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16 pages, 3396 KiB

Open AccessArticle

Application Study of Adaptive Tracking Algorithm in Active Noise Control System of Transformer

by Liming Ying, Jinwei Wang, Qin Liu and Donghui Wang

Appl. Sci. 2019, 9(13), 2693; https://doi.org/10.3390/app9132693 - 2 Jul 2019

Cited by 7 | Viewed by 2987

Abstract

Active noise control (ANC) technology can be able to reduce the low frequency noise effectively, and has been widely applied in limited enclosed equipment, such as cars, aircraft cockpits, and headphones, etc. Compared with the traditional noise reduction methods, ANC technology is a [...] Read more.

Active noise control (ANC) technology can be able to reduce the low frequency noise effectively, and has been widely applied in limited enclosed equipment, such as cars, aircraft cockpits, and headphones, etc. Compared with the traditional noise reduction methods, ANC technology is a cost-effective method in handling the low-frequency noise of transformers. An experimental ANC system in a virtual substation is designed and constructed. An adaptive signal tracking ANC algorithm is proposed, and a set of ANC experimental prototypes applied to a virtual substation is designed. Based on the proposed algorithm, the distributions of the acoustics and spectral characteristics of transformer noise in substations are analyzed. Experimental results show that the effective noise reduction can be achieved an average of 5 dB(A) in a given region with respect to the absence of the ANC system. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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11 pages, 1182 KiB

Open AccessArticle

Combination of Robust Algorithm and Head-Tracking for a Feedforward Active Headrest

by Rong Han, Ming Wu, Chen Gong, Shangshuai Jia, Tieli Han, Hongling Sun and Jun Yang

Appl. Sci. 2019, 9(9), 1760; https://doi.org/10.3390/app9091760 - 28 Apr 2019

Cited by 20 | Viewed by 3381

Abstract

Active headrest can reduce the low-frequency noise around ears based on the principle of active noise control. This paper presents a combination of robust algorithm and head-tracking for a feedforward active headrest to reduce the broadband noise for a sleeper on a high-speed [...] Read more.

Active headrest can reduce the low-frequency noise around ears based on the principle of active noise control. This paper presents a combination of robust algorithm and head-tracking for a feedforward active headrest to reduce the broadband noise for a sleeper on a high-speed train. A robust algorithm based on the feedforward active noise control is proposed to improve the noise control performance during head rotations. The head-tracking system with infrared rangefinders tracks the head position based on the Kalman filter to further improve system performance with head movements. Experiments were conducted on a model of a sleeper on a high-speed train. The experimental results show that the proposed active headrest system effectively controls broadband noise with head movements and rotations. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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12 pages, 1304 KiB

Open AccessArticle

Active Control of Broadband Noise Inside a Car Using a Causal Optimal Controller

by Liping Zhu, Tiejun Yang, Xinhui Li, Lihong Pang and Minggang Zhu

Appl. Sci. 2019, 9(8), 1531; https://doi.org/10.3390/app9081531 - 12 Apr 2019

Cited by 10 | Viewed by 2761

Abstract

This paper investigates active broadband noise control inside vehicles with a multichannel controller. The noncausal inversion of a practical nonminimum-phase secondary path is formulated, and its influence on noise-reduction performance is analyzed. Based on multiple coherence between reference signals and undesired noise, a [...] Read more.

This paper investigates active broadband noise control inside vehicles with a multichannel controller. The noncausal inversion of a practical nonminimum-phase secondary path is formulated, and its influence on noise-reduction performance is analyzed. Based on multiple coherence between reference signals and undesired noise, a novel formulation for identifying primary paths with correlated excitation signals is presented and a causal optimal controller is proposed. Meanwhile, the proposed controller can be used as an accurate predictor to estimate the maximal achievable noise reduction and provide a reference to improve the control systems. The robustness of the proposed algorithm is examined by varying the uncertainty of primary paths. Finally, the performance of the proposed causal optimal controller is validated using the data measured in a car. The results show that the proposed algorithm outperforms traditional algorithms and achieves a significant broadband noise reduction in time-invariant systems. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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12 pages, 4916 KiB

Open AccessArticle

Noise Reduction Using Active Vibration Control Methods in CAD/CAM Dental Milling Machines

by Eun-Sung Song, Young-Jun Lim, Bongju Kim and Jeffery Sungjae Mun

Appl. Sci. 2019, 9(8), 1516; https://doi.org/10.3390/app9081516 - 12 Apr 2019

Cited by 5 | Viewed by 5791

Abstract

Used in close proximity to dental practitioners, dental tools and devices, such as hand pieces, have been a possible risk factor to hearing loss due to the noises they produce. Recently, additional technologies such as CAD/CAM (Computer Aided Design/Computer Aided Manufacturing) milling machines [...] Read more.

