Soundblox type A1 units have narrow slots and unified cavities. These block are used without any fillers or septa. They are specially designed for low frequency absorption, optimum sound absorption is achieved at 125 hz.

Left-Hand and Right-Hand Units
For situations requiring a full core for vertical reinforcement, SOUNDBLOX units with open cavities on either the left- or right-hand side are available. When used in conjunction with standard SOUNDBLOX units, reinforcing bars and grout can be incorporated easily and efficiently. SOUNDBLOX left-hand and right-hand units have been approved for use in reinforced masonry construction and are allowed 90% of the shear value of ordinary hollow concrete block.