Been using a dual sub configuration lately. I've got one Nola sub straight right in front of me. I am using the second along the wall behind me and over my left shoulder.
I am beginning to understand the problems with subs and placements. I think I might have solved a problem in my room using dual subs. In fact it sounds pretty snazzy.
The natural tendency is to put both subs on the ground. This is false and bad practice IMO. I've never been able to make it work. Subs on the ground are used for ambience. The problem with placing subs on the ground is it creates to many nodes by moving bass along the ground. Even if they are are used out of phase.
Another reason for using a sub is to enhance resolution in the bottom end. The way to do that is by applying a subwoofer lifted off the ground. A good height is the distance between the woofers on your mains. Or the distance between the midrange and woofer. The thing that isn't discussed ever with subs is Subs can be used to beam a signal much like a midrange and tweeter. When you take the sub off the ground it begins to be come less ambient and takes on more beam signal. If this wasn't possible there would be no bass resolution in the sweet spot from your mains. Mains woofers can direct bass and so can subs off the ground.
So I got a sub lifted in the sweet spot and I got a sub behind
me creating ambient room info.
So subs off the ground for resolution and subs on the ground for ambience. That's in my room anyways.