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Old 17th October 2009, 10:31 AM   #31
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Quote:
Originally Posted by Few View Post
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
I could be getting a bit out of my depth here but would suggest AMT's have a better impedance match to the air than any other transducer. Notice that I said transducer; the addition of a horn can further improve the match and therefore the efficiency. As in electrical theory where R=E/I, in acoustics Za=P/U where P is pressure and U is particle velocity. For freely propagating waves the medium (air) has a natural characteristic impedance that imposes a relationship between P and U. What this means is that neither a pure pressure transducer nor a pure velocity transducer would have a good match. I think the ESL would be a velocity transducer. Whether pressure or velocity is ultimately determined by what happens to the back wave rather than the transducer motor type. A good indication of an AMT's impedance match to the air is the very benign rise in electrical impedance at resonance. Don't leave us few, for a minor departure from the topic; it is just that we need to know whether we are talking stator or statorless designs.

Micheal, you are correct in assuming that membrane mass will limit high frequency response, particularly when it is made more than it could be by using a combination of film and (stick on?) foil. I should not have used the word foil. To mention something that should be self evident, the ESAMT will not have its motor force reduced by perforations weakening the ES field, nor will its output have to pass through perforations or (in the case of the em AMT) pole pieces.

Keith
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Old 17th October 2009, 11:09 AM   #32
JeffL is offline JeffL  Australia
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Is there a Museum out there interested in buying an ancient pair of JansZen z210ah , at a rediculous price , so I can purchase these Electrostatic Speakers - JansZen , little beauties .
.
Am using tiny Peerless 832873 now for Mid/Bass ( don't laugh , traces of Bass , if I listen hard ). Not quite as good as K.Ts Orions !
.
P.S. Would David JansZen have any clues who made the unbranded ( before HiFi ) , 10" woofer in mine please ?
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Old 17th October 2009, 11:52 AM   #33
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I tried to edit a PS to my last post but fell foul of the 30 minute rule.

Unlike a cone speaker the AMT uses its motor primarily for moving air rather than accelerating a cone etc (above fo) and overcoming the system spring (below fo). Any output from a cone speaker is collateral to it moving itself, which explains why efficienceis around 1% are common. It also explains why the AMT is not going to go away any time soon, and why new models have appeared since the expiry of the Heil patents. The challenge of AMT's is motor strength, an aspect where neo' magnets have helped. David J has been quiet today, maybe he is snipping up little pieces of metalised film?

Keith
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Old 17th October 2009, 02:59 PM   #34
mige0 is offline mige0  Austria
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Quote:
Originally Posted by Keith Taylor View Post
. I should not have used the word foil.
Just for a short semantic clarification about film and foil.
Is "foil" always meant to be conductive?


Quote:
Originally Posted by Keith Taylor View Post
Micheal, you are correct in assuming that membrane mass will limit high frequency response, particularly when it is made more than it could be by using a combination of film and (stick on?) foil. I should not have used the word foil. To mention something that should be self evident, the ESAMT will not have its motor force reduced by perforations weakening the ES field, nor will its output have to pass through perforations or (in the case of the em AMT) pole pieces.

Keith
About upper limit of the frequency range I have done some investigation and calculation back then but vastly forgot and try to re-learn – hence I asked for an update from David.

My guess is that there are *five* variables that are involved in upper frequency limit of an ESAMT (sufficient polarisation and drive voltage assumed)
1. mass (determines the force needed for displacement versus frequency)
2. force (determines max displacement versus frequency)
3. capacitance (determines amp current needed for given frequency and SPL)
4. current available form the amp (determines brick wall limit in drive voltage versus frequency for given capacitance and hence in SPL versus frequency)
5. pleat depth (determines frequency of first cancellation and subsequent comb filtering effects further up)

Omitting 5, 4, 3 with the assumption that we have an ideal amp available driving a conventional ESL we – in my opinion – are left with force & mass.
Meaning if we make spacing veeeery close (for the same membrane) upper frequency limit goes up in terms of SPL limit (not in terms of a frequency response drop)
As spacing also determines low level SPL capability - by limiting displacement - we have to look after an optimum here.


Why I bring above up in detail is, that I'm actually not sure if I'm right – maybe the simple formula that mass from membrane and air load is the limiting factor – as stated by David - is enough in all practical terms.

I would appreciate any comment as I think this is crucial to determine physical dimensions of an ESAMT prototype as well

Michael

Last edited by mige0; 17th October 2009 at 03:27 PM.
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Old 17th October 2009, 04:07 PM   #35
mige0 is offline mige0  Austria
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Quote:
Originally Posted by Keith Taylor View Post
To mention something that should be self evident, the ESAMT will not have its motor force reduced by perforations weakening the ES field, nor will its output have to pass through perforations or (in the case of the em AMT) pole pieces.

Keith
Your ESAMT owns a lot of design elegance indeed!


Quote:
Originally Posted by Keith Taylor View Post
---
it is made more than it could be by using a combination of film and (stick on?) foil. Keith
If you are asking about the Shackman – well – this was a really crazy unit one would not think it could work at all.

The membrane between the stators was made as a sandwich of two – non conductive ! - Mylars plus some tissue in between.
Now- the tissue they put in salt water and let it dry. Then stuck it - with a small piece of chopper (to make a terminal for the polarisation voltage) - between the two Mylars.

Bottom line: the little salt left in the tissue after drying, together with the humidity of air formed an close to ideal high resistance (constant Q) membrane.

