An idea for a wide dispersion ESL

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I'm new to ESLs, so I'm not sure if someone has done this before, but I have an idea for an ESL that would have good dispersion characteristics.

The wavelength of a 20 kHz sound wave at sea level is about 1.7 cm, so the idea is to have the stator broken up into multiple rings which are each about that half that wide (or whatever gives the desired dispersion pattern). The signal sent to each ring would be delayed by the time it takes sound from the center of the panel to get to that ring (digitally delayed, before it is ever amplified) and then sent to separate amplifiers (one for each ring).

I know the Quad ESL had something like this (except without separate amps), but my understanding is that the delays and the rings were spaced too far apart to give good dispersion at high frequencies.

I know it could work, but I am not sure about the various factors that would possibly need to be worked out (and I would like to hear if anyone has tried to). For instance, each ring needs an amp, so for a reasonably sized panel this could get expensive quickly, and each ring needing its own transformer just compounds the problem. Is it possible to make a class-D amp that would put out the voltage necessary for an ESL without having to use a transformer?

Another problem is what to make the stators out of. Printed circuit boards seem to be almost ideal, but getting a large one made is prohibitively expensive. I'm really at a loss on this question.

I'm sure there are plenty of other things I am not thinking of, so please let me know what those are too.
 
Just a random question. I've seen a lot of these posts now about creating ESLs with wider dispersion patterns. I'm wondering if achieving greater dispersion can be accomplished without losing some of the imaging or intangible qualities of ESLs in the sweet spot.

From my experience, martin logans and such don't sound quite as dynamic in the sweet spot as planer ESLs. A wide dispersion ESL to me sounds good in theory, but I feel like there has to be a compromise in something in order to achieve this.

-Wes
 
The reason why I want dispersion (and the only reason I can think of to want it) is to have a larger sweet spot.

The original idea was to make an array of small electrodes on the stator with lots of pre-processing before the amps (one amp for each little electrode) so that the speaker could reproduce each source of sound between the far left and far right with a spherical pattern. Such a speaker would be wall sized and expensive beyond belief, but would, when coupled with an appropriate sub, be essentially ideal and have a huge sweet spot.

Since almost all recordings are stereo, I decided it would be good enough to try to reproduce two point sources rather than hundreds.
 
Hi,

as wrl pointed out, optimizing one parameter will effect another parameter in the quite opposite direction. Unsegmented panels sound more dynamic in the mid-highs than segmented ones. Curved panels and planar panels (only unsegmented ones!) sound basically the same, since the claimed wider dispersion doesn´t really happen in praxis.
The problem with small rings or strips is, that they represent a very high impedance, which has to be transformed with much larger transformation factors. Everybody skilled in building transformers knows that high transformation factors always(!) cost on bandwidth and dynamics. Unsegmented designs can work with factors down to 1:50 (often 1:75), segmented panels maybe down to 80 (often 1:100)
The older Quads worked with up to 1:270. Besides the problems of getting Your hands on such a transformer, it´ll be no doubt worse than a simpler tranny with a small transformation factor.
Besides the highimpedance prob such small rings or strips will suffer in efficiency. Think of reduced effective membrane area or increased and wasted capacitance (beneath the spacers).

I can only recommend -especially those newbies in ESL- to closely watch what the great names did....to understand why they did it the way they did and no other way. This alone will take You considerable time and maybe lead to the lesson, that those designs not only have their merits but can hardly be topped.
I still have to listen to a Quad I could like and I think that the concept has major flaws, but the engineering behind is straightforward and marvellous. Same is with MLs. Those are much more than some pieces of sheet metal and a film diaphragm.

jauu
Calvin

ps: here´s a little task for You if You like: ;-)
The point source!
Is it the one and only distribution character?
Is it the best distribution character in my living room?
Can a different dispersion character be superior?
If so under which circumstances?
Which distribution character could that be?
:D :D :D :D :D
 
Thyratrons are cheap and can drive an ESL transformerless, but are too slow for Class D and too non-linear for other amps. KOON3876 works on a concept of array speakers where the single drivers are Class D driven, but not with full resolution, so only the array as a whole gives the full signal. You could ask him about his progress.
 
First, no, curved panels don't have a wider dispersion. Or at least what I have heard says that they do not have a significantly higher dispersion.


Calvin,

I think I might not have been as clear as I would have liked. I did not mean that the diaphragm would be segmented. The stator electrodes are the only thing that would be rings. I don't think that your points hold when the diaphragm is large but the stator electrodes are in segments (the stator itself (the thing the electrodes are attached to) would not be segmented). I agree that all of your points hold true for the design you thought I was talking about though. ;)
 
Hi Folks,

i ring with a diameter of just 1,7cm will never produce adequate sound pressure. The area is much too small. So what good are widely dispersed high frequencies for you cannot hear ?

