Active Noise Reduction Using Adaptive Acoustic Filters

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Solution Overview

Problem

Conventional active noise reduction systems are expensive due to the use of acceleration sensors and suffer from deteriorated control performance when acoustic transmission characteristics change.

Innovation Solution

An active noise reduction system that uses multiple noise microphones to generate reference and error signals, eliminating the need for expensive acceleration sensors, and employs adaptive and non-adaptive acoustic transmission filters to maintain control performance despite changes in acoustic characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If an acceleration sensor is used to generate the noise signal, then the noise detection accuracy is improved, but the system cost increases

Engineering Contradiction:

Improvenoise detection accuracyVSAvoidsystem cost

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent uses multiple microphones to capture noise signals from different positions, creating redundant copies of the noise information. These multiple measurements are then processed through adaptive filtering to reconstruct the noise signal, replacing the need for an expensive acceleration sensor while maintaining detection accuracy

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent replaces the mechanical vibration sensing approach (acceleration sensor) with an acoustic field approach (microphones). By using sound pressure measurements and acoustic signal processing, the system achieves the same noise detection function through a different physical domain, reducing hardware cost

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Adaptability or versatility

If the acoustic transmission characteristics change, then the adaptability of the system is improved, but the control performance deteriorates

Engineering Contradiction:

Improveacoustic environment adaptabilityVSAvoidcontrol performance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent implements dynamic adaptation by continuously updating the acoustic transmission filter coefficients based on real-time error signals from the microphones. The adaptive filter adjusts its parameters to match changing acoustic conditions, maintaining control performance despite variations in vehicle body aging, window states, or seat positions

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system uses error microphones to continuously monitor the residual noise after active cancellation and feeds this information back to the controller. This feedback loop enables real-time adjustment of the anti-noise signal generation, allowing the system to adapt to changing acoustic transmission characteristics while maintaining effective noise control

Inventive Principle:

Principle #23Feedback

3Reliability

If all acoustic transmission filters are adaptively updated, then the control performance is improved, but the calculation load increases

Engineering Contradiction:

Improvecontrol performanceVSAvoidcalculation load

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent divides the acoustic transmission filtering into multiple independent filter channels, each handling specific frequency ranges or spatial directions. This segmentation allows selective adaptive updating of only certain filters based on current noise conditions, reducing the overall calculation load while maintaining control performance for the most critical frequency components

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system implements partial adaptive updating by selectively adjusting only the most critical acoustic transmission filters that have the greatest impact on noise control performance. Less critical filters are updated less frequently or kept fixed, achieving acceptable control performance with reduced computational effort

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS12236933B2Active noise reduction system, active noise reduction method, and non- transitory computer-readable storage medium

Publication Date: 2025.02.25 HONDA MOTOR CO LTD

AI summary

An active noise reduction system includes a controller configured to acquire a plurality of noise signals output from a plurality of noise microphones, select a plurality of reference signals and an error signal from among the plurality of noise signals, the plurality of reference signals corresponding to a noise, the error signal corresponding to an error between the noise and a canceling sound, generate a control signal from the plurality of reference signals by using a plurality of control filters, and adaptively update the plurality of control filters by using a plurality of acoustic transmission filters. The plurality of acoustic transmission filters includes at least one adaptive update filter configured to be adaptively updated, and at least one non-adaptive update filter configured to be updated based on an update value of the adaptive update filter.