Two-stage filters for canceling a one-dimensional duct noise based on transmission-line model

Active noise control (ANC) in a one-dimensional duct can be expressed in terms of a transmission line model. Thus, the proposed ANC system probes sound pressures at arbitrary two points of the transmission line, differing from a usual system such as Filtered-x. The frequency response function of ANC circuit is obtained and then the two-stage digital filter for control is realized. More concretely, the first stage filter generates the voltage and current at the secondary source position from the observations and the second one produces the secondary source. Finally the validity of the proposed theory is confirmed through simulation.