Active Noise Controller Phase Adjustment via Lookup Table
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Solution Overview
Problem
Existing active noise control apparatuses face challenges in maintaining effective sound cancellation capability across a wide frequency band due to frequency-dependent phase changes, leading to sound augmentation regions and reduced control capability.
Innovation Solution
The apparatus adjusts the phase of the canceling signal without using a phase shifter by generating an adjustment reference signal from a shifted read position in the waveform data table, allowing the canceling signal to maintain its phase and amplitude effectively across a broader frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a phase shifter (delay unit) is used to adjust the phase of the canceling signal, then the canceling sound can be brought into opposite phase to the noise at the evaluation point, but frequency-dependent phase changes occur causing sound augmentation regions and reduced control capability
Solution Approach 1:
The patent changes the parameter of phase adjustment from using a phase shifter (which causes frequency-dependent phase changes) to using a lookup table that stores pre-calculated phase values. By changing how phase is adjusted - from dynamic phase shifting to static phase value selection based on frequency - the system eliminates frequency-dependent phase changes while maintaining opposite-phase canceling sounds across a wide frequency band.
2Measurement precision
If the sound canceling region is narrowed to eliminate sound augmentation effects, then phase control is improved at the target frequency, but the bandwidth within which noises can be canceled is reduced
Solution Approach 1:
The patent changes the approach from narrowing the sound canceling region to using a lookup table with pre-calculated phase values for different frequencies. This parameter change allows the system to maintain precise phase control at each frequency while covering a wide bandwidth, effectively resolving the contradiction between phase control precision and noise cancellation bandwidth.
3Reliability
If a phase shifter is used to maintain opposite phase at the evaluation point, then sound cancellation is achieved at the target frequency, but phase delay occurs at frequencies around the target frequency reducing control capability
Solution Approach 1:
The patent changes the phase adjustment mechanism from using a phase shifter that introduces frequency-dependent phase delay to using a lookup table with pre-calculated phase values. This eliminates the harmful phase delay at surrounding frequencies while maintaining reliable control capability at the target frequency.
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 enables reliable sound cancellation across a wider frequency band, ensuring that canceling sounds are in opposite phase and have an amplitude nearly equal to the noise, thereby effectively reducing noise at the evaluation point.
Implementation Method 1
generating a canceling sound, which is in opposite phase to and has an amplitude nearly equal to the noise, for causing interference between the generated canceling sound and the noise
Data Source
AI summary
On an active noise controller, an adjustment reference signal generator generates an adjustment reference signal Sra by reading the waveform data sequentially at a read location shifted by a given amount from a read location for a reference signal Sr with respect to the waveform data at a reference signal generator. A one-tap adaptive filter generates a control signal Scp by multiplying the adjustment reference signal Sra by a filter factor W. A gain controller outputs a compensation control signal Sca generated by multiplying the control signal Scp by gain G. A speaker outputs the compensation control signal Sca as a cancellation sound.