An experimental study of sound attenuation in lead‐wool‐polyurethane composites and nickel‐Cerrobend composites was conducted for different compositions, frequencies, and pressures. At specific compositions, the attenuation reached a maximum considerably higher than the attenuation of the components. The maximum attenuation occurred where the compressional modulus is changing most rapidly with composition; at this composition, the attenuation is most unstable with pressure.