Martin Poulin
Plasma Tweeter
Upon hearing the Acapella, and their fabulous plasma (they call it ionic) tweeter at few HiFi shows, it generated an interest in me digging deeper on plasma tweeters. (Spoiler, I had an Acapella on loan afterwards and I didn't liked it at all - see other page on my site)
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Information on plasma tweeters is very limited, and a pair of Acapella tweeters costs $11K USD…please.
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Besides this, there are other sites, mostly hobbyists on how to build your own plasma tweeter. However, no deep data is provided from them. (i.e.: maximum SPL, distortion, power draw, frequency response, longevity of electrode.)
They seem to be more on "discovery projects" than true HiFi oriented.
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Since I had to start somewhere, and not wanting to blow $11K on the Acapella units, I decided to order a "demo kit" from eBay and have some fun. Maybe even horn loading it, if possible.
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The speaker showed up at my door undamaged, and actually worked when I plugged in, which is a change from the usual China quality stuff.
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It’s very limited in terms of performance. I know, it's only an affordable demo kit but I was kind of expecting more...
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The flame isn't quiet. There is a constant hiss.
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It draws 75 watts from the wall, just to maintain the plasma flame. Not exactly an efficient way to produce music.
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The sound pressure level is very low. I measured it around 80 dBs @ 30 centimeters before distortion peaked too much.
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The ozone generation (and smell) is much stronger than anticipated. You don’t want to leave this on too long unless you're outside.
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Here is a small Video I've done with it.
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putting a metal, create a column and cut the annoying hiss sound
Measuring the thing was quite hard.
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It crashed the USB microphone when I put it too close the flame.
The MiniDSP was crashing quite often as well when I plugged the RCA adaptor to the feed signal
Even my Samsung Galaxy 3 phone acted funny when it was closer than 30cm from the tweeter.
EMI generation from the device must be insane. It interfered with everything.
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After multiple tries, I managed to measure it. Sort of.
It’s almost certain the manufacturer incorporated a low pass filter built in, in order to limit distortion. You can see the roll off at lower frequency.
Even knowing this, it’s far from a smooth linear ascending curve.
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Here’s what I got for frequency response: (about 30cm away)
And the almost non audible distortion.
Just kidding. It generated 20% and above distortion.
So very, very, poor performance.
So, what’s my take on this?
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Firstly, I can now affirm that ozone generation is a very efficient method to provide an instantaneous headache.
My ozone inducted headache lasted about 1 hour... fun, fun, fun!
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Still extremely interested in plasma tweeters, but ozone neutralization will be mandatory for the next project.
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Secondly, if any efficiency is to be achieved, horn loading is a must. With heat generation, a plastic horn will melt for sure.
As a result, Lansche Audio and Acapella use a ceramic combustion chamber for a reason.
This calls for a much more elaborate design and some fastidious research.
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I know that the Corona tweeter does not produce ozone. Acapella uses something very close to the Corona tweeter, so they must be ozone free as well.
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Having had a close-up inspection at various HiFi shows, I can confirm that commercial plasma tweeter don’t smell of ozone whatsoever. The units I encountered at HiFi shows had no audible hiss either.
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If they were producing even a tad of ozone, their sales would be banned in most developed countries, let alone the potential risk of lawsuits.
I found this online from Lansche Audio.
'Our Corona tweeter does not emit ozone due to the following reasons:
1. The temperature in the combustion chamber is kept higher than 350 degrees centigrade.
2. The electrode is surrounded by quartz which acts as a catalytic converter, converting O3 (ozone) to O2 (oxygen).
3. It also does not emit any positive or negative ions. This is due to there being only AC on the electrode and the high temperature.'
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To be continued...
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The dilemma now is to build a better unit mostly copying available patents,
or try to buy a broken unit and repair it.
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Used Corona tweeters are not exactly easy to find, however.
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Update: June 2018 – I’m no longer interested in plasma tweeters.