Hi, I have (2) PB10-NSD's in my theater room, about 2000 cf. in size. They are not colocated because they can't be. There is about a 3db gain difference with the second one turned on. When I ordered these, I had the thoughts of whether they were going to be enough to satisfy my hunger for bass. I must say that I am extremely happy with them with watching movies, or listening to music/SACD's etc.
Sorry this post is a little late, but it is good to hear that you are enjoying the PB12-NSD.
Mike