Free vibrations of the reconstructed sound-conducting system of the middle human ear are studied. The modelled system consists of a circular visco-elastic plate and two hinged one to another rods. The first rod being pasted together with the membrane simulates a T-type prosthesis which replaces the malleus-incus ossicular chain, and the second one simulates a stapedius. Non-liner differential equations describing free oscillations of the middle ear mechanical system are derived. In the case of liner oscillations the transcendental equations with respect to fundamental frequencies are obtained.