wire stator design

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Hi,

the results in Matthew Lattis´s Report in AudioXpress 2005 says the opposite.
He found too that PSMs (perforated sheet metal stators) typically gave higher efficiency values. Admittedly it is difficult to compare in a ´truely comparable´ way, since there are several factors affecting efficiency which are hard to control or difficult to change without affecting other parameters as well.
For example what value is chosen for d/s? Whilst with SMS there is a plain with holes in --> easy measurement, because of constant d/s. But with round shaped wires of a WS (wire stators) You probabely have to calculate with a ´effective´ d/s value which is larger than the measured d/s. Next the insulation wires is typically a bit thicker than the insulation thickness of SMS. Next there are usually differences in the material choice of insulation and as such the epsilon-value of he insulation material itself. The open area %age is affected by this too. Really high precision built of the panels is needed with very small dimensional deviations, because even small variations affect very much the outcome.

In practise You find the more efficient panels (lower U for same SPL) amongst the PSM-hybrids.

jauu
Calvin

I will try and track down a copy of the AudioExpress report. Thanks!
Should be most interesting reading.

I agree there are many variables concerning the efficiency of the wire stators. Larger wire diameters and larger spacing between the wires, like Audiostatic, result in lower efficiency.

For my comparison I used solid 22 gauge wire with 0.016" thick PVC insulation. Spacing was measured from the outside of the PVC insulation to the diaphragm. Layers of 2 mil mylar tape on the spacers were used to equalize the spacing between the two panels as best I could. The PSM had 5 coats of epoxy paint, but I doubt it had full coverage or buildup on the sharp edges of the holes.

In all honesty, I think I probably overstated the "exactness" of the SPL matching between the wire and PSM test panels in my post above. In any case, it was very close...with in a dB...about as close as an experiment of this type could be I think. I was actually kind of surprised.

Most of the ESLs I have built were PSM hybrids with crossovers in the 250-400Hz range. Only in the last few years have I started experimenting with wires, so you probably have many years of exprience on me in this department. The reason I turned to wires is that I was having problems insulating PSM well enough that I didn't have arcing problems when trying to extend the frequency response down to 70-80Hz with its accompanying larger excursions.
 
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Wire vs PSM ESL efficiency

Hi Calvin,

I meant to add these thoughts to the end of my last post.

Based on my experiments, a wire ESL does not neccessarily have to be less efficient than a PSM ESL. At its best, a wire ESL built with small wires tightly spaced can equal a PSM ESL for efficiency. That being said, I doubt that one could build a wire ESL more efficient than a PSM ESL for a given area, spacing, and diaphragm charge.
 
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Hi,

I agree. :p
My way was quite opposite to Yours. Started with wire since I didn´t knew how to get my hands on a reliable insulation for PSM. Since this problem is solved, I prefer them over wire. But -and this is a big but- if I´d try to build a fullrange ESL I definitely would use wire. because of the larger d/s-values You need such high drive voltages that it´d be hard if not impossible to get a really reliable coating on PSMs. Even if You´d succeed in this the ´loss´ in open area would be considerable. Wires come readily with thicker insulation and are the better choice for higher d/s values. But then....why build a ´restricted´ but heavily difficult FR, if You can build a less difficult and superior hybrid? ;)

jauu
Calvin
 
i think insulation of sheet metal really isn't any problem. In the worst case you just get your metal plates powder coated, that's really a solid coating. But using special plastik 70 electrical coating should be enough. Remember, even though the voltages are high the amperage is very low.

Also plates are less flexible then wires. the wires will most definitiely flex which will probably have some (very small) effect on the sound.
 
Hi,

the results in Matthew Lattis´s Report in AudioXpress 2005 says the opposite.
He found too that PSMs (perforated sheet metal stators) typically gave higher efficiency values.

Hello Calvin,

I was able to borrow a copy of this article from a friend.
Wow! what a wealth of trend data he has provided.
I was pleased to see that uncoated wire and PSM were used for the comparison to removed that variable from the comparisons. I have only just begun to digest it all, but from what I have seen so far, his results confirm that wire stators and PSM stators built with similar open area will have similar efficiencies.

Looking at the final comparison, Figure 17, I think is a little missleading unless you look carefully at exactly what is being compared.
To simplify, lets just look at the data for 0.06" stator to diaphragm spacing since this is one of the most common spacings used.

