Electrostatic AMT?

[kenpeter]

If needing posts for support anyway, why is this "eureka" pleat
better than charged plates (insulated at one end like said posts)
between pleats of ordinary ESL sheet of one conducting surface?

It seems a lot more work to etch four conductors on one sheet,
and make all the alternting connections. Are rods as likely to hold
their shape in dipole vibration mode as charged plates?

[Capaciti]

Hi Folks,

now i followed up your posts for some days and i am wondering that you discuss about electrical field, polarizing or not.....

Once you might succeed figuring out how to drive this ESL-AMT (and at least there is no doubt about that polarizing voltage is required) but you will never be able to get this system stable.
This construction will be extremely sensitive to even minor deviations in distances between adjacent cells. Lets say you might need e.g. 0,02" distance to each other in every cell for acceptable efficiency, a variation of about 0,008" in one of the cells will cause it to collapse to his neighbour, thus widening the distance of other cells. How would you ever ensure this accuracy in construction using just a floppy foil ??

Even you solved tensioning in a very good way, within few days a lot of the cells will be collapsed to each other, making this system unusable.

Even costs might not be in consideration,

pheripherical system requests, wiring, connecting, tensioning, positioning, gluing, adjusting, coating, isolating, handling, protecting, and so on and on and on.... of this system is expected to be horrible effort.

Capaciti

[DavidJanszen]

Kieth,

Of course I did not mean suspending the strips by their ends. They would simply collapse. As initially planned, they'd be attached by their long edges to the posts. I suppose you got what I meant to begin with, but as usual, I find myself in the position of trying to deflect Michael's at best quarter baked interpretations and posts. I should have made a sketch for him, but short on time. By now, probably could have built it myself.

Also, fan-folding the pleats would be by no means harmless. That may be the worst suggestion I've read so far from Michael. I can't tell if he is joking, malicious, or well meaning. The web is a free speech medium, but wow. If you think he might have a point, just think about the electric field situation. Unlike an ED AMT apparatus, the surfaces must be as parallel as possible.

Two rows of conductive posts. Aluminized polymer film* between pairs of opposite posts, coating toward posts. Heat shrink film to get tension.

Suggested initial spacing and depth early in this thread. Would suggest a wider gap to give the sound a better "escape route", but this would take some serious voltage to drive, which is hard to get at high frequencies due to transformer parasitics and transducer capacitance.

FWIW, a 0.1" gap (0.2" from virtual stator to virtual stator) should be good with up to something like a 4 or 5 kV bias and 8 or 10 kV p-p (3500 V RMS) drive. Anyway, this is just a first pass to see if you get *any* sound. You are not going to find a transformer that will give you 3500V RMS OTS.

Just raise the bias until you get collapse, turn it off, then dial it back 10 or 20% before turning it back on. If the film lost its tension in the process, heat it again. Drive with whatever you can get. If you don't have a transformer specifically made for ESL's, one QAD option might be to use a tube amp output transformer connected "backwards".

*not actual foil, of course, "foil" being a figure of speech -- PET such as Mylar okay for prototype, 0.002" thickness okay for a base prototype, although the mass loading will roll off the top octave or two. Easier to handle than appropriately thin film.

[DavidJanszen]

Originally Posted by Capaciti

This construction will be extremely sensitive to even minor deviations in distances between adjacent cells. . . . will cause it to collapse to his neighbour . . . How would you ever ensure this accuracy in construction using just a floppy foil ??

Well, it wouldn't really be floppy, but under significant tension.

Gap variations are always a problem with ESLs. One does the best one can, and then avoids collapse by using a lower than optimal bias voltage. In this case, because everything is flexible, the bias would be even lower than for rigid stators, but the system could be made stable easily.

Originally Posted by Capaciti

. . . and so on and on and on.... of this system is expected to be horrible effort.

Indeed. But it is amazing how assembly efficiencies can be developed when sufficiently motivated. Look at cone speakers. They are complicated, and can be made cheaply.

But first, one must determine whether an apparatus stands a chance of working. At the beginning, every idea needs to be tested, and I think it is best if the inventor is the one to do it.

I am am pretty sure this one is something like putting a tiny motor on each wheel of a bicycle, having them push in opposite directions, and hoping the bicycle will propel the rider two meters straight up into the air. Of course, I hope I am wrong, because I like the idea, and I like the way Keith has put genuine thought and imagination into it. Even if it doesn't work, much will be learned that might be applied to another invention later, not to mention: prototyping is great fun.

