Gorilla type echo reduction I have done was buying those inexpensive Fleece blankets, usually 4×5 or 4×6 foot size. I make a frame using 1×2 and stretch the blanketoverit front to back covering the back of the frame.Then hang them on the wall. This gives me about a 3/4 inch gap between fabric and wall. This does a fair job of cutting the echos and you add them as you need to.
These blankets usually have a scene of some type so you have something nice to look at as well.
