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Old 7th April 2004, 11:10 PM   #1
Duo is offline Duo  Canada
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Default How about an ESL?

This topic has suddenly caught my interest and grasped my intellect with a terrible firmness.

I tried making just a quick saran-wrap and cardboard ESL, which to my surprise, worked okay. It didn't go very loud because my voltage was too low for the stator distance. I also couldn't bring the voltage up enough because of too low tension on the diaphragm. Either way, it worked well enough to make me want to build many more. It only took me about an hour to make the fully functional unit. After wrecking one diaphragm befre testing, I was disappointed, but continued on with my work.

It was a rather crude thing too; composed merely of cardboard insulators, with a tinfoil back stator and a steel mesh front stator. There was saran-wrap stretched in between and held in place with packing tape and coated with graphite powder, which I had slowly scraped off of a pencil with a knife. The power supply was composed of a 12 supply, a variable oscillator, and a flyback transformer with rectifier, filter, and driver circuitry. I was able to vary the bias voltage and efficiency with the signal generator. This was nice because I could prevent arcing. After the power supply, of course, comes the audio input. I used a simple tube output transformer coupled to a power amplifier.

Anyway, cut to the point, I am interested in any suggestions that people have toward making more efficient and ideal ESLs. I'm planning on something about 2 to 4 square feet for midrange and high in my system.

Anyone got ideas? Any good ESL builders here that could share some information?

Well, gotta go. Time for my 'other' job...
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Old 8th April 2004, 06:52 PM   #2
Duo is offline Duo  Canada
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Sorry... That post was a bit long and cumbersome. I think I had a little too much time there to write that.

...

Anyway, anyone into the topic of electrostatic drivers. \
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Old 8th April 2004, 07:19 PM   #3
SY is offline SY  United States
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Efficiency is rarely the issue, but sensitivity, driveability, and SPL sure are. I like the idea of Saran as the diaphragm, so much so that it's what I use, too. What did you use for the coating?
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Old 8th April 2004, 07:31 PM   #4
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There are 2 published books on ESLs (one by Saunders) that cover a lot of ground... available at audioXpress.

dave
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Old 8th April 2004, 08:34 PM   #5
markp is offline markp  United States
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Quote:
Originally posted by SY
Efficiency is rarely the issue, but sensitivity, driveability, and SPL sure are. I like the idea of Saran as the diaphragm, so much so that it's what I use, too. What did you use for the coating?
He mentioned pencil lead graphite.
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Old 8th April 2004, 08:49 PM   #6
SY is offline SY  United States
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Ahh, missed that! Effects of old age. Thanks.
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Old 14th April 2004, 10:14 PM   #7
Few is offline Few  United States
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I've had good luck building ESL's using perforated steel purchased from McMaster-Carr (perforated with something on the order of 50% open area). Mc-Carr was also my source for a large roll of 1/16" thick double-sided adhesive tape (that white foam tape made by 3M). The foam tape serves well as an insulating spacers and of course comes with excellent adhesive pre-applied. To narrow the spacers and reduce the excess capacitance I cut the foam spacers length-wise using a circular razor blade--the type that looks like a pizza cutter. I painted my stators with black epoxy spray paint after cleaning the perforated steel with organic solvent (and before assembling the speaker parts...). By the way, don't do the solvent cleaning step ahead of time because once the oily film is removed from the steel it rusts rather quickly! Lubricating graphite intended for locks seems to work reasonably well as a conductive coating on the mylar I used for the diaphragm. I used heat shrinkable mylar which simplifies the task of making a wrinkle-free diaphragm. My speakers are about 6.5 feet tall, and 20" wide, with about 3.5" spacing between vertically oriented spacers.

They've been running for about three years now without showing signs of major design or material flaws. Not surprisingly, they're beamy as all get-out, but it's less troubling than I expected. They're also not at all "polite". Transients really snap, reminding me of horn speakers---makes me wonder if the good impedance match between the diaphragm and air is the key.

Sorry to ramble...
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Old 22nd April 2004, 08:25 PM   #8
extremy is offline extremy  United States
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Default Diaphram materials,

Can you guide me on thickness for the diaphram material? I can find a modern Teflon PFA film down to .001 inch. This teflon product has a lot of qualities, and looks like if I can get the right coating to stick to it, I'd have a good product for the diaphram. Apart from that, it's price is not outrageous. Maybe I've missed what plans are trying to achieve by using a coating on the diaphram. Are we to only coat one side, both sides? How can a coating stick to some of the modern films? This [Teflon PFA] product may be bought coated on both sides for help in bonding.

I'm thinking about a frame made from white cutting board plastic, a fairly stable material. Otherwise I may check on a slab of marble or granite I can cut the center out of. In my design, I want a very stable frame around the panels. Seems like the frame must hold up over years to hold the tension put on the diaphram.

Talk later,
GH


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Old 22nd April 2004, 09:10 PM   #9
SY is offline SY  United States
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You don't want to use Teflon. It's impossible to get coatings to stick using commonly-available techniques, and it cannot be heat shrunk. Poor tensile strength, too. Also, 1 mil (0.001) is too thick- you want one-half to one-quarter that thickness.
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Old 22nd April 2004, 11:21 PM   #10
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OK time for a story.

back in my youth days my best friend and I used to raid this electronics junk yard from time to time. One night there was a dozen cannibalized Microwave Ovens, all the same make and model in the dumpster. It hit me right there on the spot to use the grids from the doors for an ESL project. Enough to make 6 panels. I made them using double sided tape, plastic wrap, and graphite. Like you I really didn't have enough voltage on hand to make any real use of them, but one pair got bolted to the sides of a chair in our evil lab as an awesome pair of headphones, or chairphones if you will and actually worked really well for that. Enough so that I took a pair for my bedroom (each side of the bed) and my friend took a pair for his bedroom.
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