Because then you deal with the complications of internal bracing? Yes, there are adverse affects. I NEVER use internal bracing. Why? I'm sure bracing in an acoustic suspension enclosure, a 4th order, or a 4th order bandpass wouldn't hurt. Wherever there is air flow, it causes problems. Perfect example (and not the only case), in my S10 I did no internal bracing and made the box 5.25" thick except for the baffle which was 6" thick. If you put ANYTHING in that box, score dropped. I left a drill in the box once and lost over 1 dB. In other smaller box applications, I've heard turbulence from bracing as well. Depending how your brace is, I could see it causing a problem with phase or standing waves. The only bracing I'd deem usable is thick threaded rod. Don't assume everyone is concerned about a "score". Acoustic reproduction might just hit the list as important... While they may not be concerned with a specific number, if they want "loud", that's a "score". Loud is loud, whether it be an ear or a meter. The same way you make a daily system loud, you make it loud for a meter. Your acoustic reproduction won't be accurate if you have turbulence and audible noise from it. Standing waves will give dips or spikes in response, a direct relationship to accurate reproduction. The OP asked about good enclosures not loud ones. There are a ton of people that don't care about loud at all, reference levels perhaps, but loud has connotations that are all negative IMO. If you said linear, flat, capability to blend or something sure, but loud not so much. As for your acoustic reproduction comments, true if you have audible noises it will take away from it but flexing panels will cause way worse distortion than any bracing techniques. Bracing will also help to stop standing waves and alter the inner shape of the box to a less symmetric rectangle which is also of benefit but of course we are discussing subs here which play sounds with LONG wavelengths. A solid built enclosure IS a good one. "Loud" is what you make it. Why do SQ guys have 600 watt front stages, then don't go over 90 dB? "Overhead" isn't THAT much. Having an extra thick box solves the flexing problem and won't induce any other noises. Will bracing help stopping standing waves? Sure, but so will changing the box shape. Don't make your box a cube, problem solved. There is such a thing called a "golden ratio", which should pretty well guarantee no standing waves. Besides, even if you had as standing wave of some variety, you're assuming response is linear in a lab or simulation. What about the vehicle's effect? You shouldn't have a problem with standing waves with long wavelengths anyway, unless your box is huge.