  The concept of classical and quantum free acoustic (FA) field is
theoretically considered. The equations of the free acoustic field are derived.
They coincide in the mathematical form with Maxwell equations for the free
electromagnetic (EM) field. It is accentuated, that the equations in the
mathematical form of Maxwell equations for the free EM-field are universal
equations of the Nature. They describe any free complex-vector physical field,
vector-functions of which are analytical functions. In the case of a free
acoustic field, it seems to be the strong indication taking into account the
quantum Fermi liquid model of EM-field leading to the existence of phonons,
accompanying the process of a photon formation, that FA-field and free EM-field
are the display of the single united field, both the components of which can
propagate simultaneously [however, with different velocities], for instance, in
weakly absorbing media. The theory proposed can be the theoretical basis for
the practical realization of superconducting states at high temperature in the
materials with the strong interaction of electrons with acoustic field phonons
and with microwave photons in magnetic resonance conditions.
