"Far fields." . . "Annular flow." . . "Cascade flow." . . "Air flow." . . "Active control." . . . . "Low speed, 2-D rotor/stator active noise control at the source demonstration under contract NAS3-26618"@en . . . . . . . . . . . . . . . . . . . "Noise reduction." . . "Displacement." . . "Sound transmission." . .