초록

An active noise control system reduces cabin noise levels for a propeller or propfan aircraft due to the propeller noise signature by making the output from a secondary noise source identical in amplitude but opposite in phase to the propeller noise signature.

대표청구항 ▼

An active noise control system for reducing the propeller noise signature impinging on an aircraft fuselage due to a revolving propeller comprising: (a) a microphone for measuring the propeller noise signature generated by the revolving propeller and for providing a microphone output signal equivale

An active noise control system for reducing the propeller noise signature impinging on an aircraft fuselage due to a revolving propeller comprising: (a) a microphone for measuring the propeller noise signature generated by the revolving propeller and for providing a microphone output signal equivalent to the propeller noise signature; (b) a time delay unit for receiving said microphone output signal and for delaying said microphone output signal by a predetermined time delay interval to provide a time delay output signal; (c) a programmable gain amplifier for receiving said time delay output signal and for amplifying said time delay output signal by a predetermined gain to provide a secondary noise source input signal; (d) a secondary noise source for receiving said secondary noise source input signal and for providing an acoustic output in accordance therewith; and (e) an array of microphones for measuring the noise at a plurality of locations on the aircraft fuselage due to the propeller noise signature and the secondary noise source output, and for providing an output equivalent to the measured noise at each location; (f) control means for receiving said output from said array of microphones and for controlling the time delay interval of said time delay unit and the gain of said programmable gain amplifier whereby said microphone output signal is modified in phase and amplitude so that the secondary noise source output reaching the aircraft fuselage surface reduces the noise level of the fundamental blade passage tone as well as its associated harmonics.