Feedforward Active Noise Control System Research Articles

A study on active road noise control based on operational transfer path analysis and selective subband adaptive filtering

In the feedforward active road noise control (ARNC) system, the noise reduction performance relies on the correlation between the reference signals and the target noise signals. To achieve better noise reduction performance, the operational transfer path analysis (OTPA) model with singular value decomposition was proposed to separate the road noise component from the target noise. Combined with OTPA and multi-coherence sorting method (MCSM), simulation analysis and real vehicle tests under various speeds both showed that the system with optimized reference sensor set had better road noise reduction performance, especially at the peak frequencies. To further improve noise reduction performance and reduce computational load, a selective subband adaptive filtering (SSAF) algorithm was proposed to build an active road noise control model with optimized reference sensor set. Simulation results, employing real vehicle test data, showed that the proposed method further improved the noise reduction performance and effectively reduced the amount of computational load.

A Feedback Active Control Approach to Road Noise Based on a Single Microphone Sensor to Improve Automotive Cabin Sound Comfort.

Tire-road noise deteriorates the sound quality of a vehicle's interior and affects the driving safety and comfort. Obtaining low interior noise is a challenge for passenger car manufacturers. Traditional passive noise control (PNC) is efficient for canceling high frequency noise but not useful for low frequency noise, while active noise control (ANC), according to the residual error signal, can generate an anti-noise signal to reduce the original noise. Most research has focused on improving the control effect for a feedforward ANC system. However, this paper emphasizes a feedback ANC system based on a signal microphone sensor. There are two main contributions in this study to improve automotive cabin sound comfort. One is that the algorithm of the feedback ANC system using a single microphone sensor without a reference noise signal is proposed based on the Filtered-x Least Mean Square method. The other is that the algorithm applies additive random noise online to estimate the secondary path model. A simulation was implemented based on measured real road noise data, and the simulation results indicate that the proposed feedback ANC system with the single microphone sensor can effectively attenuate road noise. This study shows the feasibility of applying a feedback ANC system in automobiles to increase the cabin sound quality.

A semi-adaptive feedforward hybrid active noise control algorithm for multichannel systems.

Broadband active noise control systems incorporating fixed controllers exhibit limited ability to reduce sinusoids. This study presents a semi-adaptive feedforward hybrid active noise control (HANC) system to address this issue. The proposed system pairs fixed high-order optimal controllers for broadband noise with adaptive low-order FXLMS-based controllers for narrowband noise. Notably, parallel broadband and narrowband controllers work independently. The proposed semi-adaptive feedforward HANC system demonstrates low computational complexity which makes it suitable for multichannel systems. Simulations and experiments validate the effectiveness of the proposed system in controlling mixed noise.

An improved stability compensation for feedforward active noise control systems with acoustic feedback

An improved stability compensation for feedforward active noise control systems with acoustic feedback

Experimental evaluation of feedforward active noise control system with optical laser microphone and proportional-integral-differential filter

In this paper, we propose a feedforward active noise control (ANC) system with an optical laser microphone utilizing a proportional-integral-differential (PID) filter. The feedforward ANC system with the optical laser microphone has been proposed to relax the causality constraint. This system adopts a first-order differentiator to modify the velocity picked up by the optical laser microphone. This modification achieves the improvement of the coherence between the velocity as the reference signal and the unwanted noise as the sound pressure. However, the frequency response of the first-order differentiator is similar to the high-pass filter and attenuates the reference signal at low frequencies. This causes the degradation of the noise reduction performance of the conventional ANC system. To solve this problem, the proposed ANC system adopts the PID filter instead of the first-order differentiator. By adjusting the coefficients of the PID filter, the proposed system avoids the attenuation of the reference signal at low frequencies. Then, the noise reduction performance can be improved. Experimental results show that the proposed ANC system reduces the unwanted noise compared to the conventional ANC system and relaxes the causality constraint compared to the basic ANC system in the real-time operation.

Coherence between error and acoustic reference microphones with two closely located noise sources

It is well known that locating acoustic reference microphones near the error microphone can improve the coherence between reference and error signals in feedforward active noise control systems. In this paper, the effects of the number of reference microphones and the distance between noise sources and reference microphones on the coherence between the reference and error signals are investigated based on an analytical model. Two scenarios when the two noise sources are located on the same side or opposite sides of the error microphone are studied. The simulation results show that the coherence coefficient can reach 1.0 regardless of the distance between the noise sources and the reference microphones if the number of reference microphones is the same as that of the noise sources. When the number of reference microphones is less than that of noise sources, the coherence coefficient in the low frequency range decreases as the reference microphones move close to the noise sources.

