bluuebunny/crossref_metadata_2025 huggingface dataset:
Fractal modeling of diffusive urban configurations
Authors: Woloszyn Philippe
Published: July 2002

This contribution is based upon the environmental specificities of the urban built form and it is part of the Research Programme CNRS-Interdisciplinary Programmes for Towns ‘‘Towards an Urban Sonic Ambience Simulator.’’ Its purpose is to develop an acoustic model based upon fractal measurements of urban interfaces, to be applied for sound simulations. The fractal technique exposed here for modeling the complexity of urban forms quantifies discrete morphologies of the town with an automatic capture procedure based on Minkowski’s operators. In order to model the complexity of urban streets, the dilution measurement is given for a collection of urban surfaces with fractal indicators to evaluate the spectral diffuseness for every element. The implementation of the diffusive acoustic model will then be performed using finite-element software, composing the diffusive surfaces collection as a complex equivalent urban configuration. The final comparison with the results of on-site experimentations will give a spectral approach of the diffusion coefficient for the urban configuration. In the near future, the technique described in this paper aims at allowing the spectral control of the acoustical parameters by connecting a fractal morphological evaluation and a qualification of the acoustical phenomenon, modeled as a diffusive process.
The University of Central Florida Community Noise Model
Authors: Wayson Roger L. , MacDonald John M.
Published: July 2002

The Community Noise Model (CNM) is a true simulation model written in Visual Basic allowing modeling of motor vehicles. User input is simplified by permitting spreadsheet input or graphical input using a mouse. Due to its simulation nature, the model handles interrupted flow traffic much better than conventional line source models. The model begins by using reference energy mean emission levels (REMELS) from a quite extensive measurement program. Propagation characteristics (geometric spreading, ground effects, atmospheric absorption, diffraction, etc.) are calculated at user-specified time step and energy is summed at user-defined locations. Using the acoustic energy summations, the model reports Leq, Lmax, and statistical levels. Traffic parameters are also reported. Validation has been performed as well as comparison to other established models and will be presented. The CNM performed quite well and at intersections outperformed other models when comparisons were done to measured data.
Planning and designing of developments against noise impacts—Hong Kong experience
Authors: Lee Chee Kwan , Lau Kwok Keung
Published: July 2002

In the next 15 years, there will be a rapid population growth in Hong Kong anticipated to be about 1.5 million people. It is a challenge for the Government of Hong Kong Special Administrative Region to find adequate land and to provide sufficient infrastructures to accommodate the increasing population while at the same time to keep up the environmental qualities. Owning to high demand for residential development, infrastructures, and other necessary facilities, it is not always possible to rely solely on buffer distance provided between noise-sensitive developments and noisy highways to avoid noise problems even for a piece of virgin land. To tackle the problems, due consideration needs to be given to minimize the potential noise impacts at the earliest planning stage when studying the alignments of highways. This paper presents the application of the above approaches in the planning of a 500 ha site.
Power output of a machine operating near elastic structures
Authors: Tomilina Tatiana M. , Korotkov Michael P. , Yashkin Vladimir B.
Published: July 2002

For predicting the noise levels produced by machinery, techniques, like SEA, based on the energy balance equations in which the radiation power of each noise source (machine) is used as an input parameter, are often employed. Usually, the standard value of the power measured in the free space is taken and it is assumed independent of acoustic environment. In the present work, it is shown experimentally and in computer simulation examples that the power output of an extended noise source operating near an elastic structure can differ significantly (several orders of magnitude) from its standard value. Possible corrections for the energy techniques are discussed.
Investigations of sound insulation of partitions used for integrated enclosures
Authors: Engel Zbigniew , Sikora Jan
Published: July 2002