Used in close proximity to dental practitioners, dental tools and devices, such as hand pieces, have been a possible risk factor to hearing loss due to the noises they produce. Recently, additional technologies such as CAD/CAM (Computer Aided Design/Computer Aided Manufacturing) milling machines have been used in the dental environment and have emerged as a new contributing noise source. This has created an issue in fostering a pleasant hospital environment. Currently, because of issues with installing and manufacturing noise-reducing products, the technology is impractical and insufficient relative to its costly nature. In this experiment, in order to create a safe working environment, we hoped to analyze the noise produced and determine a practical method to attenuate the noises coming from CAD/CAM dental milling machines. In this research, the cause for a noise and the noise characteristics were analyzed by observing and measuring the sound from a milling machine and the possibility of reducing noise in an experimental setting was examined using a noise recorded from a real milling machine. Since a milling machine generates noise mainly due to vibration of the dust collector, the possibility of reducing noise was examined by controlling vibration. This study was conducted to understand the cause for noise from the milling machine and verify the possibility of improving noise by a tactile transducer. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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18 pages, 6848 KiB

Open AccessArticle

A Model to Predict Acoustic Resonant Frequencies of Distributed Helmholtz Resonators on Gas Turbine Engines

by Jianguo Wang, Philip Rubini, Qin Qin and Brian Houston

Appl. Sci. 2019, 9(7), 1419; https://doi.org/10.3390/app9071419 - 4 Apr 2019

Cited by 22 | Viewed by 5074

Abstract

Helmholtz resonators, traditionally designed as a narrow neck backed by a cavity, are widely applied to attenuate combustion instabilities in gas turbine engines. The use of multiple small holes with an equivalent open area to that of a single neck has been found [...] Read more.

Helmholtz resonators, traditionally designed as a narrow neck backed by a cavity, are widely applied to attenuate combustion instabilities in gas turbine engines. The use of multiple small holes with an equivalent open area to that of a single neck has been found to be able to significantly improve the noise damping bandwidth. This type of resonator is often referred to as “distributed Helmholtz resonator”. When multiple holes are employed, interactions between acoustic radiations from neighboring holes changes the resonance frequency of the resonator. In this work, the resonance frequencies from a series of distributed Helmholtz resonators were obtained via a series of highly resolved computational fluid dynamics simulations. A regression analysis of the resulting response surface was undertaken and validated by comparison with experimental results for a series of eighteen absorbers with geometries typically employed in gas turbine combustors. The resulting model demonstrates that the acoustic end correction length for perforations is closely related to the effective porosity of the perforated plate and will be obviously enhanced by acoustic radiation effect from the perforation area as a whole. This model is easily applicable for engineers in the design of practical distributed Helmholtz resonators. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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17 pages, 5991 KiB

Open AccessArticle

Helicopter Rotor Thickness Noise Control Using Unsteady Force Excitation

by Yongjie Shi, Teng Li, Xiang He, Linghua Dong and Guohua Xu

Appl. Sci. 2019, 9(7), 1351; https://doi.org/10.3390/app9071351 - 30 Mar 2019

Cited by 17 | Viewed by 4946

Abstract

The low-frequency in-plane thickness noise generating from the displacement of air by rotating blades has an important influence on helicopter detection. An on-blade control technique to reduce thickness noise is developed in this paper based on the principle of sound field cancellation. Following [...] Read more.

The low-frequency in-plane thickness noise generating from the displacement of air by rotating blades has an important influence on helicopter detection. An on-blade control technique to reduce thickness noise is developed in this paper based on the principle of sound field cancellation. Following the theoretical study on the mechanism of thickness noise reduction using in-plane unsteady force, a 2-m diameter rotor with an active trailing-edge winglet are designed and tested in a fully anechoic chamber. The winglet installed on the outboard blade is used to generate the unsteady force and anti-noise to counteract the thickness noise. The results demonstrate that effective reduction of thickness noise up to 3 dB is achieved in the front of the rotor when the winglet is under the one-harmonic control with

3^{°}

of deflection angle. Moreover, the experiments of frequency, amplitude, and phase scanning are carried out to study the parametric effects of winglet motions on noise reduction. The ability of noise reduction is proportional to the deflection amplitude of the winglet in each frequency. The control phase determines where noise can be reduced. There is an optimal phase angle at each frequency to minimize the noise at the observations, and it varies with different frequencies. The relationship among observation position, control phase, and frequency is derived, and the approximate expression of the optimal phase is presented. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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20 pages, 879 KiB

Open AccessArticle

Active Noise Control over Space: A Subspace Method for Performance Analysis

by Jihui Zhang, Thushara D. Abhayapala, Wen Zhang and Prasanga N. Samarasinghe

Appl. Sci. 2019, 9(6), 1250; https://doi.org/10.3390/app9061250 - 25 Mar 2019

Cited by 11 | Viewed by 4530

Abstract

In this paper, we investigate the maximum active noise control performance over a three-dimensional (3-D) spatial space, for a given set of secondary sources in a particular environment. We first formulate the spatial active noise control (ANC) problem in a 3-D room. Then [...] Read more.

