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 http://www.barlowlabs.upgradecolumbu...rk 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.

http://www.youtube.com/watch?v=rasp8...eature=related

http://www.youtube.com/watch?v=YyVTv...eature=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.

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"Good enough is Perfect"

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Bill's: www.blueroomelectronics.com/

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?

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Uncle $crooge

Nigel Goodwin

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

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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.

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speakerguy79

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

audioguru

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.

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Mifffo

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.


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.

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Uncle $crooge

pwssr

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.

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Uncle $crooge

pwssr

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.

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