EN
The paper presents a general approach to mechanical system modification aimed at con-trolling the steady harmonic vibrations by means of passive and active methods. The rela-tive decrease of harmonic vibration amplitudes of selected elements of the mechanicalsystem has been chosen as a measure of the quality of the introduced modification. The proposed theoretical method enables to determine the parameters of the system's dynamicflexibility matrix, which show the most remarkable effect on the dynamic behaviour of thewhole system. When active control is considered the method is useful in designing thestructure and choosing the parameters of the control system. In certain cases of self-excited vibration theapproach helps examining the elements of the system, most responsible for this kind of excitation.