Active noise control system

• US 20070038441A1
• Filed: 08/08/2006
• Published: 02/15/2007
• Est. Priority Date: 08/09/2005
• Status: Active Grant

• Current Assignee: Honda Motor Co., Ltd. (Honda Motor Company)
• Original Assignee: Honda Motor Co., Ltd. (Honda Motor Company)
• Inventors: Takahashi, Akira, Kobayashi, Yasunori, Inoue, Toshio, Sakamoto, Kosuke
• Granted Patent: US 7,792,312 B2
• Time in Patent Office: Days
• US Class Current: 704/226
• CPC Class Codes: G10K 11/17817 between the output signals and the error signals, i.e. secondary path
• CPC Class Codes: G10K 11/17823 Reference signals, e.g. ambient acoustic environment
• CPC Class Codes: G10K 11/17825 Error signals
• CPC Class Codes: G10K 11/17833 by using a self-diagnostic function or a malfunction prevention function, e.g. detecting abnormal output levels
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17883 the reference signal being derived from a machine operating condition, e.g. engine RPM or vehicle speed
• CPC Class Codes: G10L 21/0208 Noise filtering

Abstract

An active noise control system prevents a continuous muffled sound from being generated as an abnormal sound under a high sound pressure from a speaker when a microphone as a sound detector is covered, and reduces noise immediately when the microphone is uncovered. A first threshold value as an upper limit value and a second threshold value as a lower limit value are provided for the filter coefficient of an adaptive notch filter. When the filter coefficient is greater than the first threshold value, a control sound is faded out according to a forgetting process. When the filter coefficient is smaller than the second threshold value, an adaptive control process is resumed. Even if the microphone is covered, the filter coefficient does not exceed the first threshold value as the upper limit value.

Claims

1. An active noise control system comprising:

a base signal generator for outputting a harmonic base signal from the frequency of noise generated by a noise source;

an adaptive notch filter for being supplied with said base signal and outputting a control signal for canceling out said noise;

a sound output unit for outputting a control sound represented by said control signal;

a sound detector for detecting a canceling error sound representing the difference between said noise and said control sound and outputting an error signal;

a correcting filter having a transfer function from said sound output unit to said sound detector, for being supplied with said base signal and outputting a reference signal;

first filter coefficient updating means for being supplied with said error signal and said reference signal and successively updating a filter coefficient of said adaptive notch filter in order to minimize said error signal;

second filter coefficient updating means for updating said filter coefficient by multiplying the filter coefficient to be updated of said adaptive notch filter by a predetermined value smaller than 1; and

switching means for alternatively switching between said first filter coefficient updating means and said second filter coefficient updating means and supplying said filter coefficient to said adaptive notch filter;

wherein said switching means switches to a filter coefficient supplied from said second filter coefficient updating means when said filter coefficient is equal to or greater than a first threshold value and switches to a filter coefficient supplied from said first filter coefficient updating means when said filter coefficient is smaller than a second threshold value which is smaller than said first threshold value.

2. An active noise control system according to claim 1, wherein said base signal generator outputs a base sine wave signal and a base cosine wave signal as said harmonic base signal;

said adaptive notch filter comprising;

a first adaptive notch filter for outputting a first control signal based on said base cosine wave signal;

a second adaptive notch filter for outputting a second control signal based on said base sine wave signal; and

an adder for adding said first control signal and said second control signal into said control signal and outputting the control signal to said sound output unit;

wherein said switching means switches to a filter coefficient supplied from said second filter coefficient updating means for said first adaptive notch filter and said second adaptive notch filter when either one of filter coefficients supplied respectively to said first adaptive notch filter and said second adaptive notch filter is equal to or greater than said first threshold value, and switches to a filter coefficient supplied from said first filter coefficient updating means for said first adaptive notch filter and said second adaptive notch filter when either one of the filter coefficients supplied respectively to said first adaptive notch filter and said second adaptive notch filter is smaller than said second threshold value.

3. An active noise control system according to claim 1, wherein said first threshold value and said second threshold value vary depending on the frequency of said base signal.

4. An active noise control system according to claim 2, wherein said first threshold value and said second threshold value vary depending on the frequency of said base signal.

5. An active noise control system according to claim 1, wherein said predetermined value is set to a value greater than 0.9.

6. An active noise control system according to claim 2, wherein said predetermined value is set to a value greater than 0.9.