Active Noise Cancellation Reference Microphone Directivity

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Solution Overview

Problem

In conventional active noise suppression systems, bringing the reference microphone and error microphone close together leads to howling and unstable operation, resulting in deteriorated noise suppression performance.

Innovation Solution

A cancellation device with a sound signal processing unit that generates a cancellation signal based on sound signals from error microphones, and reference microphones with directivity disposed near the cancellation loudspeakers, which reduces the input of suppression sound to the reference microphone.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the reference microphone and error microphone are brought close together, then the noise suppression amount increases and the suppression noise band widens, but howling occurs and stable operation cannot be achieved

Engineering Contradiction:

Improvenoise suppression performanceVSAvoidstable operation

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The reference microphone is designed with directivity characteristics that are optimized for its specific location near the cancellation loudspeaker. The directivity pattern is tailored to preferentially receive noise from external directions while rejecting sound from the loudspeaker, allowing the microphone to be placed close to the loudspeaker without causing howling.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

Instead of trying to prevent the reference microphone from receiving cancellation sound through spatial separation, the invention inverts the approach by using directivity to selectively reject the cancellation sound while accepting external noise. The microphone's sensitivity is inverted between different spatial directions.

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If the reference microphone is disposed away from the cancellation loudspeaker, then howling is suppressed and stable operation is achieved, but noise suppression performance deteriorates

Engineering Contradiction:

Improvestable operationVSAvoidnoise suppression performance

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The reference microphone's directivity characteristics are specifically optimized for its local position near the cancellation loudspeaker. The directivity pattern is tailored to match the acoustic environment in this specific location, allowing the microphone to distinguish between external noise and cancellation sound despite the close proximity.

Inventive Principle:

Principle #3Local quality

3Adaptability or versatility

If the reference microphone has omnidirectional characteristics, then it can acquire noise from all directions, but it also receives suppression sound from the cancellation loudspeaker causing howling

Engineering Contradiction:

Improvenoise acquisition capabilityVSAvoidstable operation

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The reference microphone is equipped with directional characteristics that are optimized for its specific installation location near the cancellation loudspeaker. The directivity pattern is tailored to preferentially receive noise from external directions while rejecting sound from the loudspeaker direction, creating a localized optimization for this specific spatial position.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention inverts the omnidirectional approach by using directivity to selectively reject cancellation sound while accepting external noise. Instead of receiving sound equally from all directions, the microphone's sensitivity is inverted between external noise directions and the loudspeaker direction.

Inventive Principle:

Principle #13The other way round (Inversion)

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 configuration enhances noise suppression performance while maintaining stable operation by minimizing howling and improving the suppression of noise across a wider band.

Implementation Method 1

the one or more reference microphones have directivity and are disposed in the vicinity of the cancellation loudspeakers

Methodology Applied

Scientific EffectDirectivity:

Implementation Method 2

active noise suppression (feedforward type) is effective for noise suppression in a wide band

Methodology Applied

Scientific EffectSound wave interference: Interference

Data Source

PatentUS20250046291A1Cancellation apparatus, method and program

Publication Date: 2025.02.06 NT T INC

AI summary

A cancellation device includes a sound signal processing unit 2 that generates a cancellation signal for suppressing noise acquired by one or more reference microphones 1 for acquiring noise, and one or more cancellation loudspeakers 3 that emit sound on the basis of the cancellation signal. The sound signal processing unit 2 generates the cancellation signal on the basis of sound signals obtained by one or more error microphones 4 disposed in a region where noise is desired to be suppressed, and the one or more reference microphones 1 have directivity and are disposed in the vicinity of the cancellation loudspeakers 3.