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Old 19th August 2008, 02:18 PM   #1
Nevod is offline Nevod  Russian Federation
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Default Wire stators, tension, stator bending?

Recently, i've got the guts to make an full-size ESL panel. As perforated metal is pretty much unobtainable here, wires seemed to be the only option.

For the wires, I have choice of 2 variants - either use an acoustic cable - litz wire, silicone insulated, 0.25 sq mm, or buy some single-conductor twisted pair and pull the wire out, though, probably, an untwisted wire of such kind can also be found.

So, the wires should be tensioned and then attached to stator frame. I've got a 12mm MDF board, about 130*40 cm, which I intend to use as a stretching jig. It is somewhat bent, but i plan to cut off 30 cm from the long side, cut it in half, and glue it back to increase thickness at ends - as the smallest threaded rods sold here are about 18mm in diameter.

For the stator, I've tought of using a plastic grid - from what I understood, like in an Acoustat design. After wire was tensioned, the grid was to be glued, put over the wires, and fixed by some weight till the glue firmens.

Hovewer, I weren't able to find grids yet(and I'm interested what for they are used and can be found at), and thought of gluing wire directly to PC board (glass-textolyte), which is to be used as insulator, in the same way as plastic grid could be glued. Then, in order to get rid of wire hang, supports would be cut out of PC board and glued to wires and insulator.

However, I have one doubt: bending. Quite a lot of tension is needed to straighten the wire, so, wouldn't the stators bend? Wouldn't the stretching jig bend as well? Or the tension required to straighten such a thin wire is not enough to bend MDF and PC board? Considering I plan to have about 3 wires per cm, and width of 25 cm = 75 wires?

Thanks.
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Old 20th August 2008, 03:51 AM   #2
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Default Have a look at these.....

http://esl.hifi.nl/zelfbouw/building%20an%20ESL.htm
http://esl.hifi.nl/index.htm

Personally I would look for some lighting egg crate louvre as used by Acoustat and use high voltage rated magnet wire of 30 gage and about 15 to 20 wires per inch. Hand tension is lots and the bow of the stator goes away when you bond the two halfs together. Use a 6 micron Hostaphan RE polyester film which is fully tensilised and very strong. Have fun and keep us posted. Regards Moray James.
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Old 20th August 2008, 10:34 AM   #3
Nevod is offline Nevod  Russian Federation
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moray james
The problem is that they may not be availible.. As for wire, there is some enameled wire sold here, but no one knows insulation ratings etc - it's just wire. I wouldn't dare to use it. While with PVC insulated wire I can be at least a little sure.

For the film, again, nothing less than 25 micron Mylar is availible. Bhe best bid is to try and use some friends in Ukraine to buy a 20km roll of 6 micron for ~300$, but I don't have such friends and money.

I had a suggestion to use PC board stators, ones with copper layer - cut slits using a dremel, though to me, it seems a very long job.
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Old 20th August 2008, 11:18 AM   #4
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I suppose you don't have the possibility to order stuff through the internet? Otherwise magnet wire (for winding transformers) and mylar are readily availble. 25 micron is totally unusable. You could contact forum member Martin-Jan for Mylar.
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Old 20th August 2008, 02:29 PM   #5
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Default Ues what you have to hand and experiment...

the links I posted show how the good folks in The Netherlands build wire stators without any louvre. You can purchase diaphragm and coating from a number of vendors like ER Audiohttp://www.eraudio.com.au/Components/components.htmlmaterial You can order using the postal service. Motor winding wire in a double build or high current variety should do. You can always build up a small test model. The PVC dielectric wire that Acoustat was not very strong in terms of dielectric strength so don't worry too much. Just about any good motor winding magnet wire should be as strong or stronger dielectric insulation as that used by Acoustat. You could also look locally for some "wire wrap" wire which is used in the electronics trade and normally has some type of fluropolymer insulation like tefzel. This is easy to get in 29 - 30 gage and it works well. Companies that wind motors or transformers could help you out. Over at the Audio Circuit there is a page somewhere which has a photo tour of the Acoustat factory when it was in Florida. Lots of great information there for you so you might want to search it out.
Remember that Google is your friend. If you have a roll of wire and it has the manufacturer's name with a part number on it you can search out all the data there is on it. Look to see if there is anybody in your area who builds tesla coils they would have good magnet wire to use or a Ham radio operator. You are going to have to scratch your head and see what is available locally on your own. You could use any old small gage magnet wire and if the insulation is not strong enough you can coat the inside of the stator with a few coats of urethane varnish. Make do with what you have, surplus or perhaps some builder at one of the clubs might sell you some wire and mail it to you. You have the information now it's up to you to see what you can do. I have seen esl's made with uninsulated aluminum window screen for stators. The way they were kept from arcing was to use two diaphragms with the resistive coating on one side only of each diaphragm and then facing the two coated sides toward each other. Not my first choice but they worked and sounded good. If you want this you have to make it happen.
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Old 22nd August 2008, 08:52 AM   #6
Calvin is offline Calvin  Germany
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Hi,

