Distributed Microphone Array for Earphone Noise Cancellation
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Solution Overview
Problem
Current ambient noise-cancellation systems for earphones, particularly those using the feedforward principle, struggle to effectively reduce noise above 1 kHz due to limitations in frequency bandwidth and directional dependence of sound path lengths, leading to residual noise and inefficiencies.
Innovation Solution
A distributed microphone array is placed around the perimeter of an earphone shell to detect ambient noise, ensuring time-alignment of the cancellation signal with the ambient noise at the eardrum, addressing variations in sound-source direction and electroacoustic transducer response times, thereby enhancing noise reduction up to 3 kHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single microphone is used in feedforward noise cancellation, then the system is simple to implement, but it cannot effectively handle variations in sound-source direction and frequency bandwidth is limited to below 1 kHz
Solution Approach 1:
The single microphone is segmented into multiple microphones arranged in a distributed array around the earphone shell. This segmentation allows each microphone to capture noise from different directions, enabling the system to handle omnidirectional noise sources effectively while maintaining frequency response up to 3 kHz.
Solution Approach 2:
The system transitions from a single-point microphone measurement to a spatially distributed array of microphones. By adding the spatial dimension around the earphone perimeter, the system can capture noise from all directions and provide omnidirectional noise cancellation coverage.
2Measurement precision
If the microphone is positioned to detect ambient noise, then noise cancellation can be achieved, but time-misalignment between the cancellation signal and ambient noise occurs due to variations in sound path lengths
Solution Approach 1:
The distributed microphone array is positioned around the earphone shell to detect ambient noise before it reaches the eardrum. By placing microphones at multiple locations, the system captures noise signals in advance, allowing the digital signal processor to generate and apply cancellation signals with proper time-alignment before the noise reaches the listener's ear.
Solution Approach 2:
The system replaces mechanical time-alignment methods with digital signal processing. The DSP calculates the precise time-delays required for each microphone based on its position and the sound speed, then applies appropriate delays to each channel to achieve accurate time-alignment of the cancellation signal with the ambient noise at the eardrum.
3Object-affected harmful factors
If feedforward noise cancellation is implemented, then ambient noise can be reduced, but the system becomes sensitive to time-delays and frequency response variations above 1 kHz
Solution Approach 1:
The system changes the spatial parameters of noise detection by using multiple microphones at different positions around the earphone. This allows the digital signal processor to calculate and compensate for frequency-dependent time-delays and path-length variations, extending the effective frequency bandwidth from below 1 kHz to up to 3 kHz while maintaining reliable noise cancellation.
4Object-affected harmful factors
If the earphone shell provides passive acoustic attenuation, then high-frequency noise above 1 kHz can be blocked, but this requires an ear-enclosing circumaural seal that reduces comfort and adaptability
Solution Approach 1:
The system replaces mechanical passive acoustic attenuation (circumaural seal) with active feedforward noise cancellation using a distributed microphone array and digital signal processing. This allows high-frequency noise reduction up to 3 kHz without requiring a tight ear-enclosing seal, thereby maintaining comfort and adaptability for different ear shapes and sizes.
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
The solution achieves significant noise reduction up to 3 kHz with improved time-alignment and omnidirectional performance, surpassing the limitations of existing systems, which typically operate below 1 kHz, and provides effective noise cancellation across various sound directions.
Implementation Method 1
loudspeaker means, supported within said housing, for directing sound energy into an ear of a listener
Implementation Method 2
a plurality of microphone means located externally of said housing and positioned to sense ambient noise approaching said entry location; and means for converting the sensed ambient noise into electrical signals
Implementation Method 3
The signal detected by the microphone A is inverted at C and added to the drive signal applied to a loudspeaker D, thus creating the 'cancellation signal'. The intention is that destructive wave cancellation occurs between the cancellation signal and the incoming ambient acoustic noise signal
Data Source
AI summary
A feedforward ambient noise reduction arrangement includes, within a housing, a loudspeaker device for directing sound energy into an ear of a listener. Disposed externally of the housing, and positioned to sense ambient noise on its way to the listener's ear, are plural microphone devices capable of converting the sensed ambient noise into electrical signals for application to the loudspeaker to generate an acoustic signal opposing the ambient noise. Importantly, the overall arrangement is such that the acoustic signal is generated by said loudspeaker means in substantial time alignment with the arrival of said ambient noise at the listener's ear.