becomes so great that the fluid is allowed to flow therethrough without encountering any significant resistance specifically the resistance exerted by the third orifice 32 is further smaller than that of the second orifice 21 furthermore a great amount of fluid is retained in the third orifice 32 and in response to high frequency small amplitude vibrations such as during high speed engine operation caused to resonate a ring gear 33 is provided in a peripheral portion of the underside of the movable disk 29 and held in mesh with a drive gear 34 the ring gear 33 is rotatable driven by substantially the same drive mechanism as the one associated with the movable ring 17 the movable disk 29 and the drive mechanism therefor constitute a second control device 35 which is adapted to open and close the third orifice 32 while controlling its effective sectional area the first and second control devices 25 and 35 assigned to the second and third orifices 21 and 32 respectively are independent of each other and driven by an exclusive actuator motor each the actuator motors are individually operated by suitable control signals which are associated with engine speed relative displacement of engine and.