I don’t know anything about the ESR. For the polys, would you expect 400v to have less ESR than 250V, which would be less than 160V?
I don’t have two of the same brand to compare, but I do have Audyn 4.7/800v and a Jantzen 4.7/400v
Audyn:
Jantzen:
I think this goes to show that DATS is not to be trusted for ESR of capacitors, when results are off by a factor of 100 when compared to proper instrumentation. Datasheet spec for PB15000 dissipation factor is 0.001 ohms FWIW.
To be fair measuring less than 1 ohm accurately requires ok equipment. Inductance and capacitance are both notoriously hard to measure accurately. Without kelvin leads it is probably as good as can be expected. We all know those aligator clips and wire are a weak spot. Unfortunetly the internal clmponents probably arent much better. For $100 its still a good value. I have the newest version of DATS but havent played with it yet to see if the added cost = added value.
Just to be clear, I’m using the newest version DATS.
I bit the bullet and ordered the Jantzens from PE. Those AliExpress/eBay ones are a month out, can’t wait, need stuff now!!
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These might be worth cosidering if you are still looking.
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Yeah, I should have tried those, but figured after seeing DaveFreds Solen measurement, I’d be good with the Jantzen.
PE wants $80 a piece for the Solen, that’s a hard pill to swallow.
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I’ll send the Jantzens back, Wimas up next.
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Only $51 at MAD.
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I’d really like the 250V version, but depending on the outcome of the Wima, might try that one.
And of course I got an email stating there’s an extra $9 tariff fee on the Wima…FFS! 
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JMPO… I would have stuck with the NPE caps in the woofer shunt or 3 of JF’s film caps in parallel. Did you do your final voicing with the NPE’s? I highly doubt that I personally could hear any improvement with a very spendy film cap there. Not saying you can’t.
The sim kinda sparked all of this. I never really worried about the ESR effects on things, resistance of coils, sure. But when I entered the ESR of that shunt cap and seen what it did, hey, why not try to improve things.
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We should all bring out DATS, laptops, and a few big PP and/or NPE caps to Indy. Have a ESR measurement fest during one of the breaks. 
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As was mentioned earlier, I wonder if the issue here isn’t just DATS not having the resolution at these super low resistances like we’d see for ESR.
Measure a known resistor in series with it, and see if that improves the measurement.
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I’m chasing the fact that DaveFreds Solen measurement of .07@120Hz happened. Then bettered it with the meter. I have Solens ordered.
