plasma tweeter

Jump to Latest
#103
Lord Winter said:
Okay Nixie, don't get it too serious.

My intent was to help Bostjan setting up his project, for the benefit of others, too.
Unfortunately, most of us cannot afford the equipment you're working with. Sorry, I'm just trying to be practical.

Your reaction was over-emphasized.😡
Click to expand...

Thanks Lord Winter and others for helping me.
I thought that would be interested or helping others too.

My wish to make companian with my fullrange fieldcoil speakers.

Working plasma tweeter starts from 5000Hz with 90-95dB/1m is fine with me.

Maybe i like Bernhard Plasma horn tweeter. Maybe he will show some fotos how he made it.

best regards, Bostjan
 
#105
bear said:
Keep in mind that the Hill type design requires a medium OTHER THAN AIR to work. Ie. Argon gas or HeNeAr gas... not just DC.
Click to expand...
Wrong once again! If you had read my numerous posts on MHCD-sustained discharges, you would have realized this (by the way, Hill actually used helium, not argon). It seems some people on this forum are too lazy to do some basic search, instead giving into their itchy 'Submit Reply' clicking finger!

First of all, Hill's design does not "require" a gas other than air, but simply uses it because it makes the problem more practical -- helium has a lower breakdown voltage and better discharge stability at atmospheric pressure, and the commercially important property of far less nitrogen dioxide and ozone (by distancing these air component gases from the heat). At least the former problems of breakdown and stability in an air discharge are resolved when one applies a technology that was not deveoped during the time of Hill's device, and this is the path I've taken, and posted about extensively in the forums.
 
#106
Nixie said:

Wrong once again! If you had read my numerous posts on MHCD-sustained discharges, you would have realized this (by the way, Hill actually used helium, not argon). It seems some people on this forum are too lazy to do some basic search, instead giving into their itchy 'Submit Reply' clicking finger!

First of all, Hill's design does not "require" a gas other than air, but simply uses it because it makes the problem more practical -- helium has a lower breakdown voltage and better discharge stability at atmospheric pressure, and the commercially important property of far less nitrogen dioxide and ozone (by distancing these air component gases from the heat). At least the former problems of breakdown and stability in an air discharge are resolved when one applies a technology that was not deveoped during the time of Hill's device, and this is the path I've taken, and posted about extensively in the forums.
Click to expand...


Yes, you are correct, Helium. Or HeNeAr (welding gas).

However, since the speaker is "impractical" without the gas - eg. it will not work - the gas is in effect "required."

And yes you have talked extensively about something that you've read some papers on, but have yet to determine if it can be applied to a practical speaker, or more to the point if YOU can apply it to a practical speaker.

I'd suggest spending more time on the doing, and less on the talking about what is merely an idea - albeit one that you have been suitably vague about in this forum.

_-_-bear
 
#107
but have yet to determine if it can be applied to a practical speaker, or more to the point if YOU can apply it to a practical speaker.
Click to expand...
Yet more *********. I already wrote in the relevant thread that I've built the electrodes and the MHCD-sustained discharge works fine. I only need to build the audio modulation circuit.
 
#109
bear said:
Keep in mind that the Hill type design requires a medium OTHER THAN AIR to work. Ie. Argon gas or HeNeAr gas... not just DC.

Reminder:

PLEASE RF SHIELD YOUR EXPERIMENTAL CORONA DISCHARGE SPEAKERS!!!

All it takes is some stupid window screen...
Click to expand...


Thanks Bear, i will do this first.

As Lord Winter said: this not a toy.


regards, Bostjan
 
#110
Hi,

i wrote email to italian guy who has also web page for plasma tweeter without tubes. I got info like this:

Dear Bostjan,

I have measure the following data on my tweeter (without any combustion chamber, nor horn):

- cut off frequency : 2kHz
- max spl: 95 dB
- max spl at 500Hz: 75dB

So, even if you are right when you say that usually this kind of tweeter work down to 4000kHz, my tweeter could be used even as a "mid tweeter".
Sometimes, I use my tweeter "stand alone", without any other loudspeaker ... the sound is very kind: obviusly there are no bass, but the result is beautiful and completely different from a common tweeter.

I think it is also good results, without gas.

regards, Bostjan
 
#112
Well the original Plasmatronics have electrodes near the gas as well. But the plasma shape deals with the directionality issue so that there are few reflections from that direction. The shape is one of the key contributions of Hill's patent, which I referenced and I ask again people to read.

