  A theory of the propagation of acoustic waves in a porous medium filled with
superfluid solution is developed. The elastic coefficients in the system of
equations are expressed in terms of physically measurable quantities. The
equations obtained describe all volume modes that can propagate in a porous
medium saturated with superfluid solution. Finally, derived equations are
applied to the most important particular case when the normal fluid component
is locked inside a highly porous media (aerogel) by viscous forces and the
velocities of two longitudinal sound modes are calculated.
