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Old 28th October 2010, 11:47 PM   #31
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Quote:
Originally Posted by bentoronto View Post
Seems to me there's not much doubt that big spacing and proportionally smaller diaphragm movement leads to cleaner results. A loafing big cone driver will outperform a stressed small driver and likewise for an ESL for similar reasons.
If it were a simple matter to generate large signal voltages I might agree, but this is not the case. You have to think of the ESL as a system made of either (panel + transformer) or (panel + DD amplifier). In either case, you will find the quality and bandwith of the audio signal decreases as you attempt to increase the magnitude of the signal voltage with a higher step-up ratio transformer or higher voltage DD amplifier.

In short, I agree with Calvin's advice to use only as as large a gap as you need to.
This minimizes the magnitude of the required signal voltage which maximizes fidelity.

Unlike cone drivers, ESLs are capable of low distortion reproduction all the way to their excursion limits. I haven't found the concept of "loafing" to be applicable to ESLs.
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Old 29th October 2010, 02:03 AM   #32
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Did you think I meant you should go to the lumber yard and buy the biggest spacers you can find?

I meant you figure out how big you can go within your capability, humidity level in your home, amp/transformer resources, etc. But, I think you start somewhat like with cones, with some notion of how low in frequency you want to go and work from there. I don't offer that thumbnail sketch as a prescription, just a rough from-the-hip shot at the kind of system thinking is part of initial planning.

Yes, aim for big spacing just like I think you should always aim for large woofers.

Weird special case: Mike Wright encased his speakers in sealed mylar. Then filled with inert gas. So right off (if you want to go to all this trouble and play through myler "grill cloth") you can jack up the bias voltage (easy to do) and have real sensitivity. An interesting place to start?
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Last edited by bentoronto; 29th October 2010 at 02:06 AM.
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Old 29th October 2010, 03:12 AM   #33
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Quote:
Originally Posted by bentoronto View Post
Did you think I meant you should go to the lumber yard and buy the biggest spacers you can find?
Hello Bentoronto,

What I understood you to say was that with an ESL panel of a given area and a given maximum diaphragm displacement you would prefer to use larger spacing since this would mean the diaphragm would be moving a smaller percentage of the total D/S airgap. That is what I thought you meant by ”proportionally smaller diaphragm movement”. Is this what you meant?


Quote:
Yes, aim for big spacing just like I think you should always aim for large woofers
Just curious, wouldn't aiming for large ESL area be more comparable to aiming for large woofers? I keeping thinking that somehow I am not understanding what you are meaning by aim for big spacing.

Based on Baxandall analysis and my limited experience, you should aim for the largest area you can live with because the area is the only physical parameter other than the breakdown voltage for air that defines maximum SPL capability of an ESL panel. The D/S spacing merely defines how low in frequency you can output that maximum SPL.
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Old 29th October 2010, 10:35 AM   #34
Calvin is offline Calvin  Germany
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Hi,

Quote:
The spacing, d , is not actually involved in defining the obtainable force per unit area.
That is just a part of the truth.
The formulas clearly show a anti-proportionality of attainable Forces to the distance d. It also shows that You need to increase the voltages to obtain the same Force-values when You increase d.
Since we must(!) stay below the maximum force which is defined by the flashover treshold, only the range below Fmax is of interest and here the 1/d proportionality applies. In other words. As long as the panel doesn´t flashover a decrease in spacing d will result in higher Force, hence higher SPL, if we keep Vpol and Vsig unaltered. On the other hand, if we increase d we need to increase Vpol and Vsig to rearrange for the same Force again. The choice of d should then only depend on the excursion needs. So, if we have chosen a value for d that meets the excursion demands, any further increase in d is not only obsolete, but actually counter productive, in that the required higher voltages (and associated with it increased Power) mean increased effort, inferior signal quality, less safety and speeded aging.

Quote:
1) If your step up transformer can generate the optimum stator voltages, turning up your bias beyond the optimum Vpol value will result in higher sensitivity but reduce maximum SPL.
Turning the Vpol up will result in flashover as soon as the Vsig approaches the peak-value.

Quote:
2) If your transformer generates less than optimum stator voltages, turning up your bias beyond the optimum Vpol value will result in higher sensitivity and increased maximum SPL.
This is indeed correct, but who would design so in first place?
If I were to design a F1 car, I surely wouldn´t opt for a 125ccm Motorbike engine, but a 3.000ccm racing engine. Why when You can ?
A tranny that is incabable of supplying the optimal Vsig is simply not the right tranny for that certain application.

Quote:
Seems to me there's not much doubt that big spacing and proportionally smaller diaphragm movement leads to cleaner results. A loafing big cone driver will outperform a stressed small driver and likewise for an ESL for similar reasons.
In comparison and similarity to dynamic drivers the superiority of the larger driver stems from its lower excursion needs. Increasing spacer thickness (which is how I interprete "big spacing" here) beyond what is needed to fulfill the dynamics requirements gains nothing and improves nothing.

jauu
Calvin
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Old 29th October 2010, 11:17 AM   #35
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Bolserst - your questions indicate you are paying my rambling amateur thoughts more respect than they deserve. Thank you.

