OK - some basics:
a) very nearly every speaker capacitor is non-polarized. Why? They are desi gned to work in an AC (alternating current) environment, albeit at rather l ow voltages.
b) as capacity increases, the cost of a non-electrolytic increases signific antly per uF, far more than with an electrolytic cap.
c) non-electrolytics tend to be larger than electrolytics as uF increases.
d) manufacturers, therefore, favor electrolytics as a means to lower costs and lower real-estate requirements.
Those are the most basic reasons that you will see electrolytic capacitors in speaker crossovers. "Voicing" while a very real concern will not be mate rially affected by changing out one electrolytic for another as the toleran ces are pretty sloppy as compared to non-electrolytic capacitors, and even low-end manufacturers would do some basic screening. However, if you choos e to substitute a large film cap(s) for an electrolytic, some experimentati on may be required as these days, the tolerances for film caps are commonly less than 2%. As compared to as much as +50% for electrolytics.
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This is a crossover from a Dynaco A25 speaker. Well respected speaker with excellent drivers, but from a manufacturer that pretty much did everything in the cheapest possible way. One electrolytic cap, and a bunch of sand res istors.
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This is a crossover from an AR4x speaker, contemporary to the A25, and also well respected. But from a manufacturer that did not do things in the chea pest possible way. Note the inductor, and non-electrolytic cap.
There are many ways to get there.
Peter Wieck Melrose Park, PA