Active Sound Control Research Articles

Non-stationary problem of active sound control in bounded domains

The present paper deals with the non-stationary problem of active shielding of a domain from undesirable external sources of noise. Active shielding is achieved by constructing additional (secondary) sources in such a way that the total contribution of all sources leads to the desirable effect. The problem is formulated as an inverse source problem with the secondary sources positioned outside the domain to be shielded. Along with the undesirable field (noise) to be shielded the presence of a desirable component (“friendly” sound) is accepted in the analysis. The constructed solution of the problem requires only the knowledge of the total field (noise) on the perimeter of the shielded domain. Some important aspects of the problem are addressed in the paper for the first time, such as the non-stationary formulation of the problem, existence of the resonance regimes and sensitivity of the solution to the input errors. The obtained solution is applicable to aeroacoustics problems.

Vibroacoustic Independent Contributors and Active Control of Vibration and Sound in Double Walls: Part II. Cluster Control

This paper is the second of two dealing with independent contributors to the structural kinetic and acoustic potential energy: vibroacoustic modes and clusters. In this paper, the theory of clusters is applied to a symmetric double wall composed of a pair of uniform flat panels, separated by an air gap and connected by mechanical springs, where the receiver panel is coupled to an enclosure. It is found that in the symmetric double wall, shapes of the uncoupled structural modes of the panels are clustered into an even or odd function, and these clusters independently contribute to both the structural kinetic energy of the panels and the acoustic potential energy in the air gap and the enclosure. Spatial filters to extract the individual clusters from the measured velocities of the panels are derived for the symmetric double wall. The performance of the active control system, using each cluster as the error criterion, is numerically simulated.

Supportless unidirectional acoustic sources

The results of studying the physical characteristics of unidirectional acoustic sources used in active sound control systems are presented. A discrete unidirectional source in the form of two phased monopoles and a planar array of such unidirectional sources are considered. One-dimensional boundary-value problems with two (the two-point problem) and three (the three-point problem) controlled parallel planar boundaries between homogeneous media with arbitrary impedances are studied. The boundaries (two or three) are subjected to the action of external forces. The case of the zero sum of external forces applied to the controlled boundaries corresponds to a supportless unidirectional source. It is shown that a unidirectional source can be created within the two-point boundary-value problem, whereas a supportless unidirectional source can be created within the three-point problem. Such parameters as transparency, small size, absence of support, and broad frequency band can be achieved for a unidirectional source in the form of two piezoelectric layers with the same impedance and velocity of sound as those of the surrounding medium.

Generalized Calderon-Ryaben'kii's potentials

Calderón–Ryaben'kii potentials provide the foundation for the difference potential method, which is an efficient way for solving boundary-value problems (BVPs) in arbitrary domains. This method allows us to reduce a uniquely solvable and well-posed BVP to a pseudo-differential boundary equation. The general theory of Calderón–Ryaben'kii potentials is considered via the theory of distributions. The definition of Calderón–Ryaben'kii potentials is based on the notion of a clear trace. The criterion of the clear trace is formulated. Partial differential equations of the first order and the second order are considered as particular examples. On the basis of the Calderón–Ryaben'kii potential theory, a solution of the active sound control problem is obtained in a general formulation. For the first time, the solution of the problem takes into account the feedback of the active shielding sources on the input (measurement) data. The exact transfer of the boundary conditions from the original boundary to an artificial boundary is also considered.

Frequency-domain delayless active sound quality control algorithm

This paper presents several broadband active sound quality control algorithms based on delayless frequency-domain techniques and subband adaptive filters. This efficient algorithm provides faster convergence and reduced computational complexity as compared to a time-domain active noise equalizer. An equal-loudness compensation method is also introduced for designing the shaping filter to achieve the desired sound quality. Computer simulations validate this algorithm in applications requiring high-order adaptive filters.

