I mentioned in another thread that I had some new ideas about simplified bracing. Since at least one person mentioned they were planning a build soon, I thought I would put my idea out now, even though I am not quite ready. In essence, all of the cross bracing/window bracing in the sub is a PITA to build and install. My thought is that two longitudinal braces extending from front to back on each of the four sides is all we need. Sorta like this:
And here is a SketchUp image highliting the bracing I propose (the top and its two associated braces are removed for clarity):
At the rear panel, they would stop just short of the panel, and I would run two cross braces, between the two side braces, to set the rear panel depth. With this method, there would be no critical cuts for the braces, and you could install all of the braces to the panels before attaching the panels to the rest of the enclosure, so you would have easy access for construction (clamping, glueing, nailing, screwing...).
So the new plan would have just 12 braces; 8 longitudinal braces (two per major panel) that run nearly the full length (two of these act as the slot braces), 2 stub braces on top of the slot panel to support that edge of the front baffle, and 2 cross braces at the rear that nearly span nearly the full width. Cut all of these 1/8" shorter than you need to prevent any panels from standing proud out of alignment. The front baffle will determine the forward-most position of all of the longitudinal braces (including the 2 stub braces but not the 2 slot braces) and these braces must touch and support the front baffle because there is no room for cross braces up front.
At the rear, only the short cross braces will determine the depth of the rear panel, the longitudinal braces do not need to touch the rear panel, but they do need to overlap with the cross braces to form a simple lap joint (sorry I don't have drawings just yet).
I don't have access to Finite Element Analysis to confirm my theory, but I believe this scheme is nearly as rigid as the the cross bracing shown above. Diagonal bracing is not needed either, because the panels themselves prevent any diagonal collapse in those directions. Therefore, the only real need for bracing is to prevent panel resonances.
This theory came about from my thinking about the bracing patterns in folded horns and how to make those lighter. Horns can only have longitudinal bracing, except at folds. Due to their very nature, horns can't have cross bracing anywhere along the signal path. And in the throat, they are probably exposed to even higher pressures than encountered in a sealed enclosure! Despite all this, they don't seem to suffer from excess panel resonance.
I'll keep searching for some photos . . .
Enjoy your holidays and happy building,
Edit - Drawing added and photo deleted.