ESL Stator to Diaphrame Spacing - diyAudio
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Old 3rd August 2008, 10:35 PM   #1
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Default ESL Stator to Diaphrame Spacing

Hi Everyone,
I have a quick question regarding the appropriate spacing to use in my cells. I recently picked up perforated aluminum with a thickness of 0.032" and a hole diameter of 3/16" or .1875". I've been reading Sander's book and some of his guidelines are useful, in there he states that the hole diameter should satisfy the following inequality:

2*stator thickness<hole diameter< D/S spacing

Where D/S spacing is the distance between the diaphragm and the stator.

With a thickness of 0.032" i satisfy the lower bound on this inequality, the problem is the upper bound, to satisfy it i would need a D/S spacing greater than .1875", with such a larger spacing I fear that I would have to have quite a large potential difference between the stators. I have seen posts of people who used similar stator material while there hole diameter is greater than the D/S spacing. I planned on using 0.08" thick acrylic sheets as the spacers. What do you guys thick, any help would be greatly appreciated.
Sincerely,
Bryan
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Old 4th August 2008, 12:07 AM   #2
Few is offline Few  United States
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Location: Maine, USA
Hi Bryan,
It sounds like you're embarking on a fun project. Best of luck.

I'd stick with the spacers you have rather than going any thicker. You didn't mention what frequency range you're going to try to cover, but I think you'll find most folks here recommend that you not try to build a full range ESL---certainly not as your first ESL project. Crossing over around 200-300 Hz to a woofer or set of woofers is more likely to pan out for you.

So, with the assumption that you're not going to try to run the ESLs any lower than about 200 Hz, you shouldn't need more than about 1/16" diaphragm-stator spacing (0.0625"). That's what I'm using now, and the new speakers I'm building are actually going to use slightly thinner spacers (about 1 mm). I think going any higher than 0.080" is going to lead to exactly the sorts of troubles you mentioned, and is also likely to end up giving you less sensitive speakers than you'd like.

It just occurred to me that you didn't mention the other dimensions of your stator. How big is the active area of one stator going to be?

One last thought: Be very careful to avoid putting any kinks, dents, or burrs in your aluminum. It's pretty soft stuff, and those localized defects in the surface may end up limiting your usable bias voltage and therefore your usable sensitivity. It only takes one tiny annoying spot on your stator that's closer to the diaphragm than all the rest of the stator in order for you to be stuck with premature arcing---and we all know premature anything isn't good.

Few
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Old 4th August 2008, 05:33 AM   #3
Calvin is offline Calvin  Germany
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Location: close to Basel
Hi,

hmmm...anybody noticed that all quick Qs need long answers?
Brian, it seems to me that the way You approach your design won´t end up with a good design.

So:
1) Make yourself clear what You want -e.g. over which frequency range shall the design work? What stator size is needed? What stator size is acceptable (WAF)? What dynamic range is needed? ...and so on.

2) Depending on these goals You can define the mechanical parameters based on the data of the materials you want to use or have to use.

3) Ask specific Qs! It eases the stress on the A considerably and allows for precise and correct answers that will really help You

4) The quick A to Your quick Q is therefore 42! Hope You catch the clue

jauu
Calvin
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Old 5th August 2008, 07:29 AM   #4
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Join Date: Aug 2008
Thank you for your timely response, sorry I kept my details and design objectives out. This was my first post; very happy to learn it is very active in here. In the future I can be more detailed.

Have you guys ever heard of electro-active polymers (EAPs)? Essentially it is just a parallel plate capacitor with a dielectric that completely fills the gap, no air. A potential difference is maintained between the plates and the whole structure can be made to vibrate. What’s nice is the whole device moves note just a thin film as we have here. You can get quite a deflection with little applied voltage. This could be useful because we never have to worry about the film making contact with the stator. I am going to start to experiment with them to see if we can improve its response time so that it can be made to vibrate with frequencies in the audible band. If perfected these devices will make some of the common problems we face obsolete.

It’s late where I am; so I just wanted to say thanks again for your responses and I look forward to many more discussions.
Sincerely,
Bryan
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