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Old 7th June 2012, 09:10 PM   #1
uglykid is offline uglykid  Denmark
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Default need help with low sensivity els

hi all.

I have made some els but i have a problem, the sensivity is very very low, i guess its about max 90db with 150w my own guees is that i maybe have way too much tension on the diaphragm because i can not see any movement from the diaphragm at all then music playing and thats with no croosover and the sound is bright, the size of the panel are 100cm*24cm i have made them curved and D/S is 1.5mm and the distance between the spacers are 12cm, mylar is 6um and stepup trafo have 1:80 ratio, stators are made of 1.5mm steel with 58% air and isolation is made with emalje paint and 2 component polyester resin.

Then i remove the biasvoltage wire the speaker keeps playing in about 20-25 min so i chould not have any leakage from the coating (varmason esd floor polish) and then i turn up the bias voltage from about 2kv to 6,5kv there is not much difference in sound level.

The diaphragm and its here i think the problem maybe is, are stretched so much that i right between 2 of the spacers need to put 50g of weight before the diaphragm touch the stator.

hope i have give enough information to your guys to maybe help me with my problem...

regards
uglykid
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Old 7th June 2012, 11:48 PM   #2
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Sorry to hear about your ESL problem-- it can be very frustrating but it's probably something simple, since you're configuration sounds about right to give very high output.

I really doubt the problem could be too much tension on the diaphragm.

I found out recently that a panel can play at very low volume even with a faulty bias supply and/or non-conducting diaphragm, since there can be a small potential between the diaphragm and stators in any case.

I could be totally wrong and sound like an idiot here--but I'm going to guess that, since you said the volume doesn't change much when you more than doubled the bias voltage, it sounds like the bias supply could be faulty, or it could be the diaphragm coating is not conducting sufficiently.

I would check the bias supply first. If you don't have a HV probe to measure it's output, you should be able to touch the leads together and see a good spark--- unless of course the supply uses a hugely high-value output resistor, in which case it may be perfectly functional but the high value resistor would not pass enough current to give a good spark. (my 2.7 KV bias supply uses a 20 Meg output resistor but it still passes enough current to give a pretty good spark when I touch the leads together)

If your bias supply checks good, and you can disassemble the panel without destroying it, you could see if the coating is the culprit by re-coating the diaphragm with liquid dish detergent containing sodium laurel sulfate (most brands do, and it works very well indeed)-- and if you then get good volume, that was it.

Good luck with it!

Last edited by CharlieM; 8th June 2012 at 12:01 AM.
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Old 7th June 2012, 11:52 PM   #3
Bazukaz is offline Bazukaz  Lithuania
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Tension does not affect sensitivity above resonance much, only below it.
What is the resonance frequency of the diaphragm ? I guess for your size and support spacing(if there is sufficient tension) it should be somewhere between 100-200 hz.
Bright sound can be because of beaming. Have you measured the frequency response(on/off axis) ? Normally non-segmented larger ESL elements tend to have a rise in highs.
One possible reason for low output is too high resistance of stator coating.
There is a theory that resistor divider is formed between air and coating and significant part of voltage drop is across the coating.
What hole size is ? if holes are too large, sensitivity could be reduced.
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Old 8th June 2012, 08:01 AM   #4
Calvin is offline Calvin  Germany
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Hi,

Quote:
....because i can not see any movement from the diaphragm at al
Thats a rather clear indicator not for too high mechanical tension but for no charge on the diaphragm or crossed audio tranny connections.
As soon as You switch on the bias supply You should notice a deflection of the diaphragm. This deflection can more easily be seen if the the ESL-stators are not yet married. You should always test the diaphragm bias as long as You have access to the open film membrane, i.e. as long as the panel is not finished.
How did You constuct the diaphragm contacts? Try to evaluate if the membrane surface is fully charged and that all segments of the membrane are biased. The output voltage of the bias supply alone is not a reliable indicator.
The second possibility lies in crossed audio tranny connections. Keep in mind that You have 3 contacts of which the middle is common connected to the diaphragm via the bias supply (and/or gnd-referenced). The outer connections voltages must be out of phase referenced to the middle. If they are connected in phase the output will be close to 0 (and just due to winding differences/tolerances).
High membrane tension certainly would not hinder easy deflection and output, but raise the lower bandwaith limit. High tension is in fact positive in any case as it raises efficiency and dynamic range.

jauu
Calvin

Last edited by Calvin; 8th June 2012 at 08:07 AM.
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Old 8th June 2012, 08:54 AM   #5
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If you are sure that you have done everything right, the most likely cause could be that your coating material isn't very good.

