Interesting acoustical phenomenon in my listening room

[Heavygen]

I have recently moved into a house where the home theater/stereo is in half of a 10X24 room, making the "listening room" proper 10X wide by 12X long with the back open all of the way to the back wall at 24'. The only additional thing to consider is that the room is partially divided at 12' by an arch that comes out a foot from the left side wall and about 2 feet from the right wall and about 1' from the 8 foot high ceiling. What I notice with regular listening while sitting in the sweet spot, about 9' away from the front speakers is what could be best called a "stratified bass" phenomenon. This phenomenon occurs in 2 channel music listening mode (no sub) and maybe in others, but i haven't checked. When I stand-up I hear significantly more bass (a little boomy and not very tight) and if I sit down in the exact same spot, the boomy bass goes away. Is this "stratified bass" response normal, and does anyone have any suggestions as to how I can get rid of it? The room is carpeted with curtains down most of the left wall all the way to the back wall.

Cheers,
Heavygen

[AB11]

Google "Room Modes".

You will find more than enough info out there.

But just to let you know - the phenomenon is inherent in every room and its effects can be minimized.