Theoretical convergence analysis of the FXLMS-based feedforward hybrid active noise control system

Real noise typically includes both broadband and narrowband components, such as noise generated by rotating machines. The feedforward hybrid active noise control (FFHANC) system reduces both components separately by arranging broadband and narrowband controllers in parallel. Although considerable efforts have been made to improve the FFHANC system, a theoretical analysis of its performance is still lacking. Consequently, the application of the FFHANC system lacks a solid foundation. Furthermore, the stability bounds of step sizes that guarantee convergence are not available in the literature. To address these problems, a convergence analysis of the FFHANC system based on the filtered-x least-mean-square algorithm is proposed. The analysis of the mean and mean-square convergence behaviors of the weight errors theoretically illustrates the advantages of the FFHANC system in terms of fast convergence and high reduction. The mutual coupling of parallel controllers in the mean-square sense is derived and discussed. By predicting the steady-state mean-square error and stability bounds, the proposed model can also guide the choice of step sizes. Our analysis lays the theoretical foundation for the practical application of the FFHANC system. Extensive simulations are performed to demonstrate the validity of the proposed theoretical theory.

A Complete Design of Smart Pad That Reduces Snoring

This paper presents integration of active noise control (ANC) systems with a smart pad to reduce the noise made by snoring. One reference microphone, two secondary speakers and two error microphones are used with a feedforward ANC algorithm in the smart pad design. Several smart functions including snore detection, quiet zone localization, and advanced audio integration are proposed. An effective way to satisfy the causality constraint of the feedforward ANC system is presented. The smart pad is independent of the pillow and is not in contact with the user; it is portable and is not a burden to the user during sleep. Several experiments are conducted to confirm the effectiveness of the smart pad when used on a full-size bed.

Stability Guaranteed Active Noise Control: Algorithms and Applications

Stability of the controller, robust stability of the active noise control (ANC) system, and limited output power of the hardware control board or actuators are crucial issues for ANC applications. Violation of these requirements results in output saturation, and hence nonlinear distortion by overloading the actuators. As a consequence, noise reduction performance of an ANC system will be dramatically degraded. A novel frequency-weighted leaky filtered-x least-mean-square (FxLMS) algorithm is developed in this article to fulfill these requirements. The proposed algorithm is an improvement of the traditional leaky FxLMS algorithm, where a frequency-weighted matrix is designed to replace the corresponding scalar weight. The frequency-weighted matrix, which is achieved by solving a constrained optimization problem, consists of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\it N$</tex-math> </inline-formula> frequency-weighted factors. By the frequency-weighted factors, the frequency response of the control filter is only suppressed at specific frequencies where the requirements on stability and/or limited output power are violated. Thus, the proposed control algorithm achieves better noise reduction performance than the traditional leaky FxLMS algorithm, which unnecessarily suppresses the control filter at all the frequencies. Simulations and experiments are carried out in a duct ANC system to verify the effectiveness of the proposed algorithm for both the feedforward and feedback ANC systems.

Delayless partial subband update algorithm for feed-forward active road noise control system in pure electric vehicles

Road noise is one of the dominant noise sources in pure electric vehicles. Active control for road noise is an attractive solution since this technique is suitable for controlling low-frequency noise. Feed-forward active road noise control (ARNC) systems utilize lots of reference signals and corresponding adaptive filters, and the control performance usually improves as the number of reference signals increases. To reduce the computational cost of ARNC systems so that more reference signals can be processed, we introduce the delayless subband structure into ARNC system and a delayless partial update subband with weighted reference signal normalized filtered-x least mean square (DPUS-WRS-NFxLMS) algorithm is proposed in this paper. Based on the traditional delayless subband algorithm, a partial subband update strategy is proposed to reduce the computational cost. Furthermore, the weighted reference signal is introduced for each subband filter. In this way, a modified vector is designed to assign different weights to different reference signal samples so that the convergence performance can be improved and the round-off error can be reduced. In addition, an adjustment strategy for the step size and reference signal weights is designed to make the algorithm have a better balance between the convergence rate and steady-state behavior. Finally, a purely time-delayed secondary path is constructed as the estimated secondary path to avoid the negative impact of the magnitude-frequency characteristics of the actual secondary path. The simulation results prove that the proposed algorithm achieves better control results than the traditional algorithms with lower computational complexity.

