Hearing Device Feedback Detector Using Dual Microphone Signal Comparison
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Solution Overview
Problem
Conventional hearing devices struggle to effectively detect and manage acoustic feedback, particularly in open fittings and for users with severe-to-profound hearing loss, where high gain is needed, leading to whistling issues due to the close proximity of microphones and loudspeakers.
Innovation Solution
A hearing device with two microphones, one located behind the ear and one in the ear canal, utilizing a feedback detector to compare signal strength estimates and determine the presence of acoustic feedback, allowing for improved feedback detection and cancellation through beamforming and gain control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If microphones and loudspeakers are placed in close proximity in conventional hearing devices, then the device structure is compact and easy to manufacture, but acoustic feedback occurs leading to whistling issues
Solution Approach 1:
The hearing device is divided into two separate physical units: an ear canal device containing the loudspeaker and one microphone, and a behind-the-ear device containing the second microphone and signal processing electronics. This segmentation increases the distance between microphones and loudspeaker to prevent acoustic feedback while maintaining functional integration through wireless or wired communication between the units.
2Reliability
If high gain is applied to compensate for severe-to-profound hearing loss, then hearing sensitivity is improved, but acoustic feedback and whistling increase
Solution Approach 1:
The system employs active feedback cancellation by continuously monitoring the acoustic environment with two microphones positioned at different locations, detecting feedback signals, and generating anti-phase signals to cancel the feedback. This allows high gain settings to be maintained without the whistling that would normally occur at such gain levels.
3Device complexity
If a single microphone is used in conventional hearing devices, then the device complexity is reduced, but the ability to detect and differentiate feedback from ambient sound is insufficient
Solution Approach 1:
The second microphone is positioned in a different spatial location (behind the ear) rather than simply adding another microphone near the ear canal. This spatial separation creates different acoustic transfer functions and feedback paths, providing dimensional information that enables the system to distinguish feedback signals from ambient sound sources through signal processing and comparison.
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 configuration enables clearer detection of acoustic feedback and reduces whistling, allowing for higher gain settings without the risk of feedback howl, enhancing sound quality for users with severe hearing loss.
Implementation Method 1
a first input transducer for picking up a sound signal from the environment and providing a first electric input signal, the first input transducer being located on the head, e.g. at or behind an ear, of the user; a second input transducer for picking up a sound signal from the environment and providing a second electric input signal, the second input transducer being located at or in an ear canal of the user
Implementation Method 2
a feedback detector comprising a first detector of signal strength for providing a first estimate of a signal strength of the first electric input signal; a second detector of signal strength for providing a second estimate of a signal strength of the second electric input signal; a comparator configured to compare the first and second estimate and to provide a comparison measure indicative of a difference between the first and second estimate
Data Source
AI summary
The application relates to a hearing device comprising a) first and second input transducers for picking up sound signals from the environment and providing first and second electric input signals, b) a first and signal strength detectors for providing signal strength estimates of the first and second electric input signal, the first input transducer being located at or behind an ear of the user, and the second input transducer being located at or in an ear canal of the user. The hearing device further comprises c) a signal processing unit providing a processed signal based on the first and second electric input signals, and d) an output unit comprising an output transducer for converting the processed signal or a signal originating therefrom to a stimulus perceivable by said user as sound. The hearing device further comprises e) a feedback detector comprising e1) a comparison unit operationally coupled to the first and second signal strength detectors and configured to compare the signal strength estimates of the first and second electric input signals and to provide a signal strength comparison measure indicative of the difference between the signal strength estimates, and e2) a decision unit for providing a feedback measure indicative of current acoustic feedback from the output transducer to the first and/or second input transducers based on the comparison measure. In an embodiment, the feedback measure is used to control processing in the signal processing unit, e.g. a beamformer unit and/or a feedback cancellation system, and/or an amplification unit. The invention may e.g. be used in hearing aids, in particular hearing aids comprising an ITE-part adapted for being located at or in an ear canal of a user and a BTE-part adapted for being located at or behind an ear or the user.