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Old 23rd July 2009, 07:06 PM   #161
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Hi Martin-Jan

Quote:
Originally posted by MJ Dijkstra
Did you ever notice any AUDIBLE differences between a low resistance coating (10 exp 7 or less) and a coating with 10exp11 ohm?
I would like to answer that with a 'careful yes'. 'Yes', because the difference between the two coatings from the test can be heard, and 'careful' because IMO I have not researched other differences between the coatings that might explain a different sound.

Having said that, I would expect the lower distortion to be a welcome improvement and from an engineering perspective an easy decision to make.

Quote:
I've got audiostatic ES200rs myself, maybe you are fimiliar with that type...
I had a pair of ES300RS some time ago, but it was in poor condition. After they had been standing in a corner for three years I gave them away to someone who wanted to have ago at it.
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Old 23rd July 2009, 07:28 PM   #162
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Hi Arend-Jan,

I agree that the difference in coating should be the only difference in case of a true comparison. The best test would be two identical ESLs with different coatings to directly compare. I never took the effort to do that kind of excercise.

Anyway you inspired me to do some testing myself in the future.

ps, you gave a way a 300RS ?! Call me if you want to do that again!
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Old 4th August 2009, 08:50 PM   #163
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Quote:
Originally posted by JonasKarud
It would be very nice to receive a sample of this 1720 polish. [/B]

I just received tracking information on the 1720 polish. Should arrive on Thursday. I have a stash of leak proof 3oz bottles...about 90mL I believe that should work good for mailing. Do you think this would be a useful sample size?

Anybody interesting in experimenting with it and reporting back to the list with your results, send me a message and I'll get some shipped to you. I'd appreciate reimbursment for shipping cost...Paypal would work.
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Old 6th August 2009, 12:58 AM   #164
Few is offline Few  United States
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Hi Bolserst,
Thanks very much for such a generous offer. I think your proposed sample bottle size makes sense and would work well. I'm doing a bit too much experimenting already, so I'm hesitant to add another variable to the mix. Nonetheless, if I can get my ESL and OB woofer system far enough along to contribute I might be able to participate in an informal test. I seem to be moving at a glacial pace, though, so I hesitate to make any promises.
Few
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Old 6th August 2009, 07:11 AM   #165
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Very nice offer, but i'm convinced that this 1720 polish is the same as the old DFP-410, looking at the common ingredients.

It will be very interesting to see what the diy:ers think about the 1720 polish.
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Old 6th August 2009, 08:25 PM   #166
AuroraB is offline AuroraB  Norway
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How do you measure this resistance without a $$$$$ instrument?
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Old 6th August 2009, 08:55 PM   #167
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Quote:
Originally posted by AuroraB
How do you measure this resistance without a $$$$$ instrument?
For an easy way to get an idea of the average surface resistance (ohms/square) I coat 8" x 8" section of a test diaphragm with two opposite edges terminated with 8" lengths of copper foil tape.

Then get a voltage supply (100 volts or whatever is convenient) and a digital voltmeter with a 10Mohm input impedance.

I hook the (+) of the supply to one of the copper tape edges, the other copper tape edge to the (+) input on the dVoltmeter, and the (-) of the dVoltmeter to the (-) of the supply.

So basically you have the coating connected up as the input resistance to a voltage divider.

Then you just need to convert the reading on the voltmeter to what the unkown surface resistance must be.

Vmeter = Vsupply * (10Mohm) / (10Mohm + unkown resistance)

For Vsupply = 100 volts

Resistance ===> Resulting Meter reading
1.0E+06 =====> 90.909
1.0E+07 =====> 50.000
1.0E+08 =====> 9.091
1.0E+09 =====> 0.990
1.0E+10 =====> 0.100
1.0E+11 =====> 0.010


NOTE: this gives you a good first estimate at what the resistance of the coating is. But it does not tell you if the resistance is uniform over the whole coating. For example, when testing the Licron Spray coating I got a reading of 1.0E+08 for the large 8" x 8" square, but using a smaller probe, I saw variations from 1.0E+07 to 1.0E+09 in different areas of the diaphragm. Not a good think if you are trying for low distortion and want to avoid charge migration during large diaphragm excursions.
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Old 10th August 2009, 03:33 PM   #168
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Default Techspray 1720 Polish (preliminary results)

As Jonas recommended, a few tests with the unmodified 1720 polish are being done.

With no dilution, surface resistance is ~ 4E5 ohms/sq.
With 8/1 dilution, surface resistance is ~1E8 ohms/sq.

I have another test panel curing now with 10/1 dilution.
What I am after is a very uniform 1E9 coating.

The solution is quite easy to apply. It has kind of a soapy feel to it and wets the mylar nicely and uniformly. You do need to go slowly when spreading or bubbles develop that dry in to areas of locally lower resistance. I tried spreading with a cloth, cotton balls, foam roller, standard brush, and foam brush. So far, the foam brush seems to be the easiest to use, avoid bubbles, and produce a uniform coating.
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File Type: jpg foam_brushes.jpg (16.6 KB, 500 views)
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Old 10th August 2009, 03:39 PM   #169
Few is offline Few  United States
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Thank you for the report. Do you have any sense of how much mass the coating adds to the diaphragm? Licron, for example, seems to build up quite a bit. How does your solution compare?

Few
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Old 10th August 2009, 04:21 PM   #170
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Irritating small bubbles? it must be the same as DFP-410!

The conductivity seems to be identical, maybe a tiny bit lower than
DFP-410.

Thanks for sharing.....
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