[Gogar]

I -think- you mean a capacitor that you will wire inline right before your 4x6. If you have 12s in the back, the answer is most definitely YES, unless your deck has some kind of Subwoofer, High-pass setup inside it. Some amps also have little high-pass pots that you can use instead.

But if you don't have those things in either the head or the amp, you wire the capacitor into the speaker cable, and it will take the extreme low end out of your 4x6s. That way, they're not trying so hard to make all that low end that they can't physically make anyway, and the low mids and mids get cleaned up considerably.