tube of about 0.001%, compared to atmospheric pressure (=101325 Pa). Not only that, the average pressure along the tube would be constant, and the pressure at the "peaks" of the standing wave is actually a small fluctuation around the mean. So why the higher flame? One explanation I saw invokes Bernoulli's principle, that the flow rate will be proportional to the square root of pressure. I guess that would be the square root of the difference in pressure from inside to outside, however, those fluctuations would be symmetric about the mean. So I'm guessing it might have more to do with agitation, and the heat and expansion and chemistry of the flame.

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Tracy Allen
www.emesystems.com