Wire(95% open area) ===> 65.5dB
Wire(90% open area) ===> 69.1dB
Wire(80% open area) ===> 72.0dB
PSM(40% open area) ===> 74.9dB

Obviously if you are gaining nearly +3dB going from 90% open to 80% open with wire, it shouldn't be difficult to see that the wire efficiency could go up another +3dB by the time the wire open area reached 40% to match the PSM.

On page 18, the author mentions..."My original goal was to find the specific ratio of wire spacing to diaphragm-to-stator spacing, in which increasing the wire density stopped increasing the output, bit I did not reach that point in the testing."

Thanks again for pointing out this article....not sure how I missed it.
 
double the wires per inch on the stator and you gain 3db (in theory). At twelve wires or more per inch there really is not much to argue about between wire and punched metal. If you are building with metal and the stators are flat you will have greater resonances than with wire if you build upon a base grid like light louvre as Acoustat did. Acoustats only used 6 wires per inch and had reasonable efficiency. I use 24 per inch with light gage wire which yields a very low mass stator which is well damped and very low resonance.
 
Hello all
Jumping into this thread so I can thank those who have shared projects and helped others. I've only been here five months months but have loads of info! Again thanks and for sure my soon to be diy efforts will be so much easier and better. I recently found one Acoustat M-4 w/dd amp to replace the one that was stolen back in 1985. I'm going to build Acoustat panel semi-clones and upgrade the amps. Johnny
ps carry on
 
Hi

i think insulation of sheet metal really isn't any problem. In the worst case you just get your metal plates powder coated, that's really a solid coating. But using special plastik 70 electrical coating should be enough. Remember, even though the voltages are high the amperage is very low.

Sounds like famous last words like "Oh look, that should be easy...." :rolleyes::rolleyes:
What has Amperage to do with the problem of arcing?? Nothing in first place! A arc develops because of higher voltage gradients than the withstand capability of the insulator. A sparc develops regardless of the amperage. That comes into effect when the arc has already devolped and it detemines the energy within the spark.

To be able to coat sheet metal with a constant quality to work reliable and safe within the needed voltage range is one of the major points of knowhow of any ESL manufacturer. It´s by far no trivial task! Tell You what....a powder coating that looks solid is not necessarily a ´solid´ coating in voltage terms, especially not if You need a thick build.

The coating has to be functional in first case, optics are minor.
The first asks for thick, even and homogenous build, the latter only for a thin layer.
Go and ask a coater if he´s able to powder coat a punched metal sheet with an opening percentage of app. 50% with a coating thickness of min. 12mils -if Your PMS had been deburred and rounded before- and up to 20mils if its not deburred/rounded.
If he´s a serious guy he´d probabely be loughing at You and send You away.
If he´s serious and needs the money he´d run several tests You have to pay for before and maybe he succeeds in the end.
If he needs money he´d say: "Yes, we can", take the money and give you something which probabely neither looks nor works as You wished (since You didn´t specify what kind of powder You needed and cheap PE is e.g. not the right stuff).

jauu
Calvin
 
Sorry to wake up this "old" thread.

So powder coat is not the solution, or it will work with tricks ?
How about dip powder coating (instead of spraying) ?

I remember Roger Sanders used to publish all his designs with PSM, but he seems to be using insulated wires (not PVC stranded) for his commercial products.
Does that not suggest a performance advantage ?

I am new to this, so apologies if the questions are naive.


Patrick
 
I remember Roger Sanders used to publish all his designs with PSM, but he seems to be using insulated wires (not PVC stranded) for his commercial products.
Does that not suggest a performance advantage ?

Sanders is using copper clad board---printed circuit board material---milled with a CNC machine for his latest products. I don't recall him ever using insulated wires.

There are advantages and disadvantages to each of the popular stator constructions. You just have to choose your priorities: ease of construction, ease of breaking the stator into electrically isolated segments, ease of insulation, visual transparency,... I don't think there is a single approach that is best in all situations. If there were, nearly everyone would just adopt it.

Few
 
Build one

I have posted a complete start to finish esl. now that this is going, I would be more than happy to get started instead of the he said she said stuff. Give me some measurements, some ideas, turn me loose and you will see a floor to ceiling wire stator.
I have the measurements but some better pics would help. I am having problems with the wire gig, not sure if to cut each one and then stretch all at the same time. I hate speculating so info would be nice now.
I will post pics of my gig, and i guess go from there.
 
