Fishboat, I was trying in my last paragraph to address Acoustat6's comment that "all surfaces need treatment". I thought that was an over the top statement.
FWIW, I'll try to explain the basis for my last paragraph. I'm sure you are aware that sound waves from the speakers can reach the listener directly from the speakers and bouncing from the walls on either side of both speakers from both speakers. Without attenuation they will screw up sound quality substantially something we will all agree about. For example the original signal from the right speaker will be direct to the right wall (1st reflection point) and the left wall (2d reflection point). Ditto the left speaker and both side walls. So its no secret that you want to deaden the 1st reflection point, but the 2d reflection point can also be a problem if not treated. In addition to those signals which most folks will treat for, each speaker will be putting out signals which strike other portions of the opposing side walls, bounce off the back wall, back to the side walls and back to the listening position. Untreated the room seems to have become an echo chamber.
Now all you have to do to prevent those signals from bouncing off the side walls is deaden the side walls. If you deaden the side walls you don't need to deaden the wall behind you to eliminate this signal from reaching the back wall and bouncing back to the listening position.
If you treat both walls you will never have any signals bouncing off the side wall reaching the listening position.
Or you can get most of the same effect by simply treating the wall behind the listener position in addition the the 1st and 2d positions on the side walls. (That was the reason for my rejection of the all inclusive statement by Acoustat regarding 'all' surfaces. Perhaps I just took his statement too literally.)
Now all you have to do the reduce wall reflections to an appropriate level is determine what density of materiel you need to kill/reduce those frequencies that are bothersome.
I'm not at all sure that I have effectively communicated my thoughts on this, but if I've still not cleared up for you what I meant in my post to Acoustat6, sit down with some paper and reduce this all to geometry, it might make more sense this way. I realize its not that simple but it illustrates the fundamentals regarding bouncing sound waves.
Hope that helps, if not I had fun trying to focus my fragile mind. :-)
FWIW, I'll try to explain the basis for my last paragraph. I'm sure you are aware that sound waves from the speakers can reach the listener directly from the speakers and bouncing from the walls on either side of both speakers from both speakers. Without attenuation they will screw up sound quality substantially something we will all agree about. For example the original signal from the right speaker will be direct to the right wall (1st reflection point) and the left wall (2d reflection point). Ditto the left speaker and both side walls. So its no secret that you want to deaden the 1st reflection point, but the 2d reflection point can also be a problem if not treated. In addition to those signals which most folks will treat for, each speaker will be putting out signals which strike other portions of the opposing side walls, bounce off the back wall, back to the side walls and back to the listening position. Untreated the room seems to have become an echo chamber.
Now all you have to do to prevent those signals from bouncing off the side walls is deaden the side walls. If you deaden the side walls you don't need to deaden the wall behind you to eliminate this signal from reaching the back wall and bouncing back to the listening position.
If you treat both walls you will never have any signals bouncing off the side wall reaching the listening position.
Or you can get most of the same effect by simply treating the wall behind the listener position in addition the the 1st and 2d positions on the side walls. (That was the reason for my rejection of the all inclusive statement by Acoustat regarding 'all' surfaces. Perhaps I just took his statement too literally.)
Now all you have to do the reduce wall reflections to an appropriate level is determine what density of materiel you need to kill/reduce those frequencies that are bothersome.
I'm not at all sure that I have effectively communicated my thoughts on this, but if I've still not cleared up for you what I meant in my post to Acoustat6, sit down with some paper and reduce this all to geometry, it might make more sense this way. I realize its not that simple but it illustrates the fundamentals regarding bouncing sound waves.
Hope that helps, if not I had fun trying to focus my fragile mind. :-)