A diffuser is designed to diffuse the sound, not absorb it. It is meant to reflect & spread frequencies evenly so that it minimises peaks & nulls in the listening position, and make things sound better.
If you need to soak up bass, forget thin walls, blankets, simple boards, egg shells, etc. They'll do nothing for bass below 200Hz. Bass absorption is generally about density, rigidity, girth/size, air cavities & number of layers in your wall construction. It's a very complex subject. If you're serious about needing a bass wall, you'll need to do some research. I know that's not the quick, easy solution you're hoping for. But acoustics is a dark art & misunderstood by many. The principles are easy enough to grasp if you commit to some reading, but getting the right treatments for any space requires real science & some engineering nouse.
Start with checking out the Auralex site & see what they say & have. Those acoustics sites are usually very informative.
Sincere good luck.
