I have been crossing over my system at 120 to my 18 subs. A buddy of mine said " you have dual 15's in your mains..use them." As I run in mono, I could use the other side of my stereo crossover and bring the mains (JBL MRX 525) in at a lower frequency than 120. I was thinking 65-75. Will I have problems. Most gigs I can't double stack the subs but I have about 20 -25 ft between them and of course the mains sit on top. I really want to build some stands for the mains and center the subs, but most gigs the stage is to low. I have corner loaded them and it seems in a wide bar, the subs are only good on the side I corner load them.