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Christian Carme, Technofirst (France)
Anne Montassier, Technofirst (France)
Industrialization of active control technologies is a specific trade. This new technology is not completely controlled. Several specific competences are necessary. In this paper we present a synthesis on the limitation of active control technologies, advantages, application estate, development and industrialization's tools. The second part of the document presents products using this technology.
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Osman Tokhi, The University of Sheffield
D.N. Ramos-Hernandez, The University of Sheffield
M.A. Hossain, University of Dhaka
The performance demands in practical realisation of signal processing and control strategies has motivated a trend towards utilisation of complex algorithms. This, in turn, has resulted in a resurgence in the development of high-performance processors to make real-time implementation of such algorithms feasible in practice. However, due to inefficient mapping of algorithms on processors, to take account of the computing capabilities of processors in relation to the computing requirements of the application, such a goal can still be difficult to reach. This paper presents an investigation into the development of sequential and parallel computing methods for real-time signal processing and control. Several algorithms encountered in acoustics and vibration applications are considered. These are implemented on a number of high-performance processors including the TMS320C40 parallel digital signal processing device, the Intel i860 vector processor and the Inmos T805 transputer. A comparative assessment of the performance of the processors in implementing the algorithms, revealing the capabilities of the processors in relation to the nature of the algorithms, is presented. This is used as the basis of development of new performance metrics and task to processor mapping strategies for parallel architectures. The performance metrics and mapping strategies thus developed are verified by implementing the algorithms on a number of homogeneous and heterogeneous parallel architectures.
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Xiaojun Qiu, The University of Adelaide (Australia)
Colin H. Hansen, The University of Adelaide (Australia)
A frequency domain filtered-x type least mean active sound intensity adaptive control algorithm based on waveform synthesis is developed for active control of transformer noise. The algorithm is useful for providing global control of transformer noise by minimising the mean active sound intensities for the fundamental frequency and its harmonics in the near acoustic field of the transformer. Mean active sound intensity has been found to be the most effective near field acoustic error sensing strategy for active control of free field sound radiation. The algorithm adjusts the amplitude and phase of each tone to be controlled in the frequency domain and implements the waveform synthesis process in the time domain. The transfer function of the cancellation path is included in the algorithm so that it becomes a filtered-x type adaptive algorithm.
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Xun Li, The University of Adelaide (Australia)
Colin H. Hansen, The University of Adelaide (Australia)
Xiaojun Qiu, The University of Adelaide (Australia)
Traditional means of controlling sound radiated by large electrical power transformers involve the construction of large, expensive ugly barriers or full enclosures which compromise the maintainability of the transformers. One promising alternative is to use active sound cancellation to reduce the noise. In this paper the work was concerned with the development of a resonant curved panel with a backing cavity which could be more effective, more efficient (regarding electrical power requirements) and more rugged than conventional loudspeakers. The reasons for using a curved panel rather than flat panel were twofold: first a curved panel is more easily excited by piezoelectric patch actuators because the bending vibration of the panel couples better with the extensional motion of the actuators; and second, it is not possible to adjust the resonance frequencies of the efficient modes of a flat panel so easily. An analytical model was developed to design a curved panel with backing cavity system having resonance frequencies of 100 Hz and 200 Hz for the 1,1 mode and 1,3 mode respectively. Of cause there are many possible geometric configurations which can achieve the desire result. An example configuration was designed using the analysis described in this paper and the result verified by finite element analysis (FEA). The panel was constructed, resonance frequencies were measured and sound radiation as a function of piezoelectric patch actuator excitation voltage was determined.
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A. Minguez, Universidad Politecnica de Madrid (Spain)
Manuel Recuero, Universidad Politecnica de Madrid (Spain)
This paper presents a simple adaptive algorithm based on the adaptive notch two-taps filter and the filtered-X LMS algorithm, to be used in active noise control applications. The system consists of two adaptive algorithms working together. One algorithm estimates the error path transfer function on-line and the other cancels a frequency narrowband of the residual signal. The convergence factors of the two adaptive algorithms determine the spectrum width of the cancellation and the stability of the control system. The adaptive filter used for estimating the error path has also two taps, it is only necessary to estimate the module and the phase at the center frequency of the cancellation bandwidth. The system can be generalized to a configuration of multiple cancellation frequency narrowbands and a multiple notch filter control system. This adaptive algorithm can be used in active noise control applications to cancel only frequency narrowbands and when it is not possible to get any reference signal.
