Unidirectional JMC Actuators in the Active Attenuation of Noise in Ducts

In feedforward active noise control systems in ducts, a natural solution to avoid the acoustic feedback from the canceling actuator to the reference detector is to use a unidirectional actuator. New realizable ideal unidirectional three- and two-element source configurations, based on the JMC method, are introduced. In the two-element actuator the elements act as a dipole with the monopole effect included in the same elements. The inter-channel delay in the control structure of the two-element actuator is optimized with three different ways. In one of them the delay element is omitted altogether. The output volume velocities of all the three variations of two-element Ideal Source are mutually identical and independent of the inter-channel delay optimization, and are also identical with those of Swinbanks' two-element actuator, although the procedure of attaining them is quite different. It turns out to be advantageous in the practical implementation of digital control systems that the new three- and two-element solutions can be realized with no inter-channel delays. Thus, it is possible to achieve simplified control algorithms and reduce the computing time or improve the performance.