Abstract: For a comparative material testing of similar formed parts based on their dynamic behaviour under acoustic excitation vibrations, in order to obtain clear-cut information about the material properties it is necessary to assure constant excitations of the vibration generator and a constant pressing force when coupling this to the object being tested. This is accomplished by using a piezoelectric actuator in an assembly unit with an electromechanical sensor and a coupling element, whereby the excitation voltages of the actuator are monitored and its vibrations passing into the formed part are registered by the sensor.