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Nov 1988

Volume 84, Issue S1, pp. S2-S224

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back to top Session EEE. Noise III and Architectural Acoustics VIII: Active Noise Reduction
Invited Papers
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An adaptive noise control system in air‐conditioning ducts (A)

Hareo Hamada, Tanetoshi Miura, Minoru Takahashi, and Yoshitaka Oguri

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S180-S180 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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This paper discusses an adaptive control system for the active cancellation of acoustic noise in air‐conditioning ducts. Recently, in several systems for active noise control, efforts have been focused on the use of adaptive digital filters to implement the system controller used to produce the artificial sound. The approach used in the newly proposed model assists in canceling broadband noise and also helps in improving the adaptation speed for colored noise. This model consists of a system identification (IDT) process and an adaptive noise cancellation (ANC) process. Two stand‐alone types of adaptive controllers using the fast‐least‐mean‐squares (FLMS) algorithm and the variable‐step least‐mean‐squares (VS‐LMS) algorithm were used in various experiments. Results of experiments in actual air‐conditioning ducts are presented.
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Compression system stability enhancement using active control (A)

A. H. Epstein, E. M. Greitzer, and G. R. Guenette

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S180-S181 (1988); (2 pages)

Online Publication Date: 13 Aug 2005

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All compression systems can suffer from severe dynamic instabilities, which stand as absolute limits to the system performance. The zeroth‐order instability is a planar mass flow disturbance known as surge, which involves the entire pumping system [compressor or pump, ducting, plenum(s), throttle]. The high‐order instabilities are called rotating stall and are local to the turbomachinery blading. Nonlinearities couple the modes together and in many practical machines rotating stall triggers surge, resulting in a large loss in performance and possible damage to the system. A large amount of effort has been expended over the last 35 years to understand these phenomena and engineer around them. More recently, work has begun on the use of active feedback control to artificially enhance compression system stability and prevent (or delay) rotating surge and stall, with particular application to aircraft engine compressors. Surge has been successfully controlled in small centrifugal compressors yielding a 20–50% increase in operating range. Work on the stabilization of rotating stall in axial compressors is ongoing. These are very complex systems, involving hundreds or thousands of individual airfoils. Much of the work, therefore, necessarily involves signal identification in a noisy environment using sparse sampling techniques and wavelaunch with relatively few actuators. Since aircraft compressors can consume tens of megawatts, control power requirements are of concern. Analysis has shown that, in fact, the control power requirements are not tied to the size of the machine controlled but rather to the power of the destabilizing perturbations introduced to the system. Typically, the control power required is only 103 105 of that of the machine power and, in some cases, may be zero (the instantaneous controller power input can be either positive or negative). This paper reviews the state of the art in active compression system stabilization and is a progress report on ongoing efforts.
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Active noise control based on the inverse filtering of room acoustics (A)

Masato Miyoshi and Yutaka Kaneda

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S181-S181 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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A novel active noise control method based on an inverse filtering theorem MINT [M. Miyoshi and Y. Kaneda, IEEE Trans. Acoust. Speech Signal Process. ASSP‐36(2), 145–152 (1988)] is described. According to this theorem, broadband random noise can be precisely controlled at N points (N = 1,2,…) in a room using N + 1 loudspeakers and FIR filters. Consequently, the proposed method creates a quiet zone around a given set of points. This method also has the unique property that, in a diffuse sound field, the power sum of the FIR filter coefficients is less than one. This property is employed in estimating the quiet zone attenuation. When broadband random noise is controlled at two points placed at an interval of λ/4 (where λ is the wavelength of the center frequency of the objective noise band), the estimated noise attenuation can be summarized as the following. (1) Noise attentuation of more than 14 dB is achieved at the middle of the points. (2) Over 6 dB of noise attenuation is achieved in a gourdlike quiet zone which is λ/2 long by λ/8 wide. (3) The sound‐pressure level of broadband noise observed outside the quiet zone is, at most, 6 dB higher than the noise level when the noise is left uncontrolled. An experiment was conducted for controlling random noise in the range of 50–400 Hz at two points in a room in which the reverberation time was 0.5 s. The volume of the room was about 70 m3. The experimental results showed good agreement with estimations (1), (2), and (3).
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Control criteria for active noise reduction systems (A)

Jiri Tichy

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S181-S181 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Effective control of auxiliary sources for active noise or vibration reduction can only be achieved by adaptive systems. The inputs into adaptive filters have to provide information on the signal to be canceled, as well as on the error signal from a sensor located in the area of sound field minimization. Although, in principle, some systems could achieve nearly perfect cancellation, their actual performance is limited by feedback problems from auxiliary sources which can cause system instabilities and limit the overall system performance. This problem becomes more severe with multiple feedback control which is needed, for instance, in multipath vibration transmission reduction of mechanical systems supported in several points, or multimicrophone control in enclosures. An overall analysis and approach to solutions will be presented.
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Applications for active noise control: What has been achieved and what can be achieved (A)

