Auto-Calibrating ANC Headphones Using Ear Canal Microphones
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing active noise cancellation (ANC) headphones require complex systems with multiple filters and calibration processes to accurately cancel noise, which increases cost and complexity, and often fail to accurately model the acoustic response due to variations in ear shape and seal quality.
Innovation Solution
The implementation of a simplified ANC control system using an array of microphones to directly approximate the perceived acoustic output, eliminating the need for secondary link filters and incorporating an equalization filter with automatic calibration capabilities to adjust coefficients based on user-specific feedback, thereby reducing reflections and improving noise cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a complex ANC control system with multiple filters is used, then noise cancellation accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the secondary link filter from the traditional ANC control system. By using microphones positioned to directly measure the acoustic output at the eardrum, the system removes the need for complex filtering operations, thereby reducing device complexity while maintaining noise cancellation accuracy through direct acoustic measurement
Solution Approach 2:
The patent implements a feedback mechanism where microphones positioned in the ear canal directly measure the acoustic output and feed this information back to the control system. This direct feedback loop enables the system to automatically adjust and optimize noise cancellation without requiring complex predictive filtering, resolving the contradiction between accuracy and complexity
2Reliability
If traditional ANC systems are used, then noise cancellation is provided, but they fail to accurately model acoustic response due to variations in ear shape and seal quality
Solution Approach 1:
The patent positions microphones at specific locations within the ear canal to directly measure the local acoustic conditions at the eardrum. This local measurement approach captures user-specific variations in ear shape and seal quality, enabling accurate acoustic response modeling tailored to each individual user's anatomy
Solution Approach 2:
The system performs automatic calibration by having the user wear the headphones and play test tones, during which the microphones measure the actual acoustic response. The system then automatically adjusts the equalization filter coefficients based on these measurements, enabling self-calibration that adapts to each user's unique ear characteristics without manual intervention
3Measurement precision
If automatic calibration with test signals is implemented, then user-specific acoustic response is captured, but calibration time is required
Solution Approach 1:
The patent implements automatic calibration that occurs automatically when the user first wears the headphones or when prompted, capturing the user's acoustic response in advance. This preliminary action stores the measured characteristics for future use, eliminating the need for repeated calibration and reducing the perceived time loss to a single initial calibration event
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 results in a more cost-effective and accurate noise cancellation system that provides a smooth response across the audible band, reducing noise levels by over 20 dB and minimizing distortion, while automatically calibrating to individual user conditions.
Implementation Method 1
a transducer that is disposed in the aperture and supported by the housing
Implementation Method 2
an array of microphones that are coupled to the housing and disposed over the transducer to receive sound radiated by the transducer and noise
Implementation Method 3
The equalization filter is adapted to equalize an audio input signal based on at least one predetermined coefficient
Implementation Method 4
The loop filter circuit includes a leaky integrator circuit that is adapted to generate a filtered audio signal based on the equalized audio input signal and a feedback signal
Data Source
AI summary
A sound system is provided with a headphone that includes a transducer and at least one microphone. The sound system also includes an equalization filter and a loop filter circuit. The equalization filter is adapted to equalize an audio input signal based on at least one predetermined coefficient. The loop filter circuit includes a leaky integrator circuit that is adapted to generate a filtered audio signal based on the equalized audio input signal and a feedback signal indicative of sound received by the at least one microphone, and to provide the filtered audio signal to the transducer.