In this paper, we investigate the maximum active noise control performance over a three-dimensional (3-D) spatial space, for a given set of secondary sources in a particular environment. We first formulate the spatial active noise control (ANC) problem in a 3-D room. Then we discuss a wave-domain least squares method by matching the secondary noise field to the primary noise field in the wave domain. Furthermore, we extract the subspace from wave-domain coefficients of the secondary paths and propose a subspace method by matching the secondary noise field to the projection of primary noise field in the subspace. Simulation results demonstrate the effectiveness of the proposed algorithms by comparison between the wave-domain least squares method and the subspace method, more specifically the energy of the loudspeaker driving signals, noise reduction inside the region, and residual noise field outside the region. We also investigate the ANC performance under different loudspeaker configurations and noise source positions. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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17 pages, 800 KiB

Open AccessArticle

A Novel Adaptive State Detector-Based Post-Filtering Active Control Algorithm for Gaussian Noise Environment with Impulsive Interference

by Wenzhao Zhu, Shengguo Shi, Lei Luo and Jinwei Sun

Appl. Sci. 2019, 9(6), 1176; https://doi.org/10.3390/app9061176 - 20 Mar 2019

Cited by 4 | Viewed by 2550

Abstract

For Gaussian noise with random or periodic impulsive interference, the conventional active noise control (ANC) methods with finite second-order moments may fail to converge. Furthermore, the intensity of impulsive noise typically varies over time in the actual application, which also decreases the performance [...] Read more.

For Gaussian noise with random or periodic impulsive interference, the conventional active noise control (ANC) methods with finite second-order moments may fail to converge. Furthermore, the intensity of impulsive noise typically varies over time in the actual application, which also decreases the performance of conventional active impulsive noise control methods. To address these problems, a novel adaptive state detector based post-filtering active control algorithm is proposed. In this work, information entropy with adaptive kernel size is first introduced into the cost function of a post-filtering algorithm to improve its tracking. To enhance the robust performance of adaptive filters when impulsive interference happens, a recursive optimal threshold selecting method is also developed and analyzed by statistical theories. Simulations show that the new method has fast tracking ability in non-impulsive noise environment and keeps robust when impulsive interference happens. It also works well for the impulsive noise of different degrees. Experiment results confirm the effectiveness of the proposed algorithm. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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17 pages, 3973 KiB

Open AccessArticle

Active Structural Acoustic Control of an Active Casing Placed in a Corner

by Anna Chraponska, Stanislaw Wrona, Jaroslaw Rzepecki, Krzysztof Mazur and Marek Pawelczyk

Appl. Sci. 2019, 9(6), 1059; https://doi.org/10.3390/app9061059 - 13 Mar 2019

Cited by 15 | Viewed by 2645

Abstract

Electric appliances used in workplaces and everyday life often generate a low-frequency noise, which affects human body systems. Passive methods employed to reduce noise are not effective at low frequencies. The classical approach to active noise control practically involves the generation of local [...] Read more.

Electric appliances used in workplaces and everyday life often generate a low-frequency noise, which affects human body systems. Passive methods employed to reduce noise are not effective at low frequencies. The classical approach to active noise control practically involves the generation of local zones of quiet, whereas at other areas the noise is reinforced. Moreover, it usually requires a large number of secondary sound sources. Hence, an active casing approach has been developed. The active casing panels’ vibrations are controlled to reduce the device noise emission. Efficiency of this method has been previously confirmed by the authors and the results have been reported in multiple journal publications. However, in the previous research experiments, the active casing was placed at a distance from the enclosure walls. In this research, the active casing is located in a corner and such placement is intentionally used to facilitate the active control system’s operation. The noise reduction performance is investigated at multiple configurations, including a range of distances from the corner and different error microphone arrangements. The analysis of both primary and secondary paths is given. Advantages and drawbacks of different active casing configurations are presented and discussed. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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26 pages, 15987 KiB

Open AccessArticle

Suppression of the Hydrodynamic Noise Induced by the Horseshoe Vortex through Mechanical Vortex Generators

by Yongwei Liu, Hongxu Jiang, Yalin Li and Dejiang Shang

Appl. Sci. 2019, 9(4), 737; https://doi.org/10.3390/app9040737 - 20 Feb 2019

Cited by 3 | Viewed by 4111

Abstract

The hydrodynamic noise from the horseshoe vortex can greatly destroy the acoustic stealth of underwater vehicles at low frequency. We investigated the flow-induced noise suppression mechanism by mechanical vortex generators (VGs) on a SUBOFF model. Based on the numerical simulation, we calculated the [...] Read more.