Even you might succeed in a high stepup-ratio of the transformer, the limitation is field saturation.

The output of an ESL is strongly related to area. If you compare dynamic and ESL drivers you need at least 10 times area for the ESL at comparable output.

I did some investigations and a ring of 10cm diameter performs OK. As most things have been invented, take a look in the Quad Stators. Guess what size the inner ring has ?

Capaciti
 
Jerko, I too have contemplated an acousticaly small ESL, but from a completely different starting point. Some time ago it occurred to me that it should be possible to make an electrostatic version of the Heil Air Motion Transformer. The pleated diaphragm makes no distinction between membranes and stators. One "half pleat" is conductive (metalised coating) and the other half pleat has the metal etched away and normal ESL graphite etc applied. This diaphragm would have to be tensioned around some rod like spacers to take on the serpentine (zig zag) shape.

Whilst recognising that we are up against resonance issues with the necessity for tension on the membrane the device has some very attractive features. There is no limit on the pleat depth. There are no magnets or polepieces to get in the way. There is no limit to how wide the diaphragm can be (number of pleats). As we have electrical access to each individual half pleat there occurs the possibility of a transducer that can vary its acoustic size with frequency, plus we can employ devices used in line arrays such as shading (changing the sensitivity of the central pleats compared to the end ones)

For those unfamiliar with the AMT principle Googling Heil AMT should yield an explanation. The AMT has a far better impedance match to the air than any other transducer type, as evidenced by a plot of electrical impedance versus frequency. The rise in impedance at resonance is so benign you could miss it!

Keith
 
Capaciti said:
Hi Folks,

i ring with a diameter of just 1,7cm will never produce adequate sound pressure. The area is much too small. So what good are widely dispersed high frequencies for you cannot hear ?

I did some investigations and a ring of 10cm diameter performs OK.

Capaciti


I read there had been a prototype of an ESL compression driver many years ago. What do you think about that solution?
 
Curved Panels ?

I am not a fan of curved panels of any type. At some frequency the radiation from the edge and from the peak of curvature will be out of phase and comb filtering will result .

Another reason to use flat and not curved panels is for controlled directivity. That "beaminess" in the Quad ESL is one of the characteristics of the Quad that gives it good imaging ... So-called "wide dispersion" or "Cylindrical dispersion" will suffer in comparison, not to mention getting more early reflections from the wall to smear the direct, first arrival ...
 
Hi,

@ Mr Taylor
that idea is not knew....in fact it is already patented for quite a while for electrostats, yes! (1992 and 1996, maybe some even earlier)
An externally hosted image should be here but it was not working when we last tested it.



It is indeed an interesting feature to have massive stators instead of sheet metal or wires. So efficiency could be higher than with any other construction simply because of this feature. It´ll be very hard though to built that thing, since You very probabely need a segment-wise coated diaphragm to keep losses low.

@toroid
Your´s is an opinion one does not need to share ;-)
The effect You describe is inherent to flat panels too.
And the non-beaminess is just what Quad claims, but can´t stand the practical test :whazzat:
 
Capaciti said:
Hi Folks,

i ring with a diameter of just 1,7cm will never produce adequate sound pressure. The area is much too small. So what good are widely dispersed high frequencies for you cannot hear ?

Even you might succeed in a high stepup-ratio of the transformer, the limitation is field saturation.

The output of an ESL is strongly related to area. If you compare dynamic and ESL drivers you need at least 10 times area for the ESL at comparable output.

I did some investigations and a ring of 10cm diameter performs OK. As most things have been invented, take a look in the Quad Stators. Guess what size the inner ring has ?

Capaciti

You have misunderstood what I was saying. I guess I'll try to explain it differently.

Suppose you have a diaphragm and you measure the displacement of every point on the diaphragm as a sound is incident upon it from an approximately pointlike source. Now if you can later move the diaphragm so that it reproduces the motion it had when the sound was hitting it, then it should produce a spherical wavefront coming out of the front (and, unfortunately, the back).

Now the idea that I am trying to explain is a way of producing an approximately spherical wavefront on a large diaphragm by actuating a set of rings with the appropriate delay. No single ring is producing all of the sound for a given frequency; all of them are driven with a full range signal.

The trick is that a ring will add to the soundwave that has already been produced by the rings inside of it because it is driven by a delayed signal.


Anyway, suppose that I want to do this (irrespective of its merits), what sort of material would be best for the stator? Maybe fiberglass with copper electrodes printed on it?
 
Calvin, thanks for your response re the electrostatic Heil. I can see from your diagram that someone has thought of it before. The system in the diagram is the same as my original thoughts on the design. Later I thought of the segmented membrane where we dispense with the stators. I have tried many searches using terms such as Electrostatic, loudspeaker, pleated diaphragm but have never found any references. Can you supply any patent numbers or search terms that may help me find some information?
Keith
 
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