after i treated my room with bass traps, the nulls were not measurably better.
Good point - I hope nobody goes away with the impression that bass traps can cure suckouts. I agre that it takes a significant amount of broadband bass trapping to make even a small difference. Tube traps (resonators) can do nore at specific frequencies but you really need to know what your doing - in this case best get an expert IMHO (I wouldn't dare play with tube traps given my limited knowledge and amount of time/effort I expect it would entail. Sticking large thick broadband absorbers in the room corners is a simple easy fix but designing tuned tube traps is a whole other matter...)