ESL Pre Build Checklist

[BillH]

I wanted to get your opinions on my ESL project before I start to gather the parts. I'm planning on building a pair of panels 18" x 42" with perforated steel stators. These won't be full-range, but electronically crossed over to either transmission line or w-frame woofers for the bottom end.

The panels were inspired by Sheldon Stoke's panels described here.

I'll add more details on the individual parts as time allows. For now, here's a look at the listening room.

[BillH]

Here's a look at the perforated steel for the stators. I've got a choice of 0.036" or 0.059" thick. Both are 0.188" diameter holes on 0.250" staggered centers. I like the extra stiffness of the thicker material and think it's worth the extra US$1.07/square foot it will cost.

One side will need to be ground smooth to get rid of the burrs. I can't think of any way to round the burrs more. Too many little holes to use a countersink, but I may be able to sandblast if needed. Not sure if it's worth the trouble as the punching of the steel left what will be the diaphragm with no burrs at all.

I work for a company that just got a powder coating booth, so the stators will be powder coated. My only color choice at the moment is white. I'm thinking a walnut frame with a white sock over the ESL panels would look good and have a positive SAF.

[Audiophilenoob]

Originally posted by BillH
Here's a look at the perforated steel for the stators. I've got a choice of 0.036" or 0.059" thick. Both are 0.188" diameter holes on 0.250" staggered centers. I like the extra stiffness of the thicker material and think it's worth the extra US$1.07/square foot it will cost.

One side will need to be ground smooth to get rid of the burrs. I can't think of any way to round the burrs more. Too many little holes to use a countersink, but I may be able to sandblast if needed. Not sure if it's worth the trouble as the punching of the steel left what will be the diaphragm with no burrs at all.

I work for a company that just got a powder coating booth, so the stators will be powder coated. My only color choice at the moment is white. I'm thinking a walnut frame with a white sock over the ESL panels would look good and have a positive SAF.

WOW... where did you get those stators???? amazing .... any sources???

powder coating is cool as well

[BillH]

The diaphragm will be the 3.8 micron film from ER Audio with a coating of either Tech-Spray Licron or graphite. I'm leaning toward the Licron for ease of use. Has anybody got any application advice for the Licron?

I like the DIY stretching jig done by I_Forgot, but need to figure out how to make one large enough for an 18" x 42" panel.

Maybe something like this with two inner tubes. The circumference of each half of the jig would work with a standard 26" or 27" x 1.25" diameter inner tube.

[BillH]

Audiophilenoob asks:
WOW... where did you get those stators???? amazing .... any sources???

The company I work for lets me buy raw material at wholesale cost. There's quite a selection of rod, tube, and sheet in aluminum, brass, and steel to choose from.

[BillH]

There some difference of opinion on this forum about the longevity of VHB tape as an insulator, but I choose to use it and see what happens. McMaster-Carr has a high strength vinyl foam tape I've been considering, it's their number
76545A91, 3/4" wide. It's not genuine 3M tape, but the VHB wasn't available in the 0.063" thickness I wanted to use.

The description of the tape from the Mcmaster-Carr website:
Because of its high strength, vinyl foam tape is excellent for sealing around windows. Also great for mounting identification signs and nameplates as well as fiberglass trim panels in trailers. It conforms well to irregular surfaces and is UV, weather, and solvent resistant. Made of closed-cell PVC foam with acrylic adhesive on both sides. Has a paper liner. Temperature range is -20° to +150° F (apply at temperatures above 50° F).

I'm planning on copying Stokes' method of using small dots of tape along the centerline of the panel to give the diaphragm support.

I'm open to any thoughts on this choice of insulator and thickness. From what I've read, the 0.063" thickness should work for a panel that won't be fullrange. I'm not looking for high SPL, but need to be able to get a level loud enough for me. Hehe, that's a hard thing to define. Loud, but not too loud.

[I_Forgot]

Originally posted by BillH
I like the DIY stretching jig done by I_Forgot, but need to figure out how to make one large enough for an 18" x 42" panel.

I made a set of speakers with flat steel stators that were 24" x 48". I was not pleased with the result. When you have such a large area of flat steel supported only by its edges it is very unstable. Banging on the speaker frame with my hand had the steel pieces flopping back and forth.

Martin Logan solves this problem by putting a gentle curve in the steel, but that can lead to problems with keeping the diaphragm away from the stators. They seem to have it figured out, but I have never tried to do it. Unless you're willing to try to solve THAT problem, I'd recommend breaking that large panel into a few smaller drivers. It is a pain in the butt to make the electrical connections, but the speaker will be much better behaved.

Licron is the way to go. Be sure that you have a reasonable temperature when you apply it, and mask off any insulators that may accidentally get hit by the spray. In fact, spray it outdoors, and make sure there are no insulators around (except the ones holding the diaphragm tight, and mask them off).

I_F

[BillH]

I_Forgot writes:
I'd recommend breaking that large panel into a few smaller drivers.

Any recommendation on size? I'm not against making the panels narrower, but I'm worried that the low end would suffer. That could be fixed with a shelving circuit, though. There's a lot of narrower ESLs out there, maybe it's not that much of a problem. I've only got an 84" high ceiling so I'd like to fit the panel on top of a woofer cabinet. Woofer cabinet ~12" high.

I've seen the curved panels and it's something I could do as long as the long dimension of a panel was 36" or less. One design at The Audio Circuit used monofilament line as spacers, but I'm leaning toward keeping the panels flat for my first try.

[BillH]

The bias supplies will be the Stokes design. A .pdf file is available here.

A description of the power supply from The Audio Circuit:
The standard household power (110 or 220) is brought to the board and stepped down, rectified and filtered to form low voltage DC (15 volts or so). This DC powers a small switching supply whose frequency is tuned to the resonant point of a secondary small rectifier transformer wired backwards. The amplitude of the driving signal is regulated and adjustable to variable output levels. Because this signal is at the resonant point of the transformer, the output is about twice the voltage level it would be if another frequency had been chosen. The output of this second transformer goes to a standard Cockroft-Walton voltage multiplier.

It's not the simplest design, but can be built with readily available parts. The voltage step up transformer is specified as a Microtran by Tamura, which I don't see listed at Jameco or Digikey, but it looks like any small 115/230V to 6.3V pc mount transformer should work with some tweaking of the resonant frequency of the bias supply.

Here's a look at my pcb layout. It's almost the same as Stokes' version, with the step down transformer removed, to be replaced with an AC-AC wallwart. The translation from AutoCAD to Jpeg wasn't very good, the traces and pads look much better in AutoCAD than they do in this picture.

[dstockwell]

This is the one I planned on using, any opinions on this one.