From my rambling thoughts, I would select "system" and "initial" as useful concepts. A person is sitting in their armchair thinking, "How to start....?" Their variables are things like what kind of mechanically stable panels can they make at home and, inter-relatedly, what kind of voltages for bias and drive. How big and wide? (Adding depth is, of course, very easy.) How high are the voltages that are practical for them?

I'd say hard to keep panels adequately stiff, especially as the surface dimensions grow. So there are hard limits a builder faces unless they can weld steel braces. But it is not too hard to increment voltages upwards with bigger spacing, if you have a solid mechanical base. With the high voltages around ESLs, I bet few people are rapping their knuckles on the panels or feeling them for vibration while playing - that's the way we always do it with speaker boxes. Ever wonder how badly the flimsy Quad panels rattle? Or sheets of perforated steel that everybody uses? You could trust your life to the strength of Dayton-Wright panels, by contrast. Why are we nutty about the solidity of speaker boxes but pay minimum attention to the rigidity of ESL panels?

Yes, going big in any dimension means proportionally and absolutely less diaphragm displacement - but easier to achieve with spacing. Which, I am pretty sure, means better performance. The mathematics of ESL forces are not pretty, as best as I can remember Hunt. That's why big-voltage bias HAD to be introduced, eh. I think as soon as you start serious movement, you get into exponential instead of linear forces.
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Last edited by bentoronto; 29th October 2010 at 11:23 AM.
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Old 29th October 2010, 01:28 PM   #36
markusA is offline markusA  Sweden
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Wow, this is awome.
I'm getting answers to the questions I didn't dare asking.

I'll risk it and throw in another...
Is there a way to estimate sensitivity for the panel? (SPL@1W/1m, I doubt 2.83V is the right way to go since we're taking DD amps?)
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Old 30th October 2010, 03:16 AM   #37
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I notice in this thread and others talk of the danger of the bias voltage. I understand this with regard to DD tube amps. Indeed you do not want to screw with that "spark" from a the likes of a Acoustat Servo amp. I might be wrong about that though. I have zapped myself many times however with the 5KV DC of a Acoustat Mk121 interface box. I have also touched a naked panel all over its surface and even poked a finger into the styrene grid and never received a shock. The fact is I regularly pull bare panels off the interface boxes and discharge them and have even touched the 5KV terminal by accident in the power supply and while it is damned unpleasant I can't vouch for "deadly" by any stretch. What am I missing with regard to this topic. Sorry to high jack the thread. I encourage the original discussion to commence promptly. Great stuff guys.
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Old 30th October 2010, 05:44 AM   #38
nac134 is offline nac134  Canada
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This comment is well informed!

The power supply in most electrostats charges to between 2 and 5 kv. That sounds like alot, and it is. So the natural questions is - can you fry youself? No you can't. There is not enough current available to create the internal burns that electrocution causes. Does that mean that working with electrostats is safe? No. This high voltage, despite the low current, can stop your heart, as your heart depends on the progression of electrical signals to coordinate timing - a fact that defibrillators exploit. In audiospeak, "fibrillation" is when different parts of the heart go out of phase. The defibrillator snaps them back, so that the timing re-aligns.
Where this is dangerous is when the high voltage hits a finger on one hand, and the ground hits a finger on the other - and you get high voltage acting across your chest. THIS CAN KILL YOU. The solution is to wear rubber gloves, or to keep one hand in your pocket while poking around. This is a fact that was confirmed by the inventor of the curved elecrostatic speaker, who also happens to be a medical doctor (Roger Sanders).
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Old 30th October 2010, 07:31 AM   #39
Calvin is offline Calvin  Germany
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Hi,

Walker´s and Baxandall´s calculations just provide for that.....estimation of the SPL against driving current. You just need to calculate the current values, depending on frequency, the panel´s impedance and the driving voltage. But as You can see from the Walker-equation-simulator, the results just give a hint about the range of possible results. Too many factors affect the end result. Factors like the shape of the panel, the use manufacture and type of insulation, building precision, diaphragm coating, transformer, etc. etc.

jauu
Calvin

ps. the curved Stator was ´invented´ before Sanders. And also way before ML adopted this technique, claiming it their intellectual property under the name "curvelinear stator". There´s at least one patent dated from 1957 (Austria) and one from 1961 (USA) and I really doubt that the applicants were the first who thought about curved stators. Most of all techniques were invented in the early days already. There are no really big News in ESL-tec since the 1960s.
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Old 30th October 2010, 12:39 PM   #40
markusA is offline markusA  Sweden
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Call me a dullard but I just don't see it?
I'm trying to fit it all togeather but the physics is getting a little dense for me.
Wave popagation and energy transport wasn't really covered all that well in high school physics.

Is there an other equation by Walker and Baxandall that I have missed?
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