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The problem of controlling a sound field inside a region surrounded by acoustic control sources is considered. Inspired by the Kirchhoff-Helmholtz integral, the use of double-layer source arrays allows such a control and avoids the modification of the external sound field by the control sources by the approximation of the sources as monopole and radial dipole transducers. However, the practical implementation of the Kirchhoff-Helmholtz integral in physical space leads to large numbers of control sources and error sensors along with excessive controller complexity in three dimensions. The present study investigates the potential of the Generalized Singular Value Decomposition (GSVD) to reduce the controller complexity and separate the effect of control sources on the interior and exterior sound fields, respectively. A proper truncation of the singular basis provided by the GSVD factorization is shown to lead to effective cancellation of the interior sound field at frequencies below the spatial Nyquist frequency of the control sources array while leaving the exterior sound field almost unchanged. Proofs of concept are provided through simulations achieved for interior problems by simulations in a free field scenario with circular arrays and in a reflective environment with square arrays. [ABSTRACT FROM AUTHOR]

Modeling complex vibroacoustic systems including poroelastic materials using finite element based methods can be unfeasible for practical applications. For this reason, analytical approaches such as the transfer matrix method are often preferred to obtain a quick estimation of the vibroacoustic parameters. However, the strong assumptions inherent within the transfer matrix method lead to a lack of accuracy in the description of the geometry of the system. As a result, the transfer matrix method is inherently limited to the high frequency range. Nowadays, hybrid substructuring procedures have become quite popular. Indeed, different modeling techniques are typically sought to describe complex vibroacoustic systems over the widest possible frequency range. As a result, the flexibility and accuracy of the finite element method and the efficiency of the transfer matrix method could be coupled in a hybrid technique to obtain a reduction of the computational burden. In this work, a hybrid methodology is proposed. The performances of the method in predicting the vibroacoutic indicators of flat structures with attached homogeneous acoustic treatments are assessed. The results prove that, under certain conditions, the hybrid model allows for a reduction of the computational effort while preserving enough accuracy with respect to the full finite element solution. [ABSTRACT FROM AUTHOR]

Smart foam offers a lightweight, efficient noise control solution by combining the complimentary advantages of passive dissipation in the foam material with the actuation authority of the active piezoelectric component, under appropriate control input. This study aims to implement the sensoriactuator operation of the active piezoelectric component to obtain an alternate error signal from its mechanical strain response. This can potentially replace the use of far-field microphone error sensors in active noise control applications, and hence improve the compactness of the system. The piezoelectric sensoriactuator has been implemented with the hybrid analog–digital compensation of the quasi-stable feedthrough capacitance of the actuator using an adaptive algorithm. The mechanical charge response, thus obtained, has been minimized using an adaptive algorithm and its effect on the transmission loss has been studied. Additionally, it has also been utilized in absorption and transmission control problems, using a virtual sensing strategy, with the aim of obtaining the desired control performance by minimizing an estimated virtual error signal. The experimental results are supplemented with finite element simulation of the coupled noise control system, and it provides a significant insight into the physical problem of the realization of the smart foam sensoriactuator. [ABSTRACT FROM PUBLISHER]

Smart foams combine the complimentary advantages of passive foam material and spatially distributed piezoelectric actuator embedded in it for active noise control applications. In this paper, the problem of improving the transmission loss of smart foams using active control strategies has been investigated both numerically and experimentally inside a waveguide under the condition of plane wave propagation. The finite element simulation of a coupled noise control system has been undertaken with three different smart foam designs and their effectiveness in canceling the transmitted wave downstream of the smart foam have been studied. The simulation results provide insight into the physical phenomenon of active noise cancellation and explain the impact of the smart foam designs on the optimal active control results. Experimental studies aimed at implementing the real-time control for transmission loss optimization have been performed using the classical single input/single output filtered-reference least mean squares algorithm. The active control results with broadband and single frequency primary source inputs demonstrate a good improvement in the transmission loss of the smart foams. The study gives a comparative description of the transmission and absorption control problems in light of the modification of the vibration response of the piezoelectric actuator under active control. [ABSTRACT FROM AUTHOR]

Abstract: This paper evaluates the feasibility and effectiveness, under controlled conditions, of active structural acoustic control of a helicopter main transmission in order to attenuate the vibration of the receiving roof panel and its sound radiation into the cabin. The vibroacoustic analysis of a typical helicopter drive train is conducted to extract the dominant tones generated by the various transmission stages. A finite element model of a Bell 407 transmission and simplified roof structure is developed in order to investigate various active control arrangements using piezoceramic actuators to control wave propagation in the gearbox supporting struts or receiving panel. The principal component analysis is used to extract the most significant control paths and reduce the control effort. A multiple frequency principal component least mean square (PC-LMS) algorithm is implemented on a laboratory setup and is used to successfully reduce up to seven gearbox tones simultaneously. [Copyright &y& Elsevier]

The objective of this paper is to show the feasibility of active control of tonal noise from automotive engine cooling fans using a single unbaffled loudspeaker in front of the fan. A simplified model is described for preliminary design using this configuration. A single input single output (SISO) filtered XLMS has been implemented to control the first tones in real time. At the error microphone, the sound pressure attenuation at blade passage frequency (BPF) and its first harmonics are reduced down to the broadband noise level. At low frequency, for large sound wavelength compared to the fan radius, the sound radiation is reduced in all directions, since the dipolar directivity of the secondary noise emitted by the unbaffled loudspeaker is similar to the directivity of the primary noise emitted by the fan. [ABSTRACT FROM AUTHOR]

Wave field synthesis (WFS) is a sound field reproduction technology which assumes that the reproduction environment is anechoic. A real reproduction space reduces the objective accuracy of WFS. This research involves the improvement of WFS performance by active noise control and adaptive filters. Simulations of sound field reproduction in a three-dimensional space show the physical possibility of progressive sound field reproduction in a closed space on the basis of optimal control of the reproduction errors at a sensor array. The proposed solution is adaptive wave field synthesis (AWFS). The originality of AWFS is the combination of the minimization of the reproduction error along with a penalty for any departure from the WFS solution. AWFS is theoretically analyzed on the basis of singular value decomposition. This suggests that the AWFS underlying mechanism is independent radiation mode control. Two adaptive algorithms for AWFS are developed. An experimental AWFS system is tested in different rooms (hemi-anechoic, laboratory, reverberant). It shows that AWFS performs better than WFS: AWFS significantly reduces the room effects on sound field reproduction. The algorithm based on independent radiation mode control contributes to the enlargement of the effective reproduction region. The thesis is written in French and in English. [ABSTRACT FROM AUTHOR]