[NJARC] non-Polarized Capacitors

[Ray Chase]

You bring up a very valid point about the ESR of electrolytics, an often 
overlooked parameter of capacitors that varies widely in electrolytics. 
Wonder how the ESR of electrolytics would vary over wide audio ranges?  I 
say leave the electrolytics to the job they do best; i.e. filtering and 
bypass at low frequencies.
----- Original Message ----- 
From: "davesica" <davesica at juno.com>
To: <njarc at mailman.qth.net>
Sent: Monday, October 19, 2009 10:56 AM
Subject: Re: [NJARC] non-Polarized Capacitors


> Just remember
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> _________________________________________________________
> I've always been told that wiring two electrolytics back-to-back makes a
> nonpolarized cap. I did a little reading on this subject and it seems
> that manufactured nonpolarized electrolytics ARE just back-to-back
> electrolytics in one can. As far as I can tell, these are technically
> what is known as "Bi-polar" electrolytic caps. True nonpolarized caps are
> all of non-electrolytic construction (using Mylar, polystyrene, etc. as
> the dielectric.)
>
> For some applications, using bi-polar 'lytics should work fine. But since
> we're talking about use in crossovers here, the issue of ESR (effective
> series resistance) seems to come into play. I'm as skeptical as anyone
> else here about the "magical" properties of certain audiophile
> components, especially some of those highly worshipped tubes, but it
> seems that using "nonpolarized" (or "bi-polarized") electrolytic caps in
> a speaker crossover network *could* have a noticeable effect on the
> performance of the system. The numbers I've seen are all over the place,
> and no one seems willing or able to quote hard and fast actual or typical
> ESR values, but if I'm interpreting this correctly, "typical" or "high
> ESR" electrolytic caps of values commonly used in crossover networks
> *could* have and ESR as high as 30 ohms or more, and might easily have an
> ESR of several ohms. "Low ESR" caps (the lowest ESR values are found in
> non-electrolyic caps, although "low ESR" electrolytic caps are made)
> might typically measure a fraction of an ohm.
>
> Used in series with a 4-ohm speaker, the difference between a low ESR cap
> (say, "0.2 ohms) and a standard one (at perhaps 8 ohms) would have to
> have a noticeable effect on the frequency response of the speaker system.
> If you're unlucky enough to choose a cap with an ESR of 30 ohms, putting
> that in series with the speaker is likely going to have a big effect.
>
>>From this, it seems that for best results, crossover caps should be
> genuine nonpolarized film construction rather than bi-polarized
> electrolytics. (Of course, if the original equipment used high ESR
> bi-polarized electrolytics, then using too "good" a replacement might
> also adversely affect the frequency response by making the tweeter too
> "bright!")
>
> That's what I've been able to deduce. Any "real" engineers out there care
> to corroborate my conclusions (or show me where I'm wrong?)
>
> --Dave Sica
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