Parallel Caps as a Bipolar (twin polar in combination)

Question

So, I saw a similar question about 2 caps in series to make a bipolar.

1. Lets assume polar electrolytics
2. I pretty much "get" electronics and build stuff - it works as I expect mostly.
3. I have a penchant for making mistakes and just wanting to see

So a speaker I was reconditioning had a BP cap electrolytic between it's tweeter and the parallel speaker wiring. I wanted to replace it .. was a 2.2uF cap. Instead of wiring the two negative terminals together and using positives for either end of the new combined thing I wired them so negative to positive and thus they are in parallel but one in each direction. Why? I'd rather have a higher than lower capacitance and ... anyway it works and sounds just fine. I assume its a C1+C2 combined capacitance. (I used 2 matched 2.2uf) However ... maybe one of them rejects part of the flow as it is backwards to the source of power or + (yeah I know electrons go towards + but - is heading to earth in this amp so ..) If there is reverse flow (and yes it would wouldn't it because it's Ac) then maybe that cap then readily lets it pass? So two caps in parallel but one is backwards polarity - is this just another way to make a BP style cap.

It seemed contentious on the previous article - some said, "no that will blow up" and others said "that's normal, that's how BP caps are made" when referring to the series with negative terminals together wiring.

So the upshot is that if they are in parallel but one is rejecting flow in one direction then do they actually act as a 2.2uF rather than 4.4uF working as a pair? Note, its been working fine for some time now ... so I'm guessing that no, I'm not an idiot. [Yes, I often do idiot things]. Thanks for educating, trolling or any other related ways to calculate how it would be.

What happens exactly to reverse current across a cap because you can couple AC and it passes through and people use polar electrolytics for that ... maybe they shouldn't. I do - in preamps have plenty of polar electrolytics coupling audio signal albeit line level or less - not power to speaker. Some audio power amps running with asymetric power supplies have a big cap in series with the + end to the source and the - end to the speaker. Thus I'm assuming that even a single cap isn't that easy to blow working with an AC if it doesn't exceed spec.

Answer 1

do they actually act as a 2.2uF rather than 4.4uF working as a pair?

In parallel they do act together as as 4.4 μF capacitor. This will halve the 'crossover' frequency, which could have some bad effects.

The most obvious effect is a change in the speaker system's frequency response. The tweeter is now being asked to reproduce sounds one octave lower than normal. Instead of response being rolled off at resonance, it may now get full power producing a sharp peak.

Below resonance the speaker system's impedance will be reduced due to the tweeter's low impedance in this area, increasing load on the amplifier and possibly increasing distortion. With more power going into the tweeter it may blow up at a music level that it could normally handle.

Despite all that you may not notice any effect except by doing a careful listening test or measuring the frequency response. However you might find that some music sounds a bit 'off' compared to playing it through the original speaker. This may be particularly noticeable if you only modified one speaker of a stereo pair.

What happens exactly to reverse current across a cap because you can couple AC and it passes through and people use polar electrolytics for that ... maybe they shouldn't.

So long as the waveform is pure AC and ripple current isn't too high an aluminium electrolytic capacitor can handle it fine because there isn't enough time for depolarization to occur. However in medium or high level circuits there could be measurable (if not audible) distortion. In this article published in Electronics World December 2002, A 1 μF electrolytic capacitor produced significant distortion when 2 V at 1 kHz was applied across it. In a high power speaker system the voltage could be 10 times higher than that - enough for the distortion to be audibly noticeable and perhaps causing degradation of the capacitor due to excessive ripple current