About those diffuser citations, basically what I found on some forums (mostly Gearslutz). But now I try to find it again, I see that it is a bit more complicated then just "don't use diffusers in small rooms". It probably has to do with the fact that diffusers need a bit of room to work. Also, what I read, I should have my bass "under control" before using diffusers.
Also, there is a practical thing for the rear wall. There is a hatch there for my attic. So I need to open the door completely in order to get to this. The panels I installed, I can easily remove so I can acces the Hatch, but a diffuser, or shelf or anything would be impractical I think.
When I meant, I built the panels myself, I meant, me and my dad (who is an excellent carpenter) built them, and when I say that I mean, my dad built them:) But he certainly has all the tools you'll ever need. So it won't be a problem.
I see my pictures won't show anymore? Is something wrong with the forum?
Thanks again for all the help Mike!