Active Noise Reduction Device with Step Size Adjustment
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Solution Overview
Problem
Conventional active noise reduction devices face challenges in stabilizing noise control when the state of noise in a vehicle cabin undergoes sudden changes, leading to unstable noise reduction and potential abnormal sound generation.
Innovation Solution
The active noise reduction device incorporates a μ adjuster to calculate a step size parameter based on the signal level of the reference signal, and a determiner to transition at least one of the adaptive filter or filter coefficient updater from a normal state to a restriction state when a second representative input value exceeds a threshold, reducing the noise reduction effect but stabilizing control during sudden changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the adaptive filter continuously updates the coefficient to minimize error signal, then the noise reduction effect is improved, but the system becomes unstable when noise state changes suddenly
Solution Approach 1:
The system dynamically transitions between normal operation mode and restriction operation mode based on detected noise state changes. The adaptive filter coefficient update behavior is made dynamic by adjusting the update frequency or disabling updates during restriction operation when sudden noise changes are detected, thereby adapting the system's responsiveness to changing conditions while maintaining overall stability
Solution Approach 2:
The system performs preliminary detection of sudden noise state changes using the determiner before the adaptive filter can cause instability. By detecting changes in advance and transitioning to restriction operation, the system prevents the harmful effect of unstable noise reduction and abnormal sound generation before they occur
2Adaptability or versatility
If the system responds quickly to sudden noise changes by updating filter coefficients frequently, then the adaptability is improved, but abnormal sound generation occurs due to unstable control
Solution Approach 1:
The determiner performs preliminary detection of sudden noise state changes before the adaptive filter updates coefficients. By identifying changes in advance and transitioning to restriction operation, the system prevents abnormal sound generation that would result from inappropriate coefficient updates during sudden transitions
Solution Approach 2:
The system converts the potentially harmful effect of sudden noise changes into a beneficial restriction operation state. By detecting the sudden change and intentionally reducing the noise reduction effect through restriction operation, the system prevents more severe harmful effects like abnormal sound generation and instability
Data Source
AI summary
An active noise reduction device includes: a reference signal inputter; an adaptive filter; a μ adjuster that calculates a step size parameter by multiplying a reference value for the step size parameter by a correction coefficient that is proportional to a reciprocal of a first representative input value that indicates a signal level of the reference signal in a first predetermined period; a filter coefficient updater that updates adaptive filter coefficient W by using the step size parameter calculated; and a determiner. When it is determined that a second representative input value is greater than a threshold value, at least one of the adaptive filter or the filter coefficient updater is transitioned from a normal state to a restriction state in which an effect of reducing noise is smaller than in the normal state.