Here is my flawless trick for setting up a sub. Play or stream the Beatle Come Together from their 2009 release (not the recent remix that is super bass heavy).
The bass note (Paul plucks string once and lets it sustain) at the "got to be a joker"pause is the perfect sub set up. You should be able to set the sub to where you actually just FEEL the sustained note. If you have the crossover/volume too high (or wrong sub location) the note will sound extra fat and not tight. Too low, you wont feel the sustain. The tweak to taste from there in small increments
You will thank me for this tip...trust me on this one. Try it and get back