1. An active vibration control system for controlling vibrations at a structure resulting from at least one excitation force acting upon the structure, comprising: at least one actuator located at the structure for imparting a reaction force to the structure; at least one sensor located away from said actuator, said at least one sensor producing a sensor output; a controller connected between said at least one sensor and said at least one actuator, said controller including: a system identifier for receiving said sensor output from said at least one sensor and deriving a relationship between said sensor output and said reaction force imparted to the structure by said at least one actuator; and an optimal controller connected to said system identifier to receive said relationship and for developing control driving signals from said relationship for driving said at least one actuator; said system identifier including a Hopfield based neural net-work for learning the dynamics of the structure represented in a state space form and for providing output signals that follow state variables of the structure.