Earphone Acoustic Labyrinth Low-Pass Filter
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Solution Overview
Problem
In multi-driver earphones, the use of inductors for low pass filtering is hindered by large package size and increased DC resistance, which affects sound quality due to the small volume of earphone casings and difficulty in fitting long acoustic tubes.
Innovation Solution
An elongated passageway with a tortuous path formed by stacked layers within the earphone housing acts as an acoustic filter, providing a labyrinthine structure that effectively filters high frequency sound from low frequency drivers without the need for inductors, utilizing acoustic inertance to achieve a low-pass filtering effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inductors are used for low pass filtering in multi-driver earphones, then filtering performance is improved, but package size increases and DC resistance increases
Solution Approach 1:
The patent replaces the electrical inductor-based low pass filter with an acoustic low pass filter consisting of a tortuous passageway. The acoustic filter uses the physical geometry of the sound passage (length, cross-sectional area, and tortuosity) to provide inertance-based filtering, eliminating the need for electrical inductors and their associated size and resistance problems.
Solution Approach 2:
The patent employs acoustic principles by designing a tortuous sound passage that uses air inertia (acoustic inertance) to create the low pass filtering effect. The passageway's geometry (length L, cross-sectional area A, and tortuosity) creates acoustic impedance that filters high frequencies from the low frequency driver output, replacing electrical filtering with pneumatic/acoustic filtering.
2Reliability
If inductors are used for low pass filtering, then filtering performance is improved, but DC resistance increases affecting sound quality
Solution Approach 1:
The patent replaces the electrical inductor-based low pass filter with an acoustic low pass filter consisting of a tortuous passageway. The acoustic filter uses the physical geometry of the sound passage (length, cross-sectional area, and tortuosity) to provide inertance-based filtering, eliminating the need for electrical inductors and their associated size and resistance problems.
3Reliability
If acoustic tube length is increased for filtering, then filtering performance is improved, but device volume increases
Solution Approach 1:
The patent transitions from a simple linear tube to a tortuous three-dimensional passageway that winds through the earphone housing. By utilizing multiple dimensions and spatial complexity, the design achieves a long effective acoustic path length (L) within a compact volume. The tortuosity factor (how much the path winds) allows the acoustic filter to achieve the required filtering performance without proportionally increasing the external device dimensions.
Solution Approach 2:
The tortuous passageway is nested within the existing earphone housing structure, utilizing the available internal volume efficiently. The sound passage winds through and around other components, maximizing the use of available space to achieve the required acoustic path length without increasing the overall device volume.
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 significant increase in sound passage length per unit volume, providing improved filtering of high frequency sounds while maintaining a compact earphone size, with enhanced acoustic mass and reduced distortion, allowing for independent adjustment of low frequency output and reduced inter-modulation distortions.
Implementation Method 1
Acoustic inertance, which is the impeding effect of inertia on the transmission of sound in a duct of small cross-sectional area or the mass loading of air on the transmission of sound in a duct
Data Source
Figure 1
Figure 2A~2B
Figure 2C
AI summary
An earphone assembly for an in-ear listening device and method for filtering a portion of an audible sound output are disclosed. An earphone comprises a housing configured to receive a nozzle, a plurality of drivers each having an acoustical output disposed within the housing, and an elongated passageway disposed within the housing configured to filter at least an audible portion of a sound wave output from at least one of the plurality of drivers. The method comprises providing an elongated passageway to provide an increased path length and connecting an output of the at least one driver to the elongated passageway to configure the sound output to be received within the elongated passageway to acoustically filter a portion of the sound output from the at least one driver.