Active Control Of Sound Transmission Research Articles

Radiation clusters and the active control of sound transmission through symmetric structures into free space

The purpose of this paper is attenuating harmonic sound transmission through symmetric structures into free space using error signals derived from structural vibration sensors. It is well known that structural modal functions of symmetric structures are clustered to an even function or an odd function and each of the clusters uncouples with the other cluster in the radiated acoustic field. This indicates that the clusters are orthogonal contributors, i.e., independent contributors, with respect to the radiated acoustic field. In this paper, the clusters are referred to as “radiation clusters” in contrast with radiation modes, which are conventional orthogonal contributors with respect to the radiated acoustic power. The active control of harmonic sound transmission through symmetric structures into free space based upon independently measuring and controlling the individual radiation clusters, termed “radiation cluster control”, is proposed. The approach falls into a category of middle authority control (MAC), which is between low authority control (LAC): structural modal control and high authority control (HAC): radiation modal control, possessing the benefit of practicality similar to LAC, while providing high control performance and some flexibility of control gain assignment similar to HAC. Specific examples relating to radiation cluster control of a simply supported rectangular plate in an infinite baffle are given.

New results in active and passive control of sound transmission through double wall structures

Abstract This paper presents an overview of recent results concerning active and passive control of sound transmission through double wall structures. First, the analytical simulations are presented for the active control of sound transmission through double wall structures. These are based on a coupling structural-acoustic modal model using piezoelectric materials and loudspeaker/microphones as actuator/sensors. The numerical results show the potential for employing piezoelectric sensor/actuators to improve sound transmission loss. In addition, some useful conclusions are obtained. When, for example, a volume velocity sensor is applied to a radiating plate, sound transmission loss will improve significantly, no matter what type of actuators (i.e. loudspeakers or PZT actuators on either plate) are used. With a loudspeaker/microphone configuration should be avoided for same thickness double wall structures, etc. Furthermore, current research activities on the control of sound transmission through double wall structures also include an arrangement of Helmholtz resonators (HRs) placed within the wall cavity for the passive control of sound transmission through a double wall structure. The current research goal is to find optimal parameters of HRs (damping ratio, numbers, natural frequency, etc.) in order to maximize the improvement of the transmission loss over a specified frequency range. An analytical model of fully coupled structural-acoustic-HRs within a double wall structure is established. Results indicate that tuning the HRs to the mass–air–mass resonance frequency does not guarantee the best possible improvement of the sound transmission loss. Using the frequency averaged sound transmission loss as the cost function to optimize the natural frequency of the HRs is a more effective method to find the HRs tuning frequency for maximizing the improvement of the transmission loss. The aim of this paper is to illustrate the potential of the active control approach using smart piezoelectric materials and different control actuators (i.e. loudspeakers in the cavity, PZT actuators applied to one of the plates) to improve the transmission loss through double wall structures. Additionally, new results on tuning and placement of HRs are presented. Both of these are based upon a refined model of the systems and offer good physical insight into the active and passive control of sound transmission through double wall structures.

Secondary actuation and error sensing for active acoustic structure

A typical approach to active control of sound radiation or transmission from vibrating structures involves active structural acoustic control (ASAC) and active noise control (ANC), which introduce respectively force input and compacted sound source to apply on or be close to the vibrating structure. However, for the ASAC approach, arrangement for secondary force and error sensor is heavily dependent upon the properties of the primary structure and acoustical space; for the ANC approach, a large number of compacted secondary sources are required. Hence, in this paper, based on distributed secondary sound source and near-field error sensor, active acoustic structure is proposed to construct adaptive or smart structure as a versatile module or element for controlling sound radiation or transmission at low frequencies. First, a theoretical model based on a minimization of the total sound radiation from the primary and secondary panel is established, after which, taking into consideration the relationship between the vibration modes pattern and sound radiation characteristics for secondary panels, optimal arrangement for the secondary panels is examined in detail. Finally, a near-field pressure-based error sensing approach is presented, based on two kinds of object function, and active control of sound radiation is performed.

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.

Mechanisms of active control of sound transmission through a linked double-wall system into an acoustic cavity

The mechanism of active control on sound transmission through a mechanically linked double-wall structure into an acoustic cavity is investigated in this paper. Two control methods, i.e., structural control and acoustic control under two linkage cases (soft and hard) are investigated to analyze the effect of the links on the selection of control strategies and the corresponding control mechanisms. Simulations are performed to examine the dominant control mechanism (modal suppression or modal rearrangement) in different frequency ranges for each control case. The alteration in the structural-acoustic coupling is also analyzed so as to explain the mechanisms of sound attenuation. In addition, the dominance of the acoustic mode (0, 0, 0) in the energy transmission process as well as its use in designing a more effective sensor/actuator arrangement is discussed.