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Kym A. Burgemeister, Arup Acoustics (Australia)
Scott D. Snyder, University of Adelaide (Australia)
Modal filtering has emerged as a valuable technique for the measurement of significant system parameters, such as sound power, for use in active noise and vibration control. By providing a , measure of only a few of the most significant parameters, reductions in the complexity of the adaptive control system can be achieved. The physical implementation of such a modal filter is discussed for a system for measurement of sound power radiated from a simply supported rectangular panel. The effect of frequency normalisation of the modal filter on the amount of attenuation that maybe achieved is examined. Frequency normalisation allows simplifications to the modal filter system with little degradation to resultant attenuation levels, although the effective bandwidth of the filter system is reduced.
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Scott D. Sommerfeldt, Brigham Young University (U.S.A.)
Brian L. Scott, The Pennsylvania State University (U.S.A.)
There is a broad class of active control problems involving control of the acoustic power radiated from a vibrating structure. For many of these applications, it is desirable to implement the control using structural sensors, as opposed to far-field pressure sensors. It is known that the acoustic radiation corresponds to the supersonic wavenumber components of the vibration. Previous work by the authors has demonstrated that one can design distributed sensors that provide a direct measurement of the radiated power using a spatial Fourier transform of the sensor measurements. The sensors have been much more effective in predicting the radiated power than using a similar number of point sensors on the structure. The work reported here uses this wavenumber in formation as the basis for an active control system that attenuates the far-field radiation by means of minimizing the supersonic wavenumber components. The numerical results presented compare and contrast the far-field results obtained using this active control approach with results obtained when simply minimizing the vibration signal at the discrete locations. The results indicate that significant far-field control can be achieved by directly measuring the supersonic wavenumber vibration and minimizing that vibration, while ignoring the non-radiating subsonic wavenumber components.
sv970327.pdf (Scanned) TOPMichael Podlesak, Defence Science and Technology Organisation (Australia)
Active control of low frequency pump noise in water-filled pipes is being developed at AMRL for acoustic signature control on maritime platforms. The present approach is based on separate fluid and wall-axial wave control with collocated control sources. One of the main problems encountered in the design of suitable control sources is their operating effectiveness over a large range of internal hydrostatic pressures. A prototype of a fluid-wave control source has been built which is able to provide some control at low frequencies in a steel pipe system. However, at higher frequencies, the control is considerably compromised through a mechanism believed to be linked to flanking via wall-axial wave components. This paper reports the results of experiments designed to study the effect of flanking with the ultimate aim of establishing requirements for the design of a complementary source for the control of wall-axial waves.
sv970192.pdf (Scanned) sv970192.pdf (From Postscript) TOPRonnie C N Leung, Defence Evaluation and Research Agency (U.K.)
A research programme to investigate the feasibility of using active control systems to oontrol the radiated noise of a naval platform due to the on-board machinery was first set up in the late 1970s at The Defence Evaluation and Research Agency. The programme covers the development of control algorithms, development of the hardware for the controller, a trial on a naval platform, analysis of the trial results and the development of several actuators for different transmission paths. This paper presents the experience and lessons learned from the programme. The programme demonstrated that active control of tonals associated with a machine on board a naval platform is feasible. The key to success is a clear understanding of the interactions between all the possible transmission paths from the noise source. This applies to both passive and active controls.The major obstacles to wider application of active control techniques are a lack of suitable off-the-shelf actuators and their costs.
sv970127.pdf (Scanned) TOPChris R. Fuller, Virginia Polytechnic Institute & State University (U.S.A.)
The evolution of active systems applied to the reduction of aircraft cabin noise is studied. The main objective is to establish whether there are any significant lessons relative to the general use and commercialization of active noise and vibration systems.
sv970053.pdf (Scanned) TOPPeter D Dean, Lockheed Martin Missiles and Space Co (U.S.A.)
The concept of a smart skin embodies the philosophy of a multilayer structure that includes sensing elements, actuation elements and a controller. Such an embedded system has been developed for under water vehicle applications where the objective is the control of both near and far field noise. Acoustic/structural characterization is a necessary part of optimal design, however the simulation models available for prediction of the acoustic performance of complex structures such as these are inadequate. The transfer functions necessary for control of the piston actuator elements in the array skin are derived from direct experiment using a Water Impedance Tube. This paper describes the experimental system used, the analysis performed, transfer function results and their implications in active underwater acoustic control systems.
