Nonlinearity Filtering in Vehicle Active Noise Reduction
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Solution Overview
Problem
Existing active noise reduction systems in vehicles are sensitive to user head movements, leading to instability and inefficiency in noise cancellation, particularly due to nonlinearities in sound generators like loudspeakers, and are limited to a small quiet zone.
Innovation Solution
A noise reduction system incorporating a controller with a nonlinearity filter unit to correct sound generator nonlinearities, a monitor-microphone array, and a virtual sensing algorithm that estimates error signals at multiple positions, using averaging and dynamic adjustment to stabilize and expand the quiet zone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a noise reduction system uses a small quiet zone for efficient noise cancellation, then noise suppression efficiency is improved, but the system becomes sensitive to user head movements and loses effectiveness when the ear is no longer in the quiet zone
Solution Approach 1:
The system dynamically relocates the quiet zone by adjusting the virtual microphone position based on detected head movements. The controller continuously adapts the noise reduction area's location to follow the user's head position, ensuring the ear remains within the effective quiet zone despite movements. This dynamic adaptation resolves the contradiction by making the system both efficient (maintaining focused noise cancellation) and robust (tracking head movements).
Solution Approach 2:
The system uses feedback from head movement detection to continuously adjust the noise reduction area's position. The controller receives information about head position changes and uses this feedback to relocate the quiet zone accordingly. This closed-loop feedback mechanism ensures the system maintains effective noise cancellation while adapting to user movements, resolving the contradiction between precision and adaptability.
2Adaptability or versatility
If the system relocates the noise reduction area to adapt to head movements, then robustness to head movements is improved, but the complexity of the system increases due to continuous relocation and virtual microphone adjustment
Solution Approach 1:
The system uses a virtual microphone that creates a computational copy of the physical microphone's function without requiring additional physical hardware. By implementing the microphone array signal processing algorithm, the system generates a virtual representation of sound field information, enabling noise reduction area relocation through software-based processing rather than complex hardware modifications. This reduces physical system complexity while maintaining adaptability.
3Measurement precision
If the system uses a microphone array with multiple filters to estimate residual signal, then measurement precision is improved, but the device complexity increases
Solution Approach 1:
The system divides the signal processing task into segments by using multiple filters with specific functions. Each filter in the microphone array processing chain handles a particular aspect of signal estimation, allowing the system to achieve high measurement precision through modular, specialized processing stages rather than a single complex filter. This segmentation makes the complexity more manageable and systematic.
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
The system provides enhanced stability and efficiency in noise cancellation by compensating for sound generator nonlinearities and adapting to user head movements, effectively expanding the quiet zone and maintaining noise reduction across a larger area.
Implementation Method 1
The anti-noise is superimposed on the undesired background noise in that the background noise is reduced or almost completely eliminated in a quiet zone by means of destructive interference
Implementation Method 2
a nonlinearity filter unit having a model of a non-linear transfer function of the sound generator, wherein the filter unit is configured to receive the anti-noise signal and to generate a corrected anti-noise signal by applying a nonlinear filter function on the anti-noise signal, which is based on the model of the non-linear transfer function in that the non-linear response of the sound generator is at least partially corrected
Data Source
AI summary
A noise reduction system for actively compensating background noise in a passenger transport area of a vehicle. The noise reduction system includes a nonlinearity filter unit having a model of a non-linear transfer function of the sound generator, wherein the nonlinearity filter unit is configured to receive the anti-noise signal and to generate a filtered anti-noise signal by applying a non-linear filter function on the anti-noise signal, which is based on the model of the non-linear transfer function in that the non-linear response of the sound generator is at least partially corrected when driven by the filtered anti-noise signal. Wherein the nonlinearity filter unit is further configured to output the filtered anti-noise signal to a sound generator.