Active Noise Control Adaptive Secondary Path Filter
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Solution Overview
Problem
Existing active noise control devices face challenges in maintaining effective noise reduction when the transfer characteristic between the speaker and microphone changes, as they rely on a fixed transfer characteristic, leading to inadequate sound pressure reduction.
Innovation Solution
An active noise control device that incorporates a feedforward signal processing unit, a feedback signal processing unit, and a cooperative control unit, which includes adaptive secondary path filters to update and adapt to changing sound transfer characteristics, allowing for continuous noise reduction even when the transfer characteristic changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed transfer characteristic is used for speaker control, then the device structure is simple, but the noise reduction effectiveness deteriorates when the actual transfer characteristic changes
Solution Approach 1:
The patent implements dynamic adaptation by sequentially updating the secondary path filter through feedforward signal processing to track changes in the transfer characteristic between speaker and microphone. This allows the system to adapt to varying acoustic conditions (such as temperature changes or speaker aging) while maintaining effective noise reduction, resolving the contradiction between simple structure and reliable performance.
2Adaptability or versatility
If the transfer characteristic changes between speaker and microphone, then the system becomes more adaptable to environmental changes, but the fixed control signal becomes ineffective for noise reduction
Solution Approach 1:
The patent employs feedback signal processing where the microphone detects the actual sound field including both noise and canceling sound, and this error signal is used to update the secondary path filter. This closed-loop feedback mechanism ensures the control system continuously adapts to transfer characteristic changes while maintaining effective noise reduction performance.
3Reliability
If adaptive filter updating is implemented, then the noise reduction effectiveness is maintained under changing conditions, but the device complexity increases
Solution Approach 1:
The patent divides the control system into distinct functional modules: feedforward signal processing for adaptive filter updating, feedback signal processing for error detection, and a cooperative control unit for coordinating both. This segmentation allows the complex adaptive functions to be implemented in an organized manner, managing the increased complexity while maintaining noise reduction effectiveness.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device can effectively reduce sound pressure of noise by adapting to changing conditions, improving noise reduction performance and preventing abnormal sound generation from the speaker.
Implementation Method 1
controls a speaker to output an interference sound for reducing a sound pressure of noise
Implementation Method 2
a detector that detects, at a control point, a synthetic sound of noise transmitted from a vibration source and a canceling sound output from the speaker
Data Source
AI summary
A cooperative control unit is configured to cause a muffled sound control signal processing unit to start feedforward signal processing, and set, when a secondary path filter has converged, a narrow band noise control signal processing unit to the converged secondary path filter and cause the narrow band noise control signal processing unit to start feedback signal processing.