symmetry along short axis, flutter echo

Hello, I'm looking for help to make my room better. I've tried to provide the needed information if not please let me know. Thanks for considering my request. Room use: Record small combos and solo vocalists, teach music lessons, practice sax, mix my compositions and recordings. I'd like the mix results translate reasonably well to other rooms. I'd like to have a better situation for clients to hear their mixes. Sitting at the apex of the triangle is OK for one person, but when there are 3 people listening I need a better situation. It's a relatively small room. Maybe the best plan would be to convert from a mixing to recording mode by moving furniture and treatments around. So, when the band is rehearsing to have more space for musicians and when mixing get a more accurate sound. From reading this site, I gathered lots of bass traps, reflective floor with absorptive ceiling were a good place to start. I believe I have that much OK so far. How to best reduce flutter echo? I'm thinking of installing triangular shaped Hemholtz Slat absorber tuned to ~142Hz. Indicated by the purple triangles on the east/west wall in the sketchup. I have a supply of 1" x 12" silver maple boards and several bundles of Roxul available. Maybe these could help solve some of the parallel walls issues? Window / Door treatments? I'm hanging some curtains tonight, but they're more for visual privacy than acoustic treatment. For the French doors and windows I could build inserts, Roxul in a wood frame. The south 3 panel door, I guess could benefit from heavily pleated curtains. Best treatment for the back wall? I assume absorptive panels. Speaker, placement? I think there's a better place. Currently takes a lot of floor space. Maybe I should fly the speakers in, near the ceiling along the south wall? Budget: $600US. Location: US, Missouri Room Size: W157.5" X D140.5" X H94.75" W13.15' X D11.71' X H7.9' W4.01m X D3.57m X H2.41m Height 1 : Width 1.67 : Depth 1.48 Volume 1216.5 cubic feet 11.71 * 38% = 4.44 feet from south wall Pertinent facts: Presently symmetry is along depth South wall has 3 door panels, each with full length glass. North wall had 2 doors, both with glass East Wall 2x4 on 16" centers Other wall 2x6 on 16" All filled with fiberglass bat insulation, All with 1 layer 1/2" drywall Bass Traps: North Corner SC Traps 28"x28"x37" South Corner SC Traps 14.5"x14.5"x19.5" Ceiling Clouds 4" Roxul Above Clouds R38 paper-faced fiberglass batt insulation Hardwood floor FuzzMeasure Excel graph Screen Shot of Sketchup plan Link to sketchup file: http://tinyurl.com/qhmz8s Thanks again for your time. Mark

If flutter is a direct result of parallel boundaries then what is it that you are doing with the existing windows that are parallel in this room?

Wow! That's a LOT of glass in that room! Not surprising you have problems. Any chance you can get rid of some of that glass, and replace it with drywall? Or at least build plugs to fit into the frames? If not then maybe gobos might help. US$ 600 won't go very far, though it might be enough to build some plugs and/or gobos.

Thanks for your replies. I want to address the parallel glass problems. I'll start by making plugs for the windows and french doors. I have materials so my budget is intact. Would something like wood frames, filled with Roxul and covered with burlap treated with fire retardant be suitable?