What would cause a capacitor to fail?

[weshole]

What would cause the same capacitor in a Xover network to fail. Both Xovers have had the same cap fail (at separate times). The capacitor happens to control the tweeter. Not a problem to replace. I was more curious as to why this would happen.

This happens to be the one that failed in both Xovers. One last year (which I replaced) and one just today.
Oh ya, I was definitely working them hard. But, not to the point of audible distortion.

[SnowDrifter]

Overpowering

[weshole]

I am sending them a lil bit of power

[Wicks]

Electrolytic capacitors can fail from:

1.) Over temperature

2.) Over voltage

3) Excessive ripple current

[Johnny2Bad]

Capacitors are a wear item; they begin to fail the day they leave the factory. However they should last years. Decades? Maybe, maybe not.

You should be using a film / foil type in a crossover, although for very high power applications it's common to use an electrolytic type (due to cost).

Caps, more than most components, are kind of a "living" entity. They are constantly changing in value, parameters, etc as they are energized in-circuit, and non-energized (in storage or unused device). They eventually settle into a stable set of values, but don't expect two random caps from a bin to measure the same; they won't. You can pay a little extra and some vendors will match two caps in value for you.

Sometimes being very close to spec matters, sometimes it doesn't. But for a crossover, I would say it does matter.

Capacitor manufacturers pre-form (run a current through) and age (values are adjusted so that when they are delivered for sale they meet spec) them. They do not leave the factory in spec; they leave the factory in a state where they will be in spec 3 months later (expected delivery to customer).

That is why you want to be buying from a vendor that actually moves a lot of caps.

I don't think voltage rating is a big deal but that's assuming the cap's voltage rating is appropriate. For 12V power you should be using 25V caps, for example. 16V is too close to what your alternator might put out in a charge state.

How many volts does your amp produce? Use a xor cap that has some voltage headroom. Although for tweeter use actual power @ the cutoff freq ... say, 3 Khz ... will be low; maybe 1/10th the current going to the sub; could easily be less. But if you clip the amp, now it's 100% of the power going to the sub. So how loud you play does factor in, and ... not to accuse you of anything ... lots of people prefer a little THD; high order harmonic distortion sounds initially as snappy and bright and is sometimes confused with "clean" sounding; clipping the HF driver is common enough.

Automotive environment is a demanding application for any cap; they don't like temperature extremes even when the device they're used in is not operating.

Shelf life ... buy caps that were recently manufactured (less than 1 year; the fresher the better).

Counterfeit caps are a problem; you may not be buying what you think you are buying.. Use a reliable vendor.

You don't give any details that might help with a replacement recommendation. But for substitutions, all you have to do is use the same value (eg a 3.3uf cap). There are good crossovers and there are bad ones (use cheap components). You might consider improving the voltage rating, the temperature rating, and see if you can afford a film cap if it's an electrolytic. Usually the biggest problem you have with a substitution is whether it physically fits.