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• Active vibration cancellation system using novel two reference signals for the reduction of interior noise induced by vibration of R-MSPS system. • Blocked-Force transfer path analysis (TPA) is proceeded to identify systematically major transmission path of vibration in electric vehicle. • Suitable PZT stack actuator is selected and used for generation of the secondary force for active vibration control (AVC) of R-MDPS system. • Test jig for the active vibration control of R-MDPS is made and used for the development of AVC algorithm. • The vibration of the major transfer path is reduced by the developed AVC system. This paper presents a novel active vibration control (AVC) system for a motor driven power steering (MDPS) system to reduce interior noise in an electric vehicle. The novel control algorithm used for the AVC system is developed based on selection of two reference signals. One is the frequency modulation signal using the rotation speed of motor shaft of MDPS the other one is the band passed signal of acceleration measured on the major path structure identified by the blocked transfer path (BF-TPA). In addition, the piezo stack actuator is used for generation of control force of the AVC system in the frequency over 400 Hz. An MDPS system uses electronic power steering. An MDPS system attached to the rack gear of power steering system is called an R-MDPS. The vibration generated by the R-MDPS is transmitted to the car body through mounts attached onto the car subframe. Panel vibrations of car body are sources of vibroacoustic noise generated inside the car cabin. This vibracoustic noise is a structure-borne noise and causes passenger annoyance. The frequencies of the structure-borne noise measured inside the car cabin are 460 Hz and 920 Hz, which are the rotating frequency of the R-MDPS motor shaft and the second-order harmonic of the rotating speed of the motor shaft. To directly reduce the interior noise inside the car cabin, active noise control (ANC) has been used for the active cancellation of noises with frequencies less than 400 Hz. However, because the frequency of interior noise generated by the operation of the R-MDPS is higher than 400 Hz, AVC was employed in this study for the active cancellation of vibrations transmitted to the car body through the subframe mounts of the car. For application of AVC to the test car, the control force should be known. Therefore, the actuator for generating the control force should be inserted in the mount between the subframe and R-MDPS system. Installing the actuator in the test car is challenging because of the geometry limit of commercial cars. Hence, a test jig composed of an R-MDPS system and the subframe of the test car was developed and set up in the laboratory to study the applicability of AVC to R-MDPS. All investigations of AVC were performed using the test jig in the laboratory. The proposed method was successfully applied to the active cancellation of vibration at a target point on the subframe. [ABSTRACT FROM AUTHOR]

Highlights • An active structural noise control method based on PZT material and fuzzy algorithm is presented. • A simplified vehicle cavity model with a smart plate and PZT transducers is constructed. • A fuzzy controller is designed and improved by adjusting some quantization factors. • A PZT-based system is established for active structural noise control of vehicle interior noise. • Experimental results show an effectiveness of the presented active structural noise control method. Abstract An active control approach for interior noise of vehicle based on the piezoelectric ceramic materials and fuzzy control algorithm is presented in this paper. According to the electromechanical coupling characteristics and the positive/inverse mechanism of a piezoelectric material, a theoretical model of piezoelectric ceramic plate with a sandwich structure is deduced by using impedance analysis method. The size of a piezoelectric ceramic transducer (or actuator) and its sticking position on the plate frame are determined. The structural modes and dynamic responses of a vehicle cavity model are calculated by finite element analysis for selecting optimal positions of actuator on the front wall. Furthermore, a fuzzy controller is designed for active vibration control. The fuzzy algorithm is improved by adjusting quantization factors, such as the deviation and its changing rate. Following the derived piezoelectric equations and the improved fuzzy algorithm, an active structural acoustic control (ASAC) system is developed and a functional prototype is set up by using the dSPACE platform. Experimental results show that the developed ASAC system can significantly reduce not only the vibrations of the front wall, but also the interior noises of the cavity. This implies that the proposed vibration-based ASAC method is effective and feasible, which might be a potential approach for interior noise control of vehicles. [ABSTRACT FROM AUTHOR]

