How about an ESL?

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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... :smash: :dodgy:
 
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...
 
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


:cannotbe:
 
OK time for a story. :rolleyes:

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.
 
graphite coating.

One side as far as I know.
What do you mean by which side ? It doesn't make a difference.
Your contact is from the coated side.

If it is the usual shiny film , any side is OK. If one side is duller , I guess that would hold the graphite better . I'm not sure.
 
Miscellany:

Dishwashing detergent is reputed to not be stable.

One side is sufficient. If you have surface-treated film (e.g., corona-treated, sometimes called "print-treated"), you want to coat on the side with the highest surface energy.

I've read about Nylon solutions being used as coatings- that might be interesting to pursue.

The best coatings are dispersions of colloidal carbon in a carrier polymer- stable as can be, very good control of resistivity, easy to apply. The downside is that the surfaces MUST be print-treated, and the colloids are solvent-based so must be handled with care and generally heat-cured.
 
johnkramer said:
how about a thin, pliable, sprayable paint with graphite in it? like maybe a dusting of something that will stick without having to rub in.

That's pretty close to optimum; you probably would want a high structure factor carbon black (like a channel black) rather than graphite, though, because the goal is a uniform HIGH resistivity. The main difficulty for the home constructor is getting it to stick well to diaphragm films. I home-brewed my own coating formula, but I have access to some pretty sophisticated blown plasma systems to permit proper adhesion of the coating to the film.
 
Found a possible film,

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.
How about either .00063 for one film I see, or .00015 for the other? Seems like the thinner one will work.

How about getting the tension correct? Making up a jig may work, but how important is getting the film stretched equally?

Many thanks all, for ideas in the forums,

GH

:cool:
 
I haven't seen free-standing film as thin as 0.00015- I can't see how you could handle it. What's the material?

0.00063 is a bit thicker than optimal but not outrageously so. Tension is your friend- you want lots of it for stability and to tame the fundamental resonance, which is why a heat-shrinkable material is desirable. It's pretty easy to get the tension reasonably even with a heat gun and some patience.
 
one-quarter mil mylar is what sanders used, its not heat shrinkable, he used spring scales in a jig to tension the membrane.

One question I have about shrinkable plastics. How much tension do you apply in the initial stretch of the diaphragm, before you use a heat gun?

Of all the DIY speaker building projects one can take on, an ESL is probably the easiest for an apartment dweller like me to take on. I've been pondering a project that can be made in a small kitchen with basic hand tools. The only power tools needed is a soldering iron for the electronics and maybe a heat gun
 
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