Directional Microphone Amplitude-Based Directivity Control
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Solution Overview
Problem
Conventional directional microphone devices using sound-pressure gradient type directivity synthesis face challenges with decreased sound pressure sensitivity and increased thermal noise, limiting miniaturization and directional characteristics, especially at low frequencies.
Innovation Solution
The directional microphone device controls directivity based on signal amplitude ranges, making small amplitude ranges non-directional for high sensitivity and large amplitude ranges directional, using multiple microphones with varying directivity and sensitivity characteristics, and employing noise suppression and whitening filters to manage thermal noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If directivity synthesis is performed using sound-pressure gradient type method, then directional characteristics are improved, but sound pressure sensitivity decreases and thermal noise increases
Solution Approach 1:
The patent dynamically switches between two directivity synthesis methods (sound-pressure gradient type and sound-pressure type) based on frequency conditions. At low frequencies where thermal noise is problematic, the sound-pressure type is used to maintain sensitivity. At high frequencies where directional characteristics are more critical, the sound-pressure gradient type is applied. This dynamic selection resolves the contradiction by adapting the synthesis method to operational conditions.
Solution Approach 2:
The patent changes the synthesis parameter (type of directivity synthesis) based on frequency. By switching between sound-pressure gradient type and sound-pressure type synthesis depending on the frequency range, the system optimizes both directional characteristics and sensitivity across different operating conditions, preventing thermal noise degradation while maintaining directional performance.
2Measurement precision
If directivity synthesis is performed using sound-pressure gradient type method, then directional characteristics are improved, but device miniaturization is limited due to increased thermal noise
Solution Approach 1:
The system dynamically selects the appropriate synthesis method based on frequency requirements. For applications requiring miniaturization where low-frequency sensitivity is critical, the sound-pressure type is used. For applications prioritizing directional characteristics at high frequencies, the sound-pressure gradient type is applied. This enables flexible device design without being constrained by thermal noise limitations across all frequency ranges.
Solution Approach 2:
By changing the synthesis type parameter based on frequency, the patent enables miniaturization in frequency ranges where sound-pressure type synthesis is used, while still achieving directional characteristics where sound-pressure gradient type is applied. This parameter switching allows compact device design without sacrificing directional performance in critical frequency bands.
3Measurement precision
If signals are synthesized from multiple microphone units, then directional characteristics are improved, but signal to noise ratio deteriorates due to thermal noise accumulation
Solution Approach 1:
The patent changes the synthesis parameter (type of directivity synthesis) based on frequency conditions. At low frequencies where thermal noise from multiple microphones degrades S/N ratio, the sound-pressure type is used which maintains better sensitivity. At high frequencies where directional characteristics are more important and thermal noise impact is reduced, the sound-pressure gradient type is applied. This parameter switching preserves signal quality while achieving directional performance.
Solution Approach 2:
The system dynamically adjusts the synthesis method based on frequency-dependent thermal noise characteristics. By switching between synthesis types, the system optimizes the balance between directional characteristics and S/N ratio, preventing thermal noise accumulation from degrading signal quality in critical low-frequency ranges.
Data Source
AI summary
The directional microphone device according to the present invention solves a problem of increase in thermal noise (problem of decrease in sensitivity) that occurs at the time of directivity synthesis. The directional microphone device includes: a plurality of microphones which have directional and non-directional characteristics; a control unit which generates an output signal using signals outputted from each of the plurality of microphones; and an output unit which outputs the output signal generated by the control unit. The control unit generates the output signal such that a nearly non-directional directivity and a high sensitivity are obtained in small amplitude range of the output signal, and a directivity and a low sensitivity are obtained in large amplitude range of the output signal.