Abstract: Disclosed are a variety of structural acoustical cinder blocks including locking blocks which are intended to be assembled together through the use of mortar to provide a diffusor of desired shape and configuration. Each diffusor includes a plurality of wells, the depths of which are determined through the use of number theory sequences, such as, for example, the quadratic-residue sequence developed by Karl Frederick Gauss. The surface irregularities formed in the blocks are unique in that they provide a flat power spectrum and constant scattered energy in the diffraction directions. Each of the blocks including wells also includes a low frequency sound absorbing chamber. The blocks are installed such that there is a stacked bond on the diffusing face and a running bond on the structural rear face. If desired, a single block may be made which includes an entire sequence of wells and dividers.