Angled Acoustic Driver In-Ear Earphone Feedback Stability
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Solution Overview
Problem
In-ear active noise reduction earphones face challenges in achieving effective noise cancellation due to variations in ear anatomy, which affect the impedance of the front cavity and can lead to instability in the feedback loop, resulting in reduced noise attenuation and potential mechanical instability.
Innovation Solution
The design incorporates a nozzle with a large open cross-sectional area and a specific acoustic mass, oriented at an angle, along with a feedback microphone and acoustic driver, and includes an impedance-providing structure such as acoustically resistive material or a tube filled with foam to manage impedance and prevent blockages, while using a shunt to stabilize the feedback loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the nozzle has a large open cross-sectional area and specific acoustic mass, then noise attenuation is enhanced, but the device complexity increases
Solution Approach 1:
The patent applies parameter changes by specifying precise geometric parameters for the nozzle (open cross-sectional area greater than 13 mm², length less than 14 mm, ratio l/A less than 1.4, acoustic mass less than certain values at specific frequencies). These parameter optimizations enhance noise attenuation performance while managing device complexity through targeted dimensional control rather than adding complex structures.
2Reliability
If impedance-providing structure is added to manage impedance, then feedback loop stability is improved, but the device complexity increases
Solution Approach 1:
The patent employs porous materials as impedance-providing structure, specifically acoustically resistive material (such as wire mesh) and foam-filled tubes. These porous structures provide the necessary acoustic impedance to stabilize the feedback loop without requiring complex mechanical components, thus improving reliability while minimizing device complexity.
3Object-affected harmful factors
If the acoustic driver is oriented at an angle greater than 30 degrees, then noise cancellation effectiveness is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent applies asymmetry by specifying that the acoustic driver be oriented at an angle θ greater than 30 degrees relative to the nozzle centerline, deviating from the conventional aligned configuration. This asymmetric orientation improves noise cancellation effectiveness by optimizing acoustic coupling, while the patent manages manufacturing precision requirements through clear angular specification and tolerance definition.
4Ease of operation
If structure for engaging the outer ear is added to retain the earphone, then ease of operation is improved, but the device complexity increases
Solution Approach 1:
The patent employs flexible shells and thin films in the form of a compliant nozzle that can engage the outer ear anatomy. This flexible structure provides secure retention and ease of operation by adapting to individual ear shapes, while avoiding the need for complex rigid retention mechanisms such as headbands, thus improving ease of operation without significantly increasing device complexity.
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 enhances noise attenuation across a wide frequency range, reduces mechanical instability, and maintains comfort by minimizing the need for a headband, providing effective active noise reduction without compromising passive noise cancellation.
Implementation Method 1
a feedback microphone, for detecting noise in the cavity
Implementation Method 2
an acoustic driver for transducing an output noise canceling audio signal includes the feedback noise canceling audio signal to acoustic energy that attenuates the noise
Implementation Method 3
impedance-providing structure in the opening. The impedance-providing structure may include an acoustically resistive material in the opening
Implementation Method 4
The impedance-providing structure may include an acoustically resistive material in the opening. The acoustically resistive material may be wire mesh
Implementation Method 5
The impedance-providing structure may include a tube acoustically coupling the opening and the environment. The tube may be filled with foam
Data Source
AI summary
An active noise reduction earphone includes structure for positioning and retaining the earphone in the ear of a user and, active noise reduction circuitry including an acoustic driver with a nominal diameter greater than 10 mm oriented so that a line parallel to, or coincident with, an axis of the acoustic driver and that intersects a centerline of the nozzle intersects the centerline of the nozzle at angle ϑ>±30 degrees. A microphone is positioned adjacent an edge of the acoustic driver. The earphone is configured so that a portion of the acoustic driver is within the concha and another portion of the acoustic driver is outside the concha.