A previous Swedish research project indicated the potential need for evaluating impact sound insulation from 20 Hz in buildings with lightweight constructions. This is a discrepancy compared to the commonly used frequency intervals starting from 50 or 100 Hz. The statistical significance of this groundbreaking suggestion was however not satisfactorily strong since the result was based upon a limited number of building objects. The scope of the present paper is to secure the previous study by adding additional objects to the underlying database, thereby increasing the confidence of the results. The methodology is to perform impact sound insulation measurements in apartment buildings of various construction types and to perform questionnaire surveys among the residents. The measured sound insulation is compared to the subjective rating by the occupants in order to find the parameter giving the highest correlation with respect to frequency range and weighting. The highest correlation was found when the impact sound insulation was evaluated from 25 Hz using a flat frequency-weighting factor. Frequencies below 50 Hz are of great importance when evaluating impact sound insulation in lightweight constructions. [ABSTRACT FROM AUTHOR]

The performance of active noise-canceling (ANC) headphones is typically determined in pink noise and expressed in terms of insertion loss (IL) curves. However, these curves may not be consistent with the actual noise environments. The aim of this study is to assess the performance of several commercial ANC headphones by comparing performance curves under different noise conditions with the respective IL curves obtained in pink noise. The results indicated that the passive performance remained consistent under different noise conditions. In contrast, the active performance diminished based on the noise environment, brand, and active noise controller. The decrease in performance was especially significant in highly transient events and resulted in a noise amplification extending to 20.4 dB. Therefore, the deviation between results of headphones tested in actual noise environments and those tested in pink noise strongly suggests that it is necessary to consider actual noise environments in future studies to obtain a more accurate evaluation of ANC headphones. [ABSTRACT FROM AUTHOR]

Adaptive filter techniques and the filtered-x least mean square (FxLMS) algorithm have been used in Active Noise Control (ANC) systems. However, their effectiveness may degrade due to the nonlinearities and modeling errors in the system. In this paper, a new feedback ANC system with an adaptive neural controller and variable step-size learning parameters (VSSP) is proposed to improve the performance. A nonlinear adaptive controller with the FxLMS algorithm is first designed to replace the traditional adaptive FIR filter; then, a variable step-size learning method is developed for online updating the controller parameters. The proposed control is implemented without any offline learning phase, while faster convergence and better noise elimination can be achieved. The main contribution is that we show how to analyze the stability of the proposed closed-loop ANC systems, and prove the convergence of the presented adaptations. Moreover, the computational complexities of different methods are compared. Comparative simulation results demonstrate the validity of the proposed methods for attenuating different noise sources transferred via nonlinear paths, and show the improved performance over classical methods. [ABSTRACT FROM AUTHOR]

This paper reports the binaural active noise control (ANC) system developed to deal with factory noise. The control points are located in the vicinity of the left and right ears of a worker sitting along the production line. Due to the complicated safety requirements in the factory, secondary sources and error microphones are not allowed to be placed near the worker. Therefore, the proposed ANC system employs the feedforward structure and adopts the parametric array loudspeakers (PALs) as the secondary sources. The PAL is a type of directional loudspeaker that generates a much narrower sound field as compared to the conventional loudspeaker. Once the proposed ANC system has been trained offline, the error microphones can be removed. The performance of the binaural ANC system is successfully demonstrated based on a digital signal processor (DSP) implementation. [ABSTRACT FROM AUTHOR]

Active noise control (ANC) systems employing adaptive filters suffer from stability issues in the presence of impulsive noise. New impulsive noise control algorithms based on filtered-x recursive least square (FxRLS) algorithm are presented. The FxRLS algorithm gives better convergence than the filtered-x least mean square (FxLMS) algorithm and its variants but lacks robustness in the presence of high impulsive noise. In order to improve the robustness of FxRLS algorithm for ANC of impulsive noise, two modifications are suggested. First proposed modification clips the reference and error signals while, the second modification incorporates energy of the error signal in the gain of FxRLS (MGFxRLS) algorithm. The results demonstrate improved stability and robustness of proposed modifications in the FxRLS algorithm. However, another limitation associated with the FxRLS algorithm is its computationally complex nature. In order to reduce the computational load, a hybrid algorithm based on proposed MGFxRLS and normalized step size FxLMS (NSS-FXLMS) is also developed in this paper. The proposed hybrid algorithm combines the stability of NSS-FxLMS algorithm with the fast convergence speed of the proposed MGFxRLS algorithm. The results of the proposed hybrid algorithm prove that its convergence speed is faster than that of NSS-FxLMS algorithm with computational complexity lesser than that of FxRLS algorithm. [ABSTRACT FROM AUTHOR]

