Abstract: Arrangement-angle of the secondary source on the performance of non-adaptive ANC (Active noise control) and AANC (Adaptive active noise control) systems in ducts are analyzed and tested in detail from theoretical and experimental aspects respectively. The results verified that the AANC method has great advantages，and the inclination angle between the main duct and the side-branch duct incorporated the secondary source can optimize the interfere condition between the primary noise wave and the secondary noise wave. A smaller arrangement-angle results in much more amount noise attenuation，a sooner convergence time of the AANC system，and a lower power requirement of the secondary source. For a broadband AANC system，a smaller arrangement-angle can improve the directional radiation ability of the secondary source，and reduce the acoustic feedback from the secondary source to the input microphone，and this will greatly improve the stability of the control system. Finally，several proposals for engineering design of the secondary source arrangement are presented.

Key words: Active noise control (ANC), Adaptive active noise control (AANC), Duct, Interference condition, Secondary acoustic source