Active Noise Tuning With Secondary Path Modeling Stability
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Solution Overview
Problem
Active noise control systems face challenges in effectively suppressing broadband noise due to high computing requirements and stability issues, particularly with feedback structures, and in accurately modeling the acoustic feedforward branch, which affects the convergence of adaptive filters.
Innovation Solution
An active noise tuning system that includes a sound sensor, an adaptive filter, and a sound reproduction device, with a secondary path transfer function modeled by a first filter, providing control signals for the adaptive filter to suppress noise and adjust the secondary path transfer function, using algorithms like the least mean square (LMS) for efficient noise cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a feedback structure is used in active noise control systems, then noise suppression can be achieved, but stability problems occur and unwanted direct feedback is difficult to avoid
Solution Approach 1:
The patent inverts the conventional feedback structure by using a feedforward structure where the reference microphone is positioned between the noise source and the loudspeaker. This inversion allows the system to predict noise before it reaches the listening location, avoiding the stability issues inherent in feedback structures while maintaining effective noise suppression capability
2Object-affected harmful factors
If a reference microphone is used in feedforward structure, then noise reference signal can be obtained, but it is difficult to find a suitable location and obtain a suitable reference signal
Solution Approach 1:
The reference microphone is strategically positioned between the noise source and the loudspeaker to capture the noise signal before it is affected by the loudspeaker's output. This preliminary positioning ensures that the reference signal contains only the primary noise characteristics without contamination from the anti-noise signal, simplifying the system configuration and improving reference signal quality
3Reliability
If the acoustic feedforward branch is modeled using FURLMS or HFXLMS algorithms, then the system can operate, but considerable implementation expenditure is required
Solution Approach 1:
The patent extracts and separately models the acoustic feedforward branch transfer function using a dedicated filter. This separation allows for independent optimization of the feedforward path modeling without requiring complex adaptive algorithms like FURLMS or HFXLMS, thereby reducing implementation complexity while maintaining accurate noise cancellation performance
4Object-affected harmful factors
If adaptive filters are used for noise cancellation, then noise suppression can be achieved, but convergence is affected by inaccurate modeling of the secondary path
Solution Approach 1:
The patent segments the overall noise control system into distinct functional paths: the acoustic feedforward branch and the secondary path. Each path is modeled independently using dedicated filters, allowing for precise characterization of the secondary path transfer function without interference from other system components, thereby ensuring accurate adaptive filter convergence
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 achieves significant noise suppression, with damping of up to 20 dB, improving the quality of noise reduction and enabling effective integration into hands-free devices by accurately modeling the secondary path and stabilizing the adaptive filtering process.
Implementation Method 1
A sound reproduction device (e.g., loudspeaker) connected to the adaptive filter irradiates the noise signal filtered by the adaptive filter into the surroundings of the listening location
Implementation Method 2
a sound sensor (e.g., microphone) arranged in the surroundings of the listening location for picking up the noise signal
Data Source
AI summary
Active noise control system and method for controlling an acoustic noise generated by a noise source at a listening location, in which system and method sound is picked up in the surroundings of the listening location by a sound sensor; an electrical noise signal which corresponds to the acoustic noise of the noise source is generated and filtered adaptively in accordance with control signals. The adaptively filtered noise signal is irradiated into the surroundings of the listening location by a sound reproduction device, where a secondary path transfer function extends between the sound reproduction device and sound sensor. The noise signal is filtered with a transfer function that models the secondary path transfer function. The signals which are provided by the sound sensor after first filtering serve as control signals for the adaptive filtering.