One more Question...
 

The deck I bought has a built in 80hz low pass filter... It says like "Sub LPF" Then you can choose FLAT or 80hz LPF.

Will it hurt anything to use the LPF? I have just kept it on flat.

It depends, there is not a lot of flexiblity there with only one crossover point. If your amp has a varible one you might just want to use it instead. I would definately use some type of LP filter for your subs, to prevent unwanted signals from damaging your subs, and 80Hz is a pretty good crossover point but it depends on your subs.

Oh, right... Well the amp is a DPX1800 and it does have adj. cross over.


And the sub is a single 12" Alpine R.

Totally your choice then on whether you use the one in the deck. Play with it and see if you hear a difference.

There's a difference for sure... It sounds louder and "better" with it on. I just wasn't sure whether or not it'd be good for the system.