Some of these foam panels will reflect certain frequencies rather than absorb them.
Another "cheap" acoustic solution would be a wood frame filled with fiberglas and then covered with burlap that has holes in it to absorb and trap more of frequencies including some of the lower mids depending on the size and depth of the frame.
Different acoustic fabric available besides the burlap of different weaves.
The looser weave will allow more sound to be trapped.
ShoBud The Pro 1
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Honestly, some of the most convenient, versatile, effective and aesthetically pleasing stuff you can use to "kill" a room, if that's what you're trying to do, is velour curtain.
I used to have four curtains that were made from something like a 40'x40' piece of black 20 oz. fire-proofed stage curtain that I had cut down to 7' pieces and pleated (you do want them pleated for sure), and I hung them all on a frame that I erected in a bedroom (I was renting at the time and I couldn't mount a bunch of rigging on the walls). I had maybe 8" between wall and curtain...you get different deadening depending on that distance. I kinda wish I still had those curtains... They don't do much to quiet sound going to the outside, but they sure kill a room.