Integrated enclosures, rarely applied in practice, are useful in the reduction of the excessive noisiness of machines and equipment. They are especially important for the machinery requiring constant and direct operation and maintenance, for which the application of other enclosures (e.g., fully closed) is inadmissible. Results of the sound insulation investigations of new types of partitions designed for the construction of integrated enclosure elements have been presented in the paper. Several specimens of partitions, which, according to their acoustic properties belong either to single (homogeneous and heterogeneous) or to multiple partitions (consisting of single, mixed and layered ones), were prepared for experiments. Double partitions with air cavities either empty or filled with sound absorptive materials, rigid, elastic, or granular absorbers (damping the airborne and material sound levels), appeared to be the main solution. The best partitions were used in the prototype of the integrated enclosure constructed for the engine lathe testing. The mechanical noise level of the lathe was reduced by 15 dB. The sound-insulating performance of the prototype has shown that the construction of integrated enclosures can be utilized in designing the new machines characterized by the lower acoustic activity—in comparison with the present standards.
Two surface element formulations in the time domain for the calculation of sound fields in cavities with varying boundary conditions
Authors: Kropp Wolfgang , Svensson U. Peter
Published: July 2002

Two different surface element formulations are presented which apply the equivalent source method in the time domain. The first method uses planar surface elements. The boundary condition of the cavity surface in the form of a prescribed impedance is fulfilled by using monopole elements (i.e., layers of free-field radiating monopoles with a uniform signal over the element). The second method is based on the Kirchhoff–Helmholtz integral. While the traditional boundary element technique uses the free-field Green’s functions, here a set of specialized Green’s functions is applied which is adapted to the cavity geometry. This set of functions fulfills the boundary conditions for the cavity with rigid walls. In this way the Kirchhoff–Helmholtz integral is simplified substantially and only areas of the surface with nonrigid boundary conditions have to be included in the calculations. Advantages and disadvantages of both formulations are highlighted, and results from both methods are compared for rooms of different complexity.
Some aspects of the scattering calculation using the source simulation technique
Authors: Zannin Paulo Henrique T.
Published: July 2002

In this work the source simulation technique was used to calculate the scattering of a plane wave by a cylinder with radial or elliptical transversal section. Numerical simulations have shown that: (1) the shape of the auxiliary surface, (2) the number of sources, and (3) the way the sources are distributed are the most relevant parameters to ensure an accurate solution for the problem. In the case of the single-layer method, sources should not be positioned close to the surface or to the center of the body, because the problem becomes ill-conditioned. The auxiliary surface and the scatterer should be as similar as possible in order to minimize the boundary error. With respect to the number of sources (N), there are two opposite effects: (1) if (N) is too small, the sound field is not reproduced accurately, (2) if (N) is too large, computing time increases and solution accuracy decreases. The method breaks down when excitation frequency coincides with the eigenfrequencies—a narrow range of frequencies—of the space formed by the auxiliary surface. As the auxiliary surface is frequently represented by simple surfaces (cylinder, sphere), one can easily calculate the eigenfrequencies, and therefore avoid them.
Integration of modeling and acoustic microscopy measurements for multiple layered coatings
Authors: Achenbach J. D. , Guo Z.
Published: July 2002

The determination of material constants of multiple-layered coatings by line-focus acoustic microscopy requires a combination of the V(z) measurement technique with a well-founded and accurate measurement model. This paper is concerned with the determination of the material constants of a two-layered ZrC/ZrN coating on a stainless steel substrate, as well as with an evaluation of the bond quality of the interfaces in-between the layers. A V(z) measurement model, which accounts for bond-quality variations, is developed by combining a derived spectrum of reflection coefficients with acoustic microscopy considerations. Material constants are determined by systematically minimizing the differences between measured results, obtained by line-focus acoustic microscopy, and results simulated with the measurement model. Sensitivity of the technique and accuracy of the results are briefly discussed.
Contribution of reduced audibility to subnormal localization performance in hearing-impaired listeners
Authors: Goverts S. Theo , Houtgast Tammo , Kramer Sophia E.
Published: July 2002

After speech reception, sound localization seems to be the second-most important hearing problem associated with auditory impairment. Recently a laboratory test on localization was developed which provides good resemblance to localization tasks in daily life. Subjects are presented with everyday sounds (about 1.5 s each) from eight evenly distributed directions. Only on the target sound (a telephone), presented randomly in time, were listeners required to indicate the azimuth of presentation. Data from 40 hearing-impaired listeners show a large variability in performance ranging from near normal to very poor. Aspects of hearing that may contribute to a subnormal performance are reduced audibility, incomplete or noisy spectro-temporal coding in the auditory periphery, or inadequate binaural processing. As a first step towards understanding the reduced performance for hearing-impaired listeners, results will be discussed on a localization test for normal-hearing listeners with noise-masked audiograms that match the audiograms for categories of hearing-impaired listeners. Results will be compared to previous findings on the role of audibility and spectro-temporal coding in the precedence effect.
The detection of complex submarine signals: A study of the linear frequency modulation criterium
Authors: Santon François , Tozza Agnes
Published: July 2002

