Active Noise Reduction Reference Tracking for Engine Speed Drift
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Solution Overview
Problem
Existing active noise reduction devices struggle to maintain effective noise cancellation when the frequency of noise shifts by 1 Hz from the assumed frequency, particularly during abrupt changes in engine speed, leading to unsatisfactory noise reduction and potential unusual sound output.
Innovation Solution
An active noise reduction device utilizing the SAN filtered-x LMS algorithm, which includes a frequency controller to detect and correct frequency drift by generating a second reference signal when engine speed variations exceed a threshold, and optionally incorporating a feedback filter to adjust gain coefficients, thereby improving noise reduction performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an adaptive filter is used to reduce noise by applying filter factors to a reference signal, then noise reduction is achieved under stable engine conditions, but noise reduction performance deteriorates when engine speed varies abruptly causing frequency drift
Solution Approach 1:
The system dynamically switches between two reference signal generation modes: using a fixed-frequency reference signal under stable engine conditions, and using a variable-frequency reference signal when engine speed changes abruptly. This dynamic adaptation allows the system to maintain optimal noise reduction performance across varying operating conditions.
Solution Approach 2:
The system changes the frequency parameter of the reference signal based on engine speed variations. When engine speed changes exceed a threshold, the reference signal frequency is adjusted to track the varying noise frequency, thereby maintaining effective noise cancellation despite frequency drift.
2Reliability
If the adaptive filter continuously updates filter factors based on error signals, then noise reduction adapts to gradual changes, but the system cannot respond quickly enough to abrupt engine speed changes
Solution Approach 1:
The system performs preliminary detection of engine speed changes and proactively switches to variable-frequency reference signal mode before significant frequency drift occurs. This preliminary action allows the system to prepare for upcoming frequency changes and respond more effectively to abrupt engine speed variations.
Solution Approach 2:
The system uses feedback from engine speed sensors to continuously monitor engine operating conditions. When engine speed changes exceed a predetermined threshold, the feedback mechanism triggers a switch to variable-frequency reference signal generation, enabling rapid response to frequency changes while maintaining noise reduction effectiveness.
3Device complexity
If a fixed frequency reference signal is used for noise cancellation, then the system is simple to implement, but it produces unusual cancellation sounds when engine frequency drifts from the assumed frequency
Solution Approach 1:
The reference signal generation system is designed to perform multiple functions: generating fixed-frequency signals for stable conditions and variable-frequency signals for varying conditions. This multi-functionality allows the system to maintain simplicity during normal operation while automatically adapting to prevent unusual cancellation sounds during engine speed variations.
Data Source
AI summary
An active noise reduction device includes a reference-signal generator that generates a first reference signal having a first frequency that corresponds to the engine speed of an engine, an adaptive filter that outputs a cancellation signal used to output cancellation sound by applying a filter factor to the first reference signal, the filter factor being successively updated based on an error signal output from a microphone, and a frequency controller that, when the amount of variation in the engine speed of engine has been determined to exceed a predetermined value, causes the reference-signal generator to generate a second reference signal having a second frequency and then to cause the adaptive filter to output a cancellation signal based on the second reference signal, the second frequency being obtained by correcting the first frequency.