[kenpeter]

Also stator plates would half distance (one half pleat instead of a full pleat) any
static field must span, thus needing only half as much voltage. I think, maybe
thats the maths of it??? Don't get me to lying.

You need only three connections: Two of them to stator assemblies that don't
move. You could cover the ends of any plates that must touch and support the
ribbon with strips of yellow Kapton tape. Like used for masking boards before
soldering...

[mige0]

Originally Posted by DavidJanszen

Kieth,

Also, fan-folding the pleats would be by no means harmless. That may be the worst suggestion I've read so far from Michael. I can't tell if he is joking, malicious, or well meaning. The web is a free speech medium, but wow. If you think he might have a point, just think about the electric field situation. Unlike an ED AMT apparatus, the surfaces must be as parallel as possible.

David, you're absolutely right about the Zig-Zag folding – considering the electric field (built by the virtual stators which are fairly parallel in this case) the non-parallelity of the polarised part does not matter IMO *but* it would not be possible to have the polarised film charged equally over its area.
I indeed messed up with electret films where charge is held constant over area (by the material itself) no matter what.

Originally Posted by DavidJanszen

Kieth,

Suggested initial spacing and depth early in this thread. Would suggest a wider gap to give the sound a better "escape route", but this would take some serious voltage to drive, which is hard to get at high frequencies due to transformer parasitics and transducer capacitance.

.

Capacitance goes down as spacing goes up – this should balance out.

Originally Posted by DavidJanszen

Kieth,
FWIW, a 0.1" gap (0.2" from virtual stator to virtual stator) should be good with up to something like a 4 or 5 kV bias and 8 or 10 kV p-p (3500 V RMS) drive. Anyway, this is just a first pass to see if you get *any* sound. You are not going to find a transformer that will give you 3500V RMS OTS.
.

If you can only afford – say 1/10 or less - the optimal voltages for this arrangement - consider the SPL degradation you get.

You will have problems even with measurements - ending up with possibly only 20-30dB of SN in normal rooms...

I think the dimensions of the pleats (spacing in particular) have to follow what Keith can afford from his amp / OT – including some headroom.

Michael

[Keith Taylor]

Hi Micheal, no need for any appologies and I am sorry if my explanations do not make life easy for people who's first language is, perhaps, not English. I did not set out to devise something that was elegant, rather, when the signs suddenly lined up after months of doodling around with serpentine shapes one could not fail to be struck by the elegance of the principle. It is gratifying that others agree. If only the forces in electro- magnetics were not at 90 degrees to the field we could make a killer AMT where the stators were neodymium magnets!

Few, did you devise your ES AMT idea or were you aware of the patents? It does not say much for the patent system when two patents are granted for the same idea. I guess the $64 question is have either of these inventions ever produced a sound, as they do not seem to have appeared in the market place. If someone here is going to answer this question, and the stator approach is easier to implement, so be it. The way I view the stator approach is that it is little different to my idea except that we have two extra boundaries between the pleats to reduce the volumetric efficiency (maybe not the right word).

Kenpeter, I note your remarks about the membrane being only half the distance to the stators compared to the situation were they not there, something I had thought about.

Another aspect of the "all moving" approach is that, under drive, there could be a tendency for the pleats to flatten themselves and avoid shorting. Movement "hot spots" would generate pressure maxima on one side of the membrane coinciding with maximum vacuum on the other side? This is why we need input from the likes of John Kreskovsky. I might try to PM him to join the discussion, but he could be in one of his periods of staying away from the computer to get some work done!

As for my resources I have some Mylar, metalised Mylar(sorry if I missuse the word foil) and liquid resistive coating from Rob McKinlay, ER Audio, in Western Australia. Also have a Roger Sanders supplied bias supply (one only) and audio step up transformer and the Sanders and Ronald Wagner books. Had thought of referring the centre of the bias supply to the audio transformer CT to get plus and minus supplies; realising that we need high value series R in each supply.

I have never owned or built an ESL and have rarely listened to a pair of them. The way I obtained the links to the European patents was interesting. Being the owner of the Linkwitz Orion dipole design willing to let others hear them I was contacted by a guy in London! It turned out that he was attending a conference in South Australia for patent attorneys. The links were a reward for our hospitality. Other speakers I have are the Heil Elite tweeters and the Manger bending wave zerobox design.

