little question on flutter echo

Hello, Just optimizing the room I have for music production. The dimensons are 7.3 meters long, 4.5 meters wide and a height of 2.8 meter. Backwall and the long wall with door are plaster board.The upper long wall is concrete.As you can see in the drawing the room it is only rectangular. In front of the mixing desk there is a big window which we will covered with a heavy curtain (blue). In the back there will be placed two bass absorbers in the corners and a diffusor in the middle. Just dont know what to do with the side walls. What about flutter echo ? Would be a simple wall (maybe filled with insulation or build like a slot absorber) like this be enough to avoid flutter echo in the listening position or do I have to make it all the way up to the front of the room ?(red in the drawing) Maybe any modal problems seems to have ? (this chapter is far to mathematic for me :( ) As you see I have drawn already a 5.1 system in it but currently only a stereo system is installed. 5.1 will come in around a half year. Building whole new walls inside will be no option for me cause only less money available and would take too long to build.At least it shouldnt get far more complicated as what I have already drawn in. Perhaps someone is able to help me. Greetz, Heiko

Heiko, the side absorbers you drew will help flutter, maybe make them a bit longer and at least 6 degrees each side (1:10 ratio) - also, you'll need corner absorbers at the front as well, and probably more absorption behind your speakers than just a curtain. A "cloud" over your mix position and you should be pretty good. This is generally what you need - http://www.johnlsayers.com/HR/index1.htm The corner absorbers can be just cloth-covered 75 to 100mm mineral wool, about 1 meter wide, placed diagonally across vertical corners from floor to ceiling - best weight for this is 48 kG/m^3. Same weight/type for a "cloud" - here's a couple of ways to do this http://www.recording.org/ftopict-26889.html http://www.johnlsayers.com/phpBB2/viewt ... 1&start=90 Modally, your dimensions look pretty good; but you'll still need to check out the harmon mode calculator and try to optimise location of speakers and your ears before worrying about treatments - http://www.johnlsayers.com/phpBB2/viewtopic.php?p=18059 If you're totally lost on this, and I get a chance, I may be able to help you figure this out; but I'm pretty buried these days so it may be a while... Steve