Adaptive Noise Cancellation Filter Stability Under Changing Acoustic Paths
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Solution Overview
Problem
Active noise control systems face instability and performance issues due to variations in the secondary path transmission function, affecting the speed and quality of adaptation, especially in motor vehicles where ambient conditions change frequently.
Innovation Solution
An active noise cancellation system is configured with an adaptive filter and an equalization filter, where the product of their transfer functions matches a target function, and stability is evaluated to ensure robustness and stability, using a combination of acoustic and non-acoustic sensors and adaptive band-pass filtering to adapt to harmonic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adaptive filters are used for noise control, then noise reduction performance is improved, but system stability deteriorates due to variations in secondary path transmission function
Solution Approach 1:
The patent implements dynamic adaptation of the adaptive filter coefficients in response to detected instability conditions. The system continuously monitors stability and adjusts filter parameters dynamically, allowing the system to maintain optimal noise reduction performance while adapting to changing secondary path characteristics that cause instability.
Solution Approach 2:
The patent employs feedback mechanisms where the system monitors its own stability state and uses this information to adjust the adaptive filter operation. The feedback loop detects instability conditions and modifies filter coefficients accordingly, creating a self-regulating system that maintains both performance and stability.
2Speed
If adaptive filter coefficients are continuously adjusted, then adaptation speed is improved, but system stability deteriorates
Solution Approach 1:
The patent implements periodic stability assessment rather than continuous adjustment. The system evaluates stability at discrete intervals or under specific conditions, making adaptive adjustments only when instability is detected. This periodic approach allows for sufficient adaptation speed while preventing the excessive adjustments that would cause instability.
Solution Approach 2:
The system dynamically adjusts the adaptation rate based on current operating conditions. When stability is compromised, the system reduces the rate of coefficient adjustment; when stable, it increases adaptation speed. This dynamic control of the adaptation process resolves the contradiction between speed and stability.
3Adaptability or versatility
If the secondary path transmission function varies, then adaptability to different conditions is improved, but quality of noise control deteriorates
Solution Approach 1:
The patent implements dynamic tracking of the secondary path transmission function through continuous monitoring and adaptation. The system adjusts filter coefficients in response to detected changes in ambient conditions and secondary path characteristics, maintaining high-quality noise control across varying operating conditions while adapting to new environments.
Solution Approach 2:
The system changes key parameters of the adaptive filter (such as coefficients and adaptation rate) in response to variations in the secondary path transmission function. By adjusting these parameters dynamically, the system maintains optimal performance across different ambient conditions while adapting to changing acoustic paths.
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 configuration improves the robustness and stability of the active noise control system, enabling faster adaptation and better noise reduction by equalizing the frequency response of the secondary path and detecting unstable states to alleviate adverse effects.
Implementation Method 1
Modern active noise control systems implement digital signal processing and digital filtering techniques
Implementation Method 2
The reference signal is fed to an adaptive filter which supplies a filtered reference signal to an acoustic actuator
Implementation Method 3
The filtered reference signal is supplied to an acoustic actuator (e.g., a loudspeaker). The acoustic actuator generates a compensation sound field
Implementation Method 4
the noise signal is eliminated or reduced, at least at certain locations within the listening room, due to the destructive interference between the compensation sound signal and the noise signal
Implementation Method 5
Residual noise within the listening environment and/or the listening room may be measured using a microphone. The resulting microphone output signal is used as an 'error signal'
Implementation Method 6
The filter coefficients of the adaptive filter are modified such that a norm (e.g., the power) of the error signal is minimized
Implementation Method 7
The resulting microphone output signal is used as an 'error signal' and is provided to the adaptive filter, where the filter coefficients of the adaptive filter are modified
Data Source
AI summary
An active noise cancellation system that reduces, at a listening position, power of a noise signal radiated from a noise source to the listening position. The system includes an adaptive filter, at least one acoustic actuator and a signal processing device. The adaptive filter receives a reference signal representing the noise signal, and provides a compensation signal. The at least one acoustic actuator radiates the compensation signal to the listening position. The signal processing device evaluates and assesses the stability of the adaptive filter.