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Old 21st March 2006, 01:01 AM   #1
BillH is offline BillH  United States
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Default The ESL Build Thread

This thread will detail my first ESL build. I'm still working out a few issues as I go, but the major components are either designed or built. Each ESL will have perforated steel stators, acrylic insulators, a mylar diaphragm, a 50:1 step-up transformer, and a HV power supply based on easily available low voltage transformers.

I wanted to do a multi-way driver. This quote is from an article by R.J. Matthys, printed in 'Electrostatic Loudspeaker Design and Construction' by Ronald Wagner: The efficiency of the two-way system is thirty-two times greater than a one-way system or single diaphragm speaker because of the reduced impedance mismatch. He goes on to say the efficiency of a three way system is about three times more than the two-way. The insulator design didn't allow a three-way, so I'm building a two-way.

Size was an issue, too. The 36" wide perforated sheet set the height. The width needed to be around the width of my RS225S-8 transmission line woofers. After some trial and error, I came up with two sets of 4.5" x 36" and (2) 1.5" x 36" stators per driver.

I'm going to try to get the mylar tensioned to get a resonant frequency of about 90Hz on the 4.5" midrange section and 270Hz on the 1.5" tweeter section. The woofer to ESL crossover is set by the step-up transformers to 225Hz. The ESL crossover will be somewhere between 500 and 1000Hz. Because of its relatively large size, the tweeter's dispersion starts to fall around 3000Hz.

The insulators are described in the Stacked Acrylic ESL Insulator thread. Here's a rendering from Solidworks showing a completed panel. The acrylic insulator is yellow and the stators are red to make it easier to see. The whole driver will be white in real life.
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Old 21st March 2006, 01:20 AM   #2
BillH is offline BillH  United States
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The biggest challenge with the perforated stators was deburring all those holes. I settled on a knocking down the burrs with a file and finishing with a round wire brush in my drill press. With the drill press table touching the wire brush I could slide the stator back and forth to round over the perforated holes. My US$80 drill press strained and I had to let the motor cool frequently. It suffered no major damage.

Here's a photo of the drill press and one of the smaller stators with a 3/8" brass screw for electrical connection soldered in. The screws were later changed to 1/2" steel. The screws are attached with 60/40 rosin core solder in a 1/4" milled hole. The solder connection is weak, so I'll need to fill the screw's clearance hole in the insulator with epoxy so it doesn't pull out of the stator when tightened down. Next time I'll use a smaller, countersunk hole in the stator. The stators will be powder coated white.
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Old 21st March 2006, 01:59 AM   #3
BillH is offline BillH  United States
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Audio step-up transformers with a budget like mine were a problem. In this thread, Calvin shows very positive results for using toroidal voltage step-up transformers as ESL audio transformers. I wasn't able to find the toroids I needed at a reasonable price and the custom transformer winders didn't seem interested in a two piece order.

After searching the 'net I bought a pair of M99B transformers from Russ at JustReal Music. 50:1 turns ratio, 225 Hz low frequency crossover, and very reasonably priced.
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Old 21st March 2006, 07:01 AM   #4
furly is offline furly  Canada
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Default toroids

Hi Bill,

In the thread where Calvin discussed his results with the torroids, I remember you had said you had ordered 4 of these toroids . Just wondering if you tried them out? I have just finished building my first set of panels using these.
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Old 21st March 2006, 01:18 PM   #5
BillH is offline BillH  United States
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Hi, furly. I never did get those toroids. I posted to diyAudio just before I ordered them. When I got to ordering, they were gone. It was a lesson learned that day, my mistake cost me another US$100 to get a good pair of transformers.

How are they working out for you?
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Old 23rd March 2006, 12:58 AM   #6
BillH is offline BillH  United States
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Adhesives are the dilemna of the day. I need to attach powder coated perforated steel stators to acrylic insulators. Some options are discussed here. I'm dealing with low surface energy materials which really narrows the choices of adhesives. The other challenge is the small surface area of the stator that will be glued. I've only got a 1/4" wide insulator area to glue a 50% open stator to. The same adhesive thickness needs to be used at all points to keep the planned 0.054" stator to diaphragm spacing.

3M #4932 and #4952 double sided VHB tape look like a good solution. I'll need about 32 yards of it it to hold everything together. The cost is the only thing keeping it from being my first choice.

I've been looking at some readily available adhesives lately to hold the stators to the insulators. Hardware store variety 30 minute cure epoxy was a disappointment. It sheared between the two parts easily.

Regular solvent based contact cement is a maybe. I tried one coat on each part and the bond seemed strong, but didn't end up with much contact area. Two coats on each part would have probably worked better. 3M has a #4693H contact cement (.pdf) made for low surface energy materials that looks interesting.

Tonight I'm trying common silicone sealant/adhesive on a stator and insulator sample. It's the smelly, acetic acid laced style of silicone. I've used it in bathrooms and it has been nearly impossible to remove from any surface it hardens onto.
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Old 23rd March 2006, 01:20 AM   #7
Bazukaz is offline Bazukaz  Lithuania
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Hi,
I have had success with super glue.I used plexiglass stators , don't know how does it bond to your ones. It then needs to be pressed uniformly for a few minutes.

Lukas.
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Old 23rd March 2006, 07:43 PM   #8
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I have used scotchgrip 4693 and it works VERY well, including the most difficult job of holding the tensioned diaphragm. I have some drivers I built years ago using the 4693 and they are as strong as new. The only problem with the stuff is that there is no second chance. If you make a mistake during assembly, you will have to start over...

The only other problem is obtaining the stuff. I have gone through the Thomas Register and called about twenty 3M distributors and not been able to find one that will sell me a small quantity or even stocks the stuff. If you find a source, please let me know.

I_F
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Old 23rd March 2006, 08:17 PM   #9
tommak is offline tommak  United States
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McMaster's has Scotchgrip 4693 in 1 quart, 1 gallon, or 5 oz. tube. Just go to

http://www.mcmaster.com/

and search for "scotchgrip" or go to page 3229.

Tom
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Old 23rd March 2006, 11:19 PM   #10
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Of course! Why didn't I think of that?

Thanks,

I_F
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