Vibroacoustic Modes and Active Control of Both Vibration and Sound

Vibration reduction and sound reduction are not necessarily compatible. The sum of the structural kinetic energy and acoustic power in free space (acoustic potential energy in an enclosed space) is an error criterion to control both vibration and sound. The orthogonal contributors with respect to the sum, and the frequency dependent spatial which can estimate the amplitudes of the vibroacoustic modes, modal filters, are formulated. Vibroacoustic modal filters allow a controller to coordinate both vibration and sound reduction and achieve order reduction. However, the implementation is not very easy because of the frequency dependence. The frequency independent vibroacoustic modal filters are formulated by omitting the frequency dependence. The omission of the frequency dependence mathematically proves to be valid for baffled structures in free space. Moreover, the developed theories are applied to baffled rectangular plates in free space, and the simulation results, for example, the contributions of the vibroacoustic modes to the sum of the structural kinetic energy and acoustic power, the shapes of the vibroacoustic modes, and the performance of the feedforward control using the frequency independent vibroacoustic modal are presented.

Active resonators for sound control in narrow pipes

A method of active sound control by a local device, namely, an active resonator that provides a resonance absorption or scattering of sound in a broad frequency band, is proposed. The active resonator is modeled as a sound source with an acoustoelectric feedback, which allows the correction of its motion depending on the sound field measured in the vicinity of the resonator. The performance of the method is demonstrated by two examples.

Active sound quality control of engine induced cavity noise

Active control solutions appear to be a feasible approach to cope with the steadily increasing requirements for noise reduction in the transportation industry. Active controllers tend to be designed with a target on the sound pressure level reduction. However, the perceived control efficiency for the occupants can be more accurately assessed if psychoacoustic metrics can be taken into account. Therefore, this paper aims to evaluate, numerically and experimentally, the effect of a feedback controller on the sound quality of a vehicle mockup excited with engine noise. The proposed simulation scheme is described and experimentally validated. The engine excitation is provided by a sound quality equivalent engine simulator, running on a real-time platform that delivers harmonic excitation in function of the driving condition. The controller performance is evaluated in terms of specific loudness and roughness. It is shown that the use of a quite simple control strategy, such as a velocity feedback, can result in satisfactory loudness reduction with slightly spread roughness, improving the overall perception of the engine sound.

531 振動と騒音の統合的能動制御 : PVDFフィルムを基調とした構造音響モード・フィルタの適用

531 振動と騒音の統合的能動制御 : PVDFフィルムを基調とした構造音響モード・フィルタの適用

Application of Learning Control to Active Sound Control for Fan Noise

This paper proposes an application of Learning Control algorithm to active control of fan noise. Learning control has been developed for the motion control of robot hand, for which a template of the trajectory is given. The robot learns an appropriate motion sequence by repeating trials of control when the error from the template is fed back to the controller. This control algorithm is transferred to the active control of periodic sound. The advantage of the learning control is found at compactness of the control program and quickness of the error convergence. The control experiment was successfully conducted for the fan noise applying the learning control to the periodic sound components. The experimental result proved the effectiveness of the learning control better than that of LMS feed forward control. In order to enhance the utility of the learning control the effect of the gain matrix to the quality of control is investigated by utilizing the numerical simulation. The trend of efficient matrix is shown numerically.

Linear and nonlinear problems of active sound control

AbstractThe problem of active shielding of some domain from the effect of the field generated in another domain is considered. The active shielding is implemented via the placement of additional sources in such a way that the total contribution of all sources leads to the desirable effect. The obtained solution does not require either the knowledge of the particular Green's function or any other information on source distribution and the surrounding medium. It is also important that along with undesirable field to be shielded, a desirable field can be admitted in the analysis. The solution of the problem requires only knowledge of the total field on the perimeter of the shielded domain. The active shielding sources are obtained for both the linear and nonlinear formulations of the problem. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Active Control of Sound Transmission Through Windows With Carbon Nanotube-Based Transparent Actuators