The image I posted as I had written in that post is from to Jay Philippbar, a Plasmatronics owner whom I've had some email exchange with a while back. The electrode structure I'm using to avoid gas I've not measured the sound response of as I've yet to build the amplifier, but I don't see why it should affect it, as the characteristics of the plasma which Hill develops mathematically in the patent remain unchanged. However, there are a number of practical problems with my electrode design, though only one may affect the audio -- parasitic capacitance, since the cathodes are replaced with MHCDs which have dielectric between conductive planes. Refer to the drawings I've posted in the other threads. Another issue is heatsinking these electrodes, as the use of special materials is by itself insufficient (center of plasma at least melts tungsten wire, and can probably vaporize it). In the Plasmatronics, heatsinking is trivial since the cathodes are the helium delivery tubes themselves, and thus they are their own heatsinks. In my case, this doesn't work. As for the ozone and nitrogen oxides, a catalyst-plated mesh may be necessary, if an operating point for the plasma that minimizes it cannot be found. Finally, though I've platinum-plated my electrodes and they will not oxidize, pollution and particles in the airflow can be a problem, especially at the microhollows. That means a filter will likely be necessary. One idea that I had is using gas, but instead of helium, simply burning natural gas (that also takes care of the preheating, as I can avoid electrical preheating as the Plasmatronics uses). But I still haven't tried that. With low airflow through the microhollows, the main discharge easily gets over twice as large in normal air as the Plasmatronics with their helium, using my 1.8 kW power supply. Ignition is not an issue, unlike the Plasmatronics, since the MHCDs get biased from resistors from the main anode, and then initiate the main discharge. The Plasmatronics need a special circuit and low breakdown voltage helium to ignite; here it's automatic and fine in air. Stability is not an issue. Even if a glow-to-arc transition occurs, since it functions with current drive, the arc will extinguish and the MHCDs get biased again, and reignition happens immediately. Actually I've tested this by forcing an arc and it happens thus.
 
#113
plasma01.jpg

plasma03.jpg

plasma02.jpg

Power supply with on/off logic, inrush current limiter for toroid transformer, tube filament supply, HV supply
plasma04.jpg
 
#115
Allright, point to point wiring! Good man. PCBs limit you to two dimensions and a huge surface area. I like the tube's socket mount as well. But what's the horn's throat made of?

The Plasmatronics driver is high voltage TV sweep tube whose plates drives the plasma cathodes (plasma anode is hooked up to the power supply), one tube per cathode, configured as voltage controlled current sinks. I didn't want to bother with multiple tubes, so I'm using one 4X150A ceramic transmitter tetrode per channel, driving the MHCD bottom electrodes through current sharing resistors. Still working on quieting the centrifugal blowers that cool the tubes, and I may end up doing conductive cooling if I can solve the insulation issue, or do liquid cooling with flourinert as one company did when they used forced air cooled tubes in an audio amp. I've only powered the tubes once to make sure they work, and I haven't actually driven the plasma with them. I tested my electrode configurations using salt water resistor as ballast, which is why I've yet to do audio modulation.
 
#116
I built that prototype years ago and it works flawless since then, for hours every day.
It replaced a planar ribbon tweeter in an active 4 way speaker system.
It was never intended to work full range. 😉
Electromechanical implementation would look different today...
Maybe I built another for my work space and try different horns.
 
#117
Some more comments:

I know the coils in my tweeters look horrible and are mechanical instable, over the years I collected lots of useful materials such as teflon and ceramic tubes for the coil for a more solid construction.
One day...

Still, those tweeters sound wonderful and give the "be there" feeling, no other tweeter, be it diamond or berillium or airmotion transformer has that resolution.
There are some things that could be improved, the coupling to the horn, the horn itself...
The flame is relative small, I found there is an optimal size for the flame, bigger is not better.
The horn throat is ceramic. The flame is attracted to it and burns horizontal. 😀
About the use of tubes: The tubes heat the case and the horn and kill the ozone, therefor I am not interested in any solid state solution.

Nixie, I do not know if it makes sense to have a tweeter that goes more down to the midrange. I use Infinity Emim for the mids and those are fast enough.
The whole speakers sound very clean and homogen and I have no feeling I must improve something.
I remember when I heard speakers with plasma tweeters, there was a very little problem, the 76mm domes were too slow, still those speakers were the best commercial systems I have heard.

What drivers will you use for the range below your glow dischargers ?

I know about the plasmatronics, all the gas stuff and related problems, that is nothing for me.
I love my little purple flames.



quieting the centrifugal blowers that cool the tubes
conductive cooling
solve the insulation issue
liquid cooling with flourinert
pollution and particles in the airflow can be a problem
using my 1.8 kW power supply :dead:

no, thanks :whazzat: but I really wish you good luck :nod:


Doesn't the big glow discharge blow out a lot of UV radiation ???

IMHO: little flame - little problem, big glow - big problem...

------------------------------------------------------------------------------------

:dead: each of my tweeters draws 80mA from the 600V supply, that is acceptable.
 
#119
Despite the problems, there are two advantages that more than make up for the difficulties: the glow discharge is the best driver in terms of audio performance, beating corona discharges and ESL panels (one of Hill's aims was to improve on the various ionic speaker designs, including yours, that have been around since the 60s), and can be further improved by compromising on efficiency (linearity becomes better yet when the average plasma temperature increases w.r.t. the modulation temperature amplitude), and I can have that quality over an extended part of the frequency range without horns or other such inelegant hacks (conceivably even full range though the power needed would become enormous; for headphones though full range is quite achievable with a few hundred watts -- perfectly reasonable considering my electrostatic headphone amp dissipates a hundred anyway). Being able to go far below the tweeter range with such a high quality driver is awesome.
 
You must log in or register to reply here.
Top Bottom