Idleally it best to know what the problem is before trying to correct it. You could do find modes based on your dimensions, which shows four coincident modes I believe at 141hz. More accurately, and relatively inexpensively you could do room acoustic measurements with room eq wizard.
Low frequeny pressure is highest at walls and corners, so that is why there was "excess bass". Not a problem unless you listen to music there. A secondary issue to low frequency response is modal decay time, which sounds better if generally shorter and uniform.
I have had a a lot of benefit from placing speakers using the golden ratio. Another technique is to offset speaker and espcially listener placement by a few inches relative to room width.
Higher frequencies are easier and can use simple panels or diffusers at reflection points.
Low frequeny pressure is highest at walls and corners, so that is why there was "excess bass". Not a problem unless you listen to music there. A secondary issue to low frequency response is modal decay time, which sounds better if generally shorter and uniform.
I have had a a lot of benefit from placing speakers using the golden ratio. Another technique is to offset speaker and espcially listener placement by a few inches relative to room width.
Higher frequencies are easier and can use simple panels or diffusers at reflection points.