Physical damping of the box will reduce the impedance spikes. It will also reduce the peaks in the output of the box.. Its been done many times in home audio and in vented boxes I can't recall it EVER making anything louder. When measured usually you just see a flatter overall response with smoother roll off. Subjectively it cuts down on a lot of the higher order distortion as well, sounds cleaner. Can't see it having a purpose in a SPL design.
As you already mentioned the impedance peaks in a ported design are actually the more effecient parts of the enlcosure. Power drops to 1/4 or even less at those peaks, yet we all know from listening to ported boxes there isn't a huge SPL loss at those frequencies either.
For bass race and music classes it's actually benefitial to have these peaks.. Tapped horns for example have 3 impedance peaks, which really helps with power handling thermally
As you already mentioned the impedance peaks in a ported design are actually the more effecient parts of the enlcosure. Power drops to 1/4 or even less at those peaks, yet we all know from listening to ported boxes there isn't a huge SPL loss at those frequencies either.
For bass race and music classes it's actually benefitial to have these peaks.. Tapped horns for example have 3 impedance peaks, which really helps with power handling thermally