Experimental tests of a multichannel active noise control system with single and multiple reference signals applied to the cabin of a tractor

A feedforward active noise control system represents a valid solution whenever it is necessary to attenuate a disturbing noise at low frequency. One example of application is the case of tractors, in which the agricultural operators are exposed for several hours per day to loud noise at low frequency, mainly generated by the engine. Generally, the feedforward systems make use of one reference sensor to measure the noise produced by the main source. However, this way of proceeding could be inadequate to describe the disturbing noise, especially when the noise is divided both in structure-borne and air-borne components. In this article, a comparison between the use of a single and multiple reference signals, processed in a multichannel active noise control system applied to the cabin of a motionless tractor, is proposed. In particular, an accelerometer positioned on the turbocharger is used to sense the vibration generated by the engine, while a microphone placed near the engine is used to measure the air-borne noise. The active system implements the filtered-X least mean squares (FXLMS) algorithm to produce the anti-noise signals. The results show that the use of two simultaneously acquired reference signals improves the performance of the active system.

A robust feedforward hybrid active noise control system with online secondary‐path modelling

In this study, a robust feedforward hybrid active noise control (ANC) system with online secondary-path modelling (SPM) is proposed that is capable of not only effectively suppressing the broadband and narrowband noise components but also tracking the secondary path (SP) variations. An finite impulse response online SPM subsystem as well as an efficient decoupling filter are included in the proposed feedforward hybrid ANC (HANC) system. The decoupling filter is a parallel-form bandpass filter bank that consists of multiple bandpass filters that are derived from the second-order infinite impulse response notch filters. It takes the residual noise as its input and separates the broadband component from the narrowband component, with the former used as not only a desired signal for the SPM but also as an error signal for updating the broadband sub-controller, whereas the latter adapted simultaneously to scale the auxiliary white Gaussian noise and to update the narrowband sub-controller. Extensive simulations are conducted with both the synthetic and real SPs as well as the synthetic and real noise signals that are generated by a large-scale factory cutting machine (strand-cutter) to demonstrate the advantages and effectiveness of the proposed feedforward HANC system. Comparisons are also demonstrated with the original HANC system as well as its directly extended version with an online SPM subsystem.

Head-Mounted Multi-Channel Feedforward Active Noise Control System for Reducing Noise Arriving From Various Directions

A head-mounted active noise control (ANC) system based on the single-channel ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 1 \times 1$ </tex-math></inline-formula> ) feedforward control has been studied as a noise reduction method in complicated noise environments such as factories in which various machines are located that generate unwanted noises. However, it is difficult to reduce the noise arriving from various directions because the causality constraint cannot be satisfied. To solve this problem, we developed a head-mounted ANC system based on the multi-channel ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 1 \times 1$ </tex-math></inline-formula> ) feedforward control. This ANC system has two reference microphones that satisfy the causality constraint. Therefore, the proposed head-mounted ANC system achieves the expansion of noise reducible range of 0-100° compared to that of the conventional head-mounted ANC with the range of 0-60°. In this paper, we examine the effectiveness of the newly developed head-mounted ANC system. In the experiments, we evaluate the effectiveness of placing two reference microphones on noise reduction performance in the case of various arrival direction of the unwanted noise. Experimental results demonstrate that the proposed system increases the noise reducible range and improves the noise reduction performance for two noise sources. In addition, we theoretically prove the effectiveness of the proposed system.

Feedforward Active Noise Control System Using Optical Laser Microphone to Overcome Causality Constraint

Feedforward Active Noise Control System Using Optical Laser Microphone to Overcome Causality Constraint

Multizone active noise control for impulsive scattered sound of a rigid cylinder

Active noise control (ANC) can be applied to attenuate the scattered sound from an object, rendering it invisible to incident waves. This study proposes two secondary loudspeaker placement optimization methods for multizone ANC of impulsive scattered sound from a rigid cylinder. The first method is frequency-domain weighted least absolute shrinkage and selection operator (LASSO) algorithm, and the second method is a time-domain iterative algorithm. Based on the two methods, a broadband feedforward ANC system is presented to suppress impulsive forward-scattered and backward-scattered sound. The experimental results show that compared with the configuration of uniformly placed loudspeakers and traditional LASSO algorithms, the proposed weighted LASSO algorithm and iterative algorithm achieve better control performance in the target and observing areas with less power when controlling 500 Hz–1000 Hz impulsive scattered sound.

