@portoalegre wrote:
[Are two subs better] "even if the two subs are at the corners close to the walls?"
Yes but the improvement is not as much as if the two subs are in acoustically very different locations... like one in a corner and the other along one of the walls opposite that corner.
The basic idea behind a distributed multi-sub system is this: You want each sub interacting with the room as differently from the others as is reasonably feasible, so you want them to be in locations that are acoustically dissimilar. This way each sub produces a significantly different room-interaction peak-and-dip pattern, and the SUM of these multiple dissimilar peak-and-dip patterns is smoother than any one alone, and this improved smoothness extends throughout the room. And, perceptually, "smooth" bass is "fast" bass because it is the in-room peaks which take longer to decay into inaudibility.
If you have no other option than to place your two subs in the corners, here are two things you might try: If they have adjustable phase, set their phase controls 90 degrees apart. And if you can get away with it, elevate one of the subs so that it is closer to the ceiling than to the floor.
Disclaimer: I have been commercially involved with distributed multi-sub systems for many years.
Duke