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Old 9th February 2007, 05:12 PM   #1
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Default ESL with welding Rod Stators

Hello everyone, I get to build electrostatic loudspeakers as a science project for our school. I've build conventional speakers before.
Perforated metal is too expensive so i've looked into using welding rods as a stator material, rather than wire because wire seems very time consuming.

The panels will be 72in x 24in

So if I get 36 in long welding rods would it be better to have a diameter of 1/16in or 1/8in?

Also the rods won't be able to run vertically up the panel, I'd have to lay them horizontally across the frame. This is a problem because I can't cross over certain rods to improve high frequency dispersion.

So i'm thinking i could make a very thin ESL panel to use as a tweeter perhaps 60in by 6in and then connecting it to the edge of the big panel and using a simple active crossover. But this is only after the initial success with the big panel. What are the disadvantages to this approach?

I'm also confused on segmenting the panels what is mean't be this, like when egg crate is put on top of the mylar?
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Old 9th February 2007, 06:06 PM   #2
Few is offline Few  United States
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I haven't used welding rods so I can't speak from experience, but I'd think 1/8" diameter rods would be a bit large in diameter from the acoustic transparency point of view. They'd have the advantage of being more rigid, but my guess is that the disadvantages would outweigh that advantage.

If you want a narrow tweeter for more uniform high frequency directivity, it'll have to be much narrower than 6"---there's a reason dome tweeters are 3/4" - 1" in diameter. The problem is that if you try to make a tweeter that narrow as a separate panel, the supporting structure tends to support all sorts of cavity resonances right in the frequency range you're trying to reproduce. That's why "segmenting the panel" can be a good idea. In this approach the overall panel might be 12" wide, but only the central 1" wide vertical stripe might be used to reproduce the highest frequencies. The support structure is then quite distant from the tweeter and resonances are less of a problem.

I assume that the reason you can't run the rods vertically, and then use different rods for different frequency ranges, is that the rods are too short. To solve this problem could you break the panel into two 3' tall sections, or three 2' tall sections?
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Old 11th February 2007, 12:50 AM   #3
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Thanks for that reply, I guess I could break up the panels into two or three 3' or 2' panels but wouldn't this affect the bass response. I just think its easier to get consistency with one panel. Isn't there a way to find out how much spacing is needed to still be acoustically transparent.?
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Old 11th February 2007, 05:34 PM   #4
Few is offline Few  United States
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Breaking a 6' tall panel into two or three smaller ones won't affect the bass response much because you'll need to clamp the diaphragm every few inches anyway. If you don't, the diaphragm will make contact with the stators. Sheldon Stokes's method of using dots as spacers, rather than using long strip-shaped spacers, is one way of making the resonance as low as possible while still ensuring that the diaphragm doesn't hit the stators. Take a look at his site if you haven't already.

The general rule is that most folks aim for roughly 50% open area--meaning 50% of the stator should be open space, the remainder should be conductor. I suggest going for slightly less open area, rather than more, if you deviate from the 50% rule of thumb, but others may have other advice to offer.

If you use 1/8" diameter rods, and aim for 50% open area, you'll need 1/8" of space between rods. That's a bit much if you're going with the fairly common 1/16" of space between the diaphragm and each stator. If you let the spacing between rods exceed the distance between the stator and the diaphragm you risk leaving some areas of your diaphragm experiencing a weaker electric field than others. You want the diaphragm to be uniformly driven (all points on the diaphragm feeling the same force) to maximize the speaker's sensitivity and minimize the excitation of resonances within the diaphragm.

Again, I haven't made welding rod stators, so someone with hands on experience may be able to refine these suggestions. On the other hand, the basic construction guidelines aren't terribly sensitive to the construction technique so I don't think I'm likely to be leading you to far astray.

Finally, it may or may not be easiest to get good consistency with one large panel. The project can become "all or nothing" that way. Smaller panels mean you have to repeat the contruction process more times, but the panels will be less unwieldy and you're therefore less likely to run into trouble trying to put everything together. Remember, you have to keep everything quite flat over the full size of the panel if you don't want to run into problems with the diaphragm hitting the stators. I think it'd be easier to keep small panels acceptably flat than one large one. Just something to think about.

Few
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Old 11th February 2007, 08:02 PM   #5
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Do hundreds of welding rods really cost less than a couple sheets of perforated steel?

How much is this thing going to weigh when you are done? How will you support the weight of all those rods?

I_F
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Old 12th February 2007, 02:20 AM   #6
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Thanks for your advice again few. The welding rods are cheap...

From Mcmaster I can get approximately 230 welding rods for $72. All the rods would weight about 10lbs. Perforated metal in large sheets is just too expensive.

Also I think the diaphragm spacing will be 1/8in separated by lexan.
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Old 12th February 2007, 02:37 AM   #7
maxro is offline maxro  Canada
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Default Re: ESL with welding Rod Stators

Quote:
Originally posted by angsuman
...I've looked into using welding rods as a stator material, rather than wire because wire seems very time consuming.
I fail to imagine how laying up individual welding rods and insulating them would be any less time consuming than working with pre-insulated wire. How were you planning on attaching the rods, with tack welds?
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Old 12th February 2007, 04:12 PM   #8
StanJ is offline StanJ  Germany
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@maxro,

welding rods do have the advantage of being straight by themselfes, if you are lucky enough to choose vom a batch. The isolation can be done, though costly, by using heat shrink tubes. This method has been applied commercially some 20 years ago.

Stan
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Old 12th February 2007, 11:41 PM   #9
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Yeah by time consuming i mean't making the wire straight, since this is a science project right now I might just go with my original plan at first. I just got the transformers in the 70v step up transformers. I'm wiring 4 in series-parallel arrangement. I find I can get about 600-700v this way.
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Old 13th February 2007, 11:52 AM   #10
Bazukaz is offline Bazukaz  Lithuania
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Making a wire stator becomes easy when you have built a jig. two light louvers are placed in a jig , with a wooden stick in middle between them.
The most time-consuming work is glueing the wires.Jig is shown in front of the picture.

Regards,
Lukas.
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