Adaptive Noise Control Secondary Path Estimation
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Solution Overview
Problem
Active noise control systems face challenges in achieving robustness, speed, and quality of adaptation due to variations in the secondary path transmission function, leading to instability and reduced performance, especially in dynamic environments like motor vehicles.
Innovation Solution
A dynamic system identification method is implemented, using an additional adaptive filter connected in parallel to the secondary path system, with a measurement signal independent of the reference signal to estimate the secondary path transfer function in real-time, improving the accuracy of the secondary path estimation and adapting to changing ambient conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a static secondary path model is used in the adaptive filter, then the system structure is simple, but the system cannot adapt to variations in the secondary path transmission function, leading to reduced noise cancellation performance
Solution Approach 1:
The patent implements dynamic adaptation of the secondary path model by continuously updating the model parameters based on real-time measurements of the secondary path transmission function. This allows the system to track changes in the acoustic path caused by varying ambient conditions, such as temperature, humidity, and acoustic reflections, thereby maintaining optimal noise cancellation performance without requiring an overly complex fixed structure.
Solution Approach 2:
The patent employs feedback mechanisms where the actual secondary path transmission function is measured and fed back to update the model. This closed-loop approach enables the system to correct deviations from the expected acoustic path behavior, adapting to changes in real-time while maintaining a manageable system structure through intelligent parameter estimation rather than complex hardware additions.
2Adaptability or versatility
If the adaptive filter operates in dynamic environments like motor vehicles, then the system can handle varying acoustic conditions, but the secondary path transmission function variations cause instability and reduced convergence speed
Solution Approach 1:
The patent performs preliminary identification and characterization of the secondary path transmission function before the main noise cancellation operation begins. By pre-establishing a comprehensive model of the acoustic path and its expected variations, the system can better predict and compensate for changes during operation, reducing instability and improving convergence speed in dynamic environments like motor vehicles.
Solution Approach 2:
The patent replaces direct mechanical adjustments of the acoustic path with digital signal processing techniques to compensate for variations. Instead of physically modifying the acoustic environment, the system uses adaptive filters and digital models to cancel out the effects of secondary path variations, achieving stability through computational methods rather than mechanical adjustments.
3Measurement precision
If traditional secondary path estimation methods are used, then the system is simpler to implement, but the estimation accuracy is insufficient, leading to poor noise cancellation especially in the bass frequency range
Solution Approach 1:
The patent develops a secondary path estimation method that serves multiple functions: it characterizes the acoustic path for noise cancellation, identifies system parameters for model prediction, and adapts to varying operating conditions. This multi-functional approach achieves high estimation accuracy across different frequency ranges, particularly improving bass frequency performance, while avoiding the need for separate specialized estimation systems for each function.
Solution Approach 2:
The patent employs parameter estimation techniques that adapt the model parameters based on the operating conditions and frequency range. By dynamically adjusting the parameters used in the secondary path model, the system achieves high accuracy in estimating the transmission function, particularly in the challenging bass frequency range, without requiring overly complex estimation algorithms for each specific condition.
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 stability and performance of active noise control systems by accurately tracking changes in the secondary path, reducing instability and improving noise cancellation efficiency across varying conditions.
Implementation Method 1
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 thus the noise signal is eliminated or damped
Implementation Method 2
at least one acoustic actuator radiating the compensation signal and the measurement signal to the listening position
Implementation Method 3
at least one microphone receiving a superposition of the radiated compensation signal, the measurement signal, and the noise signal at the listening position and providing an error signal
Data Source
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AI summary
An active noise cancellation system is disclosed for reducing, at a listening position, the power of a noise signal being radiated from a noise source to the listening position. The system comprises: an adaptive filter receiving a reference signal representing the noise signal and comprising an output providing a compensation signal; a signal source providing a measurement signal; at least one acoustic actuator radiating the compensation signal and the measurement signal to the listening position; at least one microphone receiving a superposition of the radiated compensation signal, the measurement signal, and the noise signal at the listening position and providing an error signal; a secondary path comprising a secondary path system which represents the signal transmission path from an output of the adaptive filter to an output of the microphone; and an estimation unit for estimating a transfer characteristic of a secondary path system responsive to the measurement signal and the error signal.