I put egg crate style foam on the walls in my little studio , and I was surprised by how much it deadened the echo.

As a test I made the same sound in an untreated hallway outside my studio, and again inside my studio... it was noticeably "deader" in the studio.

This isn't even acoustic foam.. its packing foam I got from the manager of a local FED EX. The irregular surface is what tames the echo.

Not recommended for a pro studio, but for what I do, "the price was right for the tight"