The feedback active noise control (ANC) can be seen as a predictor, the conventional method based on filtered-x least mean square (FXLMS) algorithm can only be useful for linear and tonal noise, but for nonlinear and broadband noise, it is useless. The feedback ANC using functional link artificial neural networks (FLANN) based on filtered-s least mean square (FSLMS) algorithm can reduce some nonlinear noise such as chaotic noise, but the noise cancellation performance is not very well, at the same time, it is not useful to random noise. To solve the problem above, a new feedback ANC using wavelet packet FXLMS (WPFXLMS) algorithm is proposed in this paper. By decomposing the broadband noise into several band-limited parts which are predictable and each part is controlled independently, the proposed algorithm can not only suppress the chaotic noise, but also mitigate the random noise. Compared with FXLMS and FSLMS algorithms, proposed WPFXLMS algorithm also holds the best performance on noise cancellation. Numerous simulations are conducted to demonstrate the effectiveness of the proposed WPFXLMS algorithm. [ABSTRACT FROM AUTHOR]

In this technical note, the simplified diagonal-structure bilinear filtered-X least mean square (SDBFXLMS) and channel-reduced diagonal-structure bilinear filtered-X least mean square (CRDBFXLMS) algorithms are proposed. Computational complexity for each proposed algorithm is analyzed to show the significant computational reduction in comparison with the diagonal-structure bilinear FXLMS (DBFXLMS) algorithm. For L = 15 (memory length of the bilinear filter), P = 2 (the corresponding number of the diagonal channels for the SDBFXLMS algorithm is L + 2 P = 19 and the corresponding number of the diagonal channels for the CRDBFXLMS algorithm is 2 P = 4 ) , and M = 64 (memory length of the secondary path estimate), the SDBFXLMS algorithm achieves 45% and 40% reduction of multiplications and additions, respectively, while the CRDBFXLMS algorithm acquires 78% reduction of multiplications and 76% reduction of additions. Computer simulations validate the satisfied control performances of the proposed algorithms. [ABSTRACT FROM AUTHOR]

This study attempted to control the radiated exterior noise from a rectangular enclosure in which an internal plate vibrates by acoustic excitation and noise is thus radiated from that plate. Multi-channel active control was applied to reduce the vibration and external radiation of this enclosed plate. A piezoelectric ceramic was used as a distributed actuator for multiple mode control of the vibration and radiated noise in the acoustically excited plate. To maximize the effective control, an approach was proposed for attachment the piezoelectric actuator in the optimal location. The plate and internal acoustic space in the enclosure are coupled with each other. This will change dominant frequency characteristics of the plate and, thus, those of the externally radiated noise. Active noise control was accomplished using an accelerometer attached to the plate and a microphone placed adjacent to that plate as an error sensor under acoustic excitation of sine wave and white noise. It was found that the control of radiated external radiation noise requires a microphone as an error sensor, a sound pressure sensor due to vibration of the plate, differences in the dominant frequency of externally radiated noise, and complex vibration modes of the plate. [ABSTRACT FROM AUTHOR]

Abstract: The growing use of vehicles in urban areas means that comfort in low-speed driving phase is an increasingly important consideration for manufacturers. Examining comfort in such situation requires not only field experiments but also the use of simulators to control the characteristics of the stimuli to which participants are exposed. Incorporating a visual scene with vibration and sound stimuli is one possible way of improving simulation conditions. Two experiments were conducted to measure the influence of the immersion relating to vibratory, sound and visual modes on comfort assessments. In the first experiment, participants were exposed to different combinations of vibration, noise and road videos (8 vehicles, 2 roads). The visual mode only led to a small bearing on ratings. Regardless of the mode presented, the level of vibration emerged as the crucial factor in assessing overall comfort. Little interactions between sound and vibration modes were also highlighted. The second experiment dealt with context given by the visual mode. Acoustic and vibration stimuli were combined with very different road videos, which modified participants’ expectations with regard to the situation. Results demonstrated that combining different visual settings with vibro-acoustic stimuli, no matter how much they were opposed, only exerted a small influence on participants’ comfort. In the end, with regard both to immersion and contextualisation, the effects of the visual mode are so low-scale as to be insignificant. Accordingly, they may be ignored in future similar experiments, which can make the experimental set-up easier. [Copyright &y& Elsevier]

