How would you go about doing a phase calibration? I have 2 totally different subs, an EP-350 and a 15" 500W DIY downfiring. They are in opposite corners of the room and I notice a big difference in SPL as I move around the room.

I started out with nothing & I've still got most of it left
M60 VP160 QS8 EP350
M22 VP100
Algonquins