Active Noise Control System Weighted Error Signal Adaptation
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Solution Overview
Problem
Modern active noise control (ANC) systems face challenges in achieving uniform noise attenuation across varying operating conditions, such as different engine speeds in vehicles, leading to unpleasant residual noise fluctuations at listening positions.
Innovation Solution
An ANC system that uses an adaptive filter bank with weighted error signals, where each squared error signal is weighted based on the difference or ratio between its power level and a predefined reference level, to minimize a cost function representing the weighted sum of squared error signals, ensuring more consistent noise reduction across different conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ANC systems minimize the total error signal power, then the overall noise reduction is effective, but the noise attenuation becomes non-uniform across different operating conditions
Solution Approach 1:
The patent applies local quality by introducing position-dependent weighting factors w_j^2 for each error signal e_j[n] from different listening positions. Instead of uniform treatment, each position's error signal is weighted according to its importance or characteristics, allowing differential optimization across spatial locations. This resolves the contradiction by making the cost function J[n] = sum(w_j^2 * |e_j[n]|^2) position-aware, thereby achieving more uniform noise attenuation across varying operating conditions while maintaining overall reduction effectiveness.
2Reliability
If ANC systems use adaptive filtering to minimize error signals, then noise cancellation performance improves, but residual noise fluctuations occur at different listening positions
Solution Approach 1:
The patent employs feedback by continuously monitoring error signals e_j[n] from multiple listening positions and using them to adaptively adjust filter coefficients. The cost function J[n] = sum(w_j^2 * |e_j[n]|^2) provides a feedback mechanism that guides the adaptive filter to minimize weighted error signals. By incorporating position-specific weighting factors, the feedback loop achieves more stable residual noise levels across different listening positions while maintaining high noise cancellation performance.
3Device complexity
If uniform weighting is applied to all error signals, then the system is simple to implement, but noise attenuation varies significantly across listening positions
Solution Approach 1:
The patent applies parameter changes by modifying the weighting factors w_j^2 from uniform to position-dependent values. Instead of using equal weights for all error signals, the system adjusts weights based on listening position characteristics, allowing optimization of noise attenuation uniformity. This parameter modification resolves the contradiction by achieving reliable uniform noise attenuation across positions while maintaining reasonable system complexity through the use of a weighted sum cost function.
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
This approach enhances the uniformity of noise attenuation and maintains consistent noise reduction across different operating points, improving the overall noise cancellation performance and listener experience.
Implementation Method 1
Today's systems for actively suppressing or reducing the noise level in a listening room (known as 'active noise control' or 'ANC' systems) generate a compensation sound signal of the same amplitude and the same frequency components as the noise signal to be suppressed, but with a phase shift of 180° with respect to the noise signal. The compensation sound signal interferes destructively with the noise signal and the noise signal is thus eliminated or dampened at least at certain desired positions within the listening room.
Data Source
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AI summary
The present disclosure relates to an active noise control (ANC) system. In accordance with one aspect of the invention, the ANC system includes a plurality of microphones and a plurality of loudspeakers. Each microphone is configured to provide an error signal that represents a residual noise signal. Each loudspeaker is configured to receive a loudspeaker signal and to radiate a respective acoustic signal. The ANC system further includes an adaptive filter bank, which is supplied with a reference signal and configured to filter the reference signal to provide the loudspeaker signals as filtered signals. The filter characteristics of the adaptive filter bank are adapted such that a cost function is minimized. The cost function thereby represents the weighted sum of the squared error signals.