Originally Posted by mhweb
This is a random image of the back of a monolith subwoofer, but I wanted to use it as a reference to ask how the nubs should be set for crossover, phase, and level to have proper configuration. Or at least, what should be recommendation.
This sub is in a small 15 x 12ft room with 8-9ft ceiling, and wooden floor.
Also, if understand correctly, the level should stay at THX, right?
As Wayne said, your AVR will help you to determine your subwoofer gain (level) setting. But, if I were you, I would leave the phase set at "0" and I would set the crossover at the max setting. I can't tell whether the crossover control knob is even operational unless the crossover switch is set to the "On" position. Your owner's manual may answer that question.
In any event, for calibration purposes, you will want your AVR's automated room correction system (if your AVR has one) to be able to EQ the subwoofer's full frequency range, and initially at least, you will want your subwoofer to be able to play as high as it is able to. Once your AVR sets crossovers for your various speakers that may or may not be quite as important.
With respect to the sub's level (the gain control) I would start with it at about the -12 position, and then adjust upward or downward a little, as required during the calibration process. After your AVR finishes its calibration, you would ideally like for your AVR sub trim to be in negative numbers. If you want to understand more about that, you can refer to the Cliff Notes, in the Guide linked in my signature, or you can read as much detail as you would like to in Section II.
I think that the Guide may be helpful to you as you implement your new subwoofer.