The objective of this work is to know, in the context of submarine detection, what is the effect of a linear frequency modulation on the detection of glissando’s signals. Indeed, this frequency modulation is often present in submarine signals, whether of biological or mechanical origin. Different types of glissandos are considered, increasing, increasing–decreasing, increasing with plateau, and decreasing. Differences have not been noted between the detection thresholds for the first three types of signals. In general, the detection threshold is very close to the maximum frequency of the signals threshold. In the case of a decreasing glissando, it can be noticed that the detection threshold is lower by a few dB than the threshold of the signal’s highest frequency.
Construction of a minimal set of sound parameters for multidimensional tests
Authors: Parizet Etienne , Nosulenko Valery
Published: July 2002

In a multidimensional test, the selection of sound parameters may be difficult, because these parameters must not be numerous while describing the whole perception and have to be understood unambiguously by naive listeners. The method of free verbalizations [E. Samoylenko, S. McAdams, and V. Nosulenko, Int. J. Psych. 31(6), 255–278 (1996)] allows the construction of a minimal set of parameters. A minimal set of seven parameters was built for diesel engine idle noise. These parameters were then used for a semantic differential test, with other listeners and no sound training session. It was checked that the characterizations of sounds thus obtained for each parameter were very close to those given by the first test using free verbalizations. That means that the parameters were well understood by listeners and that all semantic ambiguities were avoided. Such a parameter set can be used for routine tests in the same sound context.
On the use of active low-frequency sonar systems for the monitoring of littoral environment
Authors: Morisset Dominique
Published: July 2002

The aim of conventional low-frequency sonar systems is either to detect and classify targets (containers, fish schools, submarines, divers, mines,...) or to communicate between two or more underwater geographical locations (communication, tomography). The increase of both military and civilian interest in shallow-water areas (typically from the shelf break to the shore), requires a better understanding of the effects of oceanographic environment on acoustic propagation and reverberation. Unfortunately, the available environmental information concerning bottom characteristics, sound-speed variability (in databases or charts), is often inaccurate and unreliable and, most of the time, it does not cover very wide areas. Hence, in order to get a comprehensive environmental knowledge during operations and to improve performance prediction, low-frequency sonar systems are now equipped with environment assessment functionality. Experimental results concerning the impact of shallow-water environment on sonar signals will be presented. Two major aspects will be investigated: the impact of both sound-speed profile variability and bottom heterogeneity. The optimization of low-frequency sonar design and its use for the assessment and the monitoring of littoral environment (i.e., acoustic data inversion) will then be discussed.
ICRU Report 61: Providing reference data for tissue properties
Authors: Fairhead Andrew C.
Published: July 2002

The recently published ICRU Report 61, entitled ‘‘Tissue Substitutes, Phantoms and Computational Modelling in Medical Ultrasound,’’ will be described. As well as reviewing current practice, it specifies requirements of the materials and techniques used to make ultrasound phantoms for various purposes. It also covers that aspect of computational modeling concerned with thermal disometry, because the ‘‘body models’’ used in this activity have a similar purpose to phantoms used for measuring temperature rise. Both must simulate the part of the body of interest, to a sufficient accuracy for the intended purpose. This involves designing tissue substitutes or simulations with certain values of acoustic and thermal properties, to within a certain tolerance. If thermal measurements and computations are to be reproducible within and between organizations, these values and tolerances must be agreed. At the moment, reference data from tissues are sparse. The report suggests suitable values for a selection of tissues. In the presentation, the need for more data and the problems associated with obtaining them will be emphasized.
Thermal safety considerations for diagnostic ultrasound
Authors: Miller Morton W. , Nyborg Wesley L.
Published