I installed Larry's rings in one channel and have been doing some tests. I wanted to test for air tightness so I decided to push on the passive radiator to see how long it takes the 6.5" drivers to "deflate". Ideally if it was 100% air tight they would not slowly slink back to resting position. However, when I push the passive radiator in I hear a whistle!
After a few minutes of hunting this whistle down I determined it's coming from a hole in the back of the cabinet. I believe this is the hole that the back brace would screw in to.
I presume I should plug this hole - what do the experts recommend? I do not have the hardware to screw in the hole - but I could pick something up if I knew the dimensions - and assuming this is the best solution.