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Chaoying Bao, University of Western Australia (Australia)
R. Paurobally, The University of Western Australia (Australia)
Jie Pan, The University of Western Australia (Australia)
Active noise control technology is an attractive solution for attenuation of low frequency noise in enclosures. In terms of control strategies, feedforward control has often been used. While feedforward control has many advantages, its success relies on the availability of causal reference signals which have to be highly correlated to the noise to be cancelled. For some applications such as attenuation of random noise in office spaces or vehicle cabins, such reference signals are either not available or very expensive to obtain. In these situations, feedback control can be an alternative solution. In this paper, a single channel feedback control system for global noise attenuation in a room is presented. The controller is designed based on the compensation filter approach of the classical control theory. Experimental results are also presented.
sv970530.pdf (Scanned) TOPArturo Orozco-Santillan, Technical University of Denmark (Denmark)
A theoretical study of spatial sound equalisation in an extended region in a room has been carried out. The purpose is to reproduce sound without significant spatial fluctuations and to minimise the spectral colouration at low frequencies in a specified region of the room. The problem is first studied by means of an idealised frequency domain model. The analysis is based on the calculation of the complex source strengths that minimise the difference between the actual sound pressure and the desired sound pressure in the listening area. Results in relation to the position of the sources, the frequency range, and the size and location of the listening area are presented. However, the frequency-domain approach results in non-causal impulse responses that can be realised only at the expense of a delay. Therefore, this analysis is supplemented with a study of the equalisation carried out in the time domain. Here, a solution constrained to causality is determined. The duration of the impulse response should be minimised as well in order to avoid echos, which are undesirable in the reproduction of transient signals. This causality-constrained equalisation is compared with the optimal solution obtained in the frequency domain.
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Jing Yuan, The Hong Kong Polytechnic University (Hong Kong)
K.Y. Fung, The Hong Kong Polytechnic University (Hong Kong)
Feedforward cancellation is an effective approach to active noise control (ANC) in ducts. An ANC system synthesizes an anti-sound according to a reference signal measured between the noise source and the anti-sound. Its objective is to avoid the potential feedback of the anti-sound while canceling the directional propagation of the noise. An important advantage of feedforward ANC systems is their ability to improve performance by adaptation. The convergence of the adaptation depends on the transfer function of the error channel, which is not available conveniently. To identify the error channel, a pseudo random signal is added to excite the impulse response of the error channel. The system must separate the impulse response from the error signal when both share the same frequency range. This paper presents a new approach to feedfoward ANC in ducts. It places an additional sensor near the primary error sensor, and separates the traveling wave components from the pressure signals. The separation of traveling waves simplifies the adaptation and the problems associated with transfer functions of duct sections, The transfer functions of the error channel, loudspeaker and power amplifier can easily be identified without the annoying pseudo random signal.
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Shozo Kawamura, Kobe University (Japan)
Atsushi Morita, Kobe University (Japan)
Takuzo Iwatsubo, Kobe University (Japan)
Koki Shiohata, Hitachi Ltd. (Japan)
The active noise control, which is effective for low frequency band, has been developed, When the high control performance would be achieved in the enclosed cavity, it is necessary to measure the sound pressure at many measuring points in the cavity. But it is hard to set many sensors in the cavity because of the lack of space or cost problem. In this paper, an active noise control method is proposed for the steady state acoustic field. The fundamental idea is that the unknown sound pressure in the cavity are estimated by using structural-acoustic coupled analysis, that is, the sound pressure are virtually measured at many points. At first, the active noise control method is formulated based on the feedforward control theory. Next, the identification method of the sound pressure in the cavity, which are the cost function of the feedforward control, is formulated by using the structural-acoustic coupled analysis method. As the numerical example, the rectangular prism model is taken up, and the active noise control in the model is simulated by using the proposed method. As the result, it is shown that the proposed method is effect in the numerical simulation.
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Xia Pan, ISVR, University of Southampton
Trevor J Sutton, ISVR, University of Southampton
S.J. Elliott, ISVR, University of Southampton
The paper considers the active control of harmonic and random sound transmitted through a double-leaf partition using a single distributed actuator and a single distributed sensor. The double-leaf partition consists of a pair of small plates (300x380 mm, separated by a 100 mm air-gap). An actuator made up of shaped, distributed PVDF offers the possibility of controlling the volume velocity of a plate without giving rise to control spillover. The sensor consists of a matched PVDF sensor to detect volume velocity. For harmonic excitation with the actuator attached to either panel, substantial reductions in the transmitted sound power are possible up to around 350 Hz. A radiation mode analysis of the panels shows that the double-leaf construction provides good passive attenuation of the first radiation mode at high frequencies, so that inefficiently radiating even modes of the radiating panel make a dominant contribution to the radiated sound power. For the random excitation, an internal model control scheme is outlined for the double-panel system in which the transmission of random sound is controlled without the need for a reference signal. Cancellation of volume velocity with the distributed actuator provides reduction in random sound transmission up to 100 Hz.
