A theory is developed to describe the propagation of sound waves in a rigid isotropic and homogeneous porous medium filled with a compressible fluid, including both the effect of viscous dissipation and the effect of thermal conduction. An expression for the conductance as a function of the frequency is derived by assuming a capillaric model. A comparison is made with independent experimental results, and close agreement with the theoretical results is obtained. A discussion of the structural parameters, including a description of a method for determining their values at a given frequency, is also made.