We propose a metamaterial beam having multiple corrugated parts for broad band gaps, study its band gap properties, and investigate the potential of the proposed beam in vibration control with structural strength constraints. First, the spectral element method is used to calculate the band structure and vibration transmission of the metamaterial beam. Numerical results show that band gaps can be tuned flexibly within the low, mid, and high-frequency ranges by changing the design parameters, and demonstrate the trade-off relation between the band gap design and structural strength. Then, an emerging optimization method, the cell mapping method, is applied to study the multi-objective optimal design of the periodic beam, in order to balance low vibration amplitude and high strength. Optimization results illustrate that the Pareto set can provide more options for the design of metamaterial beams, and the optimized structures have much-improved performance for vibration control in targeted frequency bands. Modal analysis is conducted to further understand the vibration attenuation mechanism of the optimized structure, which indicates that the vibration is reduced by the strong local resonance and modal cancellation. Finally, for experimental verification, three metamaterial beams are fabricated and tested with clamped–clamped boundary conditions. Experimental results show the low vibration transmission of each optimized beam within the desired band gaps. [ABSTRACT FROM AUTHOR]

For the problem of active noise control (ANC) and active vibration control (AVC) methods, only noise and vibration can be controlled separately. Active sound quality control (ASQC) method and AVC method are combined to carry out an in-depth study on the active control method of vehicle interior sound quality, using the vibration-sound transfer function and considering the requirements of sound quality. Combined with the adaptive noise equalizer (ANE) algorithm, a sound retention factor was introduced on the basis of the hybrid vibro-acoustic filter-u and filter-x least mean square (HVA-FUXLMS) algorithm, a hybrid vibro-acoustic adaptive noise equalizer (HVA-ANE) algorithm was proposed to control the sound quality. Based on the filter-error least mean square algorithm (FELMS) algorithm, a hybrid vibro-acoustic empirical-mode-decomposition frequency-domain block filter-error least mean square (HVA-EMDFELMS) algorithm for vehicle interior sound quality was proposed. Vibration and noise at high speeds are collected and analyzed for sound quality levels. This article used HVA-ANE and HVA-EMDFELMS algorithms to perform ASQC simulation experiments. The results showed that the noise loudness was greatly reduced while the noise and vibration control was taken into account by the HVA-ANE algorithm and HVA-EMDFELMS algorithm. Hybrid vibro-acoustic active control method for vehicle interior sound quality can effectively improve the sound quality of vehicle and can be applied to the active control of vehicle noise and related engineering noise. [ABSTRACT FROM AUTHOR]

Abstract: This paper focuses on an active noise cancellation system for a home window using a transparent acoustic transducer. In a traditional active noise cancellation system, direct microphone measurements are used for reference and error signals. In the case of the window application, both external and internal sound would be picked up by such microphones. This leads to adverse effects on the performance of the active noise cancellation system and also to distortion of the internal sound. To address this problem, a wave separation technique is proposed to separate the internal and external components of sound. The wave separation algorithm is based on the use of two microphones and an algorithm that separates components based on their direction of travel. An active noise cancellation system is implemented using wave separation for both the error and reference signal measurements. The performance of the resulting ANC system is experimentally tested in a cabin equipped with a window and results are presented. Experimental results show that the new system is able to accurately preserve desired internal sound while cancelling uncorrelated external noise. [Copyright &y& Elsevier]

Abstract: This paper investigates the performance of decentralized multi-channel feedback analog control systems, which are flexible and economic for practical applications of active noise control. The generalized Nyquist theorem and Gerschgorin circle theorem are used to derive a sufficient stability condition in terms of the predefined maximum noise amplification and the geometrical configuration of the independent controllers, and the noise reduction performance of the multi-channel system is predicted with the design and geometrical configuration of the independent controllers. Simulation and experimental results are presented to illustrate the effectiveness of the proposed analysis. [Copyright &y& Elsevier]

