This paper investigates experimentally the characteristics of LQG control for controlled vibration mitigation. The control algorithm is implemented in LabVIEW RT. The controller performance is measured at a test set-up consisting of a vibrating taut cable with MR damper. Measurements of the closed-loop system clearly point out that LQG control enables damping vibrations with respect to their intensity and frequency. When the cable is excited at constant frequency, the desired control force is dissipative and proportional to the vibration velocity at the damper position. Thus, for the system under consideration, LQG control ends up in the desired viscosity. With increasing frequency of the cable excitation, the desired viscosity decreases. The desired viscosities for the first four cable modes depend on the pole locations of the observer and regulator. The nearer they are located, the higher are the desired viscosities. Therefore, a design parameter describing precisely the distance between observer and regulator poles is introduced. Based on this design parameter, the paper proposes a systematic method of LQG controller design for practical applications.