Adaptive Feed-Forward Noise Cancellation for Earcup Coupling Changes
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Solution Overview
Problem
Existing active noise reduction systems face challenges in dynamically adapting to changes in earcup coupling, leading to ineffective noise attenuation, especially around 1 kHz, due to their open loop designs and require complex hardware and processing, making them impractical for low-cost, low-power applications.
Innovation Solution
An active noise reduction device with an electronic signal processing circuit featuring a feed-forward path using a fixed compensation filter and a variable compensation filter, controlled by a feed-forward controller that adjusts a control parameter to select linear filters varying in gain and spectral shape, and an error minimization algorithm to optimize noise reduction.
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 discomfort increase
Solution Approach 1:
The patent replaces passive mechanical noise reduction (relying on earcup size and sound absorbing material) with an active electronic system that uses microphones and signal processing to generate anti-noise signals. This substitution allows effective noise attenuation without increasing device bulkiness, as the electronic system achieves noise reduction through signal manipulation rather than physical barriers.
Solution Approach 2:
The patent employs adaptive filter coefficients that dynamically adjust based on detected noise characteristics and coupling conditions. By changing the parameters of the noise cancellation system in real-time, the device optimizes noise attenuation performance without requiring larger physical dimensions or more sound absorbing material.
2Object-affected harmful factors
If feed-back active noise reduction is used, then low and middle frequency noise attenuation is improved, but bandwidth increase is limited by acoustic transport delay
Solution Approach 1:
The patent uses feed-forward noise cancellation that processes noise signals before they enter the earcup cavity. By taking preliminary action on the noise signal through external microphones and predictive filtering, the system can attenuate noise across a broader frequency range without being constrained by acoustic transport delays that limit feed-back approaches.
3Object-affected harmful factors
If fixed feed-forward filtering is used, then noise attenuation in the 1 kHz region is improved, but adaptability to changes in earcup coupling is poor
Solution Approach 1:
The patent implements adaptive feed-forward filtering where the filter coefficients are dynamically adjusted based on real-time detection of coupling conditions and noise characteristics. This dynamic adaptation allows the system to maintain effective noise attenuation across varying earcup coupling scenarios, resolving the contradiction between fixed filtering effectiveness and adaptability.
Solution Approach 2:
The patent incorporates feedback mechanisms where the system continuously monitors noise levels and coupling conditions, using this information to adjust the feed-forward filter coefficients. This feedback loop enables the system to adapt to changes in earcup coupling while maintaining effective noise attenuation in the 1 kHz region and other frequency ranges.
4Adaptability or versatility
If adaptive algorithms are used to adjust filter coefficients, then adaptability to coupling changes is improved, but processing time and power consumption increase
Solution Approach 1:
The patent applies adaptive filtering selectively rather than continuously across all frequency ranges. The system adjusts filter coefficients based on detected noise characteristics and coupling conditions, applying adaptation only when and where needed. This partial action approach reduces unnecessary processing and power consumption while maintaining effective adaptability to coupling changes.
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 provides effective noise reduction across a broader frequency range, including the 1 kHz region, with reduced power consumption and complexity, enabling adaptation to changes in earcup coupling, thus improving noise attenuation performance.
Implementation Method 1
a variable compensation filter 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
Implementation Method 2
a feed-forward controller for determining the control parameter by calculating a control signal using the first signal and the second signal and then using the control signal to determine the control parameter
Implementation Method 3
The anti-noise signal is presented to the wearer's ear using a transducer such as a headphone driver
Implementation Method 4
Within the cavity, the transduced anti-noise signal and the unwanted acoustic noise combine destructively, resulting in reduction of the net acoustic noise inside the earcup
Data Source
AI summary
In an aspect, the invention features an active noise reduction device including an electronic signal processing circuit. The electronic signal processing circuit includes a first input for accepting a first signal, a second input for accepting a second signal, an output for providing a third signal, a feed-forward path from the first input to the output, and a feed-forward controller for determining the control parameter 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 and a variable compensation filter 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.