Differential Pressure Gradient MEMS Microphone for High SPL Loudspeaker Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current techniques for measuring loudspeaker diaphragm displacement, velocity, or acceleration are sensitive to surface characteristics and prone to errors due to noise accumulation, especially when using optical sensors or accelerometers, and conventional MEMS microphones are limited by maximum operating levels of 130 dB sound pressure level (SPL) before limiting at 10% total harmonic distortion (THD).
Innovation Solution
A differential pressure gradient micro-electro-mechanical system (MEMS) microphone is positioned within the back volume of a loudspeaker, featuring a MEMS microphone enclosure with tuned primary and secondary ports to control pressure differences between the front and back sides of the diaphragm, allowing it to operate at sound pressure levels greater than 130 dB SPL with reduced sensitivity and attenuation, enabling accurate measurement of displacement, velocity, or acceleration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MEMS microphones are used, then measurement precision is adequate at normal levels, but maximum operating level is limited to 130 dB SPL before limiting at 10% THD
Solution Approach 1:
The patent changes the acoustic parameters of the microphone by introducing tuned ports with specific acoustic impedances that create a pressure gradient effect. This modifies the pressure distribution across the diaphragm, allowing the microphone to operate reliably at higher SPL levels (greater than 130 dB) while maintaining measurement precision through the pressure gradient mechanism.
2Reliability
If sensitivity of the MEMS microphone is reduced to handle high SPL, then maximum operating level increases, but measurement precision decreases
Solution Approach 1:
The patent introduces a pressure gradient mechanism as an intermediary between the acoustic field and the diaphragm. The tuned ports create a pressure difference across the diaphragm surface, which serves as a mediator that allows the microphone to handle high SPL levels while maintaining adequate sensitivity and measurement precision through the gradient effect rather than direct pressure exposure.
3Measurement precision
If optical sensors are used for measuring diaphragm displacement, then measurement precision is improved, but sensitivity to surface characteristics increases
Solution Approach 1:
The patent replaces the optical measurement system with a mechanical/acoustic pressure gradient microphone system. This substitution eliminates the sensitivity to surface characteristics that plagues optical sensors, as the pressure gradient microphone measures acoustic pressure differences directly without being affected by the visual appearance or surface properties of the loudspeaker diaphragm.
4Measurement precision
If accelerometers are placed on the loudspeaker diaphragm, then measurement precision is improved, but accumulated error from noise integration increases
Solution Approach 1:
The patent replaces the accelerometer-based measurement system with a pressure gradient microphone system. By directly measuring acoustic pressure differences rather than acceleration that requires integration, the system eliminates the accumulated error from noise integration while maintaining measurement precision, providing a more reliable measurement approach.
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
The solution allows for accurate estimation of loudspeaker diaphragm displacement, velocity, or acceleration at high sound pressure levels with reduced sensitivity and noise, effectively overcoming the limitations of conventional MEMS microphones by controlling pressure differences and maintaining thermal stability across varying frequencies.
Implementation Method 1
differential pressure gradient micro-electro-mechanical system (MEMS) microphone
Implementation Method 2
The primary port and the secondary port may be tuned to have different acoustic impedances
Implementation Method 3
a pressure difference between the front side and the back side of the diaphragm
Data Source
AI summary
A differential pressure gradient micro-electro-mechanical system (MEMS) microphone for measuring an acoustic characteristic of a loudspeaker. The microphone includes a MEMS microphone housing and a compliant membrane mounted in the MEMS microphone housing, the compliant membrane dividing the MEMS microphone housing into a first chamber and a second chamber. The first chamber includes a primary port open to a first side of the compliant membrane and the second chamber includes a secondary port open to a second side of the compliant membrane, and the primary port and the secondary port are tuned with respect to one another to control a pressure difference between the first side and the second side of the compliant membrane such that at least 10 dB of attenuation is observed in a microphone signal output relative to a microphone having a sealed first or second chamber.