You don't need much to build an effective block style acoustic diffuser. The panel is composed of 131 2-inch by 2-inch blocks cut to varying sizes and a piece of plywood that is cut to 2 feet square. You will need seven eight-foot long 2-inch x2-inch wood to make the blocks. All you need to assemble the panel is some good strong wood-glue. Any wood can be used or the blocks but maple tends to be the most cost effective.
The functionality of the diffuser resides in the blocks. The blocks will be cut to several different lengths and will be glued to the board randomly in order to create a completely uneven surface. As interfering reflections encounter the surface they will be broken up, or diffused, by the unevenness of the surface. You will need four lengths of blocks; 38 pieces that are 1 7/8 inches long, 38 pieces that are 3 3/4 inches long, 40 pieces that are 5 5/8 inches long, and 15 pieces that are 7 1/2 inches long.
The assembly of the panel is pretty strait forward. Starting at one corner of the plywood you are going to glue the blocks down flush against each other in rows. The order in which you do this is up to you. Some people recommend a set pattern but you can also order the blocks randomly. If you choose to use a random order there are a couple of things to keep in mind. First of all, there will be 13 2"x2" spaces scattered throughout the board rater than having blocks glued to them. You should try to plan for these spaces and scatter them across all of the rows. You should also do the same thing for the 7 1/2-inch blocks since there is only going to 15 of them. Once all the pieces have been glued down, let the glue dry overnight and your diffusion panel will be ready to use.