Reflection Cancelling Boundary Microphones for Feedback Control

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Solution Overview

Problem

Conventional microphones used in acoustic instruments face challenges such as feedback and undesirable resonances when placed internally, limiting their effectiveness in capturing high-fidelity sound.

Innovation Solution

Reflection cancelling boundary microphones are designed to be positioned within the pressure zone of a vibrating surface, tuned to cancel pressure waves reflected by the surface while admitting waves generated by the surface, allowing for the differentiation between direct and reflected sound pressure, thereby eliminating internal reflections and mimicking external microphone responses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional microphones are placed internally in acoustic instruments, then sound capture is enabled, but feedback and undesirable resonances occur

Engineering Contradiction:

Improvesound capture fidelityVSAvoidfeedback and resonances

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies noise cancellation technology to convert the harmful reflected sound waves into beneficial effects. The microphone capsule is positioned to receive both direct sound and reflected sound, and through noise cancellation processing, the reflected sound is subtracted from the direct sound, thereby eliminating feedback and resonances while maintaining high-fidelity sound capture.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent uses feedback mechanisms in the form of noise cancellation processing. The system continuously monitors the reflected sound waves and adjusts the signal processing to subtract these reflections from the direct sound signal, creating a feedback loop that actively eliminates harmful resonances and feedback while preserving the desired acoustic characteristics.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If microphones are used inside acoustic instruments, then sound recording is enabled, but the microphone must be used sparingly to avoid feedback

Engineering Contradiction:

Improvesound recording capabilityVSAvoidmicrophone usage intensity

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent converts the previously harmful reflected sound waves into beneficial information by using noise cancellation technology. The reflected sound, which previously caused feedback and limited microphone usage, is now processed to subtract from the direct sound, enabling continuous and intensive microphone usage without feedback problems.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent replaces the mechanical limitation of physical microphone placement with electronic signal processing. Instead of physically positioning the microphone to avoid reflections (which limited usage intensity), the system uses electronic noise cancellation to eliminate reflections digitally, allowing the microphone to be used continuously at high intensity without feedback.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If boundary microphones are used to capture ambient sound, then room sound monitoring is achieved, but internal reflections overwhelm the signal

Engineering Contradiction:

Improveambient sound captureVSAvoidinternal reflections

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent applies noise cancellation technology to convert the overwhelming internal reflections into beneficial effects. By positioning the microphone capsule to receive both direct and reflected sound, and then using noise cancellation processing to subtract the reflected sound component, the system eliminates the harmful reflections while preserving the ambient sound capture capability.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent introduces noise cancellation processing as an intermediary between the microphone capsule and the final audio signal. This intermediary process separates the direct sound signal from the reflected sound, allowing the system to capture ambient sound while eliminating the overwhelming internal reflections that would otherwise dominate the signal.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 solution effectively reduces internal reflections, allowing for high-fidelity sound capture similar to external microphones, while combining with pickups to enhance sound quality and reduce feedback issues.

Implementation Method 1

the microphone is tuned to cancel pressure waves reflected by the surface while admitting pressure waves generated by the vibration of the surface

Methodology Applied

Scientific EffectAcoustic interference: Interference

Implementation Method 2

differentiate between direct and reflected sound pressure

Methodology Applied

Scientific EffectSound pressure: Sound

Data Source

PatentUS8989399B2Reflection cancelling boundary microphones and amplification systems incorporating reflection cancelling boundary microphones

Publication Date: 2015.03.24 LLOYD BAGGS INNOVATIONS LLC

AI summary

Reflection cancelling boundary microphones are described in which a microphone capsule is mounted within the pressure zone of a vibrating surface and the microphone is tuned in such a way as to cancel pressure waves reflected by the surface while admitting pressure waves generated by the vibration of the surface. One embodiment of the invention includes a microphone capsule configured to be mounted within the pressure zone of a vibrating surface. In addition, the microphone is tuned to cancel pressure waves reflected by the surface while admitting pressure waves generated by the vibration of the surface.