Room modes is the complicated 2 word answer and room modes will emphasize certain bass frequencies while squashing other. The pub ...oops .. I mean sub crawl (pub crawl is a reward after a job well done!!) will get you bass at some frequencies and missing in others from that one listening spot only. It changes drastically when you move locations. That's the reason why sub crawls for.
The graphs I'm posting is measurements I took to try and find the sweet spot for the widest range of bass frequencies possible across all 3 listener positions (left,center,and right) seating positions on a couch. I would move the sub to one location and run 3 frequency sweeps, one for each spot on the couch.
The last spot is where I settled as it gave me the flattest response across the entire couch.
I was lucky that I was able to achieve this kind of flat response with 1 sub in this particular room (my basement). I was able to achieve this with my bedroom as well BUT I cannot do this with my 2nd system in the great room. The greatroom is too big, irreuglarily shaped so I bought a 2nd sub (which is the usual recommendation) and I will use miniDSP to integrate the two subs.
