Active Noise Control Device Phase Difference Limiting
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Solution Overview
Problem
Conventional active vibration noise control devices often result in un-uniform noise-cancelled areas and increased vibration noise at positions other than the microphone point, due to excessive optimization at the microphone point leading to phase differences between control sounds from speakers.
Innovation Solution
An active vibration noise control device with a pair of speakers, an adaptive notch filter, a microphone for error detection, a reference signal generator, and a phase difference limiting unit to ensure uniform noise cancellation by adjusting filter coefficients and limiting phase differences between control sounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the adaptive notch filter optimizes the error signal at the microphone point, then the noise cancellation at the microphone point is improved, but the vibration noise increases at positions other than the microphone point and un-uniform noise-cancelled areas occur
Solution Approach 1:
The patent applies local quality by making different parts of the noise control system have different functions. Specifically, the left and right channels use different filter coefficients (WL and WR) tailored to their respective speaker positions and acoustic paths. The phase difference limiting unit also applies local correction by adjusting only the phase relationship between channels while maintaining their individual optimization, thus achieving uniform noise cancellation across the entire interior space rather than just at the microphone point.
2Measurement precision
If the filter coefficients are updated to minimize the error signal, then the noise cancellation performance at the microphone point is improved, but the phase difference between control sounds from speakers increases
Solution Approach 1:
The patent uses feedback by continuously monitoring the error signal from the microphone and using it to update the filter coefficients through the adaptive notch filter. The phase difference limiting unit also employs feedback by calculating the phase difference between left and right control sounds and adjusting the coefficients to maintain the phase difference within a predetermined range, thus stabilizing the system while maintaining noise cancellation performance.
3Reliability
If the control sound amplitudes are increased to suppress vibration noise, then the noise cancellation effectiveness is improved, but the un-uniform noise-cancelled areas occur due to phase differences
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the filter coefficients (WL and WR) based on the error signal and phase difference conditions. The phase difference limiting unit specifically adjusts the coefficients to maintain the phase difference within an optimal range, allowing the system to achieve effective noise cancellation with appropriate control sound amplitudes without creating un-uniform noise-cancelled areas.
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 effectively suppresses un-uniform noise-cancelled areas, ensuring a wide and uniform noise-cancelled area with reduced control sound amplitudes, maintaining a silent interior by adaptively limiting phase differences and updating filter coefficients.
Implementation Method 1
an adaptive notch filter which generates a first control signal provided to one of the speakers by applying a first filter coefficient to the basic signal and generates a second control signal provided to the other speaker by applying a second filter coefficient to the basic signal
Implementation Method 2
make the speakers generate the control sounds so that the vibration noise generated by the vibration noise source is cancelled
Implementation Method 3
a microphone which detects a cancellation error between the vibration noise and the control sounds and outputs an error signal
Implementation Method 4
a phase difference limiting unit which limits a phase difference between a control sound generated by one of the speakers and a control sound generated by the other speaker
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
An active vibration noise control device having a pair of speakers, including: a basic signal generating unit which generates a basic signal based on a vibration noise frequency; an adaptive notch filter which generates a first control signal provided to one of the speakers by using a first filter coefficient and generates a second control signal provided to the other speaker by using a second filter coefficient so as to cancel the generated vibration noise; a microphone which detects a cancellation error between the vibration noise and the control sounds and outputs an error signal; a reference signal generating unit which generates a reference signal based on a transfer function from the speakers to the microphone; a filter coefficient updating unit which updates the first and second filter coefficients so as to minimize the error signal; and a phase difference limiting unit which limits a phase difference between a control sound generated by one of the speakers and a control sound generated by the other speaker. Therefore, it becomes possible to appropriately ensure a uniform and wide noise-cancelled area.