Ducted Axial Fan (ANC) U.S. Patent 5,526,432
A ducted axial fan for large diameter ducts (11) which includes equidistantly spaced sensors (22,23) upstream and downstream of an axial fan and spaced actuators (24, 26) located around the periphery of said duct to cancel tonal noise caused by the air turbulence generated by the rotation of the fan.
Denenberg, Jeffrey N., "Ducted Axial Fan (ANC) U.S. Patent 5,526,432" (1996). Engineering Faculty Publications. 105.
Denenberg; Jeffrey N.. Ducted Axial Fan (ANC) U.S. Patent 5,526,432 issued June, 1996