Here I run you through how I built three acoustic diffusers for the rear wall of the studio. As long as you put the work into the prep this is actually a fairly simple project that looks great at the end. I looked at using commercial solutions for the studio but shipping large blocks of wood all the way to New Zealand added a lot to the cost. I enjoy making things so the DIY approach was more affordable and fun for me.
The software I used was Diffuser calculator - mh-audio.nl/user/acoustic%20calculator.asp