Omnidirectional Microphone Array for Directional Sound Capture
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Solution Overview
Problem
Spherical microphone arrays face limitations in accurately capturing sound fields due to low-frequency noise amplification and high-frequency spatial aliasing issues, particularly when using directional microphones, which are bulkier and require closer spacing, leading to dimensional challenges and reduced usable frequency ranges.
Innovation Solution
A sound capture system employing a combination of omnidirectional microphones arranged in a hexahedron structure on an open sphere and a rigid sphere, with signal couplers to create directional responses, allowing for a broader frequency range by optimizing microphone placement and using omnidirectional microphones to form virtual directional microphones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If directional microphones are used to improve directional performance, then directional sensitivity is improved, but the microphone size increases and spacing requirements create dimensional challenges
Solution Approach 1:
The directional microphone is segmented into two separate omnidirectional microphones positioned at different distances from the center of the sphere. This segmentation allows the system to achieve directional sensitivity through spatial arrangement rather than using a single bulky directional microphone element.
Solution Approach 2:
Omnidirectional microphones serve multiple functions: they capture sound from all directions and, when combined through signal processing, create virtual directional microphones. This multi-functionality eliminates the need for separate directional microphone elements.
2Measurement precision
If microphones are moved closer to the center to maintain directional performance at high frequencies, then directional performance is improved, but the gap between adjacent microphones decreases causing them to touch
Solution Approach 1:
The solution moves from a two-dimensional surface arrangement to a three-dimensional volumetric arrangement by placing microphones at different radial distances from the center. This allows adequate spacing while maintaining the directional performance benefits of closer positioning.
Solution Approach 2:
The microphone array is nested within a spherical volume rather than being constrained to a spherical surface. This nesting approach allows microphones to be positioned at different radii, creating space for all elements without requiring them to be tightly packed on a two-dimensional surface.
3Stability of the object's composition
If a rigid sphere configuration is used to provide robust numerical formulation, then numerical stability is improved, but the system is less desirable for low frequency applications where large spheres are needed
Solution Approach 1:
The system changes the key parameter from sphere rigidity to microphone positional distribution. By optimizing the radial positions and angular distribution of omnidirectional microphones, the system achieves both numerical stability and broad frequency adaptability without being constrained by rigid sphere requirements.
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 enhances the system's ability to capture sound across a wider frequency range without significant artifacts, improving directional performance and reducing noise, while avoiding the dimensional issues associated with directional microphones.
Implementation Method 1
microphones equally distributed over the surface of a solid or virtual sphere for converting sounds into electrical audio signals
Implementation Method 2
a modal beamformer combining the audio signals generated by the microphones to form an auditory scene representative of at least a portion of an acoustic sound field
Data Source
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AI summary
A sound capture system may include a first number of first omnidirectional microphones that provide first output signals with an omnidirectional response pattern and that are disposed at different positions in a first equidistance from a point of symmetry. The sound capture system may further include a second number of second omnidirectional microphones that provide second output signals with an omnidirectional response pattern and that are disposed at different positions in a second equidistance from the point of symmetry, and an evaluation circuit that is configured to receive the first output signals and the second output signals, and to superimpose the first and second output signals of pairs of omnidirectional microphones for producing, in response thereto, third output signals with an directional response pattern. The second number is a multiple of two and the first equidistance is smaller than the second equidistance. Each of the second omnidirectional microphones forms with another of the second omnidirectional microphones a pair of second microphones, the microphones of a pair of second microphones being disposed in line with each other and the point of symmetry.