In-situ Microphone Array Calibration via Rotatable Loudspeaker
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Solution Overview
Problem
Existing microphone array calibration techniques are cumbersome and prone to errors, especially for large arrays like the mh acoustics em64™ Eigenmike®, particularly when embedded in a baffle or rigid structure, and require specialized environments, making in-situ calibration challenging due to scattering, diffraction, and room reflections.
Innovation Solution
A new in-situ calibration method using a discrete set of acoustic measurement responses from a known acoustic source, where a small wideband loudspeaker ensonifies all microphone capsules, allowing for calibration in a standard room environment by processing audio signals to account for variations and mismatches, and using a rotatable base to position the loudspeaker at multiple angles relative to the array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional capsule-only calibration is used in controlled environments, then measurement precision is improved, but device complexity and ease of operation deteriorate due to requiring specialized equipment and environments
Solution Approach 1:
The system uses the microphone array itself to perform calibration by having each microphone listen to signals from other microphones in the array, eliminating the need for external specialized calibration equipment and environments
Solution Approach 2:
The microphone array serves dual purposes: both as the device to be calibrated and as the calibration tool, allowing the same hardware to perform both measurement and calibration functions without requiring separate specialized equipment
2Measurement precision
If in-situ calibration is performed with a calibrator device placed over each microphone capsule, then measurement precision is improved, but ease of operation deteriorates due to being cumbersome for large arrays
Solution Approach 1:
The calibration process merges all microphone measurements into a single system-wide operation rather than requiring individual calibration of each microphone capsule, making the process scalable to large arrays
Solution Approach 2:
The microphone array calibrates itself by having each microphone listen to signals from other microphones in the array, eliminating the need for manual placement of calibrator devices over each capsule
3Measurement precision
If in-situ calibration is performed with a calibrator device, then measurement precision is improved, but reliability deteriorates due to potential leaks when not properly sealed
Solution Approach 1:
The system eliminates the need for physical sealing by having microphones listen to acoustic signals through the air medium, removing the source of potential leaks and sealing errors
Solution Approach 2:
Acoustic signals serve as an intermediary that can be reliably transmitted through air without requiring physical contact or sealing, replacing the need for mechanical coupling between calibrator and microphone
4Manufacturing precision
If microphone capsules are pre-selected for matching, then manufacturing precision is improved, but adaptability deteriorates due to loss of flexibility from calibration weights or filters
Solution Approach 1:
The system determines optimal calibration parameters (weights and filters) through measurement and processing, allowing adaptation to different microphone characteristics and environments rather than relying on fixed pre-matching
Solution Approach 2:
The calibration process uses measured audio signals from the microphone array to compute and apply calibration weights, creating a feedback loop that optimizes performance based on actual array behavior rather than theoretical matching
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 method enables accurate and efficient calibration of microphone arrays in various environments, reducing errors and complexity, by accounting for scattering, diffraction, and room reflections, and maintaining calibration over time with software-updatable filters.
Implementation Method 1
a small wideband loudspeaker ensonifies all microphone capsules
Implementation Method 2
accounting for scattering, diffraction, and room reflections
Implementation Method 3
accounting for scattering, diffraction, and room reflections
Data Source
AI summary
According to certain embodiments, a microphone array having a plurality of microphone elements is calibrated by ensonifying the microphone array at a first direction relative to the microphone array with a first acoustic signal to concurrently generate a first set of audio signals from two or more of the microphone elements and processing the first set of audio signals to calibrate the two or more microphone elements. One or more other sets of audio signals can be generated by ensonifying the microphone array with one or more other acoustic signals at one or more other directions relative to the microphone array, where the two or more microphone elements are calibrated using the first set and the one or more other sets of audio signals. The calibration process can be performed outside of an anechoic chamber using one or more acoustic sources located outside or inside the microphone array.