Active Control Of Sound Fields Research Articles

Three-dimensional characterization of spatial sound fields via acousto-optic sensing

Characterizing audible sound fields over space is at the core of many applications in acoustics and audio technology, including active sound field control, spatial audio, and the experimental analysis of sound radiation. For this purpose, arrays of microphones are commonly deployed across the sound field, with an inter-microphone spacing that depends on the highest frequency studied. Capturing sound fields at mid and high frequencies is nonetheless challenging, as the number of transducers required becomes impractically large and the scattering of sound introduced by the array is often significant. Acousto-optic sensing enables the remote and non-invasive characterization of acoustic fields, and thus it represents an attractive alternative to conventional electro-mechanical transducers in several applications. The phase-shift that laser beams experience as they travel through a pressure field are measured via optical interferometry. The optical measurements are then used to reconstruct the field that originated such phase variations. In this study, we project the measured data into a set of functions suitable to represent sound fields over space. The projection makes it possible to improve the reconstruction accuracy and extrapolate the reconstruction outside the measured region. We demonstrate the method by reconstructing the three-dimensional sound field inside a room using optical data.

Modeling and analysis of secondary sources coupling for active sound field reduction in confined spaces

This article addresses the coupling of acoustic secondary sources in a confined space in a sound field reduction framework. By considering the coupling of sources in a rectangular enclosure, the set of coupled equations governing its acoustical behavior are solved. The model obtained in this way is used to analyze the behavior of multi-input multi-output (MIMO) active sound field control (ASC) systems, where the coupling of sources cannot be neglected. In particular, the article develops the analytical results to analyze the effect of coupling of an array of secondary sources on the sound pressure levels inside an enclosure, when an array of microphones is used to capture the acoustic characteristics of the enclosure. The results are supported by extensive numerical simulations showing how coupling of loudspeakers through acoustic modes of the enclosure will change the strength and hence the driving voltage signal applied to the secondary loudspeakers. The practical significance of this model is to provide a better insight on the performance of the sound reproduction/reduction systems in confined spaces when an array of loudspeakers and microphones are placed in a fraction of wavelength of the excitation signal to reduce/reproduce the sound field. This is of particular importance because the interaction of different sources affects their radiation impedance depending on the electromechanical properties of the loudspeakers.

Cancellation, reproduction, and cloaking using sound field control

The active control of sound fields has been applied in active noise cancellation, sound field reproduction, and active acoustic cloaking; however, relatively few studies have considered the relationship between these three areas of research. This paper investigates the physical limitations on active noise control, sound field reproduction, and active acoustic cloaking in terms of the controllability and observability of the sound field. This has been achieved through a series of simulations that consider the control of the sound field in the presence of a scattering object. In terms of the controllability problem, it is shown that while active noise control and sound field reproduction are most effective when considering the interior control problem, active acoustic cloaking is most effective when facing the exterior control problem. Different sensing strategies are then considered for the cancellation, reproduction, and cloaking problems and their impact on the observability of the control problem is discussed.

Active control of scattered acoustic fields: Cancellation, reproduction and cloaking.

The active control of sound fields has been widely applied in both active noise control and sound field reproduction, however, relatively few studies have focused on active acoustic cloaking. In order to build upon the knowledge and understanding in the areas of active noise control and sound field reproduction, this paper investigates the corresponding physical limitations and compares them to the active cloaking problem when the three strategies are employed in the presence of an acoustic scatterer. The three sound field control strategies have been formulated within a consistent framework, and this has enabled insight into the physical control mechanisms. Two different three-dimensional scattering problems have then been simulated and used to investigate the performance limitations of the three strategies. The influence of the number and proximity of control sources to the scattering object have been investigated, and it has been shown that the requirements for active cloaking differ from those for active noise control and sound field reproduction. Specifically, it has been shown that there is a clear distinction between controlling the internal and external sound fields in the three cases.

Bases of active noise control

Mathematical models allowing to describe the bases of active control of sound fields are given. Results of using of active noise control system in the silencer are presented.

Active Sound Field Control in a Small Room

Active Sound Field Control in a Small Room

Active Sound Field Control System in Auditoriums

Active Sound Field Control System in Auditoriums

SIMULATION OF ACTIVE NOISE CONTROL IN ENCLOSURES USING DIRECT SOUND FIELD PREDICTION

This paper is concerned with the active control of sound fields in enclosures. Specifically, the numerical problem of determining the optimum locations of control sensors and actuators is addressed. A new method for determining the optimum secondary sources strength is proposed, based on the explicit prediction of the sound field, which makes the simulation of realistic acoustical applications feasible, in terms of the enclosure's boundary conditions. The irregular geometry of a car cabin with complex boundary conditions is used in order to demonstrate the application of the new method to a test case where the existing methods cannot theoretically apply without resolving to significant numerical error. The new method of determining the secondary sources strength is combined with a modified genetic and a gradient optimization algorithm so as to locate the optimum positions of active noise control transducers for global sound field control. The overall algorithm, constituting of the method for calculating the secondary sources' strength and the optimization algorithms, is adjusted with computational improvements for better performance.

