Eh hem!...Subwoofers... What do ya know?

I want to be clear on my position in a few ways:

• Multiple subs are great
• 1 sub, properly integrated is much better than most people know about.
  
• Hsu makes great subs too, and more people should try them.
  

Does anyone technically know what happens when you aim two subs at each other?  Say a foot or 2 feet apart . Is there an ideal distance apart to do with frequency? Does it have an affect on the opposing woofer itself such as improving the rearward movement of each other? Would have to be a specific distance i assume . A possible equation ?

Reason i ask is i have 2 x18” jbl 2245 aiming at about 20” apart and hung from the underside of floor . And they sound incredible . Not  boomy sound but accurate and on cue. They have a very black background. And only reveal themselves when there is very low program material. 

If you time align the back sub to fire when the front wave hits him and you also phase it 180 degrees, theoretically both waves cancel each other and you don't hear the reflections again

This is theoretically of course in the real world it won't happen unless the room have nothing in it, it is a geometric cube (or sphere) reflective materials all the same etc