In feedforward active noise control systems in ducts, a natural solution to
avoid the acoustic feedback from the canceling actuator to the reference d
etector is to use a unidirectional actuator. New realizable ideal unidirect
ional 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 d
elay in the control structure of the two-element actuator is optimized with
three different ways. In one of them the delay element is omitted altogeth
er. The output volume velocities of all the three variations of two-element
Ideal Source are mutually identical and independent of the inter-channel d
elay optimization, and are also identical with those of Swinbanks' two-elem
ent 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 realiz
ed with no inter-channel delays. Thus, it is possible to achieve simplified
control algorithms and reduce the computing time or improve the performanc
e.