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This paper proposes a method for global active noise control in vibro-acoustic cavities using acoustic sensing under the presence of both structural and acoustic disturbances. Global active noise control has earlier been carried out by minimizing the acoustic potential energy in the cavity expressed as the sum of squares of the acoustic pressures at discrete microphone locations. However, this approximation though holds well for a rectangular box cavity, is not applicable for the cavities of other shapes. This calls for development of an active noise control method based on the estimation of the acoustic potential energy applicable to the cavities of arbitrary shapes as encountered in practice. Virtual sensing of the acoustic potential energy has been reported in the literature based on measurement of vibration by the structural sensors. However, such approaches are applicable when only the structural disturbances act on the cavity, but cannot be used if the acoustic disturbances are also present in the cavity. This paper presents development of a global active noise control method based on virtual sensing of the acoustic potential energy in the cavity under the presence of structural and acoustic disturbances. Minimisation of the estimated acoustic potential energy through a feedforward control law is developed. Numerical studies on an irregular-shaped vibro-acoustic cavity and a car cavity are presented to evaluate the performance of the proposed technique. The results are also compared with the maximum possible reduction in the acoustic potential energy obtained using the optimal control inputs. The levels of reduction in the acoustic potential energy obtained with the proposed method are found to be close to the maximum possible reduction using the optimal control inputs. The proposed method is then also validated through an experimental study on a rectangular box cavity. © 2019 Elsevier Ltd

Department of Mechanical Engineering

World University root node

Journal of Sound and Vibration

Global active noise control in vibro-acoustic cavities using acoustic sensing

The Modal FxLMS algorithm is recently proposed for reduction of global level of noise in vibro-acoustic cavities. The algorithm minimizes acoustic potential energy expressed in modal domain which allows a choice of acoustic modes whose modal amplitudes are desired to be minimized. The working of the algorithm and its effectiveness has been demonstrated previously through a numerical study and an experimental study is required to test the effectiveness of the algorithm in practice. To meet this objective this paper presents an experimental study of this algorithm for global active noise control in a rectangular box cavity. The algorithm utilizes modal filtered reference signals and modal amplitudes of the selected acoustic modes of the cavity. To identify modal filtered reference signals, modal secondary paths are utilized. In the present study, modal secondary paths are identified using experimentally identified physical secondary paths and acoustic mode shapes. Modal amplitudes of the acoustic modes are identified on the basis of acoustic pressure measurements from eight microphones suitably placed throughout the cavity. The performance of the algorithm is studied under the presence of acoustic and structural disturbances using one or two control loudspeakers. The active control is carried out at harmonic frequencies coinciding with cavity-controlled resonances and panel-controlled resonances. It is found from the experimental results that the Modal FxLMS algorithm is successful in reducing modal amplitudes of the selected acoustic modes. When all the significantly contributing acoustic modes are chosen, a reduction in global level of noise is observed at cavity as well as panel controlled resonances. © 2019 Elsevier Ltd

Applied Acoustics

Global active control of harmonic noise in a vibro-acoustic cavity using Modal FxLMS algorithm

Interior noise in vibro-acoustic cavities may be generated due to acoustic and structural disturbances. Earlier studies have shown that for global control, the maximum reduction in acoustic potential energy can be realised by using an optimum combination of acoustic and structural actuators. However, it is observed that this reduction in interior noise may also be accompanied with an increase in kinetic energy of the cavity structure. This paper presents the development of a feedforward technique for active noise control in vibro-acoustic cavities ensuring that the noise reduction does not lead to an increase in kinetic energy. The problem is formulated as a constrained minimisation problem to minimise the acoustic potential energy subject to a constraint that the kinetic energy does not increase. Through a numerical study, it is shown that the optimum solution of the above problem indeed is favourable in terms of reduction in acoustic potential energy in the cavity and kinetic energy of the structure. The paper further proposes a method for solution of this constrained minimisation problem using a penalty function method and solution of sequential unconstrained problems. The proposed method is validated through a numerical study on a car-like cavity for single- and multi-tonal noise. © 2018 Acoustical Society of America.