The virtual microphone technique in active sound field control systems

Active Sound Field Control (AFC) has been proven very useful in reverberation enhancement applications in large rooms. However, feedback control is required in order to eliminate peaks in the frequency response of the system. The present research closely follows the studies of Shimizu in AFC, in which smoothing of the rooms transfer function is achieved by averaging the impulse responses of multiple microphones. ‘‘The virtual or rotating microphone technique’’ reduces the number of microphones in the aforementioned AFC technology, while still achieving the same acoustical effects in the room. After the impulse responses at previously specified pairs of microphone positions are measured, the ratio of transfer functions for every pair is calculated, thus yielding a constant K. Next, microphones are removed and their impulse responses are reproduced by processing the incoming signal of each pair through a convolver, where the computed K constants have been previously stored. Band limiting, windowing and time variance effects are critical factors, in order to reduce incoherence effects and yield reliable approximations of inverse filters and consequently calculations of K. The project is implemented in a church lacking low frequency reverberation for music and makes use of 2 physical and 2 virtual microphones.

압전재료와 점탄성 재료를 이용한 평판 진동 음장의 능동제어

The coupled finite/boundary element method is used in numerical analysis for acoustic radiation from the vibration of rectangular composite plate which is simply supported. This analysis is validated using the Wallace equation for an isotropic plate. Active control of sound fields has been tarried out using 3 pairs of piezoelectric sensor/actuator and a pair of viscoelastic material by Passive constrained layer damping treatment. The results show that the optimal placement of piezoelectric sensor/actuator and VE patch is required to control the sound fields from a vibrating composite plate.

Active Control of Sound Fields from Plates in Flow by Piezoelectric Sensor/Actuator

The objective is to control the sound fields induced by vibrating structures in flow by piezoelectric sensors and actuators. When thin structures such as plates are vibrating in a flow, the fluid loading effects lead to some important changes in the acoustic field and the structural vibration and cannot be neglected. The vibration of plate structures and the sound fields are analyzed using the finite element and the boundary element methods. It is found that some specific modes radiate sound very well compared with the other modes. Because the number of modes that can be controlled simultaneously is limited, the selection of controlled modes is prerequisite. For structural acoustic control, the well-radiating modes, namely, the modes contributing most to far-field sound radiation, should be selected as the controlled modes. Radiation efficiency is used as a reference for the selection of controlled modes. The optimal placement of the piezoceramic material (lead zirconate titanate; PZT) actuators and the optimal electrode shape of polyvinylidene fluoride sensors are determined by a genetic algorithm to minimize the well-radiating modes and to avoid the observation and control spillover. A linear quadratic Gaussian controller is designed to estimate the controlled modes from sensor output and to minimize the performance index. The result shows that global noise reduction can be realized by using the method.

Study of Active Sound Field Control Using Analysis of Structural-Acoustic Coupled System.

The active sound field control is effective for low frequency range and the control in an enclosed cavity is more effective by using the sound pressure data at many measureing points. It is, however hard to set many sensors in the enclosed cavity because of the lack of space or cost problem. In this paper, a new active sound field control method is proposed, where the unknown inner sound pressures are estimated by using the structural acoustic coupled analysis method. In this method, the number of measuring points of sound pressure can be imaginarily increased. As the numerical example, the rectangular prism model is taken up, and the active sound field control in the model in simulated by using the proposed method. As the result, it is shown that the proposed method is effective in the numerical simulation.

Active control of sound fields from plates in flow by piezoelectric sensor/actuator

Active control of sound fields from plates in flow by piezoelectric sensor/actuator

ACTIVE CONTROL OF SOUND FIELDS FROM A COMPOSITE PLATE USING THE ANISOTROPY AND SHAPE OF DISTRIBUTED PVDF ACTUATORS

Compared to piezoceramic material, polyvinylidene fluoride polymer has anisotropic electromechanical material properties. Using the fact that the anisotropy and shape of distributed piezopolymer actuators have coupling effects with the vibration modes of structures, studies on the design of distributed piezopolymer actuators are performed in order to improve the effectiveness of active control of the sound fields radiated from composite structures. The sound fields induced by the complicated dynamic behaviors of a composite structure was analyzed using coupled finite element and boundary element methods. Active control of sound fields is attempted through minimization of the radiated sound power from a plate. Some numerical results of sound control problems are presented with actuators of various shapes and lamination angles. The results indicate that the anisotropy and shape of distributed piezopolymer actuators are promising factors in the design of distributed piezoelectric actuators for controlling acoustic radiation from structures.

A study on the influence of room absorption on the effectiveness of active sound field control in a piano practice room

A study on the influence of room absorption on the effectiveness of active sound field control in a piano practice room

アクティブ音場制御の現状

アクティブ音場制御の現状

Active Sound Field Control System in Auditoriums

Active Sound Field Control System in Auditoriums

Adaptive active control of sound fields in elastic cylinders via vibrational inputs

A model of an aircraft fuselage is used to evaluate an active noise control system using vibrational force inputs as secondary control sources. The cylindrical shell is unstiffened, undamped, and contains no interior acoustic damping. A control system based on the filtered-x version of the least mean squares algorithm is configured, using one control source and one error sensor.

Current and future issues of active noise control.

Active control of sound fields is an emerging technology which has a great potential to become superior to many passive low frequency noise control methods. It is based on fundamental physical principles which include acoustical coupling of sources, destructive wave interference, and control of enclosure modes. The implementation of active noise control requires placing secondary sources and microphones into the controlled field. Most systems use adaptive filters to control the secondary sources to achieve maximum noise reduction. The engineering applications will require developing optimization techniques for secondary sources and controlling microphone locations. Also new types of robust actuators and controlling sensors will be needed. A brief summary of existing and future applications is provided.

Active Sound field control in auditorium

Active Sound field control in auditorium