Keith

[mige0]

Originally Posted by Keith Taylor

Hi Micheal, no need for any appologies ...

Thanks a lot for this, Keith !

Originally Posted by Keith Taylor

. Making the diaphragm more zig zag than parallel may help; something to be modelled by a fluid dynamics expert.

Keith

One good of the fault with my saw-tooth suggestion – we now know we *have* to stay in parallel with all pleats – unless you don't wanna use electret foil.

Thanks for correcting me, David

Originally Posted by DavidJanszen

Kieth,

Of course I did not mean suspending the strips by their ends. They would simply collapse. As initially planned, they'd be attached by their long edges to the posts. I suppose you got what I meant to begin with, but as usual, I find myself in the position of trying to deflect Michael's at best quarter baked interpretations and posts. I should have made a sketch for him, but short on time. By now, probably could have built it myself.
.

David, think I got you now – it wasn't to apply vertical tension as I assumed ?

You still stick with the same concept as shown in Keith' first post but diaphragm made of pieces form post to post rather than a single piece of membrane (with different areas to connect to) wrapped around all posts in order to simplify making.

On the other hand - if you have such little area to tape the sliced curtain at (half a post) - this will limit tensioning the Mylar severely – no?

Originally Posted by DavidJanszen

*not actual foil, of course, "foil" being a figure of speech -- PET such as Mylar okay for prototype, 0.002" thickness okay for a base prototype, although the mass loading will roll off the top octave or two. Easier to handle than appropriately thin film.

From this I conclude that you connect thickness of membrane (mass per area) strictly to upper frequency roll off.
Is it meant that way?

I can't bring it into coincidence with the Shackman ESL that used *two* Mylars *plus* some tissue in between as a membrane and – at least in my memory – hadn't any problems reproducing the top end (wow - what a sound in this department !)
Actually SPL limitation in the lower region was the main problem together with its notorious discharge every now and then burning a little hole into the foil each time happening.

Stator spacing was veeeeery narrow though - basically no more than using a vertical thread each 1cm 0.2" or so to keep distance over the cylindrically curved speaker.


http://shackman-electrostatic-loudsp...reromanus.net/


Michael

[mige0]

Originally Posted by Few

Keith,
When I tried to slap together an electrostatic AMT several years ago I used a somewhat simpler construction. Since I didn't take the thing to fruition I can't offer lots of practical insights, but maybe something of use will arise.
Few

Do you still remember dimensions of your ESAMT
Highth / width / pleats depth and spacing

and also
what audio and polarisation voltages you applied?

Michael

[Few]

Hi all, and FEW, in particular, I am a bit reluctant to post these links to the European patents as they are NOT what we are currently disscussing.

As I said in my original post, "The approach I described isn't the same as your no-rigid-parts design, but I thought I'd chime in just in case it triggers something useful." If my post wasn't useful then I'm sorry I corrupted the discussion. Now I'm not sure if I should answer the subsequent posts that referred to mine. I don't want to make matters worse... I guess I'll try to answer those and then bow out.

----------

Few, did you devise your ES AMT idea or were you aware of the patents? It does not say much for the patent system when two patents are granted for the same idea.

I was ignorant of the patents when I arrived at the idea of an electrostatic AMT. After I patted myself on the back for my ingenuity I found that the idea was patented---in fact I uncovered patents other than the ones you posted, so I guess it's been patented several times. In the end I was focusing on diy efforts so the fact that the idea was already patented (multiple times) wasn't really a deal breaker.

Do you still remember dimensions of your ESAMT
Highth / width / pleats depth and spacing

and also what audio and polarisation voltages you applied?

I don't remember the specifics, but they were larger than I would play with if I were to do it again. I think the pleat depth was probably on the order of 4 cm or something---I was just trying to make some sound and not yet concerned about bandwidth. The combination of difficulties wrapping the diaphragm onto the stators and life-related distractions prevented me from giving the prototype a real test.

I was also nagged by a version of David J's concerns. I figured that conventional ESLs aleady have an almost ideal impedance match between diaphragm and the surrounding air, so the AMT idea is actually degrading the impedance match. With relatively heavy ribbon-type AMTs the increased air load is more welcome. Those lingering doubts prevented me from working through my assembly difficulties and I never got around to answering the "can it make sound?" question.


Few