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Old 3rd February 2002, 05:51 PM   #1
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Talking DIY Electrostatic Stator insulation

Hi All,

I've been reading this forum for awhile, and I guess now would be a good time to start posting. '_'


I've been trying to build some electrostatic speakers. I am using Aluminum stators and 1/8" plexiglass spacers and .0005" Mylar. I'm going to scrap it and rebuild it differently as I've just burned a hole through the mylar while trying to heatshrink it... heh.. probably shouldn't have set my heat gun on its high temp setting.. : (

Anyways, I'm using a roughly 7000 volt bias supply controlled with a variac to be variable. I didn't insulate the inside of the stator, which I should probably have done, but when I set the variac to around 50 volts, so bias is around 3000, the speaker starts to arc with no material playing. the strange thing is that there seems to be a preference to arc on the first and last sections on the panel (6 ft panel split into 7 sections). Is there any explanation for it wanting to arc at those points? I'm pretty sure that the graphite I rubbed in is pretty uniform across the mylar.

Also, what would be the best high voltage insulation to use. I've search the net, and I've heard people using polyethylene, glyptol, and anodizing the stators. I want to get as high of a bias voltage as possible, at least up to 7000 volts and even higher.

thanks!

-eric
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Old 3rd February 2002, 06:21 PM   #2
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Eric,

I don't know what material you use for the stators. It's possible that the edge of the holes exhibit some very little sharp irregularities, which are the cause of arcing.

Try to reverse the stators front-back, or polish the metal with waterproof paper (used by car painters).

Regards, P.Lacombe.
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Old 4th February 2002, 01:39 AM   #3
Dave is offline Dave  New Zealand
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I have never seen a DIY solution to stator insulation. I guess you may have to dip the stator in something but that seems pretty impractical. Maybe you could find a sheet of plastic with exactly the same hole pattern as your stator and then glue that to the stator. This probably more practical but you'd most likely end up getting both parts custom perforated.
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Old 4th February 2002, 03:00 AM   #4
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I've found that perforated metal stators have two different types of edges, remnant of the perforating process. There is a "punched-in" smooth side, which should be on the inside of the ESL. The "sharp" side should be positioned toward the outside of the ESL. Also, be sure to file off any sharp edges on the edges of the stators, this is also a remnant of the shearing process.

As for insulation material, I have been having extremely good luck with a two-coat insulating scheme. The first coat is applied to the inside sides of the stators (to save money). This HV insulating paint was made by Crown Industries, and I purchased a spray can at an automotive alterenator & starter shop. It resembles a metal-oxide primer, and is orange in color. Good for 1500V for every mil separation from the diaphragm. After that dries, "bake in sun on a hot day," apply black lacquer to both sides of the stator. Don't skimp on paint.

BTW: Use Automotive-Etch to prepare the metal for painting. (available at NAPA)

Remember to mask off an area for your electrical connections!

My old un-insulated ESLs arced constantly. My insulated ones are running at higher voltage and have never arced. I play them loud, too

You may also want to consider 3/32nd inch to 1/16" spacers if you are not too concerned about bass. You panels would be more efficient with less spacing. Perforation size is also important, see my website for more info.

As for the plastic sheet idea, don't bother, it will lower the panel's efficiency. Simpler is better!

Also, consider perf'd steel stators with at least 1/8" perforations (3/16" prefered). Steel gives lots of strength, and the large hole size passes midrange and upper-bass frequencies.

Visit my website for more information:

Matthew Anker's Electrostatic Loudspeaker Page
http://home1.gte.net/res0f2t3/index.htm

Good Luck!
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Old 4th February 2002, 05:20 AM   #5
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I'm using Aluminum stators with 1/8" perforations. I'm not sure about the open area, but it is somewhere around 50%. The reason I'm using aluminum is because its so much lighter than steel. I did have some perforated steel cut for me. But I decided to change to aluminum because I was afraid the weight would stress the bonds of the glue. Also, I had already made note of the sharp and smooth side, and I think I did it correctly, though my memory is failing now of what I actually did.

What do you guys think about using styrene for the spacers? I really hate using plexiglass because its difficult to cut. I'm thinking of using Lexan or styrene when I rebuild the panels.

