Plasma Arc Speaker: How Does It Work?

[Lancelot59]

I saw THIS video and THIS OTHER ONE I was really quite surprised that such a thing was actually made to work.

I'm curious how one could create an arc such as that, and then modulate it to match an audio signal. From my interpretation the extreme voltage causes an arc between the contacts which ionizes and then superheats the surrounding air to create that plasma.

But how do you actually make the plasma oscillate in the way that would be needed to generate sound?

 

[waht]

Transformers work on the principle that AC voltage induces either a lower or a higher voltage in the secondary coil depending on winding ratio.

For the plasma arc speakers they use a TV-flyback high voltage transformer which is specifically designed to work in audio frequency range. All you have to do is connect an amplified audio (AC voltage) to the primary winding of the transformer. That way, the same audio will be induced in the secondary winding at high voltage.

Some sound will be produced in the transformer, and some in the arc.

 

[Lancelot59]

How does sound come from the transformer? Does the magnetic field cause the metal to resonate? Also, how does the arc resonate to create the sound? All I can think of that stream being is a super heated stream of ionized air.

 

[waht]

How does sound come from the transformer? Does the magnetic field cause the metal to resonate?

Yes. It's the same as 60 Hz hum near power lines, or huge transformer if you are near one. When thousand of winding of wire are vibrating pressure variations in air is created.

Also, how does the arc resonate to create the sound? All I can think of that stream being is a super heated stream of ionized air.

The arc is not DC in this case. It is induced by constantly being turned on and off at a rate equal to the frequency of audio signal.

The constant pulsing of the arc in sync with audio is what generates pressure variations in the air, and hence sound.

 

[Lancelot59]

Would that have an issue creating low frequency sounds in the bass range? Or like a guitar string could you produce a higher frequency sound with a shorter arc and vice versa? It seems like that might be an issue with producing quality sound.

I can imagine that since it has to ionize a path to break through the air resistance each time it makes a connection it might get a bit noisy (as in static). Also, since it's AC once the sound stops the arc stops and it needs to be reestablished, as in one of those videos the arc started off very broken before stabilizing, unless when the audio stops you switch to an alternate source to keep the arc going.

Thirdly, how safe can a system like this be? I can see lots of things that could result in a massive failure causing injury. You can't really contain the arcs in a glass tube, otherwise you trash the sound. I can see a metal grille with a thin plastic/glass tube to contain the arc, but wouldn't the arc want to jump to the grille?

(Yes I really do want to build this)

 

[waht]

Would that have an issue creating low frequency sounds in the bass range? Or like a guitar string could you produce a higher frequency sound with a shorter arc and vice versa? It seems like that might be an issue with producing quality sound.

That depends how you drive the transformer. If you pulse it in sync with audio then the arc pulses with audio and thus reproduces wide ranges of sound. But for that to happen, the transfomer already has to be running at some fixed frequency (perhaps outside of hearing range)

On the other hand, if you drive the flyback directly with audio to induce the secondary arc in some schematics I've seen, bass will not be reproduced because flybacks are not designed to work at low frequencies.

Thirdly, how safe can a system like this be? I can see lots of things that could result in a massive failure causing injury. You can't really contain the arcs in a glass tube, otherwise you trash the sound. I can see a metal grille with a thin plastic/glass tube to contain the arc, but wouldn't the arc want to jump to the grille?

The rule of thumb is 10,000 per centimeter of arc. Some of those flyback transformer can produce up to 4 cm sparks. But they are generally safe due to having low current.

(Yes I really do want to build this)

it's a cool project

 

[Lancelot59]

That depends how you drive the transformer. If you pulse it in sync with audio then the arc pulses with audio and thus reproduces wide ranges of sound. But for that to happen, the transfomer already has to be running at some fixed frequency (perhaps outside of hearing range)

On the other hand, if you drive the flyback directly with audio to induce the secondary arc in some schematics I've seen, bass will not be reproduced because flybacks are not designed to work at low frequencies.

So I guess I could set it to a constant frequency and pump a signal through it. But I wonder, how does the length of arc affect the sound? Would a longer arc make a louder sound? Just how long could something like this get?

The rule of thumb is 10,000 per centimeter of arc. Some of those flyback transformer can produce up to 4 cm sparks. But they are generally safe due to having low current.

Well it's the low currents that will cause your heart to fibrillate, the large ones just hurt, but just make your heart lock up.

That aside, I hope you mean 10,000 millimetres and not centimetres. Or were you referring to the voltage needed to bridge that gap? Otherwise I'm going to need to get a bigger room. :/ Can I just shield everything with a cage?

it's a cool project

That it is! Although my projects have a tendency to either burn out or explode when I accidentally push them too far, so I'll have to be careful with this if I decide to pursue it. :/

 

[Lancelot59]

Here's another question, if you move forward a bit in THIS video there's a bit of 'dark lighting' where the arc is black. What causes that?