The effect of particle viscosity, when it is at least one order of magnitude greater than that of the suspending medium, has been included in the formula, existing in the literature, for the velocity of sound in suspensions or emulsions. The corresponding coefficient of viscous absorption and cross section for scattering of sound energy have also been calculated. The hydrodynamic dispersion of the velocity of sound, due to the frequency‐dependent nature of the viscous interaction between the particles and the suspending medium, has been shown to exist in suspensions or emulsions.