Abstract: Engineered, pseudo-crystalline materials are formed of repeating arrays or lattices of similar basic elements. The materials are porous, so that a gas such as air can pass through the material. Audio waves propagating through the gas can also pass through the material, and these waves experience a passive, uneven, frequency-dependent modification as a result of passing through the material. The frequency response of this modification can be tuned by selecting the shape, size, and repetition patterns of the basic elements in the lattice, as well as the ingredients from which the pseudo-crystalline materials are made.