Microphone Unit Null Point Detection via Asymmetric Acoustic Paths
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Solution Overview
Problem
Conventional differential type microphone units experience reduced voice quality when the talker's mouth is positioned at a null point, leading to unrecognizable voice due to significant sound level reduction, as they cancel sound waves equally in phase and amplitude on both surfaces of the vibratory diaphragm, resulting in zero detection output.
Innovation Solution
A microphone unit with a housing having first and second openings and a vibratory diaphragm, where a time difference generating means creates a difference in sound propagation time between the two openings, positioning the null point such that the distances to each opening are different, ensuring non-zero sound pressure differences and thus detection of sound from the null point, while maintaining far-field noise reduction characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If sound propagation time from first opening to front surface of vibratory diaphragm is made equal to that from second opening to rear surface, then far-field noise reduction is achieved, but detection sensitivity to sound from null point becomes zero
Solution Approach 1:
The patent introduces asymmetry by making the sound propagation path lengths unequal - specifically, the sound propagation path from the first opening to the front surface of the vibratory diaphragm is made longer than the path from the second opening to the rear surface. This asymmetric design prevents complete destructive interference at null points while preserving far-field noise reduction capabilities through differential pressure detection.
Solution Approach 2:
The patent changes the parameter of sound propagation time by introducing a time difference between the two paths. By controlling the path length difference, the patent optimizes the balance between noise reduction and detection sensitivity, ensuring that sounds from null points are not completely cancelled while maintaining the bi-directional characteristics for far-field noise rejection.
2Object-affected harmful factors
If differential type microphone structure with equal path lengths is used, then bi-directional characteristics and far-field noise reduction are achieved, but voice quality deteriorates when talker is positioned at null point
Solution Approach 1:
The patent applies asymmetry by designing unequal sound propagation paths, which eliminates the complete null points that cause voice quality deterioration. The asymmetric path lengths ensure that even when a talker is positioned at what would traditionally be a null point, some sound pressure difference remains, preventing total signal cancellation and maintaining reliable voice detection.
3Device complexity
If equal sound propagation paths are designed, then simplified structure is achieved, but angular range of effective sensitivity is reduced due to null point formation
Solution Approach 1:
The patent introduces asymmetry in the sound propagation paths to eliminate sharp null points, thereby expanding the angular range over which the microphone effectively detects sound. This asymmetric design trades slight structural complexity for significantly improved angular coverage and adaptability to different talker positions.
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 design increases detection sensitivity to sound from the null point, minimizes voice level reduction, and expands the angular range of effective sensitivity, ensuring good voice quality, particularly in mobile phone applications.
Implementation Method 1
a vibratory diaphragm for detecting sound is known in which sound is guided to front and rear surfaces of the vibratory diaphragm so as to detect the sound by the vibration of the vibratory diaphragm due to a difference between sound pressures on the front and rear surfaces
Implementation Method 2
time difference generating means for generating a difference in time between sound propagation time from the first opening to the front surface of the vibratory diaphragm and sound propagation time from the second opening to the rear surface of the vibratory diaphragm
Data Source
AI summary
A microphone unit comprises a vibratory diaphragm for detecting sound input through its first and second openings. The sound input through the first opening is guided to a front surface of the vibratory diaphragm while the sound input through the second opening is guided to a rear surface of the vibratory diaphragm so as to detect the sound by the vibration of the vibratory diaphragm. The microphone unit satisfies relation 0.76≦D/Δr≦2.0 where D is difference in time between the sound propagation time from the first opening to the front surface of the vibratory diaphragm and that from the second opening to the rear surface of the vibratory diaphragm, while Δr is distance between the first and second openings. The relation D/Δr≦2.0 can reduce far-field noise, while the relation 0.76≦D/Δr can increase the detection sensitivity to sound emitted from a null point.