Originally Posted by Mark Seaton
The question is if there is any practical difference in damping higher frequency vibrations with a small contact area vs a larger strip of say a window style brace. I'm not saying the difference is huge, especially for subwoofers, but I wouldn't call it equivalent.
For a given volume of material, single point bracing to the opposing side is much more efficient than blade stiffeners. This is easily shown with simple FEA models (the braced plate bending calcs get messier than I care to trudge through). The same is true compared to panel thickness but only globally. It of course does no good to build a box from kraft paper only to have to brace it every 1/16". The primary benefit of increased wall thickness is allowing higher stiffness in unbraced spans and thus allowing bracing to be spread wider. The optimum use of material can be found with a simple spreadsheet or mathcad calc, but to be honest I've never bothered as (1) mdf and ply comes in standard thickness and (2) I don't need to optimize a design for either weight or external volume for any of my diy applications. Easy enough to just use simple rules of thumb that work. Unless I really need portability, and that seems never to be the case, I'm happy enough to just overbuild and call it done.
This all applies only to sub enclosures. The situation is more complex for full range enclosures where increasing panel stiffness may only push a resonance higher within the audible passband. Whether it is better to have a higher q resonance with less total energy or a much broader q resonance with higher total energy, or whether resonance or non-resonant sound transmission drive audibility, are not particularly straightforward to answer given that each choice demands a different distribution of mass, stiffness, and damping. Some have proposed that well damped panels should dominate and allowing some flexibility is fine. I'm not sold on the arguments that stiffness is much much less important, though it is clear that for example an efficiently stiff but undamped [corrected - my phone apparently didn't like "undamped"] panel, say a steel wall with minimal blade stiffeners, which rings like a bell is no good. In fantasy land the panels can just be stiff, massive, and well damped, like granite with a thick damping layer. In the real world it is difficult to come to a clearly best compromise.