Active Noise Control With Adaptive Filter Dip Detection
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Solution Overview
Problem
Existing active noise control systems struggle to accurately detect dips in noise frequencies and stabilize control when multiple dips are present or the overall amplitude characteristic is not constant.
Innovation Solution
An active noise control device that includes an adaptive filter, which generates a control signal by processing a reference signal based on vibration frequency, using a reference signal generation unit, amplitude characteristic calculation, smoothed signal generation, correction coefficient calculation, and adaptive filter update to accurately detect dips and stabilize noise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a dip is detected based on an average amplitude of a frequency band, then the detection process is simple, but the dip frequency cannot be accurately detected when there are multiple dips or when the overall amplitude characteristic is not constant
Solution Approach 1:
The patent segments the frequency band into multiple sub-bands and performs dip detection in each sub-band separately. This allows accurate detection of multiple dips at different frequencies while maintaining a relatively simple detection process within each sub-band.
Solution Approach 2:
The patent performs dip detection in multiple sub-bands rather than using a single average amplitude calculation. This partial action approach (detecting dips in specific frequency ranges) improves accuracy without requiring complete analysis of the entire frequency spectrum at once.
2Device complexity
If the adaptive filter is updated using conventional methods, then the update process is simple, but the control becomes unstable when the noise frequency matches the dip frequency
Solution Approach 1:
The patent performs preliminary dip detection in multiple sub-bands before updating the adaptive filter. By identifying dip frequencies in advance, the system can adjust the filter update process to avoid instability, ensuring reliable control even when noise frequency matches dip frequency.
Solution Approach 2:
The patent changes the filter update parameters (such as step size) based on the detected dip frequencies. When the noise frequency is close to a dip frequency, the update parameters are adjusted to prevent divergence, maintaining control stability without overly complicating the update process.
3Adaptability or versatility
If the step size parameter is changed in one or more filter coefficient updating means, then the control can be adjusted for dip frequencies, but the control signal may diverge and stable control cannot be achieved
Solution Approach 1:
The patent applies different step size parameters to different filter coefficient updating means based on the detected dip frequencies. This local quality approach allows the system to be adaptive to specific frequency conditions while maintaining overall control stability by not uniformly changing all parameters.
Solution Approach 2:
The patent uses feedback from the dip detection results to adjust the step size parameters in the filter update process. This closed-loop approach ensures that the control remains stable by continuously adapting parameters based on the actual system response and detected dip frequencies.
Data Source
AI summary
An active noise control device includes an adaptive filter that generates a control signal based on a vibration frequency generated by a vibration source and sequentially updating the adaptive filter, a reference signal generation device that generates a reference signal, an amplitude characteristic calculation device that acquires an acoustic characteristic including amplitude and phase information, the acoustic characteristic being an acoustic characteristic of a secondary path between a speaker and a microphone and calculating an amplitude characteristic of the secondary path, a smoothed signal generation device having a low-pass filter, a correction coefficient calculation device that calculates a correction coefficient according to a frequency, an adaptive filter update device that updates the adaptive filter by subtracting an update term including the correction coefficient from a first adaptive filter coefficient that is an immediately preceding adaptive filter coefficient, and a control signal generation device that generates the control signal.