Secondary Path Identification for Active Noise Cancellation
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Solution Overview
Problem
Conventional active noise cancellation systems in personal listening devices, such as earphones and earbuds, face challenges in achieving complete noise cancellation due to leakage variations among users and devices, leading to residual noise and audible artefacts, and require additional power-consuming sensors for position detection, increasing device complexity and cost.
Innovation Solution
The system employs a secondary path identification process using a loudspeaker and error microphone to adaptively generate anti-noise signals based on feedback, identifying users through measured frequency responses and switching between in-ear and open-air states, optimizing noise cancellation performance while reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional sensors and position sensing hardware are added to detect ear positioning, then position detection accuracy is improved, but device complexity and power consumption increase
Solution Approach 1:
The existing error microphone is made multi-functional by using it both for its original purpose (detecting residual noise for ANC feedback) and for position detection. The system analyzes the frequency response of the error microphone to determine ear positioning, eliminating the need for dedicated position sensing hardware.
Solution Approach 2:
The system uses its own operational components (loudspeaker and error microphone) to perform position detection autonomously. By analyzing the acoustic feedback already present in the ANC loop, the device determines whether it is properly positioned in the user's ear without requiring external sensors or additional hardware.
2Measurement precision
If additional sensors and position sensing hardware are added to detect ear positioning, then position detection accuracy is improved, but power consumption increases
Solution Approach 1:
The existing error microphone is made multi-functional by using it both for its original purpose (detecting residual noise for ANC feedback) and for position detection. The system analyzes the frequency response of the error microphone to determine ear positioning, eliminating the need for dedicated position sensing hardware.
Solution Approach 2:
The system uses its own operational components (loudspeaker and error microphone) to perform position detection autonomously. By analyzing the acoustic feedback already present in the ANC loop, the device determines whether it is properly positioned in the user's ear without requiring external sensors or additional power-consuming hardware.
3Device complexity
If conventional anti-noise filtering systems are used without user-specific optimization, then system simplicity is maintained, but noise cancellation performance degrades due to leakage variations
Solution Approach 1:
The system performs preliminary characterization of the secondary path (acoustic path from loudspeaker to error microphone) during an enrollment phase. By pre-measuring and storing the frequency response for different users and positioning scenarios, the system can quickly adapt the ANC filter coefficients to match the specific user-device configuration, improving performance without adding complex real-time processing.
Solution Approach 2:
The system dynamically adapts the ANC filter coefficients based on the measured secondary path frequency response. By making the filtering parameters adaptive rather than fixed, the system can compensate for leakage variations caused by different users, ear canal geometries, and positioning conditions, thereby improving noise cancellation reliability.
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 approach enhances active noise cancellation performance by customizing noise cancellation profiles for individual users, improving noise reduction and power efficiency, and eliminating the need for additional power-hungry sensors, thus providing consistent and efficient noise cancellation across different ear coupling scenarios.
Implementation Method 1
generating a corresponding anti-noise signal that is approximately equal in magnitude, but opposite in phase, to the sensed noise. The noise and anti-noise signal cancel each other acoustically
Implementation Method 2
an error microphone configured to sense sound in the noise cancellation zone
Data Source
AI summary
An active noise cancellation system has a secondary path including a loudspeaker configured to output an anti-noise signal to cancel noise in a noise cancellation zone, and an error microphone configured to sense sound in the noise cancellation zone. The ANC system further includes a logic device configured to adaptively generate the anti-noise signal for playback through the loudspeaker based at least in part on a feedback signal from the error microphone and identify a user of the active noise cancellation system based, at least in part, on a measured frequency response of the secondary path. The logic device is further configured to identify the user of the active noise cancellation system through a comparison of the measured frequency response of the secondary path to stored models and may be configured to execute a new user enrollment process, store user profiles, and/or switch between in-ear and open-air states.