Diffracting Microphone Array for Extended Frequency Range
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Solution Overview
Problem
Conventional microphone arrays face limitations in directivity at higher frequencies due to restricted inter-microphone spacing, leading to decreased beamwidth and increased side lobes, which result in signal degradation when speakers are off-axis, and are costly to construct or require additional microphones to maintain low-frequency directivity.
Innovation Solution
A microphone array design incorporating a diffraction structure with acoustically absorptive materials and digital signal processing for beamforming, allowing microphones to be spaced greater than half the acoustic wavelength, thereby extending the frequency range and maintaining constant directivity without altering the array's geometry or number of microphones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If inter-microphone spacing is increased beyond half the shortest wavelength, then frequency range is extended, but spatial aliasing and grating lobes occur causing signal degradation
Solution Approach 1:
A diffracting structure is introduced as an intermediary element between the microphones and the acoustic field. This structure diffracts incoming acoustic waves in a controlled manner, enabling the microphones to be spaced beyond the traditional half-wavelength limit while preventing spatial aliasing and grating lobes. The diffracting structure mediates the interaction between the acoustic field and the microphone array, allowing extended frequency range without signal degradation.
2Reliability
If inter-microphone spacing is restricted to half the shortest wavelength, then spatial aliasing is avoided, but frequency range is limited and array size must be reduced
Solution Approach 1:
The diffracting structure serves as a mediator that allows the system to overcome the traditional spacing limitation. By placing this structure in the acoustic path, the system can maintain reliable signal quality while extending the operational frequency range beyond what would be possible with conventional spacing restrictions.
3Adaptability or versatility
If array size is reduced to maintain low frequency directivity, then low frequency performance is maintained, but high frequency directivity decreases and side lobes increase
Solution Approach 1:
The diffracting structure mediates the acoustic field interactions at high frequencies, enabling the compact array to maintain both low frequency directivity and high frequency signal quality that would otherwise be mutually exclusive.
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 approach effectively extends the frequency range of microphone arrays beyond traditional limits, reducing costs by enabling the use of omnidirectional microphones and inexpensive digital signal processing, while maintaining consistent beam patterns and reducing grating lobes, thus improving signal quality and reducing signal degradation from off-axis speakers.
Implementation Method 1
a diffracting structure that provides the desired directivity at high frequencies
Implementation Method 2
acoustically absorptive materials and digital signal processing for beamforming
Data Source
AI summary
A conferencing unit, comprising an array of microphones embedded in a diffracting object configured to provide a desired high frequency directivity response at predetermined microphone positions, and a low frequency beamformer operable to achieve a desired low frequency directivity response, wherein the beamformer is linearly constrained to provide a smooth transition between low and high frequency directivity responses.