Yasek

the question is should i allow the deck to run its filters along with the amp or should i turn off the filters on the deck and allow only the amp to control the frequency range being out put to the speakers/sub.... i have a pioneer DEH-P7800 a rockford fosgate 450.4 amp its powering two rear speakers jbl louds 6 1/2s and other two chanels are bridged powering a sub..

tooslow

You only need one... I'm using the ones on my amps.

Creamedweasel

Just use one, but it never hurts to see which sounds best. If you have both on you'll have a very sharp roll off where the second filter kicks in.