Nonlinear Sound-Generator Filtering for Stable Vehicle Noise Reduction
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Solution Overview
Problem
Existing noise reduction systems in vehicles are sensitive to user head movements, leading to instability and inefficiency in noise cancellation, particularly due to nonlinear behavior of sound generators and environmental variations.
Innovation Solution
A noise reduction system incorporating a nonlinearity filter unit with a model of the sound generator's non-linear transfer function, combined with a virtual sensing algorithm and averaging of error signals from multiple microphones, to stabilize and enhance noise cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a noise reduction system uses active noise cancellation with a sound generator, then background noise can be reduced in a quiet zone, but the system becomes sensitive to 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 position of virtual microphones and adapting the noise cancellation parameters in real-time based on detected head movements. This allows the system to maintain effective noise reduction even when the user's head position changes, resolving the contradiction between reliable noise reduction and sensitivity to head movements.
2Reliability
If the system relocates the noise reduction area to adapt to head movements, then noise reduction effectiveness is maintained, but the system complexity increases due to continuous adaptation requirements
Solution Approach 1:
The system uses virtual microphones that replicate the functionality of physical microphones through computational algorithms. Instead of physically relocating sensors or adding complex hardware adaptation mechanisms, the system creates virtual representations of microphone positions and uses signal processing to simulate acoustic field measurements, thereby maintaining noise reduction effectiveness while reducing physical system complexity.
3Area of stationary object
If the system uses multiple virtual microphones to estimate error signals, then the quiet zone is expanded and noise reduction is improved, but the computational load increases
Solution Approach 1:
The system strategically places a limited number of virtual microphones at optimal positions to estimate error signals, rather than using excessive numbers of virtual microphones throughout the entire space. By selecting key measurement points that provide sufficient information about the acoustic field, the system expands the effective quiet zone while keeping computational requirements manageable.
4Stability of the object's composition
If the system compensates for nonlinearities in sound generators, then noise cancellation stability is improved, but the device complexity increases due to additional filter units
Solution Approach 1:
The system incorporates feedback mechanisms where the output of the sound generator is monitored and used to adjust the noise cancellation parameters. By continuously monitoring the actual sound output and comparing it with expected linear behavior, the system identifies and compensates for nonlinearities, improving stability while using feedback to manage complexity through adaptive parameter adjustment rather than fixed complex filtering.
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 stable and efficient noise reduction by compensating for nonlinearities in sound generators and adapting to environmental changes, while maximizing the quiet zone and reducing computational load.
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
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
Implementation Method 3
a virtual sensing algorithm is implemented in the control unit, which is thereby configured to estimate an error signal at a position of a virtual microphone, wherein the virtual microphone is located in the noise reduction area and the error signal is indicative of a difference between the background noise and the anti-noise at the position of the virtual microphone
Implementation Method 4
a monitor-microphone array having a plurality of monitor microphones, the monitor-microphone array being disposed adjacent to the noise reduction area and being configured to pick up background noise emitted by the noise source and anti-noise emitted by the sound generator
Data Source
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AI summary
The invention relates to a noise reduction system (20) for actively compensating background noise in a passenger transport area (4) of a vehicle (2). The noise reduction system (20) comprises a nonlinearity filter unit (60) having a model of a non-linear transfer function of the sound generator (12), wherein the nonlinearity filter unit (60) is configured to receive the anti-noise signal (A) and to generate a filtered anti-noise signal (CA) by applying a non-linear filter function on the anti-noise signal (A), which is based on the model of the non-linear transfer function in that the non-linear response of the sound generator (12) is at least partially corrected when driven by the filtered anti-noise signal (CA), wherein the nonlinearity filter unit (60) is further configured to output the filtered anti-noise signal (CA) to the sound generator (12).