Performance improvement of active noise control by hybrid control method

The filtered-x LMS algorithm which needs a reference signal to provide adva nced information about primary disturbances has been commonly used for acti ve noise control in the form of the feedforward control. Therefore, for an effective feedforward control, high correlation between primary disturbance and reference signal is required. However a real system is usually out of this condition. Because there are many cases that have no space for locatin g the reference sensor in the system while setting the reference sensor, th ere may be a problem of low correlation between the primary disturbances an d the reference signal. This study proposes a hybrid controller, which is a n assembled form of feedforward controller and feedback controller to empha size the strong points of the feedforward controller and overcome its fault s. The feedforward controller attenuates the primary disturbances highly co rrelated with the reference signal, while the feedback controller cancels n oises that is unobserved by the reference signal but observed by the error sensor (plant noise). The fact that the intensive periodic components of no ise are commonly intended for control makes the narrowband noise canceling of the feedback controller useful beyond its limits in reduction of broadba nd noise. This study proved the superiority of the hybrid algorithm hr maki ng a comparison between feedforward filtered-x LMS algorithm and hybrid fil tered-x LMS algorithm in the same excitation condition at the duct system o f which the a;ave motion is a one dimensional plane wave few. The hybrid fi ltered-x LMS algorithm is even more effective when the plant noise unobserv ed by the reference sensor is intense.