Active Noise Cancellation Using Compensation Filters
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Solution Overview
Problem
Existing active noise cancellation systems face challenges in effectively reducing noise throughout an enclosed space due to increased complexity, cost, and computational load associated with multiple microphones and wiring, as well as the inability to account for cross terms in filter coefficients, leading to inadequate noise reduction at positions away from microphone mounting points.
Innovation Solution
An active noise cancellation system is designed with a reduced number of microphones, utilizing a base signal generator, adaptive filter, correction filter, and compensation filter to update filter coefficients and correct control signals, accounting for transfer characteristics from both canceling signal emitters to the error signal detector, thereby minimizing error signals and maintaining noise reduction capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple microphones are installed to reduce noise throughout the enclosed space, then noise reduction coverage is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses a single microphone to detect noise, and through the adaptive filter and compensation filter, creates virtual noise cancellation effects at multiple positions. The filter coefficients are designed to replicate the noise cancellation effect that would otherwise require multiple microphones, thereby reducing hardware complexity while maintaining noise reduction coverage.
Solution Approach 2:
The patent introduces compensation filters as intermediary components that process the control signals from the adaptive filter. These compensation filters account for transfer characteristics between the speaker and different positions in the enclosed space, enabling a single microphone system to achieve multi-position noise reduction by mediating the control signals appropriately.
2Reliability
If multiple microphones are installed to reduce noise throughout the enclosed space, then noise reduction coverage is improved, but computational load increases
Solution Approach 1:
The patent uses a single microphone to detect noise, and through the adaptive filter and compensation filter, creates virtual noise cancellation effects at multiple positions. The filter coefficients are designed to replicate the noise cancellation effect that would otherwise require multiple microphones, thereby reducing hardware complexity while maintaining noise reduction coverage.
Solution Approach 2:
The patent pre-calculates and stores transfer characteristics between the speaker and different positions in the enclosed space. These pre-computed transfer characteristics are then used by the compensation filter to adjust control signals in real-time, reducing the computational burden during actual noise cancellation operation while maintaining accurate multi-position noise reduction.
3Device complexity
If transfer characteristic from second speaker to control point is approximated by same characteristic as first speaker to microphone, then device complexity is reduced, but noise reduction effectiveness deteriorates
Solution Approach 1:
The patent introduces compensation filters as intermediary components that process the control signals from the adaptive filter. These compensation filters account for transfer characteristics between the speaker and different positions in the enclosed space, enabling a single microphone system to achieve multi-position noise reduction by mediating the control signals appropriately.
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 effectively reduces noise across the enclosed space with fewer microphones and simplified wiring, reducing computational load and costs while maintaining noise reduction performance, by using a compensation filter to correct control signals based on combined transfer characteristics.
Implementation Method 1
a control signal generator that generates a control signal based on the base signal; a first canceling signal emitter that emits a canceling signal for canceling out the vibration or noise generated based on the control signal; an error signal detector that detects a residual vibration or noise at an evaluation point due to interference between the emitted canceling signal and the produced vibration or noise
Implementation Method 2
a correction filter that corrects the base signal, by a correction value indicating a transfer characteristic of the produced vibration or noise that corresponds to the harmonic frequency of the base signal from the first canceling signal emitter to the error signal detector
Implementation Method 3
a compensation filter that corrects the control signal by a prescribed value; wherein the correction value of the correction filter is set to a sum obtained by adding the transfer characteristic from the first canceling signal emitter to the error signal detector, and a product obtained by multiplying the transfer characteristic from the second canceling signal emitter to the error signal detector by the prescribed value
Data Source
AI summary
In an active noise cancellation system having an adaptive filter that outputs a control signal, first and second speakers that emit a canceling signal generated based on the control signal, a microphone that detects an error signal, a correction filter that corrects the base signal by a correction value to generate a reference signal and a filter coefficient updater that successively updates the adaptive filter coefficient based on the error signal and reference signal such that the error signal is minimized, the correction value of the correction filter is set to a sum obtained by adding the transfer characteristic from the first speaker to the microphone, and a product obtained by multiplying the transfer characteristic from the second speaker to the microphone by the prescribed value, thereby enabling to reduce the number of microphones and avoid the increase in parts, the amount of work to provide complicated wiring to the microphones, and the computational load involved in updating the adaptive filter coefficient, while enabling to maintain an area in which noise can be reduced to the same level as that obtained before reducing the number of microphones.