DETERMINATION OF THE LOAD IMPEDANCE OF NO ISE ABSORBING DUCTS WITH ACTIVE LINING

For the stability of active noise control structures in a feedback con figuration the load of the adjoined duct is of great importance. This load can be modeled by an impedance in the network domain. In this pap er the impedance is numerically calculated, and characteristic feature s of this impedance are presented. The results are applied to an examp le of a stability test of hybrid absorbers. It is shown that because o f very strong cross-resonances in hard-walled ducts no reasonable atte nuation with stable active absorbers can be obtained. An attenuation o f the cross-resonances with passive absorbers is possible in order to improve the absorptive behaviour of hybrid absorbers. This solution ca n only be applied to ducts lined on one side.