Active control of higher-order sound in ducts using boundary-located secondary sources

Mechanisms of using boundary-located secondary sources in ducts are studied to explore the feasibility of active control of higher-order propagating sound.Firstly,based on the modal analysis theorem of sound field in ducts and the principle of active control,the necessary conditions of the sound generated by spatially distributed secondary sources in infinite ducts are derived.Secondly,the feasiblities of using boundary-located secondary sources are analysed.A control strategy using point sources is proposed by discretizing feasible spatial distributions thereafter.Finally,the effectiveness of using boundary-located secondary sources is verified by numerical simulations.The results show that significant noise reduction can be achieved if the spatial sampling theorem of the distribution of secondary sources is satisfied in the circumferential direction and the axial dimension of secondary sources is sufficiently large.