@james633 --
+1
It’s telling seeing main speakers with bigger displacement area in their woofer section than the subs that augment them. Indeed, physically subs are quite often smaller than the mains, and knowing Hofmann’s Iron Law we know what it affects (i.e.: sensitivity) - which is not without consequences. Somewhere along the line the dominating narrative has crept in that a physically smaller sub cabinet volume makes it easier to control resonances, effectively setting an upper limit for sub size, but seeing the forest for the trees (and knowing what it’s really about here) it’s also an argument that conveniently supports audiophiles’ resentment towards large sized subs for no other reason really than the inconvenience of size.
Enclosure resonances aren’t trivial, but the question is to which degree compared to lessening the workload of the woofers; smaller/fewer woofers working nearer their limit will effectively negate the work that has gone into making the cabs rigid due to large amounts of mechanical distortion from the driver itself, so it comes down to knowing the difference ease of reproduction (from prodigious air radiation area) a good sub design can have, from cabs that are as rigid as it requires for them not to impede too severely with the overall quality of the bass (hint: it can be done without resorting to builds that weighs in excess of several hundred pounds). For those wondering about the sufficiency of what’s required to make large cabs rigid enough, as an outset at least it only matters that such sub designs produce cleaner, more palpable and effortless bass than their smaller or less efficient brethren.
If one were to abide by the "no resonances"-approach of sub cabs it follows that their weight (and price) would become the actual, practical hindrance way before the woofer size/effective air radiation area would get to a place where it really mattered. Small subs, both with regard to driver and cab size, can be made to sound well with bigger main speakers within morerate SPL’s, no doubt, but that way (unless in multiples, and of course taking for granted good implementation/distribution) one isn’t taking the fuller advantage of what subs can do and how they could complement the overall sound. Shooting for energy linearity into the subs region and seeing what’s required for this to come true is a good starting point, but it’s a rudimentary physical aspect few seem to consider or won’t practically accommodate, so there we are.