Hi,

There´s powdercoating and than there´s powdercoating ;)
A single coating layer formed by electrostatic spray coating will most definitely not be sufficient.
The process of manufacture is as such:
The cold metal sheet is hung upon a rig. It then is connected to a charged coating pistol. The coater coats the metal sheet with the powder which holds to the metal sheet because of the charging. The metal sheet is then put into an oven and the powder melts. After cooling down the metal sheet is ready. You may reach up to 100µm of layer thickness with this kind of coating technique. So You need at least a double layer coating or even a triple layer coating to reach a sufficiently thick insulative layer for ESL usage. Since the powder needs to be melted a second or even third layer is obviously difficult to do, because all layers need to be melted completely but must not be allowed to flow. A possible solution is to use different powders whith the second layer powder having a lower melting point than the first. Since You want powders with certain electrical parameter values it may be hard to find suitable powder-combinations.

The second way which looks much more promising on first glance is the electrostatically assisted fluidized bed coating. The process of manufacture is as such:
The powder is filled into a trough. Air is blown through openings from below into the trough. Now the powder behaves like a liquid. The metal sheet is heated up above the melting point of the powder. Now it is dipped into the powder which ´flows´ around the metal sheet. The powder melts and sticks to the metal sheet. After withdrawel and cooling the sheet is finished. Layer thicknesses of up to 100µm are possible within just one working cycle. But -and this is a big But- since the punched metal sheet mostly consists of holes there is not enough mass i.e. heat capacitance. The sheet cools down more quickly than the powder needs time to melt completely. The coater may use a second heating cycle in an oven, but basically this technique doesn´t lead to firstclass results (pinhole free).

The probabely best solution is a 3-layer combination of spray powder-coating and spray wet-coating. First coat is a single or double layer of powder as thick as possible (~100m-150µm) using electrostatically assisted spray coating.
The intermediate layer could be a thin colour-defining wet coating. The top layer could be from single- to quadruple-built (transparent) wet coating.
This way to coat is quite complicated and expensive but allows for nearly any color You wish and allows to use optimized materials for each layer.
The first layer may be optimized for electrical parameters and edge covering, the intermediate layer for optics and the outer layer for optics and mechanical robustness. Final coating thickness can reach 300µm and more.

The big problem with all coatings where heat/melting is involved in the coating process are the sharp hole edges. Besides the possibility of microcracks developing in the coating material when the hot powder layer cools down and shrinks, the layer thickness at the edge is minimal. So the first layer of powder needs to be chosen to allow for thick edge covering (smallest radii of constant layer thickness, a parameter seldom mentioned in the datasheets. Nylon beeing one of the best with an radii-value of 4mm).
If a punched metal sheet is not deburred or preferably has rounded edges You should at least calculate with double the layer thickness on the surface than needed.

Using powdercoating techniques the results may vary from completely useless to absolutely excellent. Powdercoating alone will hardly be sufficient. Powdercoating as part of an advanced coating process can be very good.

jauu
Calvin
 
I have found hookup wire by Belden #8076 polyester inside, amide/imide jacket. BV=5600. Is it suitable for wire stator?

Yes, this wire would be suitable for wire stators.
But, remember that with magnet wire you should not stretch the wire the way you do with PVC insulated wire.
With magnet wire, only hold the manufacturer's recommended tension when gluing to stators. If you stretch magnet wire, cracks will form in the thin insulation.

Attached is the recommended winding tension for Essex magnet wire. I'm sure the Belden wire is similar.
 

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those winding tensions are considering safe coil winding at high speed without the risque of cracking wires.

If you do static tensioning it can be tensioned further. The PU insulation should be capable to be stretched about 10% as well.

Hi Capaciti,

Have you built stators with stretched magnet wire?
I tried 4 times and all stators had numerous hair fine cracks in the insulation after stretching. They were difficult to see without a magnifying glass. But, moving a round metal bar with high voltage applied would arc when brought near the cracks. This was why I recommended staying close to the safe winding tensions published for electric motor winding to avoid insulation cracking.

For reference, I used Essex Superior AWG20-200C-11 wire on original factory spool.
Insulation type: modified polyester base coat and an improved polyamideimide topcoat

Perhaps I got a bad spool of wire...
 
Hi Capaciti,

Have you built stators with stretched magnet wire?

Insulation type: modified polyester base coat and an improved polyamideimide topcoat

Perhaps I got a bad spool of wire...
Most likely not. Permissible elongation is usually 15%. May be it's polyimide, which is rather stiff.
Having wound quite a few power toroidal transformers (up to N*100kHz) I would say that if no interlayer insulation is used, transformer fails over time, though interlayer voltage is quite low.
Alex
P.S. Thanks a lot!
P.P.S. Surprisingly enough I've just asked about the same wire type...
 
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