Ear Detection via Acoustic Transfer Function in Hybrid ANC Headphones
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Solution Overview
Problem
Existing ear mountable playback devices, such as headphones, face challenges in efficiently detecting whether they are worn on or off the ear without additional sensors, which can lead to unnecessary power consumption and design complexities, especially in wireless headphones where accurate on-off ear detection is crucial for maintaining battery life and ANC stability.
Innovation Solution
The solution utilizes the existing microphones in hybrid noise cancelling headphones, specifically the error and feedforward microphones, to detect the wearing state by analyzing filter responses and phase differences, eliminating the need for additional sensors and allowing for adaptive noise cancellation adjustments based on acoustic leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional sensors (optical proximity sensors, pressure sensors, capacitive sensors) are added to detect wearing state, then detection accuracy is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent reuses existing microphones in hybrid noise cancelling headphones for dual purposes: their original function of capturing ambient noise for ANC processing, and an additional function of detecting wearing state by analyzing acoustic transfer function changes. This eliminates the need for dedicated sensors and reduces device complexity while maintaining detection accuracy
Solution Approach 2:
The system uses its own existing components (microphones and speakers) to perform the detection function without requiring external or additional sensors. The microphones serve themselves by providing data for both noise cancellation and wearing state detection, reducing overall system complexity
2Measurement precision
If additional sensors are added for off-ear detection, then wearing state detection is improved, but manufacturing cost increases
Solution Approach 1:
The existing microphones are designed to serve multiple functions: ambient noise capture for ANC and wearing state detection. By making the microphones universal components that perform both functions, the patent eliminates the need for additional sensors, thereby reducing manufacturing costs while maintaining detection capability
Solution Approach 2:
The patent merges the wearing state detection function with the existing noise cancellation functionality by using the same microphones and processing pipeline for both purposes, eliminating the need for separate detection hardware and reducing manufacturing complexity and cost
3Reliability
If power-consuming components remain active when headphones are off-ear, then functionality is maintained, but battery life decreases
Solution Approach 1:
The system periodically checks acoustic transfer function characteristics to determine wearing state, and based on this detection, dynamically switches between active and power-saving modes. This periodic monitoring with conditional mode switching maintains functionality when needed while conserving battery life when the headphones are not being worn
Solution Approach 2:
The system dynamically adjusts its operational state based on real-time detection of wearing condition. When the acoustic transfer function indicates the headphones are off-ear, the system transitions to a low-power state by disabling non-essential components, thereby adapting power consumption to actual usage conditions and extending battery life
4Reliability
If ANC processing continues when headphones are off-ear, then noise cancellation performance is maintained, but system stability deteriorates
Solution Approach 1:
The system uses feedback from acoustic transfer function analysis to control ANC processing. When the feedback indicates the headphones are off-ear through characteristic changes in the transfer function, the system automatically disables or reduces ANC processing to prevent instability, while maintaining the capability to resume full ANC performance when properly detected to be worn
Data Source
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AI summary
An audio system for an ear mountable playback device (HP) includes a speaker (SP), an error microphone (FB_MIC), which senses sound being output from the speaker (SP), and a sound control processor. The processor is configured for controlling and/or monitoring a playback of a detection signal or a filtered version of the detection signal via the speaker (SP), recording an error signal from the error microphone (FB_MIC), and determining whether the playback device (HP) is in a first state, where the playback device (HP) is worn by a user, or in a second state, where the playback device (HP) is not worn by a user, based on processing of the error signal.