Active noise cancellation of a spherical multipole source using a radially vibrating spherical baffled piston

The creation of quiet zones in a diffuse sound field due to a multipole spherical primary source by means of a radially vibrating surface set in the side of a rigid sphere (secondary source) is investigated in this article. The formulation utilizes the appropriate wave field expansions along with the translational addition theorems for spherical wave functions to develop a closed-form solution in the form of an infinite series. The numerical results reveal that using a baffled spherical piston model as a secondary source instead of a monopole control source will obviously improve the sound minimization efficiency of such noise-control systems in all cases, especially for a dipolar primary source.