[NJARC] non-Polarized Capacitors

[davesica]

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





On Mon, 19 Oct 2009 13:48:57 GMT "w2wiq1 at juno.com" <w2wiq1 at juno.com>
writes:
> IN INFORMATIVE ARTICLE ON CROSSOVERS.
> 
> http://www.chokes.com/crossovers_explained.html
> 
> WALTER-W2WIQ

 
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