Second-Order Microphone Null for Teleconferencing Feedback
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Solution Overview
Problem
Teleconferencing devices often suffer from noise and feedback issues due to the proximity of microphones and speakers, leading to reduced sound quality, with existing solutions failing to effectively address these problems.
Innovation Solution
The use of a combination of omnidirectional and second-order microphones, where the second-order microphones are positioned to receive frequencies below 4 kHz and the omnidirectional microphones above 4 kHz, with the audio output of the speaker falling within the null of the second microphone to minimize feedback, and a processor to select the best microphone signals for processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single microphone is used for audio pickup, then the device structure is simple, but audio feedback and noise rejection performance are insufficient
Solution Approach 1:
The audio pickup function is segmented between two different microphone types: a first omnidirectional microphone for frequencies above 4kHz and a second second-order microphone for frequencies below 4kHz. This segmentation allows each microphone to be optimized for its specific frequency range, improving overall feedback rejection without requiring a complex array of multiple microphones.
Solution Approach 2:
Different microphones are assigned different directional characteristics tailored to specific frequency ranges. The omnidirectional microphone provides uniform pickup for high frequencies, while the second-order microphone provides directional pickup for low frequencies. This local quality differentiation optimizes performance across the entire audio spectrum.
2Measurement precision
If second-order microphones are used to detect audio signals below a frequency threshold, then low-frequency audio quality is improved, but noise and feedback problems occur
Solution Approach 1:
The patent introduces an intermediary frequency threshold (4kHz) that separates the operational ranges of two microphones. The second-order microphone handles frequencies below this threshold where it excels at directional pickup, while the omnidirectional microphone handles frequencies above this threshold, preventing the second-order microphone from picking up feedback noise.
Solution Approach 2:
The audio frequency spectrum is segmented into two bands: low frequencies (below 4kHz) handled by the second-order microphone with directional characteristics for noise rejection, and high frequencies (above 4kHz) handled by the omnidirectional microphone. This segmentation allows the second-order microphone to operate in its optimal range without encountering feedback problems.
3Reliability
If the speaker audio output is positioned to fall within the null of the second microphone, then feedback is minimized, but the overall audio coverage is reduced
Solution Approach 1:
The system employs different pickup patterns for different frequency ranges: the second-order microphone uses a directional pattern with nulls at specific angles to reject feedback, while the omnidirectional microphone uses a uniform 360-degree pickup pattern to maintain broad audio coverage for high frequencies. This local quality differentiation allows feedback rejection without sacrificing overall coverage.
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 significantly reduces undesirable audio feedback and noise, ensuring clear sound for both near-end and far-end users by effectively filtering different frequency spectrums and enhancing the audio reception quality.
Implementation Method 1
The second-order microphone has a first-order microphone disposed within a first platform mounted a distance from the first mounting position... the audio output of the first speaker falls within a null of the second microphone
Implementation Method 2
using the omnidirectional microphone for frequencies above about four kilohertz to generate a high pass output
Implementation Method 3
summing the high pass output and the low pass output to produce a net output
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
An audio device including a housing having a side facing outwardly of the housing, the housing further having a first mounting position disposed on the side. The side has a first portion and a second portion, the first portion opposite the second portion relative to the first mounting position. The audio device also includes a first omnidirectional microphone disposed on the first portion. The audio device also includes a second microphone disposed on the first mounting position. The second microphone may be a second-order microphone. The second-order microphone has a first-order microphone disposed within a first platform mounted a distance from the first mounting position. The audio device also includes a first speaker disposed on the second portion. The first speaker is further disposed such that an audio output of the first speaker falls within a null of the second microphone.