The weird thing though was that the sandwich was held together *only* by the tension of the Mylars – no glue!
Meaning one would assume that at forward motion the back Mylar would not be moved – but in praxis it worked
As said – the top range was excellent.

Good thing was – very few at that time knew about the inner construction details – otherwise I guess, not a single unit would have been sold...


Michael
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Old 17th October 2009, 04:31 PM   #36
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[QUOTE=mige0;1952422]Just for a short semantic clarification about film and foil.
Is "foil" always meant to be conductive?

I had a look in the dictionary where foil is described as a metal beaten into a thin sheet, so it has a rather ancient origin. In modern times we hear about foil and film capacitors where a film and a foil are separately wound into the component. Maybe not in separate operations, but the winding machine is fed from a roll of foil and a roll of film and the two are aligned and wound on together. This is distinct from metalised film where the metal is deposited on the film in an extremely thin layer.

I could agree with you points 1. and 2. about mass, and the force required to accelerate it to acoustically reproduce the input signal but would be inclined to use different words.

Keith
PS one of these days I will learn how to use quotes properly!
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Old 17th October 2009, 04:38 PM   #37
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Quote:
Originally Posted by Few View Post
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.
That is a good way of expressing the loading problem. This brings to mind that to restore the impedance match, each pair of pleats would have to be widely separated, and a series of horns used to transition the mouth of each gap to the open air, both at the front and rear. The combined area of the horn mouths would be about the same as that of a conventional ESL. That would make push-pull operation impossible, but I am just trying to make a point about loading.

Obviously I think you anticipated the outcome of an ES-AMT attempt correctly, and if your goal was to make sound, you cut your losses reasonably early.

I think the existence of patents for such devices is problematic for people without training or experience in physics/engineering, created by patent attorneys for reasons we can only speculate about. Obviously, no model was ever built and tested, and there is no requirement for proving practicality in most cases to get a patent issued by any nation's patent office that I know of.

There are tons of patents that elicit a sniff of amusement, a tear of sympathy, or a grunt of outrage from people with the pertinent technical background, and zillions that are obviously problematic to just about anyone. There are web sites or at least pages dedicated to them, though most of the listings have problems that are obvious to anyone, not just experts.

Halfbakery: Impractical Invention Class for Patents
List of Crazy Patents
Another 10 Bizarre (And Stupid) Patents - Listverse
Slashdot | Stupid Patent Contest Winners

Patents may still be a good place to learn things, but a jaundiced eye and a strong technical background are needed to steer clear of the red herrings. Researcher beware.
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Old 17th October 2009, 05:20 PM   #38
mige0 is offline mige0  Austria
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Originally Posted by DavidJanszen View Post
That is a good way of expressing the loading problem. This brings to mind that to restore the impedance match, each pair of pleats would have to be widely separated, and a series of horns used to transition the mouth of each gap to the open air, both at the front and rear. The combined area of the horn mouths would be about the same as that of a conventional ESL. That would make push-pull operation impossible, but I am just trying to make a point about loading.
.
This is basically the concept of a horn driven by an compression driver.

For an ESAMT we can omit the horn as we can stack as may pleats as needed to get sufficient front radiation area.

Despite the limiting factor of pleat depth in upper frequency reproduction I look at the ESAMT as having a conventional ELS operated with a force multiplied by the ratio of pleat width to pleat depth.
Mass is increased by the same amount of course *but* we only need a fraction of displacement - by the ration of pleat width to pleat depth - to get same SPL for same front area!

This applies IMO equally to the fixed stator ESAMT and the virtual stator ESAMT as movement is split proportionally with the virtual stator ESAMT design

Michael

Last edited by mige0; 17th October 2009 at 05:28 PM.
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Old 17th October 2009, 05:21 PM   #39
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Quote:
Originally Posted by Keith Taylor View Post
the ESAMT will not have its motor force reduced by perforations weakening the ES field, nor will its output have to pass through perforations or (in the case of the em AMT) pole pieces.
The perforations in a proper ESL don't weaken the field, unless as a rule of thumb they are bigger than the gap. They will also not impede the propagation of sound waves, unless as a rule of thumb their depth is more than a tenth or so of the shortest wavelength of interest, where the air in the hole begins to represent a column of air that must be accelerated (0.07" max depth for 20 kHz).

One of the problems for an ES AMT is that the pleat will act as a deep perforation, albeit actually a slot, creating a confined mass of air that the membranes must accelerate, rather than just making waves. Furthermore, the membranes must overcome the viscosity of the air in the pleats, since they are acting on it perpendicularly to the desired direction of motion.

Me, snipping? I am trying not to spend too much time on your interesting, impractical idea. But isn't it about time for you to give it a try?
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Old 17th October 2009, 05:30 PM   #40
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Originally Posted by mige0 View Post
This is basically the concept of a horn driven by an compression driver.

For an ESAMT we can omit the horn as we can stack as may pleats as needed to get sufficient front radiation area.

Despite the limiting factor of pleat depth in upper frequency reproduction I look at the ESAMT as having a conventional ELS operated with a force multiplied by the ration of pleat width to pleat depth.
Mass is increased by the same amount of course *but* we only need a fraction of displacement - by the ration of pleat width to pleat depth - to get same SPL for same front area!

This applies IMO equally to the fixed stator ESAMT and the virtual stator ESAMT as movement is only split proportionally with the virtual stator ESAMT design

Michael
Jeeze Louise. Just ignore this guy, Keith. He has all this stuff all muddled up, in case that is not obvious to you.
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