The ESL Build Thread

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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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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.:D

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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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.
 
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?
 
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.
 
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
 
Today's build had a couple of failures and one success.
Bazukaz writes:
I have had success with super glue.I used plexiglass stators , don't know how does it bond to your ones.

Lukas, thank you for the suggestion. I tried a small powder coated piece of perforated steel glued to a scrap of acrylic. It works great! When I tried to peel the perf. off, the powder coat came off the steel and stayed stuck to the acrylic.

The bare metal behind the white acrylic in the picture is 0.059" thick and was glued on two sides. I bent it when I pulled it off. :D
 

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The powder coating of the stators was a learning experience. When the stators came out of the oven, all of the sixteen solder joints that were holding in 6-32 screws for electrical connection failed. I had used soft solder and didn't consider at the time that the melting point of soft solder is very close to the curing temperature of powder coating.

My ego was bruised. Then I thought of something a boss said to me many years ago after I had made a whole order of parts wrong. He said "Everyone makes mistakes, you're not the first. You have to fix your mistake. Salvage all you can, do it quickly and move on." I've got a lot of time invested in the stators and didn't want to start over.

The picture below shows a a pair of small stators before and after repair. They were sandblasted, resoldered, and coated in the sandblasted area with Rustoleum Paint for Plastic.
 

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The insulators with stators are all glued up. It went very well. I used a total of 24 grams of super glue to hold the sixteen stators in.

Here's a picture of two completed assemblies. Inside shown on the left and outside on the right.
 

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I've been working on a two-way crossover circuit for the 1-1/2" wide and the 4-1/2" wide sections of the ESL panels. I've got a first order crossover at 1040 Hz that sims well using available components.

Here's the simplified circuit. The audio step-up transformer is connected on the left. The bias supply is connected on the right. Each of the four stators is connected to one of the center four points.
 

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Because of the high voltages and power dissipation of 2 and 6 watts, the resistors are series connected 1 watt Xicon carbon film. The capacitors are series connected 4700pF 1Kv Murata SMD. I'll be using SMD capacitors on the bias supplies, too. The board measures 2 x 6-5/8".
 

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Parts came in today. Almost everything is there. Two transformers are back ordered, I ordered the wrong IEC connectors, and forgot to order the 330K resistors for the bias supply. I'll have to dig through my salvaged parts for IEC connectors and resistors.

The SMD capacitors are really small! There's a strip of twenty of them circled in yellow in the photo.
 

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Here's a photo of the almost completed circuit boards for one channel.

The high voltage bias supply is at the top. It's missing a transformer that should be here this week. The black wire is a jumper to select output voltage. The inset image in the bottom left shows some of the SMD capacitors on the solder side of the board.

In the middle is the two-way crossover. It has four SMD capacitors on the solder side of the board.

The two boards at the bottom are resistors for the input side of the audio step up transformer. They're 1 ohm 10 watts per board. I wasn't sure of the value I'll need, so I made two for each channel.

The boards were done using the laser toner method. It's the first time I tried it and it worked quite well with only one defect that couldn't be fixed with solder bridges.
 

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Hi,
Here is my first wire ESL. I is not finihsed yet , but sounds already:).
For now , i have only a "U" power trafo to test it. Sound is not that bad , even with poor transformer , and it has bass, though i feel that a sub is needed.

Regards,
Lukas.
 

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