Question

Sound-absorbing structural masonry units are sometimes used in natatoriums and other building types where soft materials are not appropriate. Can you describe how these special CMUs are configured to absorb sound?

Answer

There are various designs of sound-absorbing structural masonry units, but typically they have a pair of inwardly flared vertical slots up about three-quarters of their front face that open into cavities within the block. These cavities are filled with some form of fibrous material. Sound enters through the slots and gets absorbed and trapped within the block.

These blocks can reach a Noise Reduction Coefficient (NRC) of about 0.85. For absorbing low frequencies, a curved metal septum is sometimes used in place
of or in addition to the fibrous material.