Journal of the Acoustical Society of America

Global feedforward active noise control in vibro-acoustic cavities without increasing structural vibrations

This paper proposes an algorithm called as ‘Modal filtered-x LMS algorithm’ for global active noise control in vibro-acoustic cavities. The proposed algorithm is a formulation of the conventional filtered-x least mean square algorithm in modal domain to reduce acoustic potential energy in a cavity. The formulation leads to a concept of what has been called as ‘modal secondary path’ in the paper. The active control method makes use of the reference signal filtered using modal secondary paths instead of the reference signal filtered using physical secondary paths as done in the conventional FxLMS algorithm. The method requires knowledge of acoustic modal pressures which in the present paper are estimated using acoustic pressure measurements at a discrete number of points in the cavity. The proposed method allows a modal based control of acoustic potential energy in the cavity. The proposed method also has an advantage that it reduces the computational burden associated with filtering of the reference signal with secondary paths for global control. A numerical study to actively control noise due to structural and acoustic disturbances acting on a car-like cavity is presented. Results of modal based control are compared with maximum reduction that is possible for given disturbances and control sources. It is found that the noise reduction obtained using the modal based approach is close to the maximum possible but at a lower computational cost. © 2018 Elsevier Ltd

Mechanical Systems and Signal Processing

Modal filtered-x LMS algorithm for global active noise control in a vibro-acoustic cavity

Shakers are widely used to simulate the vibrations for academic research, as well as for product testing. Thus, there is a significant necessity to study them in detail. Amongst the different types of shakers being used, the electrodynamic shaker is by far the most versatile. However, limited work has been done with regard to their integrated electro-mechanical modelling. In this work, we have developed a mobility-based lumped parameter model of an electrodynamic shaker and also a method to measure its various electrical and mechanical parameters using non-destructive and easy to use methods. Towards meeting the latter goal, we conducted experiments to determine the shaker table’s impedance and transfer functions, and used these data for subsequent parameter extraction. Such a model was later validated experimentally. Finally, we predicted the response of the shaker under loaded and unloaded conditions, and confirmed their validity through actual experimental data. © The Author(s) 2017.

Fulltext

Journal of Low Frequency Noise Vibration and Active Control

Lumped parameter modelling and methodology for extraction of model parameters for an electrodynamic shaker

The filtered-x least mean square algorithm (FxLMS) is a widely used technique in active noise control. In a conventional FxLMS algorithm, the value of convergence coefficient is kept constant which may not yield optimum performance if frequency of the primary noise changes. For some frequencies, this may result into a slower convergence and for some other frequencies, it may lead to instability. To deal with this situation, a normalized FxLMS algorithm, in which the convergence coefficient is normalized with the power of the filtered reference signal, is proposed. In the eigenvalue equalization method, the magnitude of secondary path transfer function is equalized such that the power of filtered reference signal remains equal at all the frequencies. The method proposed in this paper attempts to optimally adapt the convergence coefficient of the FxLMS algorithm for continuously varying noise. It is based on estimating how frequency of noise is varying using fast Fourier transforms of the reference signal and then, using this information to optimally adapt the convergence coefficient. The optimum value of the convergence coefficient is decided based upon the power and delay of the filtered reference signal and sampling frequency. A numerical study in a 3D acoustic cavity is presented to test the effectiveness of the proposed method and the results are also compared with the conventional FxLMS and the frequency-domain FxLMS algorithm. It is found that the proposed method leads to a faster convergence which results in higher noise reduction especially when the frequency of noise varies continuously. Simulation results show that the noise reduction obtained depends upon the rate at which the frequency of the primary noise varies. The higher the rate of variation and the duration for which the variation exist, the better the performance of the proposed method is over the conventional FxLMS algorithm in terms of noise reduction. The frequency-domain FxLMS algorithm is not found to be effective if the frequency of primary noise varies continuously. © 2016 Institute of Noise Control Engineering.

Noise Control Engineering Journal

A variable step-size filtered-x least mean square algorithm for continuously varying noise

The FxLMS is widely used technique in active noise control. In conventional FxLMS, value of convergence coefficient is kept constant which may not be optimum at all frequencies. At some frequencies, convergence speed of FxLMS is slow and at some, it is relatively fast. This leads to significant degradation in performance of FxLMS if characteristics of noise are continuously varying. Normalized FxLMS algorithm is not very effective for continually varying noise. Eigenvalue equalization method may become unstable at some frequencies. Other methods like FxGAL are computationally expensive. The method proposed in this paper attempts to optimally adapt the convergence coefficient of FxLMS algorithm for continually varying noise. It is based on estimating how frequency of noise is varying using fast Fourier transform of reference signal and then, using this information to optimally adapt the convergence coefficient. The optimum value of convergence coefficient depends upon power and phase delay of filtered reference signal. A numerical study of a 3D acoustic cavity shows that the proposed method leads to faster convergence giving higher noise reduction. It also shows that higher the rate of variation of frequency of primary noise, higher is the advantage of the proposed method over the conventional FxLMS algorithm in terms of noise reduction. © 2015 by ASME.