My HU has a hpf which I have on and the amp's hpf is on also. I am adding the Component soon.Depends on what your speakers play to and what your h/u crossover is capable of. If you can have pretty precise control from the headunit (slopes, x-over points) then I'd leave it "off" on the amp and control it from the h/u.
Having said that, you really should have some sort of HPF on your comps to keep it from playing the notes it wasn't designed for (though the passive should take care of that).
You don't have to have both on.My HU has a hpf which I have on and the amp's hpf is on also. I am adding the Component soon.
I have a Sony CDX something...You don't have to have both on.
What h/u do you have? If the h/u has adjustable slopes then I'd stay with that. Music changes, and some songs you'll want to have different settings for.
http://shopping.yahoo.com/p:Sony%20CDX-F7705X%20Car%20CD%20Player:1991431148age=large-image;_ylt=Au_uWIjawHM_nyHlwtmz3NAph74F;_ylu=X3oDMTBkZmZ1NDR2BHNlYwNwcm9kc3BlY3M-Can you get the model number for me?
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