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My Plasma Speaker

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LAN_403

Xray

Sat Oct 15 2011, 12:22AM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

I finally completed my plasma speaker project, but now I will be experimenting with different aspects of it to see if I can improve it. My goal (if physically and technically possible) is to get it to the point where it sounds at least as good and as loud as a standard paper cone speaker. I knew from the start that I would have to spend some money and a lot of time in order to build something that's powerful enough that has at least a chance of success. As you can see in the photos, I found a "monster" torroidal power transformer on Ebay. It has two 40 volt at 10 Amps secondary windings which I wired in parallel. That gives me more than enough voltage and current that I need to power the circuit. I used a heavy duty bridge rectifier which feeds two 4400uf electrolytic caps. With that much capacitance, there is very little AC ripple in the output signal.

I made the "speaker" assembly from a halogen lamp enclosure. I gutted out everything and used only the cast aluminum reflector, which makes a sort of horn speaker with the inclusion of the hv electrodes. The electrodes are spares from a Chinese plasma cutter. They are made of copper with a tiny core of Halfnium metal, which has a very high melting point. The driven electrode sits on top of a large porcelain post which serves as an insulator and a heat-sink. The other electrode is grounded to the housing through a metal bracket that I fabricated.

At this point, the speaker actually sounds pretty good, and is fairly loud. I do not yet have a video of it, but will soon be making one which I'll post when ready. Of course you won't be able to hear how loud it is by watching a video, but I know that people will want to see and hear it working anyways.

I have a schematic drawn for it, but I need to make a few corections, and I'll post that too when ready. I'm sure that some of you will have questions, so ask away!

Here are some pictures of it:

U4R1A

Sat Oct 15 2011, 02:46PM

Registered Member #3505 Joined: Sun Dec 12 2010, 06:03AM
Location: Albuquerque NM
Posts: 108

Looks awesome!! I'd like to see that vid and schematic.

Xray

Sat Oct 15 2011, 04:31PM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Here's the schematic diagram:

1318696256 3429 FT126187 Plasma Speaker Schematic

And here is the YouTube video:

Unfortunately, you can't tell how loud the sound is from watching the video. The sound is much louder in person than what gets recorded on the video. It's mainly because of the limitations of the recording equipment, the MPEG compression, and the storage/playback on YouTube.

I want to experiment with other speaker assembly designs, and if/when I make a substantial improvement, I'll post my results.

Chip Fixes

Sat Oct 15 2011, 09:10PM

Registered Member #3781 Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701

That's the best plasma speaker I have seen that's based off of a 555 timer, good job!

Xray

Sat Oct 15 2011, 10:00PM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Camp Badger wrote ...

That's the best plasma speaker I have seen that's based off of a 555 timer, good job!

Thanks very much!

Xray

Mon Oct 17 2011, 05:36AM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

I made an improvement to the arc assembly which dramatically improved the sound volume. Instead of having the arc between two electrodes (the "hot" or driven electrode and the grounded electrode) I removed the grounded electrode and I modified the driven electrode so that the tip of the electrode faces toward the rear of the aluminum housing. Now the arc is between the electrode and the housing, which makes a big difference in the loudness. I haven't figured out why, but I'm guessing because the arc is now in the focal point of the aluminum reflector. Any other ideas?

Here's an updated video. Compare the audio volume to my previous video.

U4R1A

Sat Nov 26 2011, 11:54PM

Registered Member #3505 Joined: Sun Dec 12 2010, 06:03AM
Location: Albuquerque NM
Posts: 108

Where did you pick up that MJ413 transistor? Or is there a decent substitute? All of the Motorola transistors that I can find come from China via Ebay and I try to minimize my feeding of their economy. Would this type of modulation work for a ZVS driver? Once again you did an excellent job on this project.

Alex M

Sun Nov 27 2011, 12:02AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Wow that thing is very loud!

Xray

Sun Nov 27 2011, 05:31AM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

U4R1A wrote ...

Where did you pick up that MJ413 transistor? Or is there a decent substitute? All of the Motorola transistors that I can find come from China via Ebay and I try to minimize my feeding of their economy. Would this type of modulation work for a ZVS driver? Once again you did an excellent job on this project.

I got them on Ebay. Otherwise, they were hard to find, and quite a bit more expensive. I'm sure that you can substitute many other high voltage/high current NPN transistors with similar or higher ratings.

Thanks for the nice compliment!

Xray

Sun Nov 27 2011, 05:36AM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Alex1M6 wrote ...

Wow that thing is very loud!

Actually, it's MUCH louder in person because the audio circuit in my video camera limits the volume, and I'm sure that YouTube also has a detrimental effect on the sound too. At full volume, just before it begins to distort, it's about as loud as a small 3 or 4 inch paper cone speaker. When I get close to it, the sound level hurts my ears! So that will give you some idea of how powerful it actually is. It continues to amaze me how much sound can come from a 2 inch long high voltage arc!

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