Abstract: A novel nonlinear adaptive filter based on a cascade combination of a functional link artificial neural network (FLANN) and a Legendre polynomial has been proposed in this paper for nonlinear active noise control (ANC). The performance of the new controller has been compared with that obtained by a FLANN based ANC system trained using a filtered-s least mean square (FsLMS) algorithm as well as with a Legendre neural network (LeNN) based ANC system trained using a filtered-l LMS (FlLMS) algorithm. The training of the cascaded controller has been achieved using a filtered-sl LMS (FslLMS) algorithm, which simultaneously adapts the weights of both the component adaptive controllers. The new controller has been shown to achieve improved noise mitigation capability in comparison to its constituent filters. [Copyright &y& Elsevier]

Abstract: A simple and effective approach for designing feedback controllers is proposed based on analyzing the waterbed effect of the feedback active noise control system. By flattening the noise amplification due to the waterbed effect in the whole disturbance amplification frequency band intuitively, the designed feedback controller can suppress the disturbance amplification to almost the minimum value for the given disturbance attenuation and ensure good stability of the system. Being compared with the existing approaches, the main advantage of the proposed approach is its simplicity for implementation, which avoids complicated weight function selections and the numerical optimizations of the existing approaches. Detailed design procedures and implementation of the digital controller are illustrated, simulation and experiment results are provided to show the effectiveness of the proposed approach. [Copyright &y& Elsevier]

Abstract: This paper presents the results of objective tests performed on 13 personal active noise reduction devices (earmuffs, headphones, headsets and insert earphones) divided into four groups based mainly on structure, using an acoustic test fixture (ATF). Each device was examined on its attenuation of broadband noise, overload response, internally generated noise, attenuation of impulse noise, and stability to movement. The results show a large range of responses between devices in terms of attenuation and overload, and highlight distinctive differences between the device groupings. [Copyright &y& Elsevier]

Abstract: The performance of a nonlinear active noise control (ANC) system based on the recently developed filtered-s least mean square (FsLMS) algorithm deteriorates when strong disturbances in the ANC system are acquired by the microphones. To surmount this shortcoming, a novel robust FsLMS (RFsLMS) algorithm is proposed for a functional link artificial neural network (FLANN) based ANC system. The new ANC system is least sensitive to such disturbances and does not call for any prior information on the noise characteristics. The results obtained from simulation study establish the effectiveness of this new ANC scheme. [Copyright &y& Elsevier]

Abstract: An active noise barrier with unidirectional secondary sources is investigated in this paper, where the unidirectional secondary source consists of two closely located loudspeakers with pre-adjusted phase difference. The secondary sound field of the unidirectional sources is adjusted to maximally match the primary sound field in the shadow zone behind the barrier. It is shown both numerically and experimentally that the noise reduction performance of the active noise barrier can be improved remarkably by replacing monopoles with the unidirectional sources. The mechanism for the improvement is also investigated. [Copyright &y& Elsevier]

Abstract: Conventional active noise control (ANC) in ducts has been realized with digital signal processing. The physical size of the conventional ANC systems is usually large owing to the signal processing interval, and the cost of the system depends on the price of the digital signal processor (DSP). This paper proposes a new ANC system with an analog neural network circuit, which will process signals in short time periods without DSP. The proposed neural network circuit has a simple structure consisting of analog multipliers and an integrator, and we simulated the performance of the circuit by HSPICE. We also fabricated a circuit connected to a real duct and confirmed operation of the proposed ANC system. [Copyright &y& Elsevier]

Abstract: The paper concerns active control of impulsive noise having peaky distribution with heavy tail. Such impulsive noise can be modeled using non-Gaussian stable process for which second order moments do not exist. The most famous filtered-x least mean square (FxLMS) algorithm for active noise control (ANC) systems is based on the minimization of variance (second order moment) of error signal, and hence, becomes unstable for the impulsive noise. In order to improve the robustness of adaptive algorithms for processes having distributions with heavy tails (i.e. signals with outliers), either (1) a robust optimization criterion may be used to derive the adaptive algorithm or (2) the large amplitude samples may be ignored or replaced by an appropriate threshold value. Among the existing algorithms for ANC of impulsive noise, one is based on the minimizing least mean p-power (LMP) of the error signal, resulting in FxLMP algorithm (approach 1). The other is based on modifying; on the basis of statistical properties; the reference signal in the update equation of the FxLMS algorithm (approach 2). In this paper we propose two solutions to improve the robustness of the FxLMP algorithm. In first proposed algorithm, the reference and the error signals are thresholded before being used in the update equation of FxLMP algorithm. As another solution to improve the performance of FxLMP algorithm, a modified normalized step size is proposed. The computer simulations are carried out, which demonstrate the effectiveness of the proposed algorithms. [Copyright &y& Elsevier]

