Twin-driver earphone asymmetric pipes cancel resonance
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Solution Overview
Problem
Conventional sound-isolating earphones cause a change in resonance mode when fitted, leading to unwanted frequency characteristics and a buzzing echo sound, with existing solutions either attenuating treble components or reducing sound pressure across medium to high-frequency ranges.
Innovation Solution
The use of two electroacoustic transducers with sound leading pipes of different path lengths, where sound waves generated at the same phase are combined at the entrance of the external auditory canal, suppressing sound pressure components with frequencies corresponding to half the wavelength difference between the paths, thereby canceling out undesirable resonance effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional sound-isolating earphone is fitted in the external auditory canal, then sound isolation performance is improved, but unwanted resonance peaks and buzzing echo sound occur
Solution Approach 1:
The single sound leading pipe is segmented into two separate pipes with different path lengths. This segmentation allows the system to create destructive interference for specific frequency components (particularly the resonance peak around 6kHz) while maintaining sound isolation performance. The two pipes divide the sound transmission paths to achieve frequency-selective cancellation.
Solution Approach 2:
The two sound leading pipes are designed with asymmetric path lengths, where one pipe is longer than the other. This asymmetry creates the necessary phase difference for destructive interference of unwanted frequency components. The different path lengths cause sound waves to arrive at the eardrum with opposite phases at specific frequencies, canceling out the resonance peaks.
2Object-generated harmful factors
If acoustic resistors or dampers are added to suppress resonance peaks, then unwanted frequency components are reduced, but sound pressure and volume are reduced across medium to high-frequency ranges
Solution Approach 1:
Instead of using passive absorption (acoustic resistors/dampers) that reduces all frequencies, the invention uses active destructive interference by inverting the phase of specific frequency components through the asymmetric path design. This inverts the approach from absorption to cancellation, preserving sound pressure while eliminating resonance peaks.
Solution Approach 2:
The invention changes the path length parameter of the sound leading pipes to achieve frequency-selective interference. By carefully controlling the difference in path lengths, the system targets specific resonance frequencies for cancellation without affecting other frequency ranges, thereby maintaining overall sound pressure and volume.
3Object-generated harmful factors
If two sound leading pipes with different path lengths are used, then resonance peaks are suppressed through destructive interference, but device complexity increases
Solution Approach 1:
The two sound leading pipes serve multiple functions simultaneously: they transmit sound from the transducer to the ear canal, provide sound isolation through the earpad seal, and create destructive interference for resonance peak suppression. This multi-functionality reduces the need for separate components, thereby limiting the increase in 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 approach maintains sound quality and volume while suppressing unwanted frequency peaks, achieving sound pressure-frequency characteristics comparable to those without the earphone, with increased sound pressure sensitivity and layout flexibility.
Implementation Method 1
sound waves generated by two electroacoustic transducers at the same phase and passed through sound leading pipes having different path lengths are combined at an entrance of an external auditory canal, thereby canceling out sound pressure components with frequencies corresponding to half the wavelength difference between the paths
Data Source
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AI summary
Provided is a technique for improving frequency characteristics by an acoustics-related method so that a sound is heard with natural frequency characteristics when a sound-isolating earphone is fitted in a human ear. A sound-isolating earphone is provided with two or more electroacoustic transducers, wherein independently generated sound waves are passed through isolated sound leading pipes and are mixed just before an entrance of an external auditory canal, and a sound wave of which is twice the difference between path lengths of the two sound leading pipes is attenuated. This serves to provide an easy-to-hear improved sound quality by suppressing the sound wave at around 6 kHz that is transmitted with characteristically high intensity in a sound-isolating earphone.