10 CLAIMS

• 1. In a duct having a multi-bladed axially mounted fan means with multiple blades and an intake side and an exhaust side mounted therein creating a rotating sound field, the improvement comprising
• a first sensor means mounted upstream of said fan means,
• a second sensor means mounted downstream of said fan means,
• a series of actuator means mounted around said duct means adjacent said fan means, and
• a two channel control means operatively connected to said actuator means and said first and second sensor means and adapted to directly cancel the tonal noise generated by said axial fan by canceling the pressure waves generated by said fan's rotation by generating different rotating pressure antiwaves on each side of the blade so that noise propagates from both the exhaust and intake sides of the fan to quiet said rotating sound field.
• 2. As in claim 1 wherein said actuator means comprise a series of speakers mounted inside the duct means.
• 3. As in claim 2 wherein said speakers are spaced equidistant from one another.
• 4. As in claim 1 wherein said actuator means comprises two sets of speakers mounted in said duct, each set mounted adjacent said axially mounted fan so as to be adapted to directly cancel the pressure waves generated by the fan's rotation on either side.
• 5. As in claim 4 wherein said control means is adapted to do a synchronous time to spacial transformation.
• 6. As in claim 1 wherein said actuator means comprises one set of speakers mounted in said duct, said speaker means mounted adjacent said axially mounted fan so as to be adapted to directly cancel the pressure waves generated by the fan's rotation on one side by generating a pressure gradient around said duct that has a shape opposite to the pressure gradient formed by the moving fan blades.
• 7. As in claim 6 wherein said actuator means comprises a series of speakers mounted inside the duct means.
• 8. As in claim 7 wherein said speakers are spaced equidistant from one another.
• 9. In a duct having an intake and exhaust, said duct having a multi-bladed axially mounted fan therein, said fan having a large diameter in relation to a wavelength of the tonal noise from the blade tips to create a rotating sound field, the improvement comprising:
• a first sensor means mounted adjacent said fan means,
• a series of actuator means mounted around said duct in an annular configuration adjacent said fan means, and
• a two channel control means operatively connected to said actuator means and said first sensor means and adapted to cancel the tonal noise generated by said axial fan by canceling the pressure waves generated by said fan's rotation by generating different rotating pressure anti-waves on each side of the blade so that noise propagates from both the exhaust and intake sides of the fan to thereby quiet said rotating sound field.
• 10. As in claim 9 wherein there is a second sensor means mounted adjacent said fan on the side opposite from said first sensor means and said series of actuator means comprise two annular configurations thereof one of each side of said fan.