Glenn E. Warnaka

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S181-S181 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Active noise control is currently undergoing an explosive growth throughout the world. This rapid development is occurring because the concept allows improvement in existing noise control devices, often with potential improvements in size, weight, volume, and cost. It also permits new solutions to noise control problems that were previously difficult or unsolvable. The technique is particularly attractive because, for many applications, noise may be reduced at the listener's position without physical modification of existing noise sources or their arrangement. Active noise control seems particularly well suited to the reduction of low‐frequency noise which, for technological reasons, cannot easily or conveniently be attenuated with existing hardware. Because this new concept applies to such a wide variety of industrial, commercial, and military needs, a large number of specific applications are now under development or proposed for development. This paper describes the current status of active noise control technology. It describes applications that have already been realized as well as the possibilities for future development.
Contributed Papers
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An electronic sound cancellation system for air‐conditioning ducts (A)

Hideki Hyodo, Hareo Hamada, Tanetoshi Miura, Minoru Takahashi, Ryusuke Gotohda, Yasushi Yoshimura, Taku Kuribayashi, and Akio Akasaka

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S182-S182 (1988); (1 page) | Cited 1 time

Online Publication Date: 13 Aug 2005

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Recently, research on an electronic sound cancellation system that is able to cancel noise using sound of the opposite phase has been conducted. This kind of noise control technique is referred to as active noise control (ANC). In order to realize a practical working ANC system, it has been considered desirable to apply the LMS (least‐mean‐square) algorithm to such a system's control, especially the VS (variable step)‐LMS algorithm due to its high speed of convergence. The realization of an ANC system of the stand‐alone type is presented. Experiments were conducted in actual air‐conditioning ducts having a cross section of 500 × 500 mm by using the realized stand‐alone type active noise control system with the VS‐LMS algorithm. Below the cross‐mode frequency, more than 15 dB of attenuation was obtained for broadband random noise, even in the presence of an air flow of 3.7 to 9.0 m/s.
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Application of a digital filter to active noise control in a duct (A)

Satoshi Kuraya, Yoshitaka Nishimura, Tsuyoshi Usagawa, Masanao Ebata, and Josuke Okda

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S182-S182 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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The possibility of active noise control and its frequency range are discussed using sound‐source impedance. When a digital filter is used in an active noise control system, the delay time required in the filter must be longer than those in AD‐DA converters and low‐pass filters. In order to make a two‐microphone active control system possible and to lower its frequency range, it is required that (1) the distance between the microphone set near the original source and the loudspeaker used for an additional source should be far; and that (2) the sampling frequency should be high. However, as the number of digital filter taps is fixed, there is a limitation on the sampling frequency in order to realize the characteristics in the low‐frequency range. In the proposed system with motional feedback, the active control is realized in a frequency range lower than the fundamental resonance frequency of the loudspeaker, f0. Thus f0 must be raised in order to realize a system at a higher frequency range.
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Adaptive digital filter configurations for active control of lightly damped systems (A)

D. E. Waters and R. J. Bernhard

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S182-S182 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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The application of system identification techniques using adaptive digital filters to achieve active noise control in one‐dimensional duct systems has been previously investigated [J. C. Burgess, J. Acoust. Soc. Am. 70, 715–726 (1981), L. J. Eriksson, Ph.D. thesis, University of Wisconsin, Madison (1985)]. In this investigation, efficient system identification techniques using adaptive digital filters for active control of lightly damped systems at low modal density are sought. Three cases are considered: (1) where feedback to the detector sensor exists but where the error path is negligible, (2) where the error path exists but feedback is negligible, and (3) where both feedback and error paths are important. In each case, the active controller uses two system identification algorithms in a manner similar to that developed by Eriksson. The first algorithm models the error path by driving the secondary source with its own random noise generator and sensing the resulting response at the error transducer. The error path model is shared with the second system identification algorithm which uses a detection transducer signal, the error signal, and the estimated error path to model the plant (and feedback, if necessary). In each case, both FIR and IIR filters are considered. [Work supported by Nelson Industries, Stoughton, WI.]
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A study of active control of sound transmission through a panel into a cavity (A)

Pan Jie

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S182-S182 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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A technique for controlling noise transmitted into the interior of a cavity involves use of point force actuators on the boundary structures. This paper is a study of the optimal actuator positions and the maximum theoretical reduction of the sound transmission through a panel into a rectangular cavity. Results obtained demonstrate that the noise reduction by the actuators depends upon the nature of the incident sound. Details of the manner in which the control forces act on panel‐cavity system are also discussed.
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An active noise control system by means of motional feedback without a microphone (A)

Yoshitaka Nishimura, Tsuyoshi Usagawa, Masanao Ebata, and Josuke Okda

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S182-S182 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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A method for active noise control using a motional feedback system without any microphone is described. The impedance of an electroacoustic transducer can be controlled by motional feedback, and the noise in a duct can be reduced actively by adjusting the impedance of the transducer used for an additional sound source. The characteristics of the impedance of the transducer with the motional feedback and noise reducing effect of this system are analyzed, and they are measured using both analog filter implementation and a digital one. The results show that this system is effective in controlling the noise in a duct, but it is not applicable to a wide frequency range. The advantage of this system is that it does not need any microphone which has been a weak element in conventional active control systems under undesirable circumstances, such as high pressure, high temperature, dust, air flow, and so on.
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An active noise canceling microphone (A)

