Does a 150 lb cabinet walking itself backwards an inch during the high power sweeps/THD testing count?
It was sitting on my rickety deck, so I am pretty sure that did not help things any. With music or movies? It is pretty much a non issue. Just don't park priceless china on top if it.....
For typical use, this cabinet will be fine as I built it. I probably should have used better ply, but I went with what I had available. As a result, this one is right at the edge of getting away with no bracing. I'm sure that using better ply would help.
As with anything, there is certainly room for improvement if one was so inclined. The throat panel definitely vibrates, as does the back, top and bottom. The bottom of the mouth is by far the worst, as it is essentially unsupported. If I were bracing anything, I'd concentrate on the mouth area and throat area, as well as make sure there was a brace from the approximate center of the back flare to the core portion of the fold.
Bracing is a lot more work for maybe another dB of output, especially since you won't see the effects until you're already pushing the mid-teens, which is when we noticed a bit of vibration during sine wave tests.
I say skip the bracing, just use good ply.