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Sven Nordholm, University of Karlskrona/Ronneby (Sweden)
Joergen Nordberg, University of Karlskrona/Ronneby (Sweden)
Increased use of mobile telephones in cars has created a greater demand for hands-free in-car installations. The advantages of hands-free telephones are safety and convenience. The disadvantages are poor sound quality and acoustic feedback of the far-end speaker. The filtering required to obtain a similar sound quality as for hand held telephony must suppress the loudspeaker, as well as background noise and room reverberation, without causing severe speech distortion. This paper deals with the acoustic echo feedback problem. The acoustic feedback problem is also a reality in applications such as video conferencing and hands-free office telephones. All these applications has created a demand for high-quality acoustic echo cancellation. In order to track variations in the acoustic channel the echo cancellation is made adaptive. The acoustic channel has typically a long impulse response in the order of 100ms. Typical lengths of adaptive FIR-filters are 500-1500 taps assuming a 8 kHz sampling frequency. A subband echo canceller gives several advantages compared to a full-band echo canceller such as: 1. The computational burden is essentially reduced by the number of subbands due to decimation. 2. A faster convergence since the spectral dynamic range in each subband will be less. 3. The signal controlled adaptation can be performed in each subband individually, hence, enhanced performance. 4. A well separated structure for parallel implementation is obtained. This paper presents an implementation and improvement of a delayless subband adaptive filter presented by Morgan and Thi. This adaptive filter structure employs the benefits of adaptive subband filtering, but does not suffer from the inherent delay usually found in subband schemes. This is due to the fact that the FIR filtering is performed without delay directly on the full-band signal. The following improvements are presented in this paper: 1. Improved filter bank design which gives possibilities to improve the convergence rate. 2. A signal detection scheme operating in each subband improving the convergence rate when using signal with large spectral dynamics, i.e. a speech signal.The study shows a possible echo suppression of about 30 dB and also a more rapid convergence compared to a fullband LMS-filter.
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Sven Johansson, University of Karlskrona/Ronneby (Sweden)
Mathias Winberg, University of Karlskrona/Ronneby (Sweden)
Thomas Lago, University of Karlskrona/Ronneby (Sweden)
Ingvar Claesson, University of Karlskrona/Ronneby (Sweden)
In helicopters the low frequency noise generated by the rotors and engines often masks and jeopardizes safe communication. Additionally, pilots are likely to suffer from hearing damages due to the higher sound levels in the headset produced when compens In many Active Noise Control (ANC) applications the primary noise field is either periodic or broadband which simplifies the choice of algorithm.Typically, noise up to 100 Hz is dominated by tones and in the range from 100Hz to 400 Hz the noise chara a digital feedforward controller and an analog feedback controller is employed. The feedforward controller is tachometer based and reduces the tonal components, while the feedback controller attenuates the more broadband noise. In this paper, a combination of these two techniques is evaluated on real data.
sv970240.pdf (Scanned) TOPMarek Pawelczyk, Institute of Automation (Poland)
The objective of the paper is to present and examine new concepts of noise cancellation algorithms. At the beginning, feedforward FIR filters are analysed in terms of stability. Then an algorithm named Normalised-W LMS, increasing speed of convergence and decreasing steady state error is proposed. Next, two algorithms based on physical - not automatic - approach named PHS (PHase Shifter implemented in a discrete way) and PHS2 are thoroughly explained. They are suitable for narrowband sounds with spectrum concentrated around one frequency. Having minimum number of parameters - at least an order less then for other feedforward solutions - guarantee better attenuation effects: significantly extend attenuation band and ensure attenuation up to 60 [dB] (40 [dB] in the range between 100 [Hz] and 5 [kHz]). The idea of PHS and PHS2 was extended to broadband noise and was named PHS - banks. Each bank consists of a band-pass filter and a PHS. A PHS can cover signal having spectrum not wider than about 40 [Hz], so the filters should be properly designed. Described algorithm is able to attenuate any sound in very wide band up to 40 [dB]. Investigations performed with various sampling frequencies (4, 2, 1, 0.5 [kHz]) and feedforward control show that for each sampling frequency obtained attenuation bands are adjacent or slightly overlapped and usually octave. Thus, multirate signal processing technique was successfully adopted. Feedback structures were also considered. Modified Minimum Variance Controller was proposed and tested. Finally, hybrid control algorithm integrating feedforward and feedback techniques by an arbitrary system was originally developed. This assures satisfactory attenuation in the whole band justified by plant coherence function.
