Intra-aural Headphone Error Microphone Cavity for Leak-Tolerant Noise Cancellation
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Solution Overview
Problem
Existing noise cancellation systems in audio devices, such as headphones, face challenges in achieving high-quality noise cancellation due to leaks between the device and the ear canal, which alter the acoustic coupling and result in reduced noise cancellation effectiveness, especially when the device does not form a perfect seal with the user's ear.
Innovation Solution
The audio device incorporates a speaker with a first cavity for sound emission and a separate second cavity for the error microphone, both with external openings, allowing direct acoustic coupling to the ear canal, enabling the error microphone to monitor external noise and adapt noise cancellation based on sound pressure levels, even with leaks present, and employing a feed-forward microphone with a filter for enhanced noise cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a seal is formed between the audio device and ear canal wall, then noise cancellation quality is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent introduces a separate second cavity for the error microphone that directly couples to the ear canal through a second opening, acting as an intermediary path that bypasses the need for a perfect seal through the speaker's first cavity. This mediator cavity allows the error microphone to directly monitor acoustic conditions at the ear canal entrance, resolving the contradiction by providing accurate noise measurement without requiring complex sealing structures.
2Ease of operation
If the audio device does not form a perfect seal with the ear canal, then ease of insertion and user comfort are improved, but noise cancellation effectiveness deteriorates
Solution Approach 1:
The patent employs feedback by placing the error microphone in a second cavity that directly monitors acoustic conditions at the ear canal entrance. This feedback mechanism allows the system to continuously detect actual noise levels and acoustic coupling conditions, enabling real-time adaptation of noise cancellation algorithms to compensate for leaks, thus maintaining effectiveness even when ease of insertion compromises sealing.
Solution Approach 2:
The separate second cavity system allows the device to self-adjust to different ear canal geometries and seal conditions. By directly monitoring the acoustic environment at the ear canal entrance, the system automatically adapts to various insertion depths and seal qualities without requiring precise manual adjustment or complex sealing mechanisms, achieving both ease of operation and reliability.
3Device complexity
If the error microphone is placed within the first cavity near the speaker, then device complexity is reduced, but measurement precision of external noise deteriorates
Solution Approach 1:
The patent segments the acoustic measurement function by creating a separate second cavity dedicated to the error microphone, distinct from the speaker's first cavity. This segmentation allows the error microphone to independently monitor external noise conditions at the ear canal entrance without being influenced by speaker output or internal acoustic paths, achieving high measurement precision while maintaining manageable device complexity through functional separation.
4Adaptability or versatility
If the audio device is moved within the ear canal, then adaptability to user movement is improved, but acoustic coupling between the error microphone and ear canal deteriorates
Solution Approach 1:
The second cavity acts as a stable intermediary acoustic chamber that maintains consistent coupling to the ear canal entrance regardless of device position. This mediator structure provides a fixed reference point for noise measurement that is less sensitive to movement-induced changes in the primary acoustic path, allowing the system to maintain measurement precision while adapting to user movement.
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 improves noise cancellation quality by directly coupling the error microphone to the ear canal's acoustic conditions, allowing for adaptive noise cancellation that effectively reduces external noise interference, even when the device does not form a perfect seal, thereby enhancing user experience.
Implementation Method 1
The second cavity is configured to directly couple to a volume of air within the ear canal of a user in case that the audio device is placed within the ear canal of a user. The error microphone is arranged within the second cavity and is arranged to primarily record sound within the ear canal of a user.
Implementation Method 2
The audio device comprises a speaker which is arranged within the audio device and which has a preferential side for sound emission. The first cavity is arranged at the preferential side for sound emission of the speaker.
Data Source
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AI summary
A noise cancellation enabled audio device (20), in particular an intra-aural headphone, comprises a speaker (21) which is arranged within the audio device (20) and which has a preferential side (36) for sound emission. The audio device (20) further comprises a first cavity (22) enclosing a first volume of air, where the first cavity (22) is arranged at the preferential side (36) for sound emission of the speaker (21), and an error microphone (23) which is arranged within a second cavity (24) within the audio device (20). The first cavity (22) comprises a first opening (25) to the outside of the audio device (20) and the second cavity (24) comprises a second opening (26) to the outside of the audio device (20). The first and the second opening (25, 26) are both arranged on a side of the audio device (20) which is arranged to face an ear canal (27) of a user such that the error microphone may also record sounds from the environment which may enter through controlled leakage. Furthermore, a noise cancellation system (30) including a filter is provided which takes into account the various transfer functions when the headphone is worn.