I'm trying to build a full range electrostatic panel, so bass does matter, so right now I'm insisting on 1/8" spacers. I might possibly use 3/32", but I haven't really decided yet. As far as sensitivity goes, when I had the bias set at around 3000V, the volume seemed decently loud, and I was only using a 35 W tube amp to drive it. I'm thinking I can make up for lost sensitivty by boosting the bias up further. The only probably is the arcing. If I can get that problem solved the output will be fine for me.

Matthew, how high of a bias are you running your currently insulated panels at and how high can you run it without it arcing? What was the name of that HV insulating paint? Does the second coat have to be laquer, or can it possibly be a home paint latex type? Also, did you glue the spacers on, mask off the spacers, and then paint the stators; mask off places for the spacers, paint the stators, and then glue the spacers; or paint the stators and glue the spacers onto the paint?

I know that all this messing around is giving me more experience with building electrostatic speakers, but its really starting to bite into my wallet by trying so many different things. If anybody has any useful information, please let me know.

Thanx!

-eric
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Old 4th February 2002, 01:00 PM   #6
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My ESLs are running at around 4kV, I'm sure I could go higher, but the sound levels balance out perfectly with my woofers.

The HV insulating paint is made by Crown Industries, and it does mave a model number, but I don't have it with me. Call an automotive electrical shop and ask them if they have any insulating primer.

The reason I painted them with lacquer is because it's thin and easily sprays into the perforations to coat them. The lacquer also provides a fairly decent insulation effect. I'm sure you could coat them with latex, but after you spend the time to build a "high tech" speaker, why would you paint it like your walls. Latex is also thick, it could rob you of your "effective perforation diameter," the unclogged hole size. My ESLs are coated with Harley Davidson "Vivid Black" lacquer. I jut happened to have a quart, and it's a "performance-enhancing" paint.

I first painted the stators, then glued the spacers directly to them with 3M Super 77 spray glue. Clamp and let dry overnight.

You could use Lexan for the spacers since it's easier to cut, but it is much more expensive than plexiglass. Styrene should work too. I've even seen people using double-sided foam tape!

-M.A.
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Old 4th February 2002, 01:51 PM   #7
tvi is offline tvi  Australia
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Hav you considered getting it coated commercially or would this be beyond budget?

Coatings like Kynar or ETFE are applied like a power coating then baked, the electrical performance is pretty good


ETFE/Tefzel
Electrical Properties
<table width="55%" border="1" cellspacing="0" cellpadding="4">
<tr><td > <font size="1" face="san-serif">Dielectric Strength (V/mil) short time, 1/8" thick</font></td>
<td ><font size="1" face="san serif">1,800</font></td></tr>
<tr><td ><font size="1" face="san serif">Dielectric Constant at 1 MHz</font></td>
<td ><font size="1" face="san serif">2.5</font></td></tr>
<tr><td ><font size="1" face="san serif">Dissipation Factor at 1 MHz</font></td>
<td ><font size="1" face="san serif">0.0072</font></td></tr>
<tr><td ><font size="1" face="san serif">Volume Resistivity (ohm-cm)at 50% RH</font></b></td>
<td ><font size="1" face="san serif">10<sup>17</sup></font></td></tr></table>
ETFE Is a physically tought film and can be applied up to 40mil

hope this helps
James
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Old 13th February 2002, 07:11 PM   #8
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Default Aluminium Stators

I have been running aluminium stators for some time and have found the best way to ensure insulation is to have them anodised.This builds up an Aluminium oxide layer which acts as a very good insulator. As anodising is a subtractive process the sharp edges from stamping out the holes are eroded away during the process.

You should be able to find an anodiser at a metal finishing workshop close to you-try yellow pages-and it should be quiet cheap to do providing you are prepared to wait for them to put your panels through in a batch.

You need to ask them to 'soft anodise' and they will ask you what colour you want.I stuck with natural anodised but you can ask them for a wide range of colurs-it will cost you more.

Once you have done that you might want to consider using industrial double sided tape instead of plexi glass or perspex.The stuff comes in a variety of thicknesses and you need to ensure that the type you but is low shear as the tension in the mylar can move the tape initially.Martin Logan use this approach as does Inner Sound

By the way 7000 volts is a lot-I get good volume at about 5000v
but I bandwidth limit them at 200hz and use a bass dipole for the nether regions.

Good luck and don't forget-its supposed to be fun!

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