Feedforward Noise Cancellation Using Modal Testing and MIMO Control
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Solution Overview
Problem
In large enclosed spaces like jet aircraft, active noise cancellation is complicated by multiple incoherent noise sources and changing sound transmission paths, making it difficult to achieve effective noise reduction using existing feedforward control methods.
Innovation Solution
A method involving a microphone array inside the space and modal testing on the outside surface to create acoustic mathematical models, allowing for the generation of a noise canceling signal that adapts to incoherent noise sources, using a MIMO transfer function matrix and adaptive control to predict force distributions and update noise cancellation in real-time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional feedforward control methods are used in large enclosed spaces, then the system structure is simple, but the noise cancellation effectiveness deteriorates due to multiple incoherent noise sources and changing sound transmission paths
Solution Approach 1:
The patent segments the enclosed space into multiple zones with distributed microphone arrays and speaker systems. Instead of treating the entire space as a single control volume, the system divides it into smaller regions that can be controlled independently, allowing effective noise cancellation even with multiple incoherent sources by addressing each segment separately
Solution Approach 2:
The patent performs preliminary modal testing and acoustic characterization of the enclosed space to build mathematical models before implementing noise cancellation. Transfer functions are pre-calculated based on the measured acoustic properties, allowing the system to predict sound propagation paths and optimize control strategies in advance rather than adapting in real-time during operation
2Measurement precision
If modal testing with multiple incoherent noise sources is conducted, then the acoustic mathematical models become more accurate, but the measurement and modeling process becomes more complex
Solution Approach 1:
The patent uses periodic excitation signals during modal testing to efficiently characterize the acoustic properties of the enclosed space. By applying periodic forces or vibrations at different frequencies and measuring the resulting acoustic responses, the system can extract transfer functions and modal parameters systematically, reducing measurement complexity while maintaining accuracy
Solution Approach 2:
The patent varies the excitation parameters (frequency, amplitude, location of incoherent noise sources) during modal testing to comprehensively characterize the acoustic environment. By changing these parameters and measuring the corresponding acoustic responses, the system builds a robust mathematical model that accounts for different operating conditions without requiring excessively complex measurement procedures
3Reliability
If the noise canceling signal adapts to changing noise patterns in real-time, then the noise cancellation effectiveness is improved, but the computational requirements and system complexity increase
Solution Approach 1:
The patent performs preliminary acoustic characterization and pre-calculates transfer functions during system setup or maintenance periods when computational resources are abundant. These pre-computed models are then used during real-time operation to reduce the computational burden, allowing the system to adapt to changing noise patterns without requiring excessive processing power during actual noise cancellation
Solution Approach 2:
The patent implements adaptive control algorithms that dynamically adjust the noise cancellation parameters based on real-time measurements from microphone arrays. The system continuously monitors acoustic conditions and updates control signals to match changing noise patterns, balancing computational requirements with the need for effective real-time adaptation through efficient algorithm design
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
This approach enables effective noise cancellation in complex environments with multiple incoherent sources by accurately predicting sound propagation and adapting to changing noise patterns, improving passenger comfort by reducing noise levels in turboprop and jet aircraft cabins.
Implementation Method 1
placing a microphone array inside an inner surface of the enclosed space
Implementation Method 2
a noise canceling signal is generated according to an output of the mathematical models
Data Source
AI summary
A method for feedforward noise cancellation in an enclosed space within a structure is provided. The method comprises placing a microphone array inside an inner surface of the enclosed space and conducting modal testing on an outside surface of the enclosed space, wherein the modal testing comprises multiple incoherent noise sources corresponding to locations of microphones in the microphone array. Noise generated by the modal testing is processed to create a number of acoustic mathematical models of the enclosed space. In response to incoherent noise within the enclosed space, a noise canceling signal is generated according to an output of the mathematical models.