The hydrodynamic noise from the horseshoe vortex can greatly destroy the acoustic stealth of underwater vehicles at low frequency. We investigated the flow-induced noise suppression mechanism by mechanical vortex generators (VGs) on a SUBOFF model. Based on the numerical simulation, we calculated the flow field and the sound field of the three shapes of mechanical VGs: triangular, semi-circular, and trapezoidal. The triangular VGs with an angle of 30° to the flow direction achieved a better noise reduction. The optimum noise suppression is 8.93 dB, when the distance from the triangular VGs to the sail hull’s leading edge is 0.1c, where c is the chord length. The noise reduction mechanism is such that the mechanical VGs can destroy the formation of the horseshoe vortex at the origin and produce counter-rotation vortices to weaken its intensity. We created two steel models according to the simulation, and the experimental measurement was carried out in a gravity water tunnel. The measured results showed that the formation of the horseshoe vortex could be effectively inhibited by the triangular VGs. The results in our study can provide a new method for hydrodynamic noise suppression by flow control. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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16 pages, 4084 KiB

Open AccessArticle

Quantification of Active Structural Path for Vibration Reduction Control of Plate Structure under Sinusoidal Excitation

by Dongwoo Hong and Byeongil Kim

Appl. Sci. 2019, 9(4), 711; https://doi.org/10.3390/app9040711 - 18 Feb 2019

Cited by 7 | Viewed by 3172

Abstract

The engines of electric and hybrid vehicles cause vibration and noise with complex frequency spectra. This tendency is observed especially for mid-frequency components. Therefore, there are limitations in achieving vibration attenuation using only structural changes, which is the conventional isolation method. A smart [...] Read more.

The engines of electric and hybrid vehicles cause vibration and noise with complex frequency spectra. This tendency is observed especially for mid-frequency components. Therefore, there are limitations in achieving vibration attenuation using only structural changes, which is the conventional isolation method. A smart structure-based active engine mounting system is a core technology that can continuously improve the noise, vibration, and harshness performance under various operating conditions by continuously controlling the dynamic characteristics of the mount. It can replace the existing mount technology which supports the engine by realizing both static and dynamic stiffness. This study focuses on vibration reduction for a typical mid-frequency excitation. Based on a source–path–receiver structure, a mathematical model for a 3D plate structure with three active paths is proposed. The amplitude and phase of the actuator were calculated for the reduction of given vibrations on the basis of the model. When controlling with the proposed method, it was necessary to perform a large amount of computation and to newly define the modeling according to the structural change. To solve this inconvenience, the NLMS (normalized least mean squares) algorithm was applied, and the results were compared. It is shown that the application of the NLMS algorithm to perform the overall vibration reduction is more effective than the previous method. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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16 pages, 14147 KiB

Open AccessArticle

Development of Multi-Staged Adaptive Filtering Algorithm for Periodic Structure-Based Active Vibration Control System

by Qiu Yang, Kyeongnak Lee and Byeongil Kim

Appl. Sci. 2019, 9(3), 611; https://doi.org/10.3390/app9030611 - 12 Feb 2019

Cited by 4 | Viewed by 3827

Abstract

A digital adaptive filtering system is applied to various fields such as current disturbance, noise cancellation, and active vibration and noise control. The least mean squares (LMS) algorithm is widely adopted, owing to its simplicity and low computational burden. A limitation of the [...] Read more.

A digital adaptive filtering system is applied to various fields such as current disturbance, noise cancellation, and active vibration and noise control. The least mean squares (LMS) algorithm is widely adopted, owing to its simplicity and low computational burden. A limitation of the LMS algorithm with fixed step size is the trade-off between convergence speed and stability. Several studies have tried to overcome this limitation by varying the step size according to filter input and error; however, the related algorithms with variable step size have not been suitable for signals with complex frequency spectra. As the error decreases, the quality of the output signal deteriorates due to the increase in the higher-order components, depending on the characteristics of the algorithm. Therefore, a novel adaptive filtering algorithm was proposed to overcome these drawbacks. It increased the stability of the system by decreasing the step size using an exponential function. In addition, the error was reduced through normalization using the power of the input signal in the initial state, and the misadjustments in the system were adjusted properly by introducing an energy autocorrelation function of instantaneous error. Furthermore, a novel multi-staged adaptive LMS (MSA-LMS) algorithm was introduced and applied to active periodic structures. The proposed algorithm was validated by simulation and observed to be superior to the conventional LMS algorithms. The results of this study can be applied to active control systems for the reduction of vibration and noise signals with complex spectra in next-generation powertrains, such as hybrid and electric vehicles. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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17 pages, 5194 KiB

