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Old 27th August 2009, 03:09 PM   #21
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Quote:
Originally Posted by Calvin View Post
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.

Last edited by bolserst; 27th August 2009 at 03:21 PM. Reason: added PVC insulation thickness = 0.016"
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Old 27th August 2009, 06:39 PM   #22
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Default 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.

Last edited by bolserst; 27th August 2009 at 06:41 PM.
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Old 28th August 2009, 07:34 AM   #23
Calvin is offline Calvin  Germany
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Hi,

I agree.
My way was quite opposite to Yours. Started with wire since I didnīt 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 Iīd 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 itīd be hard if not impossible to get a really reliable coating on PSMs. Even if Youīd succeed in this the īlossī 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 īrestrictedī but heavily difficult FR, if You can build a less difficult and superior hybrid?

jauu
Calvin
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Old 31st August 2009, 09:55 AM   #24
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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.
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Old 31st August 2009, 07:57 PM   #25
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Quote:
Originally Posted by Calvin View Post
Hi,

the results in Matthew Lattisīs 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.
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Old 31st August 2009, 11:24 PM   #26
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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.
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Old 2nd September 2009, 04:34 PM   #27
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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
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Old 14th September 2009, 07:53 AM   #28
Calvin is offline Calvin  Germany
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Hi

Quote:
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...."
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. Itīs by far no trivial task! Tell You what....a powder coating that looks solid is not necessarily a īsolidī 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 heīs 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 heīs a serious guy heīd probabely be loughing at You and send You away.
If heīs serious and needs the money heīd run several tests You have to pay for before and maybe he succeeds in the end.
If he needs money heīd say: "Yes, we can", take the money and give you something which probabely neither looks nor works as You wished (since You didnīt specify what kind of powder You needed and cheap PE is e.g. not the right stuff).

jauu
Calvin
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Old 18th July 2010, 06:59 AM   #29
EUVL is offline EUVL  Europe
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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
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Old 18th July 2010, 03:41 PM   #30
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I have found hookup wire by Belden #8076 polyester inside, amide/imide jacket. BV=5600. Is it suitable for wire stator?
Sincerely,
Alex
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