The theory of controlling adjustable tuned vibration absorbers (incl. the adjustable Helmholtz resonator) is reviewed. The theory review is completed with analytical models containing a two-degrees-of-freedom spring-mass model in which the spring constant between the primary system and the vibration absorber is controlled. The main focus of this paper is on the Helmholtz resonator in a hydraulic system, so all parameters are adapted to hydraulics. Two control methods are presented, open loop and closed loop. Both methods are modelled analytically and the models are experimentally verified by means of hydraulic test equipment consisting of a main pipe and an adjustable Helmholtz resonator. The open-loop control identifies the disturbance frequency and then adjusts the volume of the adjustable resonator accordingly by using a previously produced control list that contains information on frequency and corresponding cavity volume (piston position). The closed-loop control adjusts in order of different volumes of the resonator while con- tinuously measuring the response of the system, and after this identifying phase the resonator is adjusted to the volume that produced the most favourable response. The peak-to-peak values in the main pipe were measured and the 20 dB attenuation level was measured when the resonator was used.

Keywords: control, helmholtzresonator, hydraulics