Active Noise Reduction Device Using Segmented Adaptive Filters

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Solution Overview

Problem

Existing active noise reduction devices face challenges in effectively reducing noise when the frequency shifts by 1 Hz from the assumed frequency and are costly for broadband noise reduction, requiring advanced sensors and digital signal processors.

Innovation Solution

An active noise reduction device utilizing the SAN filtered-x LMS algorithm, comprising multiple adaptive filters, feedback filters, adders, band elimination filters, and gain adjusters, which outputs cancellation sound by updating filter coefficients based on error signals to reduce broadband noise while minimizing the waterbed effect.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional active noise reduction devices are used, then narrowband noise at a specific frequency can be reduced, but the noise reduction effectiveness deteriorates when the frequency shifts by 1 Hz from the assumed frequency

Engineering Contradiction:

Improvefrequency accuracyVSAvoidfrequency range adaptability

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent divides the noise reduction task into multiple parallel channels, each handling a specific frequency band. Instead of using a single adaptive filter for the entire frequency spectrum, the system segments the frequency range and processes each segment independently, allowing precise control at each frequency while maintaining overall adaptability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements dynamic frequency tracking by continuously updating the center frequencies of the bandpass filters based on the actual noise characteristics. This dynamic adjustment allows the system to adapt to frequency shifts in real-time, maintaining effective noise reduction even when the assumed frequency changes.

Inventive Principle:

Principle #15Dynamics

2Reliability

If advanced sensors and digital signal processors are used for broadband noise reduction, then noise reduction effectiveness is improved, but device cost increases

Engineering Contradiction:

Improvebroadband noise reduction effectivenessVSAvoiddevice cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent makes existing audio components (loudspeakers and microphones) serve dual purposes: their primary function for audio playback and recording, and a secondary function as actuators and sensors for active noise reduction. This eliminates the need for separate advanced sensors and processors, reducing device cost while maintaining broadband noise reduction effectiveness.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The system uses the device's own audio components to perform noise reduction without requiring external specialized equipment. The loudspeakers generate cancellation sounds and the microphones detect error signals, allowing the system to self-service the noise reduction function using existing infrastructure.

Inventive Principle:

Principle #25Self-service

3Adaptability or versatility

If multiple adaptive filters are used to broaden noise reduction frequency range, then frequency range coverage is improved, but filter coefficient overload occurs

Engineering Contradiction:

Improvenoise reduction frequency rangeVSAvoidfilter coefficient stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent segments the frequency spectrum into multiple bands, with each adaptive filter responsible for a specific segment. This segmentation prevents coefficient overload by limiting each filter to a manageable frequency range, while the collective coverage of all filters provides broad frequency range noise reduction.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies feedback filters that multiply cancellation signals by gain coefficients less than 1, intentionally using partial action to prevent over-correction. This approach stabilizes filter coefficients by avoiding excessive adjustments, ensuring reliable operation across the extended frequency range.

Inventive Principle:

Principle #16Partial or excessive action

4Reliability

If feedback filters with gain coefficients are introduced, then filter coefficient stability is improved, but system complexity increases

Engineering Contradiction:

Improvefilter coefficient stabilityVSAvoidsignal processing structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the feedback filter functionality into the existing adaptive filter structure. Rather than adding completely separate feedback loops, the system integrates gain adjustment and feedback mechanisms within the adaptive filter framework, maintaining coefficient stability while minimizing structural complexity.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS20250006171A1Active noise reduction device and mobile object

Publication Date: 2025.01.02 PANASONIC AUTOMOTIVE SYST CO LTD

AI summary

An active noise reduction device includes: a plurality of first adaptive filters; a plurality of feedback filters; an adder that adds a cancellation signal outputted by each of the plurality of first adaptive filters, and outputs a cancellation signal resulting from the addition; and a band elimination filter that is disposed in at least one of a first path from each of the plurality of first adaptive filters to a loudspeaker or a second path from a microphone to each of the plurality of first adaptive filters.