what head unit you using? basically the HPF LPF is to set the frequency where above it, goes to your speakers, below it goes to your woofer. my setup is mbquart 4" coaxials and bazooka 8" tube only. previously my head unit dont have HPF LPF, and i used a SPL pre-amp with sub crossover. as a result, my sub only cover up to say, about 80Hz, and the coaxials can only comfortably handle 100+Hz and above. hence there is a band of freq in between that is 'lost'. when i try to turn up the bass for my coaxials, distort because only 4". cannot produce much bass. now with the HPF LPF, i set at 120Hz, below go to sub, above go to speakers. wonderful. can play loud volumes, very full sounding.
actually i thought of changing to 6.5" components to handle more mid bass, but after realising what HPF LPF all about, solve all my problem. basically set your HPF LPF both to the same frequency. above this will go to your speakers, below will go to the sub. see to your liking, play around.
