Active Noise Control with Sequential Acoustic Path Identification
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Solution Overview
Problem
In aircraft and railroad coaches, existing noise reduction methods, both passive and active, face challenges such as weight increments, material strength issues, and inefficiencies in measuring acoustic transmission functions when multiple noise reduction devices are installed, leading to suboptimal noise reduction and service quality degradation.
Innovation Solution
A noise reduction system comprising noise sensors, controllers, and error sound sensors that generate and identify acoustic transmission functions using identification sounds, allowing multiple devices to identify their functions sequentially and accurately without interference from external or adjacent noise reduction devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If passive attenuating measures using sound insulating material are taken, then noise reduction 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 electronic signal processing. The system generates anti-phase acoustic waves through speakers based on noise detected by microphones, eliminating the need for heavy sound-absorbing materials while achieving noise reduction through acoustic interference rather than physical barriers.
Solution Approach 2:
The system changes the phase parameter of the acoustic wave by 180 degrees to create destructive interference with the noise. By generating sound waves with opposite phase to the detected noise, the system achieves noise cancellation through parameter modification rather than physical attenuation, avoiding the weight penalty of traditional materials.
2Object-affected harmful factors
If multiple noise reduction devices are installed, then noise reduction coverage is improved, but measurement of acoustic transmission function becomes inaccurate due to external noise interference
Solution Approach 1:
The system performs preliminary identification of acoustic transmission functions for each device before full operation begins. By pre-measuring and storing the acoustic characteristics of each speaker-microphone pair in isolation, the system establishes baseline data that can be used during multi-device operation, eliminating the need for continuous measurements that would be contaminated by other devices' sound output.
Solution Approach 2:
The system uses periodic identification sounds at specific intervals to update acoustic transmission functions only when necessary. During normal operation, devices rely on previously identified parameters, and re-identification occurs periodically or when conditions change, reducing interference from simultaneous measurements while maintaining measurement accuracy when updates are performed.
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
Enables fast and accurate identification of acoustic transmission functions for multiple noise reduction devices, improving noise reduction efficiency and service quality by minimizing interference and optimizing noise reduction in complex noise environments.
Implementation Method 1
a noise sensor for sensing a noise
Implementation Method 2
an error sound sensor for sensing an error sound between the noise and the controlling sound
Implementation Method 3
a controlling sound output section for outputting a controlling sound to be superposed on the noise
Data Source
AI summary
A noise reduction device is disclosed, in which noise reduction device, a controlling sound generator outputs a white noise generated by a white-noise generator, and this white noise is sensed by an error sensor for identifying an acoustic transmission function covering a path from the controlling sound generator to the error sensor. At this time, an identification controller prompts the white noise generator to generate a white noise for identifying the acoustic transmission function provided that an ambient noise level sensed by the error sensor is not greater than a given threshold.