Acoustic Apparatus Phase-Shifted Microphone Array Noise Cancellation
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Solution Overview
Problem
Existing audio conference apparatuses with multiple directional microphones suffer from high noise levels due to diffraction and harsh sound collection from sources at equal distances, leading to unwanted noise pickup from equipment like air-conditioning systems.
Innovation Solution
The apparatus features a circular arrangement of sound collection sections with phase-shifted sound signals from microphone arrays, combined to cancel out sounds from equidistant positions while focusing on directivity and incorporating an adaptive echo canceller to suppress echo.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple directional microphones are arranged to collect sounds from all directions, then sound collection coverage is improved, but noise from equidistant sources (e.g., air-conditioning equipment) is collected at high levels
Solution Approach 1:
The patent applies asymmetry by introducing phase shifts that are asymmetric with respect to the sound source position. Sounds from equidistant positions undergo different phase shifts depending on their angular position, causing destructive interference for overhead noise while preserving sounds from conference participants. This asymmetric phase manipulation resolves the contradiction by selectively canceling unwanted noise while maintaining useful sound collection coverage.
Solution Approach 2:
The patent changes the phase parameter of sound signals based on the angular position of sound collection sections. By applying position-dependent phase shifts to sounds collected from different directions, the system transforms the uniform noise field from overhead sources into canceled signals, while preserving directional sounds from conference participants. This parameter change resolves the contradiction between comprehensive sound collection and noise rejection.
2Volume of moving object
If the apparatus is miniaturized by omitting the speaker case, then device size is reduced, but diffraction sound volume increases
Solution Approach 1:
The patent converts the harmful diffraction effect into a beneficial feature by using the diffracted sounds as additional sound collection paths. The phase shift processing is designed to accommodate and utilize diffraction patterns, transforming what would normally be degraded sound quality into enhanced sound collection capability. This resolves the contradiction by making the miniaturization-induced diffraction effect work in favor of the system rather than against it.
3Adaptability or versatility
If sounds from all directions are collected with equal gain, then omnidirectional sound collection is achieved, but sounds from particular regions become excessively large in level
Solution Approach 1:
The patent applies local quality by assigning different phase shift characteristics to sound collection sections based on their angular positions. Instead of uniform processing, each section's output is processed with phase shifts tailored to its position, creating locally optimized sound collection that collectively achieves global noise cancellation. This resolves the contradiction by making the processing quality position-dependent rather than uniform.
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 effectively reduces noise levels from equidistant sources and minimizes echo, providing a stable sound collection environment by canceling out unwanted noise and maintaining high sound levels from relevant directions.
Implementation Method 1
a sound signal processing section that delays a phase of a sound signal output from each of the sound collection sections by an angle on the circumference at an installation position of each of the sound collection sections
Implementation Method 2
sounds emitted at positions (axis direction) extending toward an upper face and a lower face from a center position of a case are collected with substantially the same level by all the sound collection sections, but are combined after phase shifts. As a result, the sounds are canceled.
Data Source
AI summary
An acoustic apparatus without increasing noise etc. even when plural directional microphones collect sounds from a place of the same distances is provided. Sound signals output from the microphone arrays are subjected to phase shift by phase shift circuits 211A to 211H, and the sound signals are combined by an adder 212. The phase shift circuits 211A to 211H performs phase shifts according to installation positions of the microphone arrays. The phase shift circuit 211A makes the shift 0 degree, the phase shift circuit 211B makes the shift 45 degrees, the phase shift circuit 211C makes the shift 90 degrees, and sequentially to the phase shift circuit 211H, the shifts are made according to rotational angles.