Active Noise Control Apparatus for Aircraft Cabin Acoustic Management
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Solution Overview
Problem
Conventional noise reduction methods in hermetically sealed structures like aircraft cabins face challenges in effectively reducing noise when the time causality limitation between noise detection, control sound generation, and the silencing center cannot be satisfied, particularly due to multiple noise sources, leading to inadequate noise reduction performance.
Innovation Solution
A noise reduction apparatus employing a feed-forward control system with adaptive filtering and band-limited control sound signals, where microphones and speakers are strategically positioned to optimize noise detection and cancellation, even when the time causality limitation is not met, by using band-limited control sound signals and positioning microphones close to the control point to enhance noise reduction efficacy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If passive attenuation means (sound insulating materials) are used to reduce noise, then noise reduction effect is achieved, but weight increases and fuel consumption increases
Solution Approach 1:
The patent replaces passive mechanical sound insulation materials with an active noise control system that uses microphones, speakers, and signal processing to generate anti-phase sound waves. This substitutes heavy physical materials with lightweight electronic and acoustic components, achieving noise reduction without the weight penalty of traditional soundproofing materials.
2Object-affected harmful factors
If microphone is positioned close to speaker and silencing center to reduce noise, then noise reduction effect is enhanced, but time causality limitation cannot be satisfied
Solution Approach 1:
The system performs preliminary action by predicting future noise conditions based on past and present microphone signals. The adaptive filter processes the microphone input to generate control signals that anticipate the noise that will reach the silencing center, allowing the system to prepare anti-phase cancellation signals in advance without violating time causality.
Solution Approach 2:
The patent implements dynamic adaptation by continuously adjusting the filter coefficients in real-time based on changing noise characteristics. The adaptive filter dynamically modifies its response to maintain optimal noise cancellation performance as noise sources vary, allowing flexible positioning of components without fixed time delay constraints.
3Object-affected harmful factors
If adaptive filter processes entire frequency band, then comprehensive noise reduction is achieved, but processing complexity increases and performance degrades when time causality limitation is not satisfied
Solution Approach 1:
The patent segments the frequency spectrum by applying bandpass filters to divide the full frequency band into multiple narrower bands. Each band is processed independently by separate adaptive filters, which reduces the computational complexity and processing burden on each individual filter while maintaining comprehensive noise reduction across the entire frequency range through the combined effect of all band processors.
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 apparatus achieves effective noise reduction across a controlled frequency band, even when the time causality limitation is not satisfied, by generating control sound signals with an upper limited frequency, thereby improving the noise reduction effect in environments with multiple noise sources.
Implementation Method 1
generating a control sound with an opposite phase to that of the detected noise signal to cancel noise
Implementation Method 2
noise from the noise source is detected with the microphone
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
In a noise reduction apparatus for controlling noise up to a predetermined upper limited frequency, a distance from a noise source to control point X is made larger than a distance obtained by subtracting a one-half wavelength from a distance, obtained by adding up a distance from the noise source to a noise detecting microphone, a distance corresponding to time as a sum of respective delay time of the noise detecting microphone, a noise controller, and a control speaker, and a distance from the control speaker to control point X, where one wavelength is a period corresponding to the upper limited frequency.