Active Noise Reduction Microphone Placement for Phase Margin
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Solution Overview
Problem
Active noise reduction headphones face challenges in effectively attenuating frequency response aberrations caused by resonances of acoustic driver components and maintaining phase margin in feedback circuits, leading to instability and limited bandwidth.
Innovation Solution
The implementation of an acoustic driver with a highly damped diaphragm and a voice coil, along with a microphone positioned close to the diaphragm's motion direction, and a compensator with a positive slope frequency response above 10 kHz to reduce time delays and frequency response aberrations, enhancing phase margin and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the microphone is positioned close to the diaphragm (within 2mm) along the force application line, then the phase margin is improved and time delay is reduced, but the microphone may be more susceptible to mechanical vibrations and resonance from the acoustic driver components
Solution Approach 1:
The patent introduces a damping structure as an intermediary element between the acoustic driver components and the microphone. This damping structure acts as a mediator that absorbs and attenuates mechanical vibrations and resonance from the diaphragm and voice coil, preventing these harmful vibrations from directly affecting the microphone while still allowing the microphone to be positioned close to the diaphragm for optimal phase margin and time delay performance.
2Reliability
If the diaphragm is highly damped to reduce resonances, then frequency response aberrations are attenuated, but the acoustic energy radiation efficiency may be reduced
Solution Approach 1:
The patent applies local quality by implementing damping only in specific regions of the diaphragm structure rather than uniformly across the entire diaphragm. The damping is concentrated in areas where resonance occurs, while other areas of the diaphragm maintain their vibration characteristics for effective acoustic energy radiation. This localized damping approach reduces frequency response aberrations while preserving overall acoustic radiation efficiency.
3Measurement precision
If the microphone opening is positioned on the line parallel to the intended direction of motion, then the measurement precision of acoustic pressure is improved, but the microphone is more exposed to direct mechanical force from the voice coil
Solution Approach 1:
The damping structure serves as a protective intermediary between the voice coil and the microphone. It allows the microphone to be positioned on the force application line for optimal acoustic pressure measurement while the damping structure absorbs and attenuates the direct mechanical force from the voice coil, preventing it from reaching and damaging the microphone.
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 improves the phase margin, extends the system's bandwidth, and increases the effective noise reduction capabilities by minimizing time delays and compensating for phase shifts, resulting in enhanced noise cancellation performance.
Implementation Method 1
a voice coil, for applying mechanical force to the diaphragm along a force application line to cause the diaphragm to radiate acoustic energy into the cavity
Implementation Method 2
cause the diaphragm to radiate acoustic energy into the cavity
Implementation Method 3
a microphone enclosed by the cavity for transducing acoustic energy in the cavity to a noise signal
Implementation Method 4
structure for attenuating frequency response aberrations resulting from resonances of components of the acoustic driver. The structure may include a damped diaphragm
Data Source
AI summary
A method and apparatus for increasing phase margin in a feedback circuit of an active noise reduction headphone. The method includes providing an acoustic block comprising an acoustic driver comprising a voice coil mechanically coupled along an attachment line to an acoustic energy radiating diaphragm, the acoustic block further comprising a microphone positioned along a line parallel to an intended direction of vibration of the acoustic diaphragm and intersecting the attachment line, the acoustic block characterized by a magnitude frequency response compensating the magnitude frequency response by a compensation pattern that has a positive slope over at least one spectral range above 10 kHz.