Radiation clusters and the active control of sound transmission into a symmetric enclosure

Radiation cluster control is proposed for the purpose of attenuating harmonic sound transmission into a symmetric enclosure using error signals derived from structural vibration sensors. The approach falls into a category of middle authority control, which is between LAC (low authority control: structural modal control) and HAC (high authority control: radiation modal control), possessing the benefit of practicality over LAC, while providing high control performance and some flexibility of control gain assignment similar to HAC. The structure of a radiation cluster control system is outlined, showing that it is possible to control a target cluster without affecting the other clusters. A design procedure for the radiation cluster control system is then proposed. Numerical results are also presented.

339 モード制御によるアクティブ遮音法に関する研究

339 モード制御によるアクティブ遮音法に関する研究

Active noise control of a mechanically linked double panel system coupled with an acoustic enclosure

Active control of sound transmission through a mechanically linked double-wall structure into an acoustic enclosure is investigated in this paper. Based on a fully coupled vibro-acoustic model, the effect of mechanical links on the selection of control strategies is studied by examining (a) cavity control using acoustic sources inside the air gap and (b) structural control using structural actuators between the two panels. The relationship between the transmission path and the control strategies is explored. Numerical results show that cavity control can provide good noise attenuation for soft links when acoustic transmitting path dominates, while either structural or cavity controls can be used with the increase of stiffness of links depending on the frequency range of interest. For each case, the dominant control mechanism is examined and the alteration in the structural–acoustic coupling is analyzed to explain the mechanisms of attenuation. The effect of the acoustic mode (0,0,0) on active control of energy transmission is also discussed, giving guidance to choosing the appropriate control arrangement to ensure the maximum control performance.

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.

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.

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.

An experimental investigation of two module configurations for use in active segmented partitions

Individual modules intended for active segmented partitions should be carefully analyzed before they are advanced as viable tools for active sound transmission control. In this paper we present experimental evaluations of two vibration-controlled modules: a single-composite-leaf (SCL) configuration and a double-composite-leaf (DCL) configuration. Experimental apparatuses and procedures are introduced to assess their normal-incidence transmission losses over a bandwidth from 40 to 1970 Hz. The average transmission loss of the passive SCL module is found to be 21 dB. If its transmitting diaphragm acceleration is minimized through active control, transmission loss increases somewhat at lower frequencies but decreases at higher frequencies, producing no increase in the average value. The average transmission loss of the passive DCL module is found to be 43 dB. After its transmitting diaphragm acceleration is actively minimized, the transmission loss increases substantially at all frequencies (especially at low frequencies), to produce an average value of 77 dB. Thus, while both configurations have the same underlying control objective, the DCL module yields a 56 dB average improvement over the SCL module through simple configurational changes. An alternative control scheme is investigated that minimizes acoustic pressure in the DCL module cavity, but it is found to be less effective.

Active control of sound reflection, absorption and transmission using thin panels

This study explores the development of thin panels that can be controlled electronically so as to provide surfaces with desired reflection coefficients. Such panels can be used as either perfect reflectors or absorbers. They can also be designed to be transmission blockers that block the propagation of sound. The development of the control system is based on the use of wave separation algorithms that separate incident sound from reflected sound. In order to obtain a desired reflection coefficient, the reflected sound is controlled to appropriate levels. The incident sound is used as an acoustic reference for feedforward control and has the important property of being isolated from the action of the control system speaker. In order to use a panel as a transmission blocker, the acoustic pressure behind the panel is driven to zero. Detailed experimental results are presented showing the efficacy of the algorithms in achieving real-time control of reflection or transmission. The panels are able to effectively...

Active Control of Sound Reflection, Absorption and Transmission Using Thin Panels

This study explores the development of thin panels that can be controlled electronically so as to provide surfaces with desired reflection coefficients. Such panels can be used as either perfect reflectors or absorbers. They can also be designed to be transmission blockers that block the propagation of sound. The development of the control system is based on the use of wave separation algorithms that separate incident sound from reflected sound. In order to obtain a desired reflection coefficient, the reflected sound is controlled to appropriate levels. The incident sound is used as an acoustic reference for feedforward control and has the important property of being isolated from the action of the control system speaker. In order to use a panel as a transmission blocker, the acoustic pressure behind the panel is driven to zero. Detailed experimental results are presented showing the efficacy of the algorithms in achieving real-time control of reflection or transmission. The panels are able to effectively block transmission of broadband sound. Practical applications for these panels include enclosures for noisy machinery, noise absorbing wallpaper, the development of sound walls and the development of noise-blocking glass windows.

