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|20th February 2013, 08:32 PM||#11|
Join Date: Feb 2008
Yes, I did properly test these stator's with a grounded probe touching the rods and there were no arcs.
I also show a test of window screen with the same method in the coatings thread in this forum.
PVC insulation is good for about 500v per mil as you mentioned I am getting at least 3 times that if not 4.
In order to achieve good performance with a small panel, large voltages are required as it has a much smaller surface area to work with.
I ran my last panel typically form 5KV to 7.5 Kv of bias and had pushed to to 10KV but it didn't last very long as the coating was aging.
It broke down frequently at those voltages after I made it to 25KV P-P on the stators and exploded.
Due to the type of construction it was nearly impossible to repair it and I would have spent much better time just making a new one.
A Desktop ESL Build
Many of theses picture are already in these threads, But things get buried quickly and it is getting more difficult to find them as I have made this same discussion many times.
Anyhow, That is when I started researching coatings and testing out what I had and found it to be very good actually if it was done properly.
To test the coatings I built a variable precision regulated HV supply so that when an arc occurs it will maintain the exact same voltage after the arc has stopped.
This way I can note what the voltage was when the breakdown occurred.
That project is in these threads and has been re-documented here as well,
Does anyone have schematics of a varible HV power supply
I don't have any humidity issues where I live at the moment and running it at about 4Kv to5Kv works very good just the same.
It took quite a few more coats of clear acrylic on top of the Powder coated screen to safely get to and above 7Kv.
Yes, I have been using about a 1:256 step up ratio in my final tests and it is difficult on the amp due to just the transformers capacitance alone as the panels capacitance is only 50pf.
At a 1:128 ratio they run very nicely but with a drop in sensitivity as expected.
I think at 1:128 and 7KV of bias I am able to nearly match the sensitivity of my woofer.
With two or three panels of the same size it matches up quite nicely and I found this to be about 1 sq foot or even the size of a piece of paper (8.5" X 11").
A normal 1:128 ratio works well too but doubling the ratio increases the sensitivity by 6db as does doubling the bias voltage.
If this was a larger panel this would not be necessary to achieve a high output.
I got about +105db at 1 meter with this panel at at less than 20v Peak into the transformer.
And no more than a 5V peak was all that was needed to be around 90db for normal listening.
My small amp was very happy with this range, and so was I! He,he,he,he.
I was trying to fully document this when I switched to a larger amp as the little one would shut down every time I hit a peak that it didn't like.
Being a cheapy cpu controlled cd player type it took for ever to go through all of the settings just to get back to square one with no EQ or DSP.
This is when the panel failed for the last time and it was just time to build a new one.
I was running the usual 20 P-P at about 105db pushed it a little farther and as I was sweeping the frequency up the very exact same spot that had been giving me problems had gave out.
I had, Had enough so I let it burn and watched the show.
It was a good test to see a much current the screen could actually handle as it got orange.
The after math of that test is some where in these threads as well.
These little panels were meant to be for nearfield listening at about .5 meter and did do incredibly well for this application.
Pushing the voltages is mainly just to see how far I can go to squeeze out every last gram of efficiency I can and find what the limits of the materials are.
Then to apply what I have learned to a more larger highly efficient panel.
I have had them so high that the air was ionizing in the gap but not arcing or distorting, although, it was so loud the it was difficult to tell without closing my ears.
After about 10 minutes the stator coating failed and it exploded from the side causing the plastic to catch fire.
I was using 4 cores at 1:64 each( total of 1:256) and the full output of a Crown DC300A II with 60v rails when this happened.
I am only after Mid/High frequency use for hybrid systems at the moment but you do need a good amount of D/S spacing for excursion's in order to get down to the 200HZ or 300hz range to help make up the difference of dipole cancellation's.
Thus the second reason for using such high voltages.
My next panel using the same design will be two 3 foot section and its width will be increased to about 6".
I will use that with my main woofer system.
Eventually I am thinking about using the same plastic grid and window screen design method to build some 8" to 12" wide X 4 foot long bass panels.
About 8 or 16 of them and corner load them in the room as in the David Lucas's design called the "Shockwave ESL Subwoofer System".
It will be interesting, But it will be some time before I get to that!!
My panels were 7 years old when I started pushing the voltages and survived any abuse I gave them up to that point.
The coatings never failed and the original Licron never deteriorated after many years of been environmentally been abused with sand and road salt as well.
In fact the panel that I burned up (much to my surprise) was using the original Licron formula (then 9 years old) and not the Crystal formula as I had thought.
I had only rediaphragmed one of them to do a side by side comparison and never re did the second one.
After 7 years they fired up the very first time and then I decided to clean them and eventually recoat them and start pushing the voltages.
So no reliability issues there, just as long as they weren't over voltaged !!!
Last edited by geraldfryjr; 20th February 2013 at 09:00 PM.
|25th February 2013, 05:24 PM||#12|
Join Date: Mar 2004
Location: Den Haag
Using PCB would get you same result , or combining louvre like acoustat only for increasing rigidness, for smask panel you can get away with 1 mm PCB, I got a shity cnc I build for fun that coul mill all the holes and their copper around it so it won't arc. Use some paint for wooden floors to seal the copper side and ur done.
Plate of 1000mm x 500 mm x1mm thick is like 35 euro.
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