Glenn E. Warnaka

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S183-S183 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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This paper describes a noise canceling microphone that uses the principles of active noise control. Both physical (acoustic) cancellation, by means of a loudspeaker, and electronic cancellation have been applied to the problem. The results show that a high level of performance may be obtained while removing the requirement to have the microphone extremely close to the lips. Excellent cancellation was achieved at a distance of 24 in. from the signal source using tones, harmonic noise, pink noise, and a variety of cockpit noises from a helicopter, a turbo‐prop, and a jet fighter. Conventional microphones may be used to implement the active noise canceling microphone, or a conventional noise canceling microphone may also be used as a basis for implementation of this concept. The active noise control microphone is superior to conventional noise‐canceling microphones in rejecting background noise.
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Active noise control on systems with time‐varying sources and acoustical elements (A)

L. J. Eriksson, M. C. Allie, C. D. Bremigan, and J. A. Gilbert

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S183-S183 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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An active noise control system has been developed based on a system identification concept using a recursive adaptive filter to model the direct and feedback elements of an acoustic system. An independent random noise source is used with a second adaptive filter to provide a model of the output transducer and error path transfer functions. This system has the ability to continuously cancel narrow band and broadband noise. The system identification configuration combined with adaptive filter techniques enables the system to respond quickly and accurately to changes in time‐varying sources, such as frequency or amplitude, and changes in the acoustical system, such as temperature. Noise reduction results will be presented. The system capabilities will be demonstrated on a variety of time‐varying sources and time‐varying acoustical elements. The ability of the system to track these changes in real‐time as well as implications for actual applications will be discussed.
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Consideration of active noise control in space (A)

Josuke Okda, Tsuyoshi Usagawa, and Masanao Ebata

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S183-S183 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Active noise control in space is classified into four groups based on physical aspects, which can be further reduced into two groups, namely, the sound pressure or the sound power, and the ability or nonability of an additional sound source to act on the sound radiation of an original source. The latter is equivalent to the problem of whether the mutual impedance between the two sound sources must be considered or not. The noise reduction process in each group is analyzed using the impedance of the sources. The desirable condition of the additional source is discussed, and, when this condition is realized, the noise reduction effect is estimated. In general, when the additional source is placed near the original one, the more tightly they are coupled, the more effectively both the sound pressure and the sound power are reduced. It is difficult, however, to find the most desirable condition for reducing the sound power by means of an experimental procedure.
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Active noise absorption as an inverse source problem (A)

Woon S. Gan

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S183-S183 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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In an ordinary approach to three‐dimensional active noise absorption (ANA) the degree of noise cancellation will increase with the increasing number of small secondary sources used. Here, a three‐dimensional ANA is formulated as an inverse source problem and acoustical holography is used to realize the secondary (absorbing) sources. The advantage is that one does not have to approximate the number of secondary sources used to obtain identical field to the primary source which is a prerequisite for ANA. The use of generalized holography is proposed. Here, the generalized hologram is constructed by recording the field and its normal derivative over a closed surface surrounding the primary noise source. This gives the Huygens' sources. The required secondary sources are obtained by the reconstruction of the generalized hologram, by allowing the recorded field and normal derivative to backpropagate into the space region containing the primary source. To test the theory, computer simulation is proposed. The three‐dimensional primary noise source chosen is a transformer noise source. The required simulation algorithm is derived in terms of a deconvolution process.
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The use of electronic noise cancellation in the mining industry (A)

Leonard C. Marraccini and Dennis A. Giardino

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S183-S183 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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In order to reduce the noise exposure of people working in the mining industry, various types of noise control applications have been used. These have included standard retrofit noise controls, machinery redesign, and administrative controls such as modifying employee work cycles. Currently, the Mine Safety and Health Administration is investigating the use of electronic noise cancellation techniques for reducing worker noise exposure. This paper characterizes this work including background information, a description of the laboratory development work involving electronic noise cancellation, and the application of this technology in a field situation. By using the electronic cancellation system and loudspeakers, a zone or area of noise cancellation is produced.
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Mechanisms of active sound control (A)

Colin H. Hansen, Scott D. Snyder, and David A. Bies

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S183-S183 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Active noise control applied to sound propagating down ducts has been successfully demonstrated by a number of researchers. The active control of small three‐dimensional sound fields (such as those found in ear muffs) has also met with considerable success. However, application of active control techniques to large three‐dimensional sound fields, such as those found in rooms and vehicle interiors, has only been partially successful, generally resulting in sound reduction in some locations at the expense of an increase in other locations. The lack of success is easily explained if the mechanism by which successful active control is achieved is fully understood. This paper presents the results of an experiment that demonstrates the mechanism by which successful active control is achieved in a duct and conclusions are made regarding the requirements for successful active control in large three‐dimensional spaces, which would enable an overall, rather than just a local, reduction in sound level to be achieved. [Work supported by the Sir Ross and Sir Keith Smith fund and the University of Adelaide.]
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