room setup

I also have one window in the room.
I needed equallze the sound, coming from both sides, since
the window side was too bright and the other side was too dull.

I treated the window and the corresponding area on the
opposite wall the same way.  I covered the widow frame with
a thin plank of wood from Home Depot, and attached the
same sized piece, at the corresponding position, on the opposite wall.

As I am only married to "pursuing great sound" and don't care about
visual appearance, this is working well for me.  I use decals
to decorate and manage the vibration of the panels.

thanks for the replies. I'm going to try the setup with the window in the rear. If everything goes well I will post pics.

I think the main issue is optimizing symmetry forward of the listening position.  If both short walls are perfectly symmetrical left to right, and in either case, both right and left walls are perfectly symmetrical forward of the listening position, then put the window behind the listening position.   In a room having these dimensions (I'm assuming 8 ft ceilings) you are going to have some challenges.   11 ft is a bit narrow for good imaging, but it can be done.  Treatment of the corners will be important, as will treatment of the front and rear walls.  Front wall treatment will probably be mostly low frequency absorption (preferably limp membrane type panels) and back wall will be aimed more at addressing early reflections. I would opt for absorption rather than diffusion in a room this size.   I can provide more details if you want to take the discussion off line.

OP,

Look into acoustic panels from GIK Acoustics. They offer free consultation, reaching them out while you’re in building phase would be a good idea. 
Good luck!