Active Noise Control System Transfer Function Adaptation
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Solution Overview
Problem
Existing active noise control systems fail to adapt effectively to changes in transfer functions from noise sources to the ear or microphone positions, leading to inadequate noise cancellation.
Innovation Solution
An active noise control device with learning processing units that set and adapt transfer functions for filters to account for changes in transfer functions from noise sources to ear or microphone positions, ensuring continuous noise cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the error signal is corrected using previously obtained differences between transfer functions, then the transfer function can be set to cancel noise at the user's ear position, but the system cannot adapt when the transfer functions change
Solution Approach 1:
The patent implements dynamic adaptation by continuously monitoring the error signal and updating the transfer function estimates in real-time. The system transitions from static pre-obtained transfer function differences to dynamic continuous adaptation, allowing the noise cancellation system to respond to changing acoustic conditions between the noise source, microphone, and user ear positions.
Solution Approach 2:
The system uses the error signal from the microphone as feedback to continuously refine the transfer function estimates. By feeding back the actual noise and cancellation signal measurements to the adaptive filter, the system automatically adjusts to transfer function changes without requiring external recalibration, resolving the contradiction between initial precision and ongoing adaptability.
2Reliability
If a microphone is disposed near the user's ear to generate cancellation sound, then noise can be canceled at the ear position, but the system fails to adapt when transfer functions change
Solution Approach 1:
The system performs preliminary adaptive filtering to establish initial transfer function estimates between the noise source, microphone, and ear position. These pre-established filters provide a foundation for noise cancellation that can be quickly refined through continuous feedback, enabling the system to maintain reliability while adapting to changes.
Solution Approach 2:
The noise control system performs self-adjustment by using its own error signal to automatically update its transfer function estimates. The system serves itself by continuously learning from the acoustic environment without requiring external intervention, maintaining both reliability and adaptability through autonomous operation.
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 cancels noise at the ear position by adapting to changes in transfer functions, ensuring consistent noise reduction even when these functions change, and can be applied to on-vehicle audio systems.
Implementation Method 1
generates an anti-noise signal to drive a speaker to produce sound waves to destructively interfere with an undesired sound
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
There is provided an "active noise control system and an on-vehicle audio system" which are most suitable for acoustic control in a vehicle and adapt to a change in a transfer function. Audio (noise source) is output as a cancellation sound through a variable filter (151) and a first filter (154) and transmitted to the second filter (155), a subtractor (156) subtracts an output of a second filter (155) from an output of a microphone (16), and an adaptive algorithm execution unit (152) updates a transfer function of the variable filter (151) so that the subtracted result becomes 0. A transfer function A for the first filter (154) is a transfer function which can cancel noise at a position of a user's ear by setting, as the cancellation sound, a sound obtained by applying the transfer function A to audio at the time of learning, and a transfer function B for the second filter (155) is a transfer function which can eliminate, for the cancellation sound, a difference between a sound obtained by applying the transfer function B to audio and the output of the microphone (16).