Yes set it all the way up to 150 hz if you're using the sub output from your receiver. The phase switch or dial on your sub adjusts it so that it is in phase with your main speakers. This is used when you place your sub far away from your mains. It;s kinda hard to explain, you adjust it so that the bass gets to your ears the same time that it does for your main speakers. Do a search on it and you'll understand better. Your sub should have a switch or dial for it. If you're not using the sub output on your receiver, I'll explain how to go about doing the crossover later.

-Joey