The biggest detriment to bass is the room itself. Cancelation is the issue and there are a few ways to help correct it. You can use treatments like bass traps or you can correct it electronically with something like an Antimode which is self contained and does wonders or move up to a Minidsp and use room correction software. I have lived in enough houses (same speakers for 30yrs) over the years that it eventually became apparent that not all rooms favor your speakers. Subs are handy in the respect that you can move them around and if you use 2 you can fill the nulls if you have room to move them.
Some good reference found
HERE I did not realize how drastic this was until I added a antimode to my 2 channel system.
Richard
