Active Noise Control Error Path Model Correction via Phase Cross Correlation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing active noise control (ANC) devices face instability in error path characteristic modeling due to time-dependent changes in vehicle environments, requiring a pseudo engine sound for correction, which can be uncomfortable for occupants and necessitates a special structure.
Innovation Solution
An ANC device with a simpler structure that adjusts adaptive filter coefficients using a filtered-x LMS algorithm, determining phase characteristic differences through cross correlations to correct the error path characteristic model without outputting an identification sound, thereby maintaining stable control without discomfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pseudo engine sound is used to correct the error path characteristic model, then the model correction accuracy is improved, but the device complexity increases and occupants experience discomfort
Solution Approach 1:
The system uses the existing noise cancellation sound already being emitted by the speaker for model correction, rather than requiring a separate pseudo engine sound generation system. The error path characteristic model is corrected by analyzing the relationship between the reference signal and the microphone output during normal noise cancellation operation, allowing the system to self-correct using its own operational signals.
Solution Approach 2:
The noise cancellation sound serving its primary function of reducing engine noise simultaneously serves a secondary function of enabling error path characteristic model correction. This multi-functionality eliminates the need for dedicated correction signals and simplifies the overall system structure while maintaining correction accuracy.
2Measurement precision
If a pseudo engine sound is used to correct the error path characteristic model, then the model correction accuracy is improved, but the ease of operation deteriorates due to uncomfortable feeling for occupants
Solution Approach 1:
The system uses the existing noise cancellation sound already being emitted by the speaker for model correction, rather than requiring a separate pseudo engine sound generation system. The error path characteristic model is corrected by analyzing the relationship between the reference signal and the microphone output during normal noise cancellation operation, allowing the system to self-correct using its own operational signals.
3Device complexity
If the error path characteristic model is not corrected, then the device complexity remains low, but the stability of noise cancellation deteriorates over time
Solution Approach 1:
The system continuously monitors the error signal from the microphone and uses this feedback to periodically correct the error path characteristic model. The phase characteristic difference determining means calculates the phase difference between the modeled and actual error paths, and the correcting means adjusts the model accordingly, creating a closed-loop feedback mechanism that maintains stability without complex additional hardware.
Solution Approach 2:
The error path characteristic model is corrected in advance based on phase characteristic differences detected during normal operation, before significant deviations accumulate and cause instability. This preliminary correction approach maintains noise cancellation stability proactively rather than reactively.
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
An error path characteristic model correction control unit determines the deviation of the phase of an actual transfer function from the phase of an error path characteristic model, from a cross correlation between an error signal output from a microphone and a signal in which the error path characteristic model is applied to a noise cancellation sound to be output and a cross correlation between the error signal and a signal in which a transfer function having a phase characteristic deviating by +90 degrees from the phase characteristic of the error path characteristic model is applied to the noise cancellation sound. The error path characteristic model correction control unit then corrects the error path characteristic model so that the determined deviation is reduced to +90 degrees.