Active Noise Control Stabilization via Frequency Segmentation
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Solution Overview
Problem
Conventional active noise control apparatuses face challenges in suppressing abnormal noise caused by background disturbances without impairing the noise silencing effect, particularly when using methods that mute control sounds or adjust step sizes, leading to reduced effectiveness in noise cancellation.
Innovation Solution
An active noise control apparatus that includes a sound source signal generating unit, a control signal filter, a stabilization processing unit, a reference signal filter, and a filter coefficient updating unit, which allows signals in the control frequency band to pass through while blocking disturbance frequencies, thereby stabilizing the control signal and preventing reduction of noise-effective frequency components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If disturbance suppression processing is applied to error signals to reduce abnormal noise, then abnormal noise is reduced, but the noise silencing effect is impaired
Solution Approach 1:
The error signal is segmented into multiple frequency components through Fourier transformation. By separating the signal into frequency domains, the system can selectively process different frequency components - suppressing disturbance frequencies while preserving noise cancellation frequencies, thus resolving the contradiction between reducing abnormal noise and maintaining noise silencing effect
Solution Approach 2:
Different processing qualities are applied to different frequency components of the error signal. Frequency components corresponding to disturbances receive suppression processing, while frequency components corresponding to effective noise cancellation signals are preserved. This local differentiation allows simultaneous reduction of abnormal noise and maintenance of noise silencing effect
2Object-affected harmful factors
If the control sound is muted constantly to suppress disturbance, then abnormal noise is reduced, but the noise silencing effect is lost fundamentally
Solution Approach 1:
Instead of constant muting, the system dynamically adjusts the processing applied to the error signal based on frequency analysis. The degree of suppression is varied continuously - strong suppression for disturbance frequencies and minimal or no suppression for effective cancellation frequencies. This dynamic, frequency-selective approach eliminates abnormal noise while preserving the noise silencing effect
Solution Approach 2:
The system changes the processing parameters (suppression strength) based on the frequency characteristics of the error signal. By transforming to frequency domain and applying frequency-dependent processing, the system adapts its response to different signal components, suppressing only the harmful disturbance frequencies while maintaining the useful cancellation signals
3Stability of the object's composition
If the step size is suppressed constantly to stabilize control, then control stability is improved, but the ability to follow a change in noise is lost
Solution Approach 1:
The system implements dynamic step size adjustment based on frequency content analysis. For frequency components identified as disturbances, constant or reduced step sizes provide stability. For frequency components corresponding to changing noise, larger step sizes enable rapid tracking. This dynamic, frequency-selective step size control simultaneously achieves stability and responsiveness
Solution Approach 2:
The control parameters are segmented by frequency component. Different adaptation parameters (step sizes) are applied to different frequency bands - smaller steps for stable disturbance frequencies and larger steps for dynamically changing noise frequencies. This segmentation allows the system to maintain stability where needed while following changes where required
Data Source
AI summary
An active noise control apparatus (100) includes: a sound source signal generating unit (1) generating a sound source signal from a control frequency determined in accordance with a noise source (400); a control signal filter (2) generating an original control signal by filtering the sound source signal; a stabilization processing unit (5) generating a control signal by filtering the original control signal to allow a signal in a frequency band including the control frequency to pass through, and to block a signal in a frequency band including disturbance added to the noise; a reference signal filter (3) generating a reference signal by filtering the sound source signal. The apparatus further includes: a filter coefficient updating unit (4) updating a filter coefficient sequence of the control signal filter using an error signal being an interference between a secondary noise generated from the control signal and the noise, and the reference signal.