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Christian Carme, Technofirst (France)
G. Valentin, Dassault Electronique (France)
In 1995, we presented the first results about the Active seat ANCAS (R), jointly developed by Dassault Electronique and TechnoFirst. Strongly concerned by progressing to an improved product, TechnoFirst has carried on research in order to enlarge the universalit y of this technology, either in aeronautic or automotive applications. Furthermore, the behaviour of the ANCAS (R) when used in a set of active seats, has been invcstigated. This paper contains the work recently performed experimental results and several industrialapplications. on the ANCAS (R) including experimental results and several industrial applications.
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Christian Carme, Technofirst (France)
Anne Montassier, Technofirst (France)
M. Rehfeld, Saint Gobain Vitrage (France)
Looking at the increasing request concerning sound insulation in building, Technofirst (R) and Saint-Gobain-Vitragc propose an active double-glazing window. In this partnership TechnoFirst (R)brings its experience in active control system, The product will be characterized by a global insulation never obtained. It deals with anacoustic treatment of the air volume. Modelisations have been done and show the contribution of each acoustic mode. The experiments have confirmed these informations. This publication shows first results obtained with a prototype. The electroacoustic system which allows this treatment can be fitted into the width of the air volume.
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Christian Carme, Technofirst (France)
David Derrien, Technofirst (France)
Pierre De Man, Technofirst (France)
In 1981, we started a development of Active Noise Control headsets. 1 The results of these works were presented at EUROMECH 213 in 1986 and INTERNOISE 1988. The new filtering developed for this technology was able to improve the bandwidth and the level ofnoise reduction. Today, we have continued the development and the purpose of this paper is to present a headset with a feedback control which avoid an increase of noise in high freqencies when Active Noise Control is on. The second point presented in this paper is an improvernent of speech transmission when ANC is on. With this new solution, the speech transmission has no more interuptions due to the vibration of the headset with ANC switched on. In that way, this headset may be weared in a jolting environment as a vehicule. These technical progresses allowed the realization of a new serie of headsets inorder to meet all industrialists and general publics requirements.
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Christian Carme, Technofirst (France)
Virginie Delemotte, Technofirst (France)
Pierre De Man, Technofirst (France)
Because of the increasing demand about sound insulation in building, tradesmen have today to find and apply new solutions to reduce noise. With this aim in view, Aldes Aeraulique company, French leader in ventilation, and TechnoFirst company decided to develop an active muffler in partnership. TechnoFirst, specialized in active noise and vibration control, brings its know-how for the development and the industrialization of systems based on this new technology. From research works realized by the "Laboratoirc de Mecanique et dAcoustique", TechnoFirst has developed a single system which will be cornpatible with all the configurations of the products proposed by Aldes. Technical choices had been made to obtain optimum conditions about acoustic performances (great noise attenuation), dimensions and negligeable charge loss. Today, Aldes and TechnoFirst are in position to propose a muffler on the ventilation market, eombining passive and active effects. The acoustic attenuation of this device is greater than the one obtained with a standard waffle muffler, with less charge loss introducing. This single system can be installed anywhere in the duct whatever diameter.
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Christian Carme, Technofirst (France)
David Derrien, Technofirst (France)
Pierre De Man, Technofirst (France)
NOVACS(TM) has been a complete success, This pioneer multichannel controller commercialized since 1989 is based on a specific philosophy : providing to an active control neophyte the tools and means in order to design serious experimentations. NOVACS(TM) is equiped with a standard digital signal and may process till 11 input signals and 8 output signals. NOVACS (TM) allows the developments of active control system closed to industrial products and the rapid characterization of the main problems to solve avoiding to physicist to be snowed under specific electronic computing. In this new NOVACS (TM) version, TechnoFirst (R) company proposes its last innovation which has been patented in 1995 and which is now available in its products : the hybrid control. Hybridcontrol / combines the advantages of feedforward and feedback control without their respective drawbacks. In this paper we make the comparison between this new technology and the two classical ones. It will appear that TechnoFirst has defined a new way to design active noise and vibration control system.
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