Open AccessArticle

Exploiting the Underdetermined System in Multichannel Active Noise Control for Open Windows

by Jianjun He, Bhan Lam, Dongyuan Shi and Woon Seng Gan

Appl. Sci. 2019, 9(3), 390; https://doi.org/10.3390/app9030390 - 23 Jan 2019

Cited by 11 | Viewed by 3127

Abstract

Active noise control (ANC) is a re-emerging technique to mitigate noise pollution. To reduce the noise power in large spaces, multiple channels are usually required, which complicates the implementation of ANC systems. In this paper, we separate the multichannel ANC problem into two [...] Read more.

Active noise control (ANC) is a re-emerging technique to mitigate noise pollution. To reduce the noise power in large spaces, multiple channels are usually required, which complicates the implementation of ANC systems. In this paper, we separate the multichannel ANC problem into two subproblems, where the subproblem of computing the control filter is usually an underdetermined problem. Therefore, we could leverage the underdetermined system to simplify the ANC system without degrading the noise reduction performance. For a single incidence, we compare the conventional fully-coupled (pseudoinverse) multichannel control with the colocated (diagonal) control method and find that they can achieve equivalent performance, but the colocated control method is less computationally intensive. Furthermore, the underdetermined system presents an opportunity to control noise from multiple incidences with one common fixed filter. Both the full-rank and the overdetermined optimal control filters are realized. The performance of these control methods was analyzed numerically with the Finite Element Method (FEM) and the results validate the feasibility of the full-rank and overdetermined optimal control methods, where the latter could even offer more robust performance in more complex noise scenarios. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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24 pages, 8455 KiB

Open AccessArticle

The Generation Mechanism of the Flow-Induced Noise from a Sail Hull on the Scaled Submarine Model

by Yongwei Liu, Yalin Li and Dejiang Shang

Appl. Sci. 2019, 9(1), 106; https://doi.org/10.3390/app9010106 - 29 Dec 2018

Cited by 24 | Viewed by 5359

Abstract

Flow-induced noise from the sail hull, which is induced by the horseshoe vortex, the boundary layer separation and the tail vortex shedding, is a significant problem for the underwater vehicles, while has not been adequately studied. We have performed simulations and experiments to [...] Read more.

Flow-induced noise from the sail hull, which is induced by the horseshoe vortex, the boundary layer separation and the tail vortex shedding, is a significant problem for the underwater vehicles, while has not been adequately studied. We have performed simulations and experiments to reveal the noise generation mechanism from these flows using the scaled sail hull with part of a submarine body. The large eddy simulation and the wavenumber–frequency spectrum are adopted for simulations. The frequency ranges from 10 Hz to 2000 Hz. The simulation results show that the flow-induced noise with the frequency less than 500 Hz is mainly generated by the horseshoe vortex; the flow-induced noise because of the tail vortex shedding is mainly within the frequency of shedding vortex, which is 595 Hz in the study; the flow-induced noise caused by the boundary layer separation lies in the whole frequency range. Moreover, we have conducted the experiments in a gravity water tunnel, and the experimental results are in good accordance with the simulation results. The results can lay the foundation for the design of flow control devices to suppress and reduce the flow-induced noise from the sail hull. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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12 pages, 2622 KiB

Open AccessArticle

A Multi-Tone Sound Absorber Based on an Array of Shunted Loudspeakers

by Chaonan Cong, Jiancheng Tao and Xiaojun Qiu

Appl. Sci. 2018, 8(12), 2484; https://doi.org/10.3390/app8122484 - 4 Dec 2018

Cited by 16 | Viewed by 3307

Abstract

It has been demonstrated that a single shunted loudspeaker can be used as an effective low frequency sound absorber in a duct, but many shunted loudspeakers have to be used in practice for noise reduction or reverberation control in rooms, thus it is [...] Read more.

It has been demonstrated that a single shunted loudspeaker can be used as an effective low frequency sound absorber in a duct, but many shunted loudspeakers have to be used in practice for noise reduction or reverberation control in rooms, thus it is necessary to understand the performance of an array of shunted loudspeakers. In this paper, a model for the parallel shunted loudspeaker array for multi-tone sound absorption is proposed based on a modal solution, and then the acoustic properties of a shunted loudspeaker array under normal incidence are investigated using both the modal solution and the finite element method. It was found that each shunted loudspeaker can work almost independently where each unit resonates. Based on the interaction analysis, multi-tone absorbers in low frequency can be achieved by designing multiple shunted loudspeakers with different shunt circuits respectively. The simulation and experimental results show that the normal incidence sound absorption coefficient of the designed absorber has four absorption peaks with values of 0.42, 0.58, 0.80, and 0.84 around 100 Hz, 200 Hz, 300 Hz, and 400 Hz respectively. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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20 pages, 1279 KiB

