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Old 11th January 2007, 02:07 AM   #1
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Default ESL AMT device...

a number of years ago I ran across a US patent on an electrostatic version of a Heil AMT device. I have since lost the patent number inside of a sick hard drive. Does anyone have the patent number? Thanks. Moray James.
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Old 12th January 2007, 10:01 PM   #2
Few is offline Few  United States
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I know you're really looking for US patents, but I thought I'd post these in case someone following the thread finds them interesting:

folded ESL 1 and folded ESL 2 from this list.

Any chance the one you're looking for is one of those listed?

Few
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Old 13th January 2007, 02:36 AM   #3
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Default Thank you...

Few: the list is too old, the design that I saw was I believe either eighties or ninties and I know that it was american though it may well have be patented in europe as well. Thanks for the help. That's a good list. Best regards Moray James.
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Old 13th January 2007, 04:45 PM   #4
Few is offline Few  United States
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If you do manage to come up with a source of the patent you're looking for, please post it! I have a longstanding interest in the ESL Heil approach---dating back to the time when I naively thought I was the first to think of it...

Few
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Old 14th January 2007, 11:56 PM   #5
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Hi Moray,

I checked the US Govt. Patent Office db and came up with a couple of numbers you might check out:

US Patent 04006317 issued to Freeman, Miller - Feb 1 1977 and may very well be the one you are looking for.

US Patent 04207442 issued to Freeman, Miller - June 10 1980.

Hope this helps.
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Old 15th January 2007, 10:16 PM   #6
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Quote:
Originally posted by Few
I know you're really looking for US patents, but I thought I'd post these in case someone following the thread finds them interesting:

folded ESL 1 and folded ESL 2 from this list.
That's very interesting. Back when I worked at ESS, I did
something very similar, and probably should have patented
it. There was a slight disagreement between ESS and I over
the $1 licensing, so this was not pursued, nor was a version
of the Heil woofer which did reach the application stage.

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Old 15th January 2007, 11:08 PM   #7
Few is offline Few  United States
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Interesting indeed! I didn't realize the idea had gotten that far down the development stage. Was the result promising? I've been sketching such devices in various forms for a few years, and did a bad job of putting a really simply prototype together, but have always had the nagging feeling the idea might be doomed and so never really pursued it aggressively. If I knew going in that it was possible to make it work well, I might finally get off my tail!

Thanks for posting.
Few
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Old 15th January 2007, 11:15 PM   #8
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Hi Nelson,

I remember when we were both fixing stereos for Sun Stereo over on Arden way and you would go on for hours about some type of new amp design you were working on. But I could still fix the turntables better than you!

Thomas J.
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Old 16th January 2007, 03:45 AM   #9
Few is offline Few  United States
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Nelson,
As I reread your post I realized I wasn't quite clear about whether you built a folded ESL and tested/listened to it, or whether it was more of an abstract exercise. Did you actually put a working model together, and if so, could you share a few details? There have been a few questions nagging at me concerning the design. Here are two of them:

1) If one of the points of the ribbon-type Heil driver is to improve the impedance match between the driver and the air, and if a typical ESL diaphragm is already nearly perfectly impedance-matched to the air, would folding an ESL diaphragm actually be too much of a good thing? Would the impedance of the air actually end up being higher than the impedance of the driver? If so, does this kill the efficiency?

2) What determines the correct depth of the folds? If the folds are, say, 4 cm deep, does that limit the bandwidth of the driver because sound from the deepest part of the fold starts to interfere with sound generated right near the opening? Unlike the ribbon situation it would clearly be quite easy to make the folds almost any depth; I'm not clear about what effects need to be balanced.

I hope these questions makes at least some vague sort of sense...

Few

P.S. I sent my students to your website to read your description of how op amps work (embedded in your article on building your own discrete op amps). It was great to have such a straightforward and clear description to get them started. Thanks for taking the time to generate such things!
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