Active noise reduction device, mobile object, and active noise reducing method

An active noise reduction device for reducing noise caused by revolution of a power source provided in a mobile object by outputting cancellation sound from a loudspeaker in a space of the mobile object in which the loudspeaker and a microphone are installed,

• the active noise reduction device comprising:
• an updater that updates the filter factor in accordance with an update formula that includes a parameter related to a rate of updating;
• a reference-signal generator that generates a first reference signal having a first frequency that corresponds to an engine speed of the power source;
• an adaptive filter that outputs a cancellation signal used to output the cancellation sound by applying a filter factor to the first reference signal, the filter factor being successively updated based on an error signal output from the microphone;
• and
• a frequency controller that, when an amount of variation in the engine speed of the power source has been determined to exceed a predetermined value, causes the reference-signal generator to generate a second reference signal having a second frequency and then to cause the adaptive filter to output a cancellation signal based on the second reference signal, the second frequency being obtained by correcting the first frequency,
• wherein, when the amount of variation in the engine speed of the power source has been determined to exceed the predetermined value, the frequency controller changes the parameter to make the rate of updating of the filter factor higher than when the amount of variation in the engine speed of the power source has been determined to be less than or equal to the predetermined value.

An active noise reducing method to be executed by a computer,

• the active noise reducing method being a method for reducing noise caused by revolution of a power source provided in a mobile object in a space by outputting cancellation sound from a loudspeaker in a space of the mobile object in which the loudspeaker and a microphone are installed,
• the active noise reducing method comprising:
• generating a first reference signal having a first frequency that corresponds to an engine speed of the power source;
• outputting cancellation signal used to output the cancellation sound by applying a filter factor to the first reference signal, the filter factor being successively updated based on an error signal output from the microphone;
• when an amount of variation in the engine speed of the power source has been determined to exceed a predetermined value, generating a second reference signal having a second frequency and outputting a cancellation signal based on the second reference signal, the second frequency being obtained by correcting the first frequency;
• calculating the amount of variation in the engine speed of the power source to determine whether the amount of variation in the engine speed of the power source exceeds the predetermined value;
• and
• when the amount of variation in the engine speed of the power source has been determined to exceed the predetermined value, increasing an amount of correction for correcting the first frequency to the second frequency with increasing amount of variation in the engine speed of the power source.