4 Pack Large Block Foam Cube Corner Bass Traps 12" X 12" X 12"IN Acoustic Foam Studio Wall Sound Absorption Treatment -Fireproof (BLACK)

Based on their depth, they will absorb bass waves fully down to 58hz then roll off gradually down to 29hz. They are effective. After I filled the room's corners with them, stacked 6 high, bass performance increased noticeably. Previously, all of my bass would "pile up" in the corners with almost nothing in the middle of the room. With these, the corners aren't as boomy while there is now bass in the center.The packaging could be a little better. The cubes did not all expand until they were perfectly square, but all expanded enough to be 100% useable. I was able to stack them on top of each other in each corner and they were stable. There is a tiny bit of odor at first but it went away quickly and didn't smell that bad in the first place.