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Old 25th September 2002, 11:20 AM   #11
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Firstly a correction for my last post, I meant that I will use graphite, not ink. Was in my head, just didn't come out that way.

Okay, upon later investigation I have decided on 1000mm H x 450mm W. This seems to be approx what a few other people with successful ESL's have chosen.

I will build my prototypes hopefully by the weekend, and I will get back with my results.

Mike
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Old 25th September 2002, 11:42 PM   #12
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What type of stretching rig are you using? Also, what was your Mylar source? I've yet to find a satisfactory source of Mylar.

Let us know how they turn out!

-Dan
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Old 26th September 2002, 03:06 AM   #13
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stretching rig will be the sticky tape, table, bike tube and pump method. it seems easy, and i have a few bike tubes laying about.
Unsure how well this will stretch it and how evenly.

Mylar source I am hoping to find tomorrow. I am also yet to find any sources local to me (Melbourne/Australia)

http://www.dymark.com.au/packaging&marking/pg48.htm

I am going to try that place, because where my dad works (and me too sometimes) they use DYmark line marking paints, so I can get the boss to order it in for me etc.

I sent an email off to them just before regarding the thickness of the film itself to make sure it isn't too thick, and the thickness I am looking up now on what is best, although I thikn thinner is better for higher frequency reproduction due to the lower mass.

http://www.insulectroexpress.com/express/Linecard2.pdf
Some mylar products here if you want to have a look aswell phishead8
At the bottom is says they are based in Lake Forest, California and a quick search says Pasanda is in CA so give it a go

Anyway, back to work for me.

=Mike
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Old 26th September 2002, 02:47 PM   #14
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The bike tube on a table method will stretch it VERY evenly and to VERY high tension. You will not be disappointed.

I came up with the table idea after trying out the metal bars with screws at the corners method with disastrous results. The problem with the bars is that tightening the screws at the corners puts huge tension on the film right at the corners, and decreasing tension as you move toward the center of the diaphragm. Flex in the bars only makes the situation worse.

I get a lot of email from people asking about the tensioning table and for some reason they don't seem to understand how fast and easy it is, or how well it works. I think the problem comes from the idea that the diaphragm is held in place with tape. It is easy to see that and say "how much tension can you get if tape can hold it?"

Here's a little experiment to try- tie a weight to the end of a shoe lace or piece of rope or string. Go out to a strairway or balcony railing. Hang the weight over the railing and pull on the string and see how much effort it takes to raise the weight. Now wrap the string around the railing once, and try raising the weight again. You'll see that the effort required is MUCH greater with the string wrapped around the railing. The friction between the railing and the rope is what makes the difference.

On the stretcher table, the film is bent over 3 corners of the edge of the table, greatly increasing the friction between the film and the table (the rubber tube adds to the friction, too). That bending is what allows relatively weak tape to hold the diaphragm under huge tension. Since the air in the tube is free to move about, it will tend to move to where the diaphragm has the least tension, and tighten it up. That means it will tend to even out the tension over the entire surface of the diaphragm, so even if you didn't tape the film down evenly, the air pressure in the tube will tend to even things out for you.

MR
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Old 26th September 2002, 03:01 PM   #15
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Quote:
has anyone ever found a DIY electrostatic amplifier schematic? i have looked everywhere and can't find anything
http://www.ultranalog.com/9912/p25/
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Old 27th September 2002, 12:25 AM   #16
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Hi ultranalog, I am the one who you recommended not to try the directly-coupled amp as I would probably end up putting myself 6 feet under. Thanks yet again however.

Quote:
The ESL needs a high voltage DC bias supply. Generally speaking, the higher the bias voltage you use, the higher the sensitivity of your speaker. However, there are considerations beyond speaker sensitivity. If your speakers do not have plastic coated stators, then 1500-2000 Volts is about the highest voltage you will want to use, regardless of insulator frame thickness. Higher bias than that leads to corona discharge and its attendant whining sound. If your speakers use plastic coated stators, you can probably use higher voltages, but that will depend upon the insulator frame thickness also
Regarding that, what kind of properties should the stator coating posess? Insulative? Thick/Thin? Heat proof? I want to try and locate the most appropriate coating I can, as there are so many different paints and coatings these days, there is surely something suitable... and he also mentions plastic coating, I am not sure if he means plastic dipped, or some kind of platic paint coating or similar.
I was thinking powder coating, but am unsure if it is suitable?

Any ideas?

- Mike

Annotation:

Quote:
Diaphgram is made of 6 micron Mylar and coated with graphite. Steel stator has polyethylene coating which has been tested with 15 kV. This allow rather high polarization voltages to be used. Current voltage is 6.8 kV but it is little too high at summer when humidity is high. Spacers have been made from optimally stiff foam material which has very low dielectricity factor
http://www.ele.tut.fi/~artoko/audio/...rs/hybrid.html
This guy uses a polyethylene coating. Anyone else comment on their choice of coating if any, and their voltages
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Old 27th September 2002, 01:54 AM   #17
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Default http://powersourcing.com/

http://powersourcing.com/

I had to add that, I found it excellent for sourcing suppliers of stuff
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Old 27th September 2002, 03:13 AM   #18
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Default Information Note for Australians

Polyethylene coating for stators

http://www.plasticprotection.com.au/
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Old 27th September 2002, 03:32 AM   #19
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For an insulating coating, try a high voltage spray on insulator. I found it at a local alternator repair shop. Just call around and ask them for an isulating varnish in a spray can. The stuff I had was red and it seemed to be the norm. I can't give you more info than that though, sorry. Ideally, after applying this stuff it will reduce the chance of the mylar arcing to the stator. I didn't get to try it out, as I bought the stuff right before a move and I haven't been able to start making ESLs again, yet. Of course, you can paint over the insulator to your taste.
Good luck
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Old 30th September 2002, 06:16 AM   #20
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I have got everything for my speakers except the mesh, which was supposed to be ready by friday... so it should be ready hopefully tomorrow, and at latest Wednesday. so I will post further when the mesh gets in and I put together my prototype

-Mike
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