Vehicle Microphone Noise Cancellation via Phase Inversion

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Solution Overview

Problem

Conventional microphones in vehicles face challenges in providing consistent hands-free performance and voice recognition accuracy due to ambient noise, particularly in dynamic environments like cars, where noise levels fluctuate and the microphone position is variable, leading to issues with signal-to-noise ratio and feedback.

Innovation Solution

A microphone system with multiple transducers and a remote processing circuit, including a phase inverter and impedance matching circuit, is used to improve signal quality by canceling line-induced noise and enhancing directional sensitivity, while also incorporating acoustic ports and windscreens to reduce noise interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the microphone is mounted near the driver's head to improve hands-free performance, then the speech signal quality is improved, but the microphone detects more ambient noise and the position is difficult to control

Engineering Contradiction:

Improvespeech signal qualityVSAvoidambient noise

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent divides the microphone system into two separate transducers: a first transducer positioned to primarily receive speech signals and a second transducer positioned to primarily receive ambient noise. This segmentation allows each transducer to be optimized for its specific function, with the speech transducer capturing clear voice signals and the noise transducer capturing ambient disturbances, which are then processed separately to improve overall signal quality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a noise cancellation circuit as an intermediary component that processes signals from both transducers. This circuit acts as a mediator by taking the speech signal from the first transducer and subtracting the noise component captured by the second transducer, thereby producing a cleaned speech output that removes ambient noise while preserving the original speech quality.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If the microphone wire is mounted on the surface of the vehicle interior, then installation is simple, but the appearance is not aesthetically pleasing

Engineering Contradiction:

Improveinstallation simplicityVSAvoidaesthetic appearance

Core Design Contradiction:

Ease of manufactureVSShape

Solution Approach 1:

The patent utilizes the vehicle's existing interior trim panels and surfaces as flexible mounting substrates. The microphone system is designed to be integrated into these existing structures, allowing the wiring and components to be concealed within or behind the trim panels while maintaining easy installation through snap-fit or adhesive mounting methods that don't require complex disassembly.

Inventive Principle:

Principle #30Flexible shells and thin films

3Adaptability or versatility

If the microphone position is made variable to improve adaptability, then user flexibility is improved, but the signal-to-noise ratio becomes unpredictable

Engineering Contradiction:

Improvemicrophone placement flexibilityVSAvoidsignal-to-noise ratio

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent implements an adjustable microphone mounting mechanism that allows the microphone position to be dynamically changed by the user. The system includes a movable mount with adjustment features that enable repositioning along specified trajectories or angles, providing adaptability for different user preferences while maintaining predictable acoustic characteristics through controlled movement paths.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent incorporates signal quality feedback mechanisms that monitor the speech signal-to-noise ratio and provide information to the user about optimal microphone positioning. This feedback loop allows users to adjust the microphone position while receiving real-time guidance on how positioning affects signal quality, enabling them to achieve both adaptability and consistent performance.

Inventive Principle:

Principle #23Feedback

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

The system achieves improved signal-to-noise ratio and directional sensitivity, enhancing hands-free communication and voice recognition performance even in noisy conditions by effectively canceling noise and improving microphone placement flexibility.

Implementation Method 1

a phase inverter circuit provided proximate the second transducer for inverting the phase of the second audio signal

Methodology Applied

Scientific EffectPhase inversion:

Implementation Method 2

incorporating acoustic ports and windscreens to reduce noise interference

Methodology Applied

Scientific EffectAcoustic filtering: Filter (physical)

Data Source

PatentUS7616768B2Vehicle accessory microphone having mechanism for reducing line-induced noise

Publication Date: 2009.11.10 GENTEX CORP

AI summary

A microphone assembly includes one or more transducers positioned in one or more housings. A processing circuit is coupled to the transducer for outputting an electrical signal such that the microphone in combination with the processing circuit very effectively cancels noise. The microphone assembly can be employed in a vehicle accessory.