A new feedforward and feedback hybrid active noise control system for excavator interior noise

Excavator interior noise is composed of the engine order narrowband noise and the impulsive broadband noise caused by working device. In situations where only narrowband reference signal can be obtained, the feedforward active noise control (ANC) system can just eliminate the narrowband component, failing to control the broadband noise. Hybrid feedforward and feedback ANC (HANC) systems are useful for such applications where the reference signals can be partially obtained. However, existing HANC systems have the following drawbacks: coupling between subsystems; inaccurate error and reference signals; high computational complexity; performance degradation in response to the impulsive noise. To solve the above problems, this paper proposes a new feedforward and feedback HANC system consisting of 3 subsystems, namely, a delayed feedforward narrowband subsystem, a robust feedback broadband subsystem, and a supporting error calculating (SEC) subsystem. In the proposed HANC system, not only subsystems are decoupled, but also accurate error and reference signals are provided by SEC subsystem. In addition, calculating efficiency is improved by applying the delayed notch least mean square (DLMS) algorithm to the feedforward subsystem, and the system robustness is promoted by adopting the robust algorithm into the feedback subsystem. Numerous computer simulations are performed on the excavator interior noise measured under actual operating conditions. The corresponding results demonstrate the superior performance of the proposed HANC system in terms of the power spectral density of residual error, average noise reduction, robustness of the system, and calculation efficiency to the existing HANC systems. Real-time experiments on excavator interior noise showed that the proposed HANC system was efficient in eliminating broadband and narrowband mixture noise in practice.

Hybrid active and passive noise control in ventilation duct with internally placed microphones module

A feedforward active noise control (ANC) system combined with the passive silencer is built to reduce the acoustic noise propagating through the ventilation duct. The passive silencer consists of two layers which are made of aluminum plate and the perforated panels respectively, the cavity between the two layers is filled with the melamine foam. To overcome the two issues encountered in the active noise control for ventilation duct, i.e., the turbulent flow noise and the acoustic feedback, the emphasis of ANC system is the internally placed microphones module. The module is made of a perforated panel shell filled with the melamine foam, the reference and error microphones are both placed in the melamine foam. The real experiments show that the passive silencer has more than 20 dB noise attenuation at frequencies above 600 Hz, ANC can obtain more than 10 dB noise attenuation from 70 Hz to 200 Hz (the maximum 17 dB at 150 Hz) when the wind speed increases from 5 m/s to 10 m/s. In addition, the module is easy to install and maintain, and its manufacturing cost is also acceptable.

Multi-functional active noise control system on headrest of airplane seat

This work describes a multi-functional active noise control (ANC) system installation in an airplane seat. Most researchers in the field have focused on systems that cancel narrowband noise on headrests owing to the causality constraint of ANC system. Therefore, ANC systems in seats have limited performance. In this paper, an ANC system is designed for an airplane seat and the electronic delay of the ANC system is reduced to meet the causality requirement of a feedforward ANC system. An infrared sensor is used to detect the head of the occupant of the seat, so the ANC system can automatically cause the quiet zone to surround the ears of users with various sitting postures. Multiple noise sources and the automatic activation function of the ANC system are discussed. Experimental results show that the proposed ANC system for an airplane seat effectively reduces recorded airplane noise without the need for earplugs or an ANC headset.

Multi-channel feedforward active noise control system for reducing snore noise with snore noise-term detection

In this paper, a multi-channel feedforward active noise control system for reducing snore noise with noise-term detection is proposed. The snore noise consists of a noise-term and a silent-term, and it is difficult to reduce the snore noise by the active noise control system. Since the conventional multi-channel feedforward active noise control system updates the noise control filters even in the silent-term, the conventional active noise control system updates the noise control filters unnecessarily. Therefore, the proposed multi-channel feedforward active noise control system introduces threshold processing to update the noise control filters only in the noise-term. Owing to this process, it is possible to reduce the update count of the noise control filters. Simulation results show that the proposed active noise control system can reduce the snore noise as same as the conventional active noise control system and can reduce the update count of the noise control filters compared to the conventional active noise control system.

A modified feedforward hybrid active noise control system for vehicle

The feedforward hybrid active noise control (HANC) system combines the strengths of the narrowband ANC (NANC) system and the broadband ANC (BANC) system. Taking this advantage into account, this paper applies it to attenuate the vehicle interior noise mixed with narrowband and broadband components. However, in the HANC system, the NANC subsystem and BANC subsystem are fed a common error signal which depends on the combined secondary signals from the both subsystems. This causes the problem of mutual coupling and hence affects the noise reduction performance. To tackle the problem, we propose a modified HANC (MHANC) system in this paper. In the MHANC system, the error signal of each ANC subsystem is independently synthesized on the basis of the estimated primary and secondary signals. Note that the NANC system for engine order noise control suffers performance deterioration when the fluctuating real-time engine speed signal is used for constructing internal reference signals. For performance improvement, an enhanced NANC (ENANC) system is developed by smoothing the fluctuating engine speed signal. Meanwhile,the ENANC system is incorporated in the MHANC system to form an enhanced MHANC (EMHANC) system. Simulations were performed on the vehicle interior noise recorded under actual driving conditions. The corresponding results demonstrate the superiority of the proposed MHANC and EMHANC systems.