CIC Hearing Instrument Feedback Stability via Receiver Orientation
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Solution Overview
Problem
Conventional completely-in-canal (CIC) hearing aids experience instability and sharp frequency peaks when acoustic gain exceeds 40 dB, primarily due to receiver vibrations causing feedback, and inconsistent performance due to variable receiver positioning within the shell.
Innovation Solution
A CIC hearing instrument design featuring a shell, a suspended receiver with its membrane parallel to a calculated plane of minimal vibration, and a faceplate microphone inlet hole centered along the line of minimal vibrational sound pressure to minimize feedback, allowing for increased acoustic gain stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the acoustic gain of a CIC instrument is increased to improve hearing amplification, then the amplification capability is enhanced, but the instrument becomes unstable and begins to oscillate due to feedback
Solution Approach 1:
The patent extracts the harmful feedback path by positioning the microphone inlet hole at a specific location on the faceplate that minimizes pickup of receiver-generated sound pressure. This spatial separation removes the feedback loop that causes instability, allowing higher acoustic gain without oscillation.
Solution Approach 2:
The faceplate acts as an intermediary element between the receiver and microphone. By carefully positioning the microphone inlet hole on the faceplate at a location with minimal vibrational sound pressure, the faceplate mediates the interaction between receiver vibrations and microphone pickup, reducing feedback while maintaining acoustic coupling for amplification.
2Device complexity
If the receiver is directly attached to the shell for simplicity, then the device complexity is reduced, but the receiver vibrations cause the faceplate to radiate sound pressure into the microphone creating feedback
Solution Approach 1:
The patent applies local quality by suspending the receiver at specific locations within the shell using vibration-damping materials rather than direct attachment. This localized treatment at the receiver mounting points reduces vibrational sound pressure radiation to the faceplate while maintaining structural support.
Solution Approach 2:
Vibration-damping materials serve as intermediary elements between the receiver and shell, and between the receiver and faceplate. These materials absorb and dissipate vibrational energy, preventing direct transmission of receiver vibrations to the faceplate and subsequent radiation into the microphone.
3Ease of manufacture
If the receiver position is not fixed during assembly, then the ease of manufacture is improved, but the performance becomes inconsistent across different instruments
Solution Approach 1:
The patent performs preliminary action by pre-calculating the optimal receiver position and orientation during the design phase, specifically positioning the receiver so that its membrane is parallel to the calculated plane of minimal vibration. This pre-planned positioning ensures consistent performance across all instruments while maintaining ease of assembly, as workers simply need to follow the predetermined position indicators.
Solution Approach 2:
The patent introduces asymmetry by defining a specific orientation for the receiver membrane relative to the faceplate (parallel to the calculated plane of minimal vibration). This asymmetric positioning requirement, rather than allowing random placement, ensures that the receiver consistently operates from an optimal position that minimizes feedback while simplifying the assembly process through clear positioning guidelines.
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 design achieves a superior feedback threshold 10 dB higher than typical CIC instruments, ensuring consistent performance by optimizing receiver placement and minimizing vibrational sound pressure at the microphone inlet, thereby enhancing feedback stability.
Implementation Method 1
The purpose of the receiver is to convert the electrical signals into an acoustic sound pressure
Implementation Method 2
a force is exerted on the armature 1.40 by the magnetic field generated by the magnetic member 1.35
Implementation Method 3
The receiver 100 is suspended inside of the shell 12 with a vibration-damping material
Data Source
AI summary
A CIC hearing instrument and appertaining method are provided that improve feedback stability. Accordingly, the microphone inlet is located on the faceplate of the instrument at a position of least vibration. Furthermore, the receiver is located in the device such that its vibrating membrane is parallel to a plane calculated to include a line of minimal vibration on the faceplate and a center of gravity for the instrument.