Speed of a Plane Wave in a Gross Mixture

The speed of a plane compression wave in a gross mixture (a suspension or a porous medium) which obeys a simple density mixture law is derived. The results agree with a relation proposed by Wood and others. The derivation of these investigators requires an addition to a density mixture law an assumption concerning the compressibility of the mixture in terms of the constituent compressibilities. It is shown that the latter assumption is a direct consequence of the density mixture law, and is hence not required. It is indicated that the derivation is applicable to waves of arbitrary amplitude.