Thank you so much for you post. But even with your clear post, i still have some question
Will "room gain" apply if 4 sealed subwoofer play in a room that is greatly treated with enormous bass trap like "helmotz resonator" for example, and with an optimization like Dirac Live Bass Management for the 4 sub? Because the mode from like 20hz to higher will be really reduced by the treatement and the bass optimization. What i understand from your post, room gain exist beacause of the 0hz mode only, not those after?
I'm asking you this question because I have to buy 4 subwoofers, preferably sealed and I can't afford to buy them to be disappointed not to reach 20Hz at high volume... And I like to learn more about acoustics...
Thank you in advance (sorry for my english, I'm french.)