Agreed.
Should also add that you need to know exactly what frequencies you’re dealing with, and by how much. SPL meter is a bare minimum for the toolbox.
Yeah, I should re-emphasize that I have provided a couple of "quick and dirty" tests to help determine what you are dealing with, and you (
@Rickroll ) can likely make some improvements, but if it is room modes you are dealing with; REW, Umik, and miniDSP are the true way to get the actual facts and get it under control (aside from room crawl/sub placement).
However, I think these Q&D tests will also be useful as stepping stones to become familiar with why you would want to invest the time (learning) and money into the miniDSP/REW system!
That said, you might be lucky, or, not so picky (as long as you are happy, it is good!), and get away with sub crawl and/or manual EQ as a solution!