@george_r I started my first build using the 'North Creek Handbook'. Excellent read for anyone interested in building their own.
@foggyus91 Concrete speakers are not a new idea. Same as solid granite or Corian. I dont see any new, space aged materials outperforming properly designed MDF. What your trying to achieve is a 'dead' cabinet that doesn't ring or turn vibrations into un-wanted sound. MDF also machines well and in most cases dampens better than most plywood. In this application it's hard to beat.
Very dense, thin, ridgid panels still flex/ring. Even Baltic birch plywood rings more than MDF in the same thickness, even though it's stiffer.
A great combination is bonding two or three layers. Oddly the glue joints adds lots of strength. One layer MDF and the other layer Baltic birch. Better yet would be inner layer of 3/4" MDF glued to another 1/2" panel MDF with 3/4" baltic birch on the outer layer.
Then the interior of the cabinet gets a coating of high density "Glop" to further dampen. Like 'No rez". I use a non-hardening blend of clear silicon mixed with play sand and coat the entire interior of the cabinet. This yields a cabinet that's dead. There are NO new materials that are more inert.
FYI... years ago someone made a concrete filled sandwich between two layers of marine plywood.Pretty high mass design probably really good but difficult to build.
@bartsw the wood used in a violin or cello should resonate and adds a sound characterist but you want the opposite in a speaker cabinet. Speaker Cabinet should have NO sound/ringing and only have sound from the drivers and that's why MDF is widely used.
Hope this helps.
