The paper is devoted to modelling and numerical analysis of the middle ear with an implantable middle ear hearing device. The main focus is put on electromechanical coupling between the biomechanical subsystem of the middle ear and the electrical subsystem of the implant. The electromechanical coupling describes the interaction between the electrical and mechanical systems, and it is defined as a nonlinear dependence between magnet position and coil transducer centre. This is a novel approach, one that generates new resonances, instabilities, subharmonic as well as chaotic stapes vibrations depending on the voltage excitation. Numerical results of the stapes motion stimulated by a floating mass transducer are compared with the results of experiments performed on the human temporal bones. Findings of this study can be used in practice to develop a better design of a floating mass transducer.