Fan noise canceller

A fan noise canceller comprising:

• rotation information detecting means for detecting rotation information of a fan including a blade passing frequency of noise generated with the rotation of the fan and converting the detected information into an electric signal;
• a plurality of band-pass filters as frequency component extracting means operable according to the fan rotation information detected by the rotation information detecting means for independently extracting the blade passing frequency and one or more harmonic components of the fan noise;
• a plurality of output control means for independently controlling the output level and phase of the blade passing frequency and one or more harmonic components extracted by the band-pass filters;
• and
• a canceling loud-speaker for converting signals outputted from the output control means into sound signals and providing the sound thereof for propagation in an interfering relation to the noise propagated from the fan;
• wherein an adder for combining the outputs of the output control means is provided between the output control means and the canceling loud-speaker and the output control means includes a phase controller for setting a cancellation signal having an opposite phase to the phase of the input electric signal corresponding to the blade passing frequency, and a level controller for setting said cancellation signal to a predetermined level which is opposite in polarity to the signal level of the electric signal corresponding to the blade passing frequency, the output control means control the phase and level of the blade passing frequency and harmonics of the blade passing frequency to provide the opposite blade passing frequency and harmonics thereof, which are added together in the adder as an output synthesizer, and the output of the adder is coupled to the canceling loud-speaker, which thus provides a sound wave in opposite waveform relation to each feature frequency of the fan noise.

A fan noise canceller for canceling noise generated by a fan having plural blades, said fan noise canceller comprising:

• a fan blade passing frequency detector, including a sensor for directly detecting passage of said fan blades and for generating a blade passing frequency signal indicative of the frequency at which said fan blades pass said sensor;
• an output control means coupled to the fan blade passing frequency detector for controlling the amplitude and phase of the blade passing frequency signal in a desired manner to generate a noise cancellation signal;
• and
• a canceling loud-speaker coupled to the output control means for converting the noise cancellation signal into a sound signal and for causing the sound signal to propagate in an interfering relation to the noise generated by the fan;
• wherein the output control means includes a phase controller for setting the opposite phase to the phase of an electric signal obtained from the blade passing frequency signal, and a level controller for setting a level which is of the opposite polarity with respect to the level of the electric signal obtained from the blade passing frequency signal.

A fan noise canceller comprising:

• rotation information detecting means for detecting rotation information of a fan including a blade passing frequency of noise generated with the rotation of the fan and converting the detected information into an electric signal;
• a plurality of operational amplifiers coupled to the rotation information detecting means for independently extracting the blade passing frequency to provide a blade passing frequency signal and one or more harmonic components of the fan noise and for independently controlling the output level and phase of the blade passing frequency signal and one or more harmonic components;
• an adder coupled to the operational amplifiers for combining the outputs of the operational amplifiers;
• and
• a canceling loud-speaker coupled to the adder for converting signals outputted from the adder into sound signals and providing the sound thereof for propagation in an interfering relation to the noise propagated from the fan;
• wherein the operational amplifiers are configured to output a signal having the opposite phase with respect to the blade passing frequency signal and of the opposite polarity with respect to the blade passing frequency signal.