as PVC-coated wire you might use H07-VU or H05-VU which is used in normal household wiring (Audiostatic use this). Especially with the thicker and rather ´strong´ H07-VU You can build ´copies´ of the Audiostatics which use just a few supports over the hight of the panel without the need of the ugly plastic supports. It´s a fine solution when the d/s is >than 2mm because you need much less wires per width unit. Smaller d/s require thinner wire like the H05-VU or similar.

With wire-wrap wire you should look for Kynar coating which is a PA-derivative. The above mentioned Tefzel-coating is a fluoropolymere which is too high in impedance and too low in epsilon and which could give problems with how to glue it to a supporting structure.

Bending of the stators is just a problem when using soft multiple strands litz-wire which I don´t regard as a good idea anyway since it imposes quite strong forces continuously on the panel. With a hard single wire Hxx-VU you pull the wire straight and glue it on the supporting structure after releasing the tension. The often cited resonance problem of hard single-strand wires is rather a case for the Myth-Busters than a practical problem at all.

jauu
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Old 24th August 2008, 09:40 AM   #7
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Default wire stator wire

so it sounds like a good choice to make a acoustat type esl is to use pvc coated wire just like j. strickland recommended/ used for acoustats.
But
1. looks like my acoustat 2+ 2's use very thin guage copper(?) is there an ideal guage.
2. is there an ideal thickness pvc insulation around that wire
3. I cant find any wire at home depot etc. stores that actually say if the insulation is pvc or something else. I know j strickland in his white paper states that his first speakers used something other than pvc and it was too good of an insulator and didn't work well.
I've searched on line and they don't seem to say what the insulation is either?
If you want a thin guage wire, I would think phone type wire would work well, but is it pvc insulated?
thanks,
Paul
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Old 24th August 2008, 11:45 AM   #8
SY is offline SY  United States
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If it doesn't specify and the insulation is easily cut and removed, it's almost certainly PVC. It's the cheapest and by for the most common insulation.
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Old 25th August 2008, 08:19 AM   #9
Calvin is offline Calvin  Germany
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Hi,

as SY pointed out ´standard´ wire is almost always PVC-insulated.
Other materials are normally stated as special ´parameter´ of the wire and the prices are higher.

The ´ideal gauge´ depends on several factors among those are d/s, size of the panel/segments, the work effort You are willing to spent, etc.
From the viewpoint of field density and homogenity thinner wires are better. From the viewpoint of stability (number and distances of the supports) thicker wire is better. From the viewpoint of electrical safety thicker wire is better since it usually comes with a thicker insulation.
From a viewpoint of efficiency thinner wire is better. From the viewpoint of work effort a thicker wire is better (just for fun calculate the number of wires for a given panel width and eg. 50% openness)
And so on...
In short: the ideal gauge value is a compromise resulting from the needs that depend on the design of the panel.

As far as I remember Acoustat experimented with Teflon insulated wire. The important parameters to look at are the resistances of the material (volume and surface) and the dielectric constant epsilon.
Resistance values around 10^12Ohms and high epsilon values (>4) are preferable.

jauu
Calvin
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Old 29th August 2008, 07:15 AM   #10
Nevod is offline Nevod  Russian Federation
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Thanks to everyone

Well, in general, I don't really want to order something from abroad as it takes some serious time and isn't completely reliable. I'm somewhat financially restricted, that's the main reason.

Well, for the wire - i'll probably try to test the tensioning jig with single-conductor cat5 twisted pair - untwist the wires and solder them at the ends. Just to test.

For the enameled wire - it can be found only on electronics bazaar here, and I quite doubt that sellers know about insulation properties of wire. Though I just have to go and ask - if they know, and they do have transformer&motor suitable wire, i'll use it. After all, it's significatly cheaper than PVC-coated.

For the louvres - seems there are some, but expensive they are! About 40$ per about 1.2*0.3m one, if I'm not mistaken.

Though it seems that the problems are quite solveable, it's just that the materials aren't perfect, but i guess it will work.
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