Concrete Audio Speakers...Speaker Enclosures made out of Concrete ?..

If you wanted to make big concrete speakers, the way to do it would be to make them modular.  Stack 6" high sections on top of each other separated by thick gaskets. They need to be something that is assembled in place.  You don't want to try to move 500lbs of concrete in one piece.  I don't know if concrete by itself is great idea but it could certainly be a big part of a great box.  It's incredibly dense and won't resonate at low frequencies.  Maybe some high frequency damping is in order but that's certainly doable.