Speed of sound and densities of binary mixtures involving phosphinic acids (Cyanex 301) with different diluents such as benzene, toluene, xylene and n-butanol have been studied over the entire range of mole fraction at 303.15 K and at atmospheric pressure. This study involves evaluation of different thermo-acoustic parameters along with the excess properties, which are interpreted in the light of inter-molecular interaction between polar extractants with non-polar and polar diluents. Besides, the experimental velocities have been compared with theoretically estimated velocities using different empirical theories and relations, and the relative merits of these theories and relations have been discussed in terms of percentage variations.