Active Noise Control System Harmonic Distortion Suppression
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Solution Overview
Problem
Active noise control devices experience harmonic distortion due to changes in environmental conditions, leading to abnormal noise from harmonics of the noise canceling sound, which are audible to occupants.
Innovation Solution
A noise control system that includes a harmonic detection unit to monitor and control the output level of noise canceling sound, using adaptive filters to minimize error signals and suppress harmonic components, ensuring the noise canceling sound's level does not exceed a predetermined threshold, thereby reducing harmonic noise output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the noise control system increases the output level of noise canceling sound to improve noise cancellation effectiveness, then the noise cancellation performance is improved, but harmonic distortion increases causing abnormal noise to be heard by occupants
Solution Approach 1:
The system uses a microphone to detect harmonic components in the output sound and feeds this information back to the control unit. The control unit then adjusts the output level of the noise canceling sound to suppress harmonic distortion while maintaining effective noise cancellation. This closed-loop feedback mechanism allows the system to dynamically optimize performance and avoid abnormal noise.
Solution Approach 2:
The output level of the noise canceling sound is made dynamically adjustable rather than fixed. The control unit continuously monitors harmonic components and adjusts the output level in real-time based on environmental conditions and system response, allowing optimal balance between noise cancellation effectiveness and harmonic distortion suppression.
2Adaptability or versatility
If the system operates in low temperature environments, then the noise control function remains active, but the speaker produces harmonic distortion causing abnormal noise
Solution Approach 1:
The feedback mechanism detects harmonic components generated under low temperature conditions and triggers output level adjustment. The microphone continuously monitors the acoustic output and provides feedback to the control unit, which then suppresses the output level when harmonic distortion is detected, allowing the system to adapt to environmental conditions while preventing abnormal noise.
Solution Approach 2:
The system changes the output parameter (output level) in response to environmental parameter changes (temperature). When low temperature conditions cause harmonic distortion in the speaker, the control unit adjusts the output level parameter to suppress the distortion, allowing the system to maintain functionality across different environmental conditions without producing abnormal noise.
Data Source
AI summary
An active noise control unit generates a noise canceling sound of a single frequency that cancels engine sound heard by an occupant and outputs the noise canceling sound to a speaker through an amplifier. A second harmonic detector and a third harmonic detector detect a magnitude of a harmonic component of the noise canceling sound included in sound collected by a microphone. A controller controls a frequency of the noise canceling sound generated by the active noise control unit to a fundamental frequency of the engine sound based on a rotation frequency of the engine, and in addition, causes an output level control unit to control a level of the noise canceling sound to be output to the amplifier so that the level of the noise canceling sound becomes higher when the magnitude of the harmonic component exceeds a predetermined threshold value.