Open AccessArticle

Frequency-Domain Filtered-x LMS Algorithms for Active Noise Control: A Review and New Insights

by Feiran Yang, Yin Cao, Ming Wu, Felix Albu and Jun Yang

Appl. Sci. 2018, 8(11), 2313; https://doi.org/10.3390/app8112313 - 20 Nov 2018

Cited by 68 | Viewed by 8156

Abstract

This paper presents a comprehensive overview of the frequency-domain filtered-x least mean-square (FxLMS) algorithms for active noise control (ANC). The direct use of frequency-domain adaptive filters for ANC results in two kinds of delays, i.e., delay in the signal path and delay in [...] Read more.

This paper presents a comprehensive overview of the frequency-domain filtered-x least mean-square (FxLMS) algorithms for active noise control (ANC). The direct use of frequency-domain adaptive filters for ANC results in two kinds of delays, i.e., delay in the signal path and delay in the weight adaptation. The effects of the two kinds of delays on the convergence behavior and stability of the adaptive algorithms are analyzed in this paper. The first delay can violate the so-called causality constraint, which is a major concern for broadband ANC, and the second delay can reduce the upper bound of the step size. The modified filter-x scheme has been employed to remove the delay in the weight adaptation, and several delayless filtering approaches have been presented to remove the delay in the signal path. However, state-of-the-art frequency-domain FxLMS algorithms only remove one kind of delay, and some of these algorithms have a very high peak complexity and hence are impractical for real-time systems. This paper thus proposes a new delayless frequency-domain ANC algorithm that completely removes the two kinds of delays and has a low complexity. The performance advantages and limitations of each algorithm are discussed based on an extensive evaluation, and the complexities are evaluated in terms of both the peak and average complexities. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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17 pages, 1441 KiB

Open AccessArticle

Multichannel Feedforward Active Noise Control System with Optimal Reference Microphone SelectorBased on Time Difference of Arrival

by Kenta Iwai, Satoru Hase and Yoshinobu Kajikawa

Appl. Sci. 2018, 8(11), 2291; https://doi.org/10.3390/app8112291 - 19 Nov 2018

Cited by 13 | Viewed by 4986

Abstract

In this paper, we propose a multichannel active noise control (ANC) system with an optimal reference microphone selector based on the time difference of arrival (TDOA). A multichannel feedforward ANC system using upstream reference signals can reduce various noises such as broadband noise [...] Read more.

In this paper, we propose a multichannel active noise control (ANC) system with an optimal reference microphone selector based on the time difference of arrival (TDOA). A multichannel feedforward ANC system using upstream reference signals can reduce various noises such as broadband noise by arranging reference microphones close to noise sources. However, the noise reduction performance of an ANC system degrades when the noise environment changes, such as the arrival direction. This is because some reference microphones do not satisfy the causality constraint that the unwanted noise propagates to the control point faster than the anti-noise used to cancel the unwanted noise. To solve this problem, we propose a multichannel ANC system with an optimal reference microphone selector. This selector chooses the reference microphones that satisfy the causality constraint based on the TDOA. Some experimental results demonstrate that the proposed system can choose the optimal reference microphones and effectively reduce unwanted acoustic noise. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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16 pages, 4111 KiB

Open AccessArticle

Impact and Control of Reflected Noise from an Overpass Bottom

by Chi-Chwen Lin, Yen-Ping Peng, Yung-Pin Tsai, Yu-Chen Chang and Ku-Fan Chen

Appl. Sci. 2018, 8(10), 1908; https://doi.org/10.3390/app8101908 - 14 Oct 2018

Cited by 3 | Viewed by 3774

Abstract

This study examines the effects of noise reflected from the overpass bottom under various conditions using onsite measurements and model simulation. Reflected noise from the overpass bottom may be as high as 8 dB(A). Bottom materials (steel and reinforced concrete (RC)) have no [...] Read more.

This study examines the effects of noise reflected from the overpass bottom under various conditions using onsite measurements and model simulation. Reflected noise from the overpass bottom may be as high as 8 dB(A). Bottom materials (steel and reinforced concrete (RC)) have no discernible effect on the reflected noise level. As the height of an overpass increases, the level of reflected noise decreases. When an overpass is parallel to the noise source (i.e., the freeway), the size of the area impacted by reflected noise increases. As the sound absorption rating of the material installed at the overpass bottom increased, the level of reflected noise decreased. A sound absorbing material with a sound absorption rate of at least 0.60 is recommended to reduce reflected noise level. When the distance between the overpass side and a receiver exceeded 30 m, the level of reflected noise level reduced significantly. Therefore, if the distance between a residential area and overpass could be increased to create a buffer zone coupled with the installation of sound absorbing material at the overpass bottom, the impact of reflected noise on nearby residents can be reduced. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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19 pages, 6147 KiB

