Adaptive Active Noise Control Device for Dynamic Transfer Characteristics
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Solution Overview
Problem
Existing active noise control devices fail to effectively reduce noise pressure when the transfer characteristic between a speaker and a microphone changes, as they rely on fixed transfer characteristics.
Innovation Solution
An active noise control device that includes a signal processing unit with adaptive filters to generate and update control signals based on error signals, allowing it to adapt to changes in the transfer characteristic, using a feedback filter, extraction filter, and secondary path filter to minimize noise pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed transfer characteristic is used between speaker and microphone, then the device complexity is reduced, but the noise reduction effectiveness deteriorates when transfer characteristic changes
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed transfer characteristic to adaptive filters that continuously update their parameters. The secondary path filter and extraction filter are dynamically adjusted based on real-time error signals, allowing the system to adapt to changing acoustic conditions while maintaining noise reduction effectiveness.
Solution Approach 2:
The patent implements feedback mechanisms where the error signal from the microphone is fed back to continuously update the adaptive filters. The secondary path filter updating unit and extraction filter updating unit use this feedback to minimize the error signal, ensuring the system maintains optimal performance despite transfer characteristic changes.
2Reliability
If adaptive filters are introduced to handle transfer characteristic changes, then the noise reduction effectiveness is improved, but the device complexity increases
Solution Approach 1:
The patent segments the complex adaptive filtering process into distinct functional units: a secondary path filter updating unit that handles speaker-to-microphone transfer characteristics, an extraction filter updating unit that handles noise extraction, and a feedback filter setting unit that coordinates them. This segmentation manages complexity by organizing adaptive processing into modular, specialized components.
3Reliability
If the feedback filter gain is increased to improve noise cancellation, then the noise reduction effectiveness is improved, but uncomfortable sound levels may be emitted by the speaker
Solution Approach 1:
The feedback filter gain is made dynamic rather than fixed. The feedback filter setting unit continuously adjusts the gain based on real-time conditions, increasing it when noise cancellation is needed and reducing it when the canceling sound becomes uncomfortable, thus adapting to prevent harmful effects while maintaining effectiveness.
Solution Approach 2:
The error signal serves as feedback to the feedback filter setting unit, which uses this information to adjust the feedback filter gain. This feedback mechanism allows the system to monitor and control the output sound levels, preventing uncomfortable sound levels while maintaining effective noise cancellation when conditions require higher gain.
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 device can continuously reduce noise pressure even when the transfer characteristic changes, ensuring effective noise cancellation and preventing uncomfortable sound levels from being emitted by the speaker.
Implementation Method 1
an interference sound is output from the speaker. The sound pressure of noise such as road noise is reduced by the interference sound.
Data Source
AI summary
An active noise control device controls a speaker so as to output a canceling sound for canceling noise transmitted from a vibration source. The active noise control device includes a control signal generating unit configured to perform signal processing on a basic signal corresponding to a predetermined frequency by a feedback filter and a extraction filter, which is an adaptive notch filter, to generate a control signal that control the speaker, a secondary path filter updating unit configured to update sequentially and adaptively a secondary path filter, and a feedback filter setting unit configured to set the feedback filter based on the secondary path filter.