Is the blue graph worth a rebuild of the box? I currently have the green graph but could get the blue graph with a new box. Cost is not an issue. I'm curious if the additional 3db at 20hz is worth the effort?
What matters most is in-room response, not predicted response. You may have an actual in-room f3 of 15Hz, in which case nothing needs fixing. Only by actually measuring the in-room response will you know.
I did check with rew and I do get flat to about 18hz. I was just curious if there was an advantage to getting that result with a larger box vs eq.
EQ eats up power and driver excursion. If you can't reach your desired listening levels down low without stressing the amp, voice coil or driver suspension then a larger box may help. The way to know that is by taking a THD reading at your desired maximum output levels; you don't want to see it higher than 10%. I don't know if REW has that capability. I use HolmImpulse, and it does.