[advanced101]

I have a rectangular room, speakers on short wall.  Halfway into the room on the right side there is an open hallway.  Has anyone ever done anything with the opposite side of the room?  Maybe a on-wall trap to even the room, since sound is exiting into the hallway.  I'm thinking adding absorption that mirrors the hallway will even things out? 

Adding a door to the hallway or placing a temp trap isnt an option. 

[max190]

Do you have a picture of your setup that you can post?
Is your room treated now with bass traps and or diffusors?

[advanced101]

The room is fully treated with corner traps, soffits and traps at first reflection points. 

Just beyond the first sidewall reflection on the right side lies the hallway.  I wanted to put a trap on the opposite wall that mirrors the hallway.  I have some extra traps, so I will probably experiment.  Just wanted to know if anyone has experience or theory on doing this.

[max190]

If this area opposite the hallway is a 2nd reflection then I think it will make a difference. Balance is key in acoustics.

[Glenn Kuras]

I have a rectangular room, speakers on short wall.  Halfway into the room on the right side there is an open hallway.  Has anyone ever done anything with the opposite side of the room?  Maybe a on-wall trap to even the room, since sound is exiting into the hallway.  I'm thinking adding absorption that mirrors the hallway will even things out? 

Adding a door to the hallway or placing a temp trap isnt an option. 

If the opening is not in the early reflection "zone" then you do not need to treat the opposite wall. Saying that though if you did treat the opposite wall it would help with the overall decay in the room.
http://www.gikacoustics.com/video-early-first-reflection-points/