Adaptive Feed-Forward Noise Reduction for Headphones
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Solution Overview
Problem
Existing active noise reduction systems face challenges in dynamically adapting to changes in earcup coupling, leading to suboptimal noise attenuation, especially around the 1 kHz frequency band, due to their open loop designs and power-intensive hardware requirements, making them impractical for low-cost, low-power applications like consumer headphones.
Innovation Solution
An adaptive noise reduction system incorporating a feed-forward path with a variable compensator and controller that adjusts the transfer function based on the difference between the actual and average earcup coupling, using a family of linear filters to optimize noise cancellation, and a simple error minimization algorithm to adjust the parameter β, allowing for efficient noise reduction without complex hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If passive noise reduction techniques are used with increased sound absorbing material and larger earcup size, then noise attenuation is improved, but device bulkiness and comfort deteriorate
Solution Approach 1:
The patent changes the approach from passive physical parameters (material quantity, earcup size) to active electronic parameters (electrical signals, transfer functions). The system uses electronic compensation with variable transfer functions to achieve noise attenuation without increasing physical size, resolving the contradiction between noise reduction performance and device bulkiness.
2Object-affected harmful factors
If feed-back active noise reduction is used to reduce low frequency noise, then noise attenuation is improved, but system complexity and power consumption increase
Solution Approach 1:
The patent extracts the essential function of active noise reduction from the complex feed-back system and implements it through a simplified feed-forward approach. By taking out only the necessary compensation function and implementing it with a variable transfer function in the feed-forward path, the system achieves low frequency noise attenuation with reduced complexity.
3Object-affected harmful factors
If open loop feed-forward filtering is used to improve attenuation around 1 kHz, then noise attenuation is improved, but adaptability to coupling changes deteriorates
Solution Approach 1:
The patent introduces dynamics into the feed-forward path by implementing a variable transfer function that can adapt to coupling changes. The transfer function is modified based on detected coupling conditions, allowing the system to maintain both improved 1 kHz attenuation and adaptability to changing earcup coupling conditions.
4Adaptability or versatility
If adaptive algorithms are used to compensate for coupling changes, then adaptability is improved, but power consumption and hardware complexity increase
Solution Approach 1:
The patent uses a simplified adaptive approach that requires minimal computational resources and power consumption. Instead of complex adaptive algorithms, the system uses a variable transfer function with a single adjustable parameter that can be updated with simple measurements, achieving coupling compensation with low power and hardware requirements.
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 system effectively compensates for variations in earcup coupling, improving noise attenuation across a broader frequency range with reduced power consumption and complexity, making it suitable for low-cost, low-power applications like consumer headphones.
Implementation Method 1
The anti-noise signal is then presented to the wearer's ear 108 using a transducer such as a headphone driver 112
Implementation Method 2
a microphone 106 to sense unwanted acoustic noise in a cavity formed by a coupling of the earcup 101 and a wearer's head 109, and convert it to an electrical signal
Implementation Method 3
an earcup can be designed such that its size, fit to a wearer's head, and sound absorption properties cause passive attenuation of ambient acoustic noise
Implementation Method 4
hearing protection ear muffs such as those worn on the flight deck of an aircraft carrier can be designed to absorb and reflect potentially damaging acoustic noise
Implementation Method 5
Within the cavity, the transduced anti-noise signal and the unwanted acoustic noise 104 combine destructively, resulting in reduction of the net acoustic noise inside the earcup
Data Source
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AI summary
The invention features an active noise reduction device (300) including an electronic signal processing circuit. The electronic signal processing circuit includes a first input (216) for accepting a first signal (104), a second input (106) for accepting a second signal, an output (112) for providing a third signal, a feed- forward path (220) from the first input to the output, and a feed- forward controller (326) for determining the control parameter (324) by calculating a control signal using the first signal and the second signal and then using the control signal to determine the control parameter. The feed- forward path includes a fixed compensation linear filter (218) and a variable compensation filter (322) having an input for receiving a control parameter that applies a selected linear filter from a family of linear filters that vary in both gain and spectral shape and are selectable by the control parameter.