Microphone Arrays with Nonconcentric Rings for Directivity
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Solution Overview
Problem
Existing microphone arrays face challenges in achieving high directivity in the horizontal plane without emphasizing high frequencies from other directions and are susceptible to cavity resonance effects, especially when trying to synthesize second-order or higher directivity while maintaining high audio quality over a wide frequency range.
Innovation Solution
A compact sound capture device featuring two nonconcentric rings of directional microphone capsules, each ring oriented at an angle of at least 70 degrees relative to a reference axis, with each capsule having intrinsic pressure and velocity sensitivity, and tilted to reduce cavity resonance effects, allowing for coherent matrix processing to derive Ambisonic signals with high signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spherical arrays with second-order or higher directivity are used, then directional resolution is improved, but high-frequency response from other directions is excessively emphasized
Solution Approach 1:
The array is segmented into multiple rings of capsules at different orientations rather than using a single spherical configuration. This segmentation allows independent control of directional responses and reduces unwanted high-frequency emphasis while maintaining directional resolution.
Solution Approach 2:
Different rings of capsules are assigned different orientations and weighting factors to optimize local directional responses. This local quality approach allows the array to achieve high directional resolution in specific planes while controlling high-frequency response characteristics.
2Measurement precision
If outward-pointing directional capsules are used, then directivity is improved, but cavity resonance effects increase
Solution Approach 1:
The array uses asymmetric orientations of capsule rings rather than symmetric outward-pointing configurations. This asymmetry disrupts the formation of cavity resonances while maintaining the directivity benefits of directional capsules.
Solution Approach 2:
Instead of having all capsules point outward from a central cavity, the invention uses capsules oriented in various directions including inward-pointing and tangential orientations in different rings, effectively inverting the traditional outward-pointing approach to eliminate cavity resonance.
3Measurement precision
If closely spaced directional capsules are used, then directivity order is improved, but cavity resonance susceptibility increases
Solution Approach 1:
The invention transitions from a two-dimensional planar array to a three-dimensional multi-ring structure with capsules oriented in different spatial dimensions. This dimensional change allows closely spaced capsules to be arranged in a way that achieves high directivity order while minimizing cavity resonance through varied orientation angles.
Data Source
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AI summary
A compact multi-element microphone has two rings of directional sensors. Using simple analog electronics, it delivers first-order outputs with low noise, wide bandwidth and tight transient response. The double-ring structure provides exceptionally high directional fidelity in the horizontal plane, while also keeping out- of-plane behaviour under control. This enables faithful capture of ambience, reflections and reverberation. A non-radial capsule arrangement moderates cavity resonances and reduces shading. Combined with digital electronics, the array can efficiently provide second-order and higher-order horizontal directivities that maintain their performance over a wider frequency range than with prior solutions. Outputs can be mono, two-channel stereo and multichannel surround sound. Applications include 360-degree immersive audio, with-height concert hall recording, and advanced voice capture using electronic steering of beams and nulls.