This paper explores the development of active sound transmission control systems for windows that can achieve a significant reduction in window noise transmission. Two major challenges need to be addressed in order to make the development of such noise blocking windows feasible. These are the need for a distributed actuation system that is optically transparent and the unavailability of a real-time reference signal that can be used by the active control system to provide advance information on the noise affecting the window. To address the first challenge, a transparent thin-film actuator (speaker) is first developed for the control system, which consists of a piezoelectric poly (vinylidene fluoride) (PVDF) thin film coated with compliant carbon nanotube-based transparent conductors on both sides. The developed thin-film speaker shows excellent acoustic response over a broadband frequency range, and has the advantages of being flexible, transparent, thin, and lightweight. To address the second challenge of providing a time-advanced reference signal from a moving noise source, a small microphone array distributed on the outside wall of the home is used. New noise source identification algorithms are employed, by which an appropriate microphone from the array can be chosen to provide a reference signal. Experimental results show that over 12 dB reduction in sound transmission is achieved globally in the case of broadband sound, which demonstrates the effectiveness of the control system in blocking sound transmission.

Active Control of Both Vibration and Sound in Free Space

Orthogonal contributors in terms of both structural kinetic energy and radiated acoustic power are derived for the purpose of simultaneous attenuation of both vibration and sound. The orthogonal contributors are referred to as “vibroacoustic modes”. The vibroacoustic modes have eigenvalues and eigenvectors along with structural modes and radiation modes. The eigenvalues of the vibroacoustic modes indicate the vibroacoustic modes' contributions to the sum of the structural kinetic energy and radiated acoustic power. The eigenvectors of the vibroacoustic modes indicate the modal shapes of the vibroacoustic modes. The complex modal amplitudes of the vibroacoustic modes can be measured by filtering error signals from discrete structural sensors attached on a structure. It is found that the sum of the structural kinetic energy and radiated acoustic power can be estimated by the sum of the squared complex modal amplitudes of few of the vibroacoustic modes which have higher contributions (higher eigenvalues). This allows one to get a reduced order controller. To verify the validity of vibroacoustic modal control, numerical results relating to an isotropic plate in an infinite baffle are presented.

1104 振動と騒音の統合的アクティブ制御(騒音と振動,OS2 交通・物流システムの高速化・利便性・快適性の向上)

1104 振動と騒音の統合的アクティブ制御(騒音と振動,OS2 交通・物流システムの高速化・利便性・快適性の向上)

Active Control of Sound for Composite Regions

We present a methodology for the active control of time-harmonic wave fields, e.g., acoustic disturbances, in composite regions. This methodology extends our previous approach developed for the case of arcwise connected regions. The overall objective is to eliminate the effect of all outside field sources on a given domain of interest, i.e., to shield this domain. In this context, active shielding means introducing additional field sources, called active controls, that generate the annihilating signal and cancel out the unwanted component of the field. As such, the problem of active shielding can be interpreted as a special inverse source problem for the governing differential equation or system. For a composite domain, not only do the controls prevent interference from all exterior sources, but they can also enforce a predetermined communication pattern between the individual subdomains (as many as desired). In other words, they either allow the subdomains to communicate freely with one another or otherwise have them shielded from their peers. In the paper, we obtain a general solution for the composite active shielding problem and show that it reduces to solving a collection of auxiliary problems for arcwise connected domains. The general solution is constructed in two stages. Namely, if a particular subdomain is not allowed to hear another subdomain, then the supplementary controls are employed first. They communicate the required data prior to building the final set of controls. The general solution can be obtained with only the knowledge of the acoustic signals propagating through the boundaries of the subdomains. No knowledge of the field sources is required, nor is any knowledge of the properties of the medium needed.

A speech communication environment using open source software library for active sound image control

This paper describes a three-dimensional (3-D) conference system using an open source software library on conventional PCs. We will attempt to use both 3-D graphics and audio to construct a virtual conference environment for effective communication between remote parties. A rough prototype system was developed using OpenGL and OpenAL. The system uses local files for voice output, whose image location is rendered according to the user input. We initially evaluated the perceived sound image location accuracy of the rendered sound image using the prototype. Users were asked to identify the location of the rendered sound image from among four choices: front, back, left, and right. The users were able to identify the left and right images correctly at virtually 100%, but the front and back identification were lower than 10% for some sounds, particularly male speech. We plan to implement audio-streaming functions to achieve real-time audio conferencing and evaluate the benefits of 3-D audio for conferences. We would also like to implement HRTF (head-related transfer function) and RTF (room transfer function) for improved audio image localization, especially to achieve accurate elevation perception.

Development of adaptive algorithm for active sound quality control

This paper develops an active sound-quality control (ASQC) system based on the active noise equalization (ANE) technique, and optimizes it with the filtered-error least mean square (FELMS) algorithm and normalized reference signal generator. The ASQC system controls the sound quality of products such as engines by changing the amplitudes of harmonics. This optimized system uses the FELMS algorithm to limit disturbances in the passband caused by uncorrelated interferences with high gains in the secondary path, thereby increasing the system stability. It achieves fast convergence by normalizing the amplitudes of internally generated sinusoids in the reference signal according to the magnitude response of the secondary path at the corresponding frequencies. Computer simulations demonstrate the desired spectral shaping capability with faster convergence and reduced passband disturbance.

An experimental investigation of two active segmented partition arrays

This paper addresses the construction, measurement, and analysis of two active segmented partition arrays (ASP arrays) for use in active sound transmission control. The control objective for each array was to actively minimize principal transmitting surface vibrations to induce high transmission loss. The arrays incorporated four adjacent lightweight modules with composite single or double leaves and small loudspeakers as actuators. A normal-incidence transmission loss measurement system was developed to evaluate their performances under passive and active conditions. Measurement results were compared to results for passive benchmark partitions and theoretical predictions. Four decentralized single-error-input, single-output filtered-x controllers were used with the arrays. They were shown to perform at least as well as a centralized multiple-error-input, multiple-output controller, with good error signal reductions and stability. Scanning laser vibrometer measurements confirmed the ability of the double-composite-leaf ASP to efficiently and globally minimize its transmitting surface vibrations to produce high transmission loss. Its average transmission loss over the active measurement bandwidth (30–290Hz) was 56dB—a full 34dB greater than that of the single-composite-leaf ASP. The work confirms that a properly configured lightweight ASP can produce very high transmission loss through vibration control techniques.

Development of transparent thin film speaker and its application for active sound transmission control through windows

Homes close to airports and highways in major metropolitan areas suffer from serious noise problems. Typically, windows constitute the primary path through which noise enters a home. As an effective method for attenuating low frequency noise, active noise cancellation approach has drawn increasing interest. A small voice coil actuator can be used to vibrate a glass panel and achieve significant reduction in noise transmission at its location. However, global noise cancellation over the entire panel can not be achieved with such a single point actuator. Using multiple voice coil actuators is also not practical, since several actuators on a windowpane would destroy the aesthetics of the window. This necessitates the development of thin film actuators that can provide distributed canceling sound over the entire surface of large sized glass panels. The need of transparence for the windows application poses a great challenge to the development of such thin film actuators. In this paper, transparent thin film speakers are developed, based on the use of carbon nanotubes for conductive films that are coated on polzerized PVDF films. Preliminary experimental results show that the transparent thin film speaker has the potential to be a promising solution for the ANC windows.

A theoretical and numerical analysis of vibration-controlled modules for use in active segmented partitions

Many applications of active sound transmission control (ASTC) require lightweight partitions, high transmission loss over a broad frequency range, simple control strategies, and consistent performance for various source and receiving space conditions. In recent years, researchers have begun to investigate active segmented partitions (ASPs) because of their potential to meet such requirements. This paper provides a theoretical and numerical analysis of four ASP module configurations that are candidates for these applications. Analogous circuit methods are used to provide normal-incidence transmission loss and reflection coefficient estimates for their passive and active states. The active control objective for each configuration is to induce global vibration control of various transmitting surfaces through direct vibration control of a principal transmitting surface. Two characteristic single-composite-leaf (SCL) configurations are unable to use the strategy effectively. However, design adjustments are investigated to improve their performances. Two double-composite-leaf (DCL) configurations use the strategy much more effectively to produce efficient global control of transmitting surface vibrations and achieve high transmission loss over a broad frequency range. This is achieved through a minimum volume velocity condition on the source side of each module. One DCL configuration enhances module isolation in full ASP arrays while satisfying other design and performance criteria.