Originally Posted by Jeremy1998
Hmm. In normal situations, it is bad to have your subs "opposing" each other. So, I guess the rules are different in IB?
Dual opposed means that the drivers still move outward, into the listening room in phase with one another. However, their reactionary forces that otherwise would affect the cabinet, manifold, etc., cancel. Similarly, a dual opposed box subwoofer utilized a driver on opposite sides of the box, ...thus canceling reactionary forces that would otherwise be transfered to the box.
Below is an example of a dual opposed, IB manifold,.... driver config, they are firing into the listening room;
If you merely mount the drivers without a manifold, extra stiffening of the surface (whether that's a ceiling, wall, etc) would be warranted because any reactionary motion of the surface, lessens the ideal transfer of energy to the listening room. Previous builds have illustrated that these forces are significant, and some DIYers have regretted not heeding other's warnings about their significance. It's doable, just be mindful it takes quite a bit of extra bracing. However, utilizing a dual opposed manifold, renders these concerns a non issue.
Thanksedit, missed the above post, clarifying things