Wachara C.
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Old 8th June 2012, 09:20 AM   #6
Calvin is offline Calvin  Germany
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Hi,

had a look at the Statguard floor finish 220521.
It says it is a aqueous acrylic emulsion with a solids content of 18%. That sounds like EC-powder linked in a polymer matrix (EC: electro-conductive) similar to Zelec Millikens ECPs.
The specced surface resistance obviously varies with coating thickness, ranging up from 10e7Ohms. A specced reach of 49m/L translates to a wet coating thickness of ~20m which is similar to a thin coating of a typical color laquer. Depending on the procedure of coating the wet thickness may be too thin, though I regard this aspect rather improbable, since ECP-based coatings may be very thin (dried-coating-thickness of >0.5m).
Anyway, the transition from a highly conductive copper strip to a low conductance material will give (lowlevel) corona that may eat away the coating over time. As such the design of the contacts influences the longtime stability of the panel. Talking about a new panel I regard this possibilty also rather improbable.
If the Statguard is a ECP-based antistatic it should perform well and stable (conductivity is not affected by humidity/water), its useablity rather a matter of how well it wets and sticks to the diaphragm material (which would be a matter of the resins used, the diaphragm material and its preparation)

jauu
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Old 8th June 2012, 09:59 AM   #7
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If you turn the bias up from 2kv to 6.5Kv you should easily hear close to a 6db increase of output level.
If there is no change then I would suspect the supply.

Since you are getting at least a 90db output this is a substantial amount of volume and your coating appears to to working.
What happens after you leave the bias supply on for a while?

Your coating is specified at around 10^9 and this is a bit high ,but it should still work,and by your report it does,so I don't suspect the coating unless you didn't get a good coverage.
How well did it wet the mylar when you applied it?

Just a few questions,But you definitely should have heard a difference if you increase the bias!!

You might try doubling your transformation ratio also and see if it make a difference as it should.

But recheck your bias though,many times I have seen this as the cause of low output of a panel.

If your supply is putting out 6.5kv then it should be blowing you out of the room even much more so with a 1:160 transformation ratio.
I run my little panels at those same voltages and they are 1/4 the size of the ones you have and I get +99db at one meter with a 6.8Kv bias.
Only I run a 1:256 transformation ratio on them.



Jer

Last edited by geraldfryjr; 8th June 2012 at 10:11 AM.
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Old 8th June 2012, 10:28 AM   #8
Calvin is offline Calvin  Germany
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Hi,

Quote:
..max 90db with 150w
uglykid
Quote:
..least a 90db output this is a substantial amount of volume
geraldfryjr

Jer, Youre really settle for 90dB@150W if You easily gain the same SPL with just 1W?
Man, Your ears must be exceptionally sensitive

jauu
Calvin
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Old 8th June 2012, 05:53 PM   #9
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No,Calvin,Actually I like it quite loud but 90db is for good nearfield listening and is about average really.

Anymore than than that ear fatigue starts to set in quickly for me as I have listen to very loud systems for many years.
After the fatigue starts to set in it has to go louder in order for me too feel the same effect,Actually at least 105db is more comfortable for me.

He,he,he,he !!

Your right Calvin he should be getting 90db with only a 5V to 10v peak signal input to the step up transformer,Like I said I run those same voltages and get +99db at 1 meter and 110db at the diagphram and that wasn't even pushin' it yet.
As I have mentioned many times before, Stator coating failure was the demise of one of those little panels before I got to see the ultimate performance of them agian to measure.

They did it before but they didn't that day.

:Cheers:

jer

Last edited by geraldfryjr; 8th June 2012 at 06:06 PM.
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Old 8th June 2012, 09:07 PM   #10
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150 watts? What's the actual voltage to the transformers?

Ben
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