Where can you get those blocky, textured studio baffles? There's one behind Joe on the left... I see them all over the place and don't know the name of the brand or anything about them... they're really cool!
That is a form of RPG or Reflection Phase Grating diffusor. There is quadratic math (which you can find on the net) behind the various heights and sizes of the blocks. I don't see it on Auralex's site although they do make a similar product with bordered cells.
The reason for pointing out the math is that if you want to do this on your own it's not that hard, but to be effective you need to look up the system and either take it off an on-line calculator or plug it into a spreadsheet.
You will get diffusion out of any random bunch of blocks, but to get a frequency balanced diffusion, or to tune it to a mode somewhere in your room, you need to work out the math.