Active Noise Reduction Filter Update Without White Noise
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Solution Overview
Problem
Existing active noise reduction systems of the IMC type discomfort occupants with white noise during adaptive update of secondary path filters, leading to inaccurate updates.
Innovation Solution
An active noise reduction system that adaptively updates the secondary path filter using a primary path filter without white noise, employing a controller with normalization of adaptive update amounts and weighting coefficients to ensure quick convergence and stability, allowing for noise reduction without discomforting occupants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If white noise is output from the canceling sound output device for adaptive update of the secondary path filter, then the adaptive update can be performed, but the white noise may be heard by the occupant causing discomfort
Solution Approach 1:
The patent extracts the white noise generation function from the canceling sound output device and implements it separately through the primary path filter. This allows the adaptive update process to use generated noise signals without requiring the main canceling sound device to output uncomfortable white noise directly to the occupant's environment.
Solution Approach 2:
The patent introduces an intermediary mechanism where the primary path filter generates noise signals that are used for adaptive update purposes, rather than directly outputting white noise through the canceling sound output device. This intermediary approach enables the update process while avoiding direct exposure of occupants to harsh white noise.
2Object-affected harmful factors
If the white noise level is reduced so that the occupant does not hear it, then occupant comfort is improved, but the adaptive update of the secondary path filter cannot be performed accurately
Solution Approach 1:
The system uses the primary path filter to generate the necessary noise signals for adaptive updating, making the system self-sufficient for calibration purposes without relying on external white noise input that would compromise occupant comfort.
Solution Approach 2:
The patent changes the source and characteristics of the noise signal from traditional white noise output to noise generated through the primary path filter, altering the signal parameters to achieve both accurate adaptation and occupant comfort.
3Reliability
If the secondary path filter is updated using conventional methods, then the filter can be adapted, but the convergence speed may be slow due to fluctuations in the other filter
Solution Approach 1:
The patent performs preliminary normalization of adaptive update amounts using a common normalization divisor before the actual filter updates occur. This preliminary action stabilizes the update process and prevents fluctuations that would otherwise slow down convergence.
Solution Approach 2:
The system implements a feedback mechanism where the adaptive update amounts of both filters are normalized using a common divisor, creating a balanced feedback loop that ensures stable and quick convergence of both filters simultaneously.
Data Source
AI summary
An active noise reduction system of an IMC type includes a canceling sound output device, an error microphone, and a controller. The error microphone is configured to generate an error signal. The controller includes a control filter and a secondary path filter. The secondary path filter is configured to generate a canceling sound estimation signal. The control filter is configured to generate a control signal based on a reference signal generated based on both the error signal and the canceling sound estimation signal. The controller further includes a primary path filter configured to generate a noise estimation signal based on the reference signal. The secondary path filter and the primary path filter are configured to be adaptively updated based on a virtual error signal generated based on both the reference signal and the noise estimation signal.