Open AccessArticle

Noise-Canceling Office Chair with Multiple Reference Microphones

by László Sujbert and Attila Szarvas

Appl. Sci. 2018, 8(9), 1702; https://doi.org/10.3390/app8091702 - 19 Sep 2018

Cited by 3 | Viewed by 5744

Abstract

Office employees are exposed to acoustic noise, especially in an open office environment. Passive or active headsets sufficiently reduce the level of noise, but their long-time wear is uncomfortable. The paper presents an active headrest system built into a chair. Feedforward control is [...] Read more.

Office employees are exposed to acoustic noise, especially in an open office environment. Passive or active headsets sufficiently reduce the level of noise, but their long-time wear is uncomfortable. The paper presents an active headrest system built into a chair. Feedforward control is utilized with multiple reference microphones, and flexible gooseneck microphones serve as error sensors. The reference sensors surround the chair, allowing the suppression of sound waves arriving from any direction. The concept of multiple reference control has been tested by extensive experiments showing that multiple reference signals help to increase the suppression in normal rooms where reverberation occurs, even if only one noise source is present. The preliminary experiments are completed by a series of simulations aiming to explore the zones of quiet at the user’s ears. The paper introduces the construction details of the noise-canceling chair: The two loudspeakers are controlled by the signals of two error microphones and four reference signals. The controller is based on the normalized filtered error least mean squared algorithm, implemented on an Analog Devices ADSP-21262 signal processor-based hardware. Experimental results are reported that show the efficient suppression of tonal, as well as broadband disturbances. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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22 pages, 8769 KiB

Open AccessArticle

A New Method for Active Cancellation of Engine Order Noise in a Passenger Car

by Sang-Kwon Lee, Seungmin Lee, Jiseon Back and Taejin Shin

Appl. Sci. 2018, 8(8), 1394; https://doi.org/10.3390/app8081394 - 17 Aug 2018

Cited by 48 | Viewed by 5876

Abstract

This paper presents a novel active noise cancellation (ANC) method to reduce the engine noise inside the cabin of a car. During the last three decades, many methods have been developed for the active control of a quasi-stationary narrowband sinusoidal signal. However, since [...] Read more.

This paper presents a novel active noise cancellation (ANC) method to reduce the engine noise inside the cabin of a car. During the last three decades, many methods have been developed for the active control of a quasi-stationary narrowband sinusoidal signal. However, since the interior noise signal is non-stationary with a fast frequency variation when the car accelerates rapidly, these methods cannot stably reduce the interior noise. The proposed method can reduce the interior noise stably even if the speed of the car is changed quickly. The method uses an adaptive filter with an optimal weight vector for the active control of such an engine noise. The method of determining the optimal weight vector of an adaptive filter is demonstrated. In order to validate the advantages of the proposed method, a conventional method and the proposed method are simulated with three synthesized signals. Finally, the proposed method is applied to the cancellation of booming noise in a sport utility vehicle. We demonstrate that the performance of the ANC system with the proposed algorithm is excellent for the attenuation of engine noise inside the cabin of a car. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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11 pages, 1968 KiB

Open AccessArticle

Development and Evaluation of Light-Weight Active Noise Cancellation Earphones

by Sen M. Kuo, Yi-Rou Chen, Cheng-Yuan Chang and Chien-Wen Lai

Appl. Sci. 2018, 8(7), 1178; https://doi.org/10.3390/app8071178 - 19 Jul 2018

Cited by 20 | Viewed by 8176

Abstract

This paper presents the development of active noise control (ANC) for light-weight earphones, and proposes using music or natural sound to estimate the critical secondary path model instead of extra random noise. Three types of light-weight ANC earphones including in-ear, earbud, and clip [...] Read more.

This paper presents the development of active noise control (ANC) for light-weight earphones, and proposes using music or natural sound to estimate the critical secondary path model instead of extra random noise. Three types of light-weight ANC earphones including in-ear, earbud, and clip phones are developed. Real-time experiments are conducted to evaluate their performance using the built-in microphone inside KEMAR’s ear and to compare with commercially-available ANC headphones and earphones. Experimental results show that the developed light-weight ANC earphones achieve higher noise reduction than the commercial ANC headphones and earphones, and the in-ear ANC earphone has the best noise reduction performance. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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16 pages, 3009 KiB

Open AccessArticle

Modified LMS Strategies Using Internal Model Control for Active Noise and Vibration Control Systems

by Byeongil Kim and Jong-Yun Yoon

Appl. Sci. 2018, 8(6), 1007; https://doi.org/10.3390/app8061007 - 20 Jun 2018

Cited by 8 | Viewed by 4583

Abstract

Traditional adaptive filtering algorithms are non-recursive systems that cannot use a time-variant reference input in real time and are not appropriate for control signals with uncertainties and unanticipated conditions. The main purpose of this research is to design novel adaptive digital filtering algorithms [...] Read more.