Abstract: This paper investigates the issue of the acoustic feedback during online operation of active noise control (ANC) systems. In the existing approach, two FIR filters are used for this task: adaptive for feedback path modeling (FBPM) and fixed for feedback neutralization (FBN). Previously, a simplified method is proposed where these two tasks of modeling and neutralization have been combined into one feedback path modeling and neutralization (FBPMN) adaptive filter. Here we introduce an intuition based variable step size (VSS) parameter, for LMS equation of FBPMN filter. This VSS is motivated from the fact that the error signal of FBPMN filter contains a disturbance-component that is decreasing in nature. The computer simulations are carried out for single-channel and multichannel ANC systems. It is demonstrated that the proposed method achieves better performance than the existing methods. [Copyright &y& Elsevier]

Abstract: The active control of radiation from large structures is a difficult, though important practical problem. The major reason for the difficulty is the ‘system’ size, as a large number of sensors and actuators are required for successful implementation, thus making it hard to design a robust, efficient system that integrates all sensors and actuators. This work examines the active attenuation of the global error, sound power, from the point of view of two sensing/control strategies that seek to be generalised; thus are applicable to a wide range of applications and are independent of knowledge of structural dynamics. In each approach the idea is that the required hardware can simply be attached, turned on, and immediately being to attenuate global noise. The two strategies are compared based on the level of attenuation of the global error sound power, the attenuation per total control force, and attenuation per actuator (in a structural-acoustic situation). The first strategy is the collocated-decentralised approach, which is built on measuring and controlling local vibration in an attempt to influence the global acoustic error. An alternative approach, termed the hybrid approach is firstly developed. The approach is termed ‘hybrid’ because it is a mix between a fully ‘centralised’ and ‘decentralised’ approach; but still measuring and controlling the global acoustic error directly. The attenuation of sound power is compared for both strategies on two structural sources; using 16 identically placed velocity sensors and 16 secondary point sources, in simulation in an attempt to suggest efficient sensing and control approaches for the global control of sound radiation from large structural sources. [Copyright &y& Elsevier]

Abstract: Based on the analysis of active noise control system with multi-channel monopole secondary sources, a kind of compound secondary source is proposed in this paper. The proposed compound secondary source consists of two closely located monopole sources with their distance much smaller than a wavelength. The characteristics of the compound source are analyzed, and the performances of the active noise control system with the compound secondary sources on the monopole primary sound field and sound radiated by a plate are investigated both numerically and experimentally. It has been found that the proposed compound secondary sources control system can provide higher noise reduction for free field noise radiation control with the same number of control channels. It is shown that the better performance in noise reduction of the compound secondary sources control system is mainly due to the directivity of the secondary sources where the energy radiation pattern of the compound sources is similar to that of the primary sources. [Copyright &y& Elsevier]

Abstract: In this paper a multi-input, multi-output (MIMO) active noise control system with the aim of global reduction of broadband noise in a telephone kiosk is addressed. The model selected for this optimization problem is the acoustic environment of an enclosure taking into account the effect of coupling of secondary sources used for control purpose. This optimization involves finding the best locations for loudspeakers and microphones inside the enclosure as well as optimizing the control signals considering secondary source coupling. Previous results show that in order to be able to reduce acoustic noise globally inside the enclosure, the frequency range of 50–300Hz must be selected for control purpose. The mean of acoustic potential energy of the enclosure, when excited in this frequency range, is adopted as a performance measure. This performance index is penalized with the power of the signal required to excite secondary loudspeakers, in order to avoid placements that may need high voltage power amplifier for a desired performance. To find the solution of this problem, i.e. the global minimum of the performance index, several genetic algorithms are proposed and compared. In order to attain the best achievable performance in reaching the global minimum, the parameters of these genetic algorithms are tuned, and used for optimization purpose. Numerical simulations of the acoustical potential energy as well as the sound pressure at different heights of the kiosk, when active noise control (ANC) system operates, confirm the optimality of the locations proposed by the genetic algorithm. [Copyright &y& Elsevier]

