Headphone Off-Ear Detection via Acoustic Feedback
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Solution Overview
Problem
Conventional active noise cancellation (ANC) headphones continue to drain battery power when not in use, as they lack an effective method to detect when the headphones are removed from the user's ears, often relying on mechanical sensors that increase cost and complexity.
Innovation Solution
Integration of a microphone-based system within ANC headphones to acoustically detect whether the headphones are on or off the user's ear, using a tone injection method to determine the presence or absence of the ear, thereby controlling power consumption and ANC features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mechanical sensors (contact sensors or magnets) are added to detect whether headphones are being worn, then the detection accuracy is improved, but the device complexity and cost increase
Solution Approach 1:
The patent applies multi-functionality by using the existing feedback microphone (originally designed for ANC) to serve dual purposes: both noise cancellation and off-ear detection. This eliminates the need for separate mechanical sensors while maintaining detection capability, thereby reducing device complexity without sacrificing measurement precision.
Solution Approach 2:
The system uses the feedback microphone's inherent capability to sense acoustic signals in the ear cavity to detect whether the headphones are on or off the ear. The microphone essentially detects its own operational context through acoustic feedback, eliminating the need for additional dedicated sensors.
2Reliability
If the ANC system continues to operate when headphones are removed, then the system reliability is maintained, but the energy consumption increases
Solution Approach 1:
The patent implements dynamic operation by enabling the system to automatically adjust its state based on real-time detection. When off-ear detection is activated, the system dynamically transitions to a low-power or shutdown state, optimizing energy consumption while maintaining reliability through proper state management.
Solution Approach 2:
The system uses acoustic feedback from the feedback microphone to detect whether the headphones are on or off the ear. This feedback mechanism enables the system to automatically adjust its operational state, shutting down or reducing power consumption when removed from the ear while maintaining reliability through continuous monitoring.
3Adaptability or versatility
If additional mechanical sensors are integrated into the headphones, then the off-ear detection capability is improved, but the manufacturing cost increases
Solution Approach 1:
The patent makes the feedback microphone multi-functional, using it for both ANC operations and off-ear detection. This eliminates the need for additional mechanical sensors, thereby maintaining adaptability while reducing manufacturing cost and simplifying the production process.
Solution Approach 2:
The system uses the feedback microphone's inherent acoustic sensing capability to perform off-ear detection without requiring additional specialized sensors. This self-service approach leverages existing components to achieve new functionality, reducing manufacturing costs while maintaining detection capability.
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
The system effectively reduces power consumption by determining when the headphones are removed, allowing for automatic power-saving features and eliminating the need for additional mechanical sensors, thus enhancing user convenience and reducing costs.
Implementation Method 1
the feedback microphone is configured to detect a feedback signal received from a feedback transducer of the headphones
Implementation Method 2
the feedforward microphone senses ambient noise but does not appreciably sense audio played by the speaker
Data Source
AI summary
Disclosed is a signal processor for headphone off-ear detection. The signal processor includes an audio output to transmit an audio signal toward a headphone speaker in a headphone cup. The signal processor also includes a feedback (FB) microphone input to receive a FB signal from a FB microphone in the headphone cup. The signal processor also includes an off-ear detection (OED) signal processor to determine an audio frequency response of the FB signal over an OED frame as a received frequency response. The OED processor also determines an audio frequency response of the audio signal times an off-ear transfer function between the headphone speaker and the FB microphone as an ideal off-ear response. A difference metric is generated comparing the received frequency response to the ideal off-ear frequency response. The difference metric is employed to detect when the headphone cup is disengaged from an ear.