Acoustic Intensity Vector ANC With Dual Error Microphones
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Solution Overview
Problem
Conventional mobile devices with a single error microphone for noise cancellation can provide misleading acoustic pressure measurements, as they measure pressure at the earpiece rather than the user's eardrum, leading to suboptimal noise cancellation performance due to varying coupling between the ear and the speaker.
Innovation Solution
Incorporating a second error microphone aligned parallel to the first, both facing the user's ear, to calculate an acoustic intensity vector that is proportional to the acoustic field at the eardrum, allowing for more accurate adjustment of the ANC algorithm and detection of off-ear events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single error microphone is used to measure acoustic pressure at the earpiece, then the device complexity is reduced, but the measurement precision of acoustic field at the user's ear is compromised
Solution Approach 1:
The patent transitions from measuring only acoustic pressure (scalar quantity) to measuring acoustic intensity vector (vector quantity with direction). By adding a second error microphone and calculating the acoustic intensity vector from pressure gradients between the two microphones, the system obtains directional information and more accurate representation of the acoustic field at the user's ear, resolving the measurement precision limitation of a single microphone.
2Reliability
If acoustic pressure is measured at the earpiece instead of the eardrum, then the device complexity is reduced, but the reliability of noise cancellation performance monitoring deteriorates
Solution Approach 1:
The patent uses the acoustic intensity vector calculated from two error microphones as an intermediary measurement that correlates with the acoustic field at the eardrum. Instead of placing a microphone directly at the eardrum (which would be invasive and complex), the system uses the intensity vector from the earpiece microphones as a proxy that reliably indicates the actual acoustic conditions at the user's ear, enabling accurate noise cancellation monitoring.
3Adaptability or versatility
If the acoustic intensity vector is calculated and used to adjust the ANC algorithm, then the adaptability of noise cancellation is improved, but the computational complexity increases
Solution Approach 1:
The patent implements feedback by continuously calculating the acoustic intensity vector from the two error microphones and using this information to dynamically adjust the ANC algorithm. The acoustic intensity vector provides real-time feedback about the acoustic field conditions at the user's ear, allowing the system to adapt the noise cancellation parameters to match the actual listening conditions, improving adaptability while keeping the computational burden manageable through efficient vector calculations.
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 enhances the accuracy of noise cancellation by directly measuring acoustic intensity at the user's ear, improving sound quality and enabling adaptive noise control based on precise acoustic impedance calculations, thereby reducing unwanted noise when the device is removed from the ear.
Implementation Method 1
calculating a parameter proportional to acoustic particle velocity based, at least in part, on the first signal and the second signal... calculating a pressure gradient between the first microphone and the second microphone
Implementation Method 2
The acoustic intensity vector calculated from the input signals of the first and second error microphones is proportional to, or equal to, the acoustic intensity vector at the user's ear drum
Implementation Method 3
The acoustic intensity vector may also be input to an algorithm to calculate an input impedance of the first and second error microphones
Data Source
AI summary
A second error microphone may be incorporated in a mobile device to allow computation of additional parameters for modifying an adaptive noise cancellation (ANC) algorithm. For example, a first and second acoustic pressure may be calculated from a first and second error microphone of the mobile device. The first and second acoustic pressure may be input to an algorithm for determining an acoustic intensity vector. The ANC algorithm may receive the acoustic intensity vector as an input, and adapt an anti-noise signal to reduce the acoustic intensity vector. Additionally, an input impedance for the error microphones may be calculated from the acoustic pressure to determine coupling between a speaker and a user's ear. The anti-noise algorithm may be adjusted or disabled when the input impedance indicates the user has removed the phone from the user's ear.