At specific velocities, intense noise can be generated by the flow around a cascade of flat plates due to acoustic resonance. To reduce the aerodynamic noise, dielectric barrier discharge (DBD) plasma actuators (PAs) were utilized. The aim of this investigation was to clarify the control effects and the mechanism of noise reduction. To do this, wind tunnel experiments and computations were carried out for three vertically aligned flat plates. The PAs were mounted on both sides near the leading-edge of the vertically central flat plate. Moreover, to optimize the deployment of the operated PAs for control, PAs divided in the spanwise direction were utilized, where the PA was composed of 2 parts on each side. Experiments with various combinations of operated PAs were performed. The noise reduction achieved increases as the applied voltage of PAs increases. The maximum reduction of the tonal noise was 10.8 dB and was achieved by operating the whole array of PAs at a velocity of 13.5 m/s. The velocity profiles downstream of the PAs changed and the frequency of vortex shedding in the wake of the flat plate decreased with control of the PAs. The velocity corresponding to the maximum acoustic resonance was increased by operating the whole array of PAs. When the array of PAs are partially operated with a spanwise asymmetric deployment, it intensifies the three-dimensionality of the flow. Consequently, the acoustic radiation was weakened with a wider range of frequencies compared to the control by operating the whole array of PAs. The present results indicated that spatial asymmetry deployment is preferred to reduce aerodynamic noise.