A system (20) which includes a frequency-dependent decoupler (21) arranged in a series-spring relationship with an actuator (26) for supplying active forces to cancel vibration. The system (20) also includes a spring (28) for providing a primary load path. The system (20) is responsive to at least one sensor (32, 34, 36 or 38) and is controlled via controller (30). The decoupler (26) has greater frequency dependency than the spring (28) and allows the actuator (26) to be effectively decoupled at low frequency, yet coupled at high frequency. This frequency dependent coupling allows the system (20)to accommodate transient static and low frequency loads and motions by allowing motion across the decoupler (21). However, at high frequency, the decoupler (21) becomes stiffer and couples the actuator (26) with the moving members (22) and (24) such that motion across the decoupler (26) is minimized and the actuator (26) becomes more effective at high frequency attenuation. Alternate embodiments of the decoupler (21) include elastomer decouplers (21b), friction decouplers (21c), glass-transition decouplers (21d), and fluid decouplers (21e),(21f),(21g), and (21h).