Microphone Array Acoustic Element for Wideband Alias Mitigation

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Solution Overview

Problem

Microphone arrays face challenges in capturing wideband acoustic signals over 20 KHz without causing spatial aliasing, requiring a large number of microphones that are not practically feasible in small form-factor devices, and achieving the right balance between bandwidth and directionality for applications like virtual reality.

Innovation Solution

Incorporating passive directional acoustic elements with elongated openings covered by acoustically resistive materials between microphones in an array, allowing for effective beamforming and reducing spatial aliasing while maintaining a limited number of microphones, thus achieving a target sensitivity pattern.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a large number of microphones with close spacing are used to capture wideband acoustic signals, then the bandwidth is improved, but the device complexity increases and spatial aliasing occurs

Engineering Contradiction:

ImprovebandwidthVSAvoidnumber of microphones

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

A passive directional acoustic element is introduced as an intermediary component between microphones. This element includes a pipe with an elongated opening covered by acoustically resistive material, which modifies the acoustic field before it reaches the microphones, enabling wideband capture with fewer sensors by mitigating spatial aliasing effects

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

Acoustically resistive material (a porous material) is used to cover the elongated opening of the pipe. This porous structure allows selective acoustic transmission while suppressing spatial aliasing, enabling the system to capture wideband signals with reduced microphone count

Inventive Principle:

Principle #31Porous materials

2Object-affected harmful factors

If microphones are spaced closely to reduce spatial aliasing, then spatial aliasing is reduced, but the device complexity and form factor increase

Engineering Contradiction:

Improvespatial aliasingVSAvoidmicrophone spacing

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The passive directional acoustic element serves as a mediator that actively suppresses spatial aliasing effects. By placing this element between microphones, the system can maintain larger microphone spacing while still preventing spatial aliasing, thus reducing device complexity and enabling smaller form factors

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If passive directional acoustic elements are added between microphones, then spatial aliasing is mitigated and bandwidth is improved, but the device complexity increases

Engineering Contradiction:

Improvespatial aliasing mitigationVSAvoidacoustic element structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The use of acoustically resistive porous material provides an effective solution for mitigating spatial aliasing. The porous structure naturally filters and diffuses acoustic waves, reducing spatial aliasing effects without requiring complex active electronic components or sophisticated signal processing hardware

Inventive Principle:

Principle #31Porous materials

Solution Approach 2:

The passive directional acoustic element uses simple, inexpensive materials such as porous foam or fabric for the acoustically resistive covering. These are passive, static components that require no power or active control, reducing overall system complexity while effectively mitigating spatial aliasing

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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

Enables high-fidelity wideband audio capture with reduced spatial aliasing and appropriate directionality, suitable for small form-factor devices such as VR applications, by using a smaller number of microphones and passive directional acoustic elements.

Implementation Method 1

an acoustically resistive material covering at least a portion of the elongated opening

Methodology Applied

Scientific EffectAcoustic absorption: Acoustic Absorption

Data Source

PatentUS10299038B2Capturing wide-band audio using microphone arrays and passive directional acoustic elements

Publication Date: 2019.05.21 BOSE CORP

AI summary

The technology described in this document can be embodied in an apparatus that includes an array of multiple microphones, and a passive directional acoustic element disposed between at least two of the multiple microphones. The passive directional acoustic element includes a pipe having an elongated opening along at least a portion of the length of the pipe, and an acoustically resistive material covering at least a portion of the elongated opening. One or more structural characteristics of the passive acoustic element is configured for capturing a target frequency range in accordance with a target beam pattern associated with the array.