Abstract: This paper investigates the potential of active absorbers for reducing low-frequency noise transmission through an enclosure. Active absorbers are intended to obtain a purely real prescribed impedance at the front face of a porous layer. This is achieved by an active control system which cancels the acoustic pressure at the rear face. The test bench was a simplified enclosure: a rigid-wall cavity coupled to a baffled elastic plate. The modeling of the system was based on an analytical modal approach. The purpose of this simulation was first to calculate the optimal impedance, providing maximal reduction in radiated power, and then to define a sub-optimal strategy for actual absorber production. Two 3-cell configurations were implemented on the test bench. Active control used a multichannel feedforward algorithm. In line with prediction, the absorbers provided a 5.5dB overall reduction while covering only 2% of the cavity surface. [Copyright &y& Elsevier]

A hybrid active noise controller (ANC) is proposed to solve some existing problems, which are related to the non-minimum phase (NMP) path models between uncollocated sensors and actuators in many ANC systems. For hybrid ANC schemes, the NMP path causes design difficulties to both feedforward and feedback control. These problems can be solved effectively by adding an extra actuator in the ANC system. A new design procedure is presented to take the greatest advantage of the extra actuator. Theoretical analysis and experimental results are presented to show the improved performance of the proposed ANC. [Copyright &y& Elsevier]

Active Noise Reduction (ANR) technique has been available for hearing protectors and communication headsets for years. However, no standard testing method for ANR headsets has emerged. In this study, we measured insertion losses of four types of commercially available ANR headsets using an Acoustic Test Fixture (ATF) to examine the feasibility of using ATF for this kind of measurement. The measurement outlined required a minimum of instrumentation and was relatively simple to implement. The results show that this method should be especially useful for testing of prototypes and for quality control as well. [Copyright &y& Elsevier]

This paper describes an experimental investigation of an actively controlled double-glazed window. It is the second of two companion papers of which the first treated results obtained employing adaptive feedforward control. Herein, the outcome using adaptive feedback control is presented. This adaptive feedback controller has been tested in different configurations, i.e. fully and partially connected controllers. The differences between fully connected controllers with few filter coefficients and partially connected controllers with many filter coefficients are discussed. Additionally, tests with different traffic noise examples have been performed showing the ability of the actively controlled window to enhance protection against traffic noise. [Copyright &y& Elsevier]

• A fast-speed parameter identification method using the multi-objective genetic algorithm optimization. • The system parameters are identified from vibration test data. • The identified system parameters are averaged for different brands of trucks with the same seating system. • The parameter sensitivity analysis has been conducted and verified. • The full state feedback controller and PID controllers have been compared for the vibration reduction performance. This paper has developed a 5-DOF driver and seat suspension system model for active vibration control. A novel fast system parameter identification method from vibration measurement data has been proposed for the seat-occupant system based on the multi-objective Genetic Algorithm optimization (GA). This system parameter identification method can identify the seat system parameters of a 5-DOF lumped mass-spring-dashpot biodynamic seat-occupant model from vibration test results quickly and accurately. Without calculation and measurement of materials, the physical parameters of the seat suspension system such as masses (m), stiffness (k), and damping coefficients (c) are estimated through matching the measured resonant frequency and transmissibility amplitude at a specific frequency with the simulated ones. This is one of the main contributions of this paper. The characteristics of the human body vibration in the low-frequency range are analyzed through the seat to head transmissibility (STHT) ratio. The experimental and simulation results of the STHT values have been calculated and compared to verify each other. The sensitivity analysis of the seat effective amplitude transmissibility (SEAT) values over the seat system parameters have been conducted and validated by the measured results of the transmissibility ratios. A full state feedback controller has been developed to reduce the human body vibration in the seat suspension system, which is another new contribution of this paper. The simulation results show that the proposed controller has better vibration attenuation performance than the conventional PID controller. [ABSTRACT FROM AUTHOR]