Traditional adaptive filtering algorithms are non-recursive systems that cannot use a time-variant reference input in real time and are not appropriate for control signals with uncertainties and unanticipated conditions. The main purpose of this research is to design novel adaptive digital filtering algorithms based on internal model control (IMC). The new methods consist of a process model for the target plant so as to estimate its dynamic behavior for active vibration and noise attenuation schemes in order to improve the stability, robustness, and tracking performance. On the basis of on the existing least mean squares, the methods are combined with an internal model controller, or the whole adaptive filtering system could become a feedback control system structure based on IMC. The performances were validated in numerical simulations with various conditions that could have happened in realistic applications, and the results were compared with the original algorithms. This study shows that the active noise and vibration systems that are applied to vehicles, mechanical systems, and other targets are enhanced through improving the performance of conventional adaptive filtering algorithms and by using internal model control effectively. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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11 pages, 3920 KiB

Open AccessArticle

Acoustic Improvement of Stator–Rotor Interaction with Nonuniform Trailing Edge Blowing

by Wenjie Wang and Peter J. Thomas

Appl. Sci. 2018, 8(6), 994; https://doi.org/10.3390/app8060994 - 19 Jun 2018

Cited by 3 | Viewed by 3945

Abstract

The results of unsteady-flow simulations and experiments are discussed to investigate active noise-reduction effects on the stator–rotor interaction in a single-stage low-speed compressor with nonuniform trailing edge blowing. It is found that for the investigated type of stator–rotor interaction noise, nonuniform trailing edge [...] Read more.

The results of unsteady-flow simulations and experiments are discussed to investigate active noise-reduction effects on the stator–rotor interaction in a single-stage low-speed compressor with nonuniform trailing edge blowing. It is found that for the investigated type of stator–rotor interaction noise, nonuniform trailing edge blowing has beneficial noise-reducing effects. The overall aim is to demonstrate that nonuniform trailing edge blowing can compensate momentum loss and reduce the axial thrust on rotor blades. The results illustrate how nonuniform trailing edge blowing influences the sound pressure level of the blade-passing frequencies and results in active noise reduction effects. The study was conducted using a trailing edge blowing system, a four-hole dynamic flow-field measurement system, and phase lock technology. The results obtained show that nonuniform trailing edge blowing leads to substantial noise-reduction effects, lowering sound levels by more than 10 dB with about 5‰ of inlet mass flow. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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11 pages, 2007 KiB

Open AccessBrief Report

A Time-Efficient Method for Determining an Optimal Scaling Factor and the Encoder Resolution in the Multichannel FXECAP-L Algorithm with Evolving Order for Active Noise Control

by Ángel A. Vázquez, Xochitl Maya, Juan G. Avalos, Giovanny Sánchez, Juan C. Sánchez, Hector M. Pérez and Gabriel Sánchez

Appl. Sci. 2019, 9(3), 560; https://doi.org/10.3390/app9030560 - 8 Feb 2019

Cited by 3 | Viewed by 2683

Abstract

Affine projection (AP) algorithms have demonstrated faster convergence speed than conventional least mean square (LMS) algorithms, thus providing an attractive solution in the active noise control (ANC) field. However, the AP algorithms demand high computational cost, restricting their practical use in real-time ANC [...] Read more.

Affine projection (AP) algorithms have demonstrated faster convergence speed than conventional least mean square (LMS) algorithms, thus providing an attractive solution in the active noise control (ANC) field. However, the AP algorithms demand high computational cost, restricting their practical use in real-time ANC applications. Recently, a multichannel filtered-x error-coded affine projection-like (FXECAP-L) algorithm with evolving order has been proposed to reduce the computational burden by maintaining the convergence speed of AP algorithms. In order to obtain an efficient and robust FXECAP-L algorithm with evolving order, the scaling factor and encoder resolution need to be adjusted manually, which is a time-consuming and costly effort that must be carried out by expert designers. To reduce these costs and efforts, we introduce, for the first time, a strategy for automatic adjustment of the scaling factor and encoder resolution that benefits the rapid development of practical ANC applications. To demonstrate its practical use, we applied the proposed strategy for controlling the noise in an acoustic duct. The practical results demonstrate the automatic adjustment of the FXECAP-L algorithm which maintains high convergence speed at the expense of a small compromise in terms of processing time. Full article

(This article belongs to the Special Issue Active and Passive Noise Control)

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