In my 12x17 HT I have a null in the 40-60 range with the sub in either of the front corners of the room. If I put the sub in the rear corner the 40-60 null is gone but I have a null in the 15-25 range. I have tried both ways for a few months each and overall prefer the sub in the front of the room. Either way I have a null, but in my particular room I can tell the sub is in the rear when a big explosion happens or something like that and it detracts from the effect. Explosion happens in front of you and boom is heard over my shoulder. I cant tell most of the time that the sub is in the rear, but it happens enough that it bothers me. In the front the sub blends beautifully with the rest of the system and never draws attention to itself which is the way it should be. Everything is calibrated with Avia including phase to optimize the sub in either location. Having the sub in the rear just is unatural to me. Ideally what I would like to do is to get another pb12/2 ultra for the rear (or pb12 ultra) so I can have the 40-60 range back at my primary listening spot. Would putting one sub in the front left corner and one in the rear right corner work together well or would they cancel each other out and not solve my problem? Like I said I have a pb12/2 ultra, 80hz cross, 12x17 fully enclosed room, and everything calibrated with avia. I cant move the couch either. Would dual subs not co-located help or worsen my situation? If having a second sub in the back would solve my null I could deal with having the second sub in the back especially since I will have one in front.