For a piece of 10m2, 2 M2 foam behind the monitors have almost everything you flutter echo. I complete in two other panels on the other walls and it is at the top.
Cot set up, I stuck without difficulty on the foam panels with glue AGLO suggested by Thomann. The finish is not acceptable for me to type with my wife, I add a little edge to the varnished wood frames.
It's incredibly effective! fatigue over the sound of the reverb, is much stro prcise, and dtails resortent without pushing the sound back.
I do not know the foam "professional" but they are effective for the price trs. Had I known, I would have purchased from the beginners!