Zobel network, with a twist (a notch filter). Corrects phase issues. IF you're working with woofers I found an active crossover eliminates all the funky passive XOs trying to fix the bass boo boos, passives CAN'T.
Active crossovers, direct amp to driver coupling, aided with mechanical correction is almost as good as servos. You get the bass to do anything you want lets put it that way, without having to fiddle with passive parts.. PITA passive is NEVER great in every room.
I've tried a lot of filters, notches, nothing. If you can afford an active system, you're miles ahead of the crossover crapshoot with a lot of the factory stuff. They are usually pretty cheap components. I really like it when manufactures seal their XOs. YOU know there is some real cheap crap used then.. WHY hide it? I know it makes it work better. :-)
Outside the box works even better, so we can see the cheap-a$$ parts they used in 200k speakers. Nothing is better than outside the box. Period.. The problem in this case is what is left inside the box is still messed up, add a filter? I say chuck the whole mess.. LOL
The money spent on filter would replace factory passives with TUBE driven actives. Here is a two way.
STL in Canada. They are into BIG valve tech, BIG time.. 100s of valve combinations..