ANC Earphone Calibration Fixture Using Acoustic Path
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Solution Overview
Problem
Active noise cancelation systems in headphones face instability issues due to variations in sensitivity and efficiency of speaker and microphone transducers, leading to suboptimal noise rejection performance and potential oscillations.
Innovation Solution
A calibration method using an ear model and acoustic path to determine characteristics of audio signals and adjust gain values in ANC systems, specifically for feedforward and feedback paths, to stabilize the noise cancelation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the feedback ANC gain is increased to improve noise cancelation performance, then the amount of noise cancelation increases, but the system may experience spontaneous oscillations and instability
Solution Approach 1:
The patent applies preliminary action by performing calibration of the feedback ANC gain before actual operation. The system determines transfer functions and calculates optimal gain values in advance, preventing instability issues before they occur during normal noise cancelation operation.
Solution Approach 2:
The patent uses feedback mechanisms by monitoring the actual performance of the ANC system and adjusting the feedback gain based on measured transfer functions. The system continuously adapts the gain values based on real-time measurements from microphones and speakers, ensuring stable operation while maintaining effective noise cancelation.
2Reliability
If the feedforward ANC gain is increased to improve noise cancelation performance, then the amount of noise cancelation increases, but ambient noise may bleed in to the headphone
Solution Approach 1:
The patent applies preliminary action by determining the feedforward transfer function and calculating optimal feedforward gain values during calibration before actual operation. This pre-characterization of the acoustic path allows the system to set appropriate gain levels that maximize noise cancelation while preventing ambient noise from bleeding in.
Solution Approach 2:
The patent uses parameter changes by dynamically adjusting the feedforward gain based on the determined transfer function characteristics. The system modifies gain parameters according to the specific acoustic environment and transducer characteristics, optimizing the balance between noise cancelation effectiveness and prevention of ambient noise intrusion.
3Measurement precision
If calibration is performed to precisely tune filter gain values, then noise cancelation performance is optimized, but the gain may still vary from one part to another due to transducer variations
Solution Approach 1:
The patent applies self-service by enabling the ANC system to automatically characterize its own acoustic environment and transducer characteristics through calibration procedures. The system performs self-measurement of transfer functions and self-adjustment of gain values, compensating for variations in speaker and microphone sensitivity without requiring manual calibration for each device.
Solution Approach 2:
The patent uses parameter changes by determining actual transfer functions that capture the specific characteristics of each transducer assembly. The system measures and adapts parameters such as speaker efficiency, microphone sensitivity, and acoustic path characteristics, then adjusts filter coefficients accordingly to compensate for manufacturing variations and ensure consistent performance across different devices.
Data Source
AI summary
A fixture for calibrating an active noise canceling (ANC) earphone, the calibration fixture including an ear model and an acoustic path. The ear model is configured to support an ANC earphone and includes an ear canal extending from an outer end of the ear canal to an inner end of the ear canal. The acoustic path is external to the ear canal and extends from, at a first end of the acoustic path, the inner end of the ear canal of the ear model to an opposite, second end of the acoustic path. The acoustic path is configured to transmit a mechanical sound wave received from the inner end of the ear canal to a region external to the ear model and adjacent the outer end of the ear canal.