Active Control of Sound Transmission Utilizing the Mechanism of Anti-resonance Phenomenon

Active Control of Sound Transmission Utilizing the Mechanism of Anti-resonance Phenomenon

Research in the field of active sound transmission control

Sound transmission through an unperforated partition may be described as the vibro-acoustic process in which fluid-borne sound waves incident upon the partition from the source side force it to vibrate and consequently radiate transmitted fluid-borne sound waves into the space on the opposite (receiving) side. Active reduction of sound transmission through partitions, or active sound transmission control (ASTC), denotes an active modification to this process. It may be defined as the reduction of transmitted sound through the action of electro-mechano-acoustical devices regulating any or all stages of the vibro-acoustic sound transmission process. In certain analyses, this branch of active noise control has referred to situations in which electro-mechanical actuation is applied only to a partition through which sound is transmitting. However, since ASTC may be achieved by other means, and since much research in the field has utilized other techniques, this limitation is clearly too restrictive. This paper reviews and categorizes many research efforts in the field, and provides a brief history of the efforts based on an extensive bibliography of the subject matter. It also identifies research areas that could be pursued in the future.

Vibration-controlled modules for use in active segmented partitions

Active segmented partitions (ASPs) have become an important topic in the research of active sound transmission control (ASTC). Many ASTC applications require lightweight partitions, high transmission loss over a broad frequency range, and applicability to a variety of source and receiving space conditions. This paper provides theoretical, numerical, and experimental evaluations of specific ASP module configurations used to satisfy these requirements. The control objective for each is to induce global vibration control of its various transmitting surfaces through direct minimization of the normal vibration of its principal transmitting surface. Normal-incidence transmission loss estimates are based on equivalent circuit analysis and corresponding experimental measurements are made using plane wave tube techniques. The paper explains why characteristic single diaphragm configurations are unable to use this strategy effectively. It also discusses two dual diaphragm configurations that use the control scheme particularly well to produce efficient global control of their transmitting surfaces and achieve very high transmission loss over a broad frequency range. The designs facilitate incorporation into full ASP arrays and satisfy other useful criteria.

An analytical and experimental investigation of active structural acoustic control of noise transmission through double panel systems

An analytical and experimental investigation of active control of sound transmission through double panel systems has been performed. The technique used was active structural acoustic control (ASAC) where the control inputs, in the form of piezoelectric actuators, were applied to the structure while the radiating pressure field was minimized. Results verify earlier experimental investigations and indicate the application of control inputs to the radiating panel of the double panel system resulted in greater transmission loss (TL) due to its direct effect on the nature of the structural-acoustic (or radiation) coupling between the radiating panel and the receiving acoustic space. Increased control performance was seen in a double panel system consisting of a stiffer radiating panel due to its lower modal density and also as a result of better impedance matching between the piezoelectric actuator and the radiating plate. In general the results validate the ASAC approach for double panel systems, demonstrating that it is possible to take advantage of double panel system passive behavior to enhance control performance, and provide design guidelines.

Impacts of structural–acoustic coupling on the performance of energy density-based active sound transmission control

This paper investigates numerically the performance of the active sound transmission control into a rectangular cavity through a flexible panel under the energy density-based error-sensing algorithm. Full coupling between the sound transmitting panel and the enclosed space is considered. A pure vibration actuator, a pure acoustic source and a combined control source system are used as the secondary control source in the active control and their performances are studied. Formulae for the coupled eigenfrequencies of the cavity and the flexible panel are also derived. The strength of the structural–acoustic coupling, the ratio between the first eigenfrequencies of the cavity and the panel and the difference between the excitation frequency and the coupled eigenfrequencies, especially the latter, are found to have crucial impacts on the performance of the active control regardless the type of control source used.

Experimental validation of a collocated PVDF volume velocity sensor/actuator pair

The active control of sound transmission through a rectangular panel is experimentally verified. The control system is based on a collocated volume velocity sensor/actuator pair which measures and excites the first radiation mode of the panel. Suppression of the first radiation mode is an efficient strategy to control the low frequency sound radiation from the panel. This configuration leads to a simple single-input single-output control system, to which feedback control can be applied. Two implementations of the volume velocity sensor/actuator pair are tested. First, a polyvinyledene fluoride polymer (PVDF) volume velocity actuator foil with shaped electrodes is used in combination with an identical PVDF volume velocity sensor foil. Due to the mechanical coupling between the PVDF sensor and actuator foil, it is shown that a direct velocity feedback control scheme is not feasible because higher order structural modes will be destabilized. Instead integral force feedback is applied, such that the open-loop transfer function has a roll-off towards higher frequencies. Experiments show that this control strategy results in a reduction of the sound pressure in the receiving room of 10 dB at the first structural resonance without spillover to higher order modes. Due to the roll-off towards high frequencies, the control over higher order modes remains limited. Second, a discrete volume velocity sensor is constructed by summing the signals from 12 point sensors placed on the panel. The volume velocity actuator consists of two PVDF foils, glued on each side of the panel and driven in opposite phase. Direct volume velocity feedback is applied to this system, which is minimum phase. This control system is capable of reducing the sound pressure in the receiving room below 300 Hz by 10–15 dB without spillover to higher order modes.