Homebuilt plasma arc speaker

[Mifffo]

hello, i recently saw videos of home built plasma arc speakers in action and i tought they looked really neat. I would deffinetly like to build my own plasma speaker but finding complete schematics on the internet proved almost impossible, i did find this schematic https://www.barlowlabs.upgradecolumbus.com/YSU Webpage/ADVcircuits/SparkSpkr/Spark Speaker.pdf but this is not a complete schematic for an arc speaker (the arc speaker schematic and design begins on page 7, the designs before are for a plasma speaker shooting out into open air). The pdf seems to use a flawed design of altering the frequenzy the arc arcs across the 2 ignition coils to produce sound, which means that the arcing occurs way to seldom and causes one to hear the actual arcing since it arcs at the frequenzy of the music being played. What i have understood of plasma speakers is that the arcing should occur at a set frequenzy prefferably above 45 Khz and that the music should then be modulated in on that frequenzy, causing the arcings to be of different strenght or time making the air expand differently depending on the heat of the arc.

I have built a plasma speaker following the schematic but it proved very bad, producing mostly hiss and noise sounds only some music was audiable and the amount of arcing was completely dependent on the music suggesting the design only changes at which frequenzy the transistors should open and close. And this is not what is desired.

So i would require help for a design that would make an arc occur at around 100Khz constantly between a flyback and ground or 2 automotive ignition coils or 1 ignition coil and ground. And then the audio would need to be modulated into that arc, increasing the heat of the arcs depending on the music being played.

i would greatly appreciate help on this project


2 videos of superb home made plasma speakers.

https://www.youtube.com/watch?v=rasp88nbsRw&feature=related

https://www.youtube.com/watch?v=YyVTvtgm11o&feature=related

 

[ericgibbs]

hi,
It was called an Ionophone back in the good old days.

http://www.roger-russell.com/ionovac/ionovac.htm

I actually attended the first public demo's of the Plessey and Fane systems back in the 1960's at the Harrogate Audio Shows.

In those days they produced a reasonable sound quality compared to the cone speakers of the day.

 

[Mifffo]

Yes this is sort of old, and i guess it has been dismissed as "not worth it" and i can agree on that. But it does look very awesome so i would love to build a home made one, something alike that which is found in the video. But to my knowledge that speaker had to have a supply of a kind of gas to function, or if it was to neutralize the ozone emissions.

 

[audioguru]

I hate listening to a speaker with a broken woofer.

Those sparky speakers have extremely distorted high frequencies. UTube had an example of one that sounded much better but it still didn't have any bass.

Is it loud enough?

 

[Nigel Goodwin]

I hate listening to a speaker with a broken woofer.

Those sparky speakers have extremely distorted high frequencies. UTube had an example of one that sounded much better but it still didn't have any bass.

Is it loud enough?

Well reading the article, they appear to be tweeters only, so not really that much use?.

 

[Mifffo]

well, they are not meant to produce bass. And they are loud enough.


But to my recent searches, it might be so that those home built plasma speakers use FM to produce the sound. Seeing as nearby FM radios pick up the music that plasma speakers play.

Is it possible to have a FM transmitter circuit switch a transistor at frequencies around 100 Khz? the transistor would then drive the flyback which would create the audio spark. approximetly 50 volts DC is needed as input into the flyback and probably 1 or 2 amperes. And into the FM transmitter circuit a audio signal would be supplied.

what is your take on this?

 

[audioguru]

Your hearing detects AM, not FM.

The description and schematic in the article AM modulates the RF carrier frequency. it is a very simple modulator so it probably produces a little amount of FM also. Harmonics reach up to the FM broadcast band.

 

[Speakerguy]

Can anyone tell what kind of transformer he is using? It looks like he is PWM'ing at ~110Khz.

 

[audioguru]

Can anyone tell what kind of transformer he is using? It looks like he is PWM'ing at ~110Khz.

Which circuit?
The one from the school kids is a mix-mash of unlabelled circuits. Some circuits were used but most were not. It uses car ignition coils.
It doesn't use an oscillator.

It uses an LM386 little power amplifier to drive the base of the darlington-connected 2N3055 transistors. It uses a DC bias current through the coils (from a pot without any negative feedback) and the audio turns the transistors on and off. The poor little LM386 is driving a dead short of two junctions in series to ground.
The distortion from the overloaded driver and from the switching must be horrible.

 

[Mifffo]

Which circuit?
The one from the school kids is a mix-mash of unlabelled circuits. Some circuits were used but most were not. It uses car ignition coils.
It doesn't use an oscillator.

It uses an LM386 little power amplifier to drive the base of the darlington-connected 2N3055 transistors. It uses a DC bias current through the coils (from a pot without any negative feedback) and the audio turns the transistors on and off. The poor little LM386 is driving a dead short of two junctions in series to ground.
The distortion from the overloaded driver and from the switching must be horrible.

well yes it is horrible and useless, i think its safe to forget about that PDF school schematic using car ignition coils.



the youtube speaker is deffinetly the way to go and yes it does look like he is PWM the signal going into the flyback at 113 Khz in the youtube video, he however says it is FM

an extract from the youtbue video:
"This is a prototype of a FM modulated plasma arc speaker / tweeter. Have since built this circuit on a custom PCB & made an improved vertical discharge setup, using tungsten-tipped electrodes (see my other videos). This stops the plasma hopping about and causing the distortion you can hear...

Technical stuff : Supply voltage for output stage in this design is 50V DC - driver is a single IRF740 HEXFET power Mosfet. Flyback driver uses a SMPS IC from a computer power supply. External oscillator & High-pass filter for the audio, is a uPC4570. EHT output is roughly 60KV"

i guess the second part explains much, but it would require more knowledge about electronics then i have to build my own plasma speaker.

Can anyone tell what kind of transformer he is using? It looks like he is PWM'ing at ~110Khz.

it looks like a Flyback transformer from a TV and he says it is a flyback in the comments, most likely it is one

 

[audioguru]

Pulse-width-modulation makes AM, not FM.

 

[pwssr]

Pulse-width-modulation makes AM, not FM.

Care to explain that, please?

 

[audioguru]

When PWM produces a wide pulse then the average output voltage is high. when PWM produces a narrow pulse then the average output voltage is low. The amplitude of the average voltage is changed which is AM.
The frequency of the carrier is not changed so there is no FM.

The guy who made the circuit for the video doesn't know the difference between AM and FM.

 

[pwssr]

When PWM produces a wide pulse then the average output voltage is high. when PWM produces a narrow pulse then the average output voltage is low. The amplitude of the average voltage is changed which is AM.
The frequency of the carrier is not changed so there is no FM.

The guy who made the circuit for the video doesn't know the difference between AM and FM.

Thanks for your explanation. I have been in the field for years (officially an "old fart") and never really thought of it that way. I'm still having trouble with the "modulation" part as, to my mind, you aren't modulating the amplitude, you are limiting the average output. Guess I need to think about it for a bit and try to wrap my head around it!

 

[audioguru]

The power of the arc is modulated strong and weak. Its heat does the same and it heats and cools the air around the arc. Hot air expands. Expanding and contracting air waves produces sound.

 

[Speakerguy]

I think I might have figured out why he's calling it FM.

When I was working with HV at my last job, I pulled apart an electronic NST. I ripped out the output transformer. It had a primary wound with magnet wire, a continuous ceramic core, and a potted secondary. It was a resonant transformer, which I thought was odd. When driven at 30kHz it would massively step up the voltage on the secondary to 10kVpk-pk. If you shifted down to 25kHz or up to 35kHz, it would drop to <1kVpk-pk.

If you were to take an audio input and use it to modulate the frequency of a sine wave so that it fluctuated between 25 and 30kHz, you could achieve an amplitude modulation of the spark voltage on the secondary. The linearity would depend on the linearity of the transfer function of output voltage as a function of frequency, but there might be ways to avoid or compensate for that.

Does that sound like a possibility AG? I'm tempted to go whip one up. I've been meaning to do a plasma speaker for a while, and this I could definitely whip something like this up. I've got a Tektronix rep swinging by next week to show me their new DPO3000 scope and I could ask for a quote on one of their HV probes.

 

[audioguru]

A super-regen "radio" has an AM detector. It uses "slope-detection" like you did with the resonating high voltage coil to detect FM when it is tuned to one side of an FM station.

Another guy on another site and I don't think a car's ignition coil will work at an ultrasonic frequency.
A V8 engine running at 6000RPM produces a frequency in the coil of only 800Hz.
Some cars use an ignition coil on each sparkplug so it can fire at a lower frequency.

The flyback transformer from a TV might barely reach 20kHz.

 

[Speakerguy]

I've worked with ignition coils before. I could get a specialized drag racing coil to do 10kHz but the primary wasn't being fully charged. It was $250 for that single ignition coil, so I doubt there's much better out there. The more common ignition coil I had on hand was limited to a few kHz.

 

[audioguru]

One of the videos you linked to has an 8kHz carrier frequency that is audible.

 

[Hero999]

I think I might have figured out why he's calling it FM.

When I was working with HV at my last job, I pulled apart an electronic NST. I ripped out the output transformer. It had a primary wound with magnet wire, a continuous ceramic core, and a potted secondary. It was a resonant transformer, which I thought was odd. When driven at 30kHz it would massively step up the voltage on the secondary to 10kVpk-pk. If you shifted down to 25kHz or up to 35kHz, it would drop to <1kVpk-pk.

If you were to take an audio input and use it to modulate the frequency of a sine wave so that it fluctuated between 25 and 30kHz, you could achieve an amplitude modulation of the spark voltage on the secondary. The linearity would depend on the linearity of the transfer function of output voltage as a function of frequency, but there might be ways to avoid or compensate for that.

Does that sound like a possibility AG? I'm tempted to go whip one up. I've been meaning to do a plasma speaker for a while, and this I could definitely whip something like this up. I've got a Tektronix rep swinging by next week to show me their new DPO3000 scope and I could ask for a quote on one of their HV probes.

Yes, the same technique is used in quasi resonany converters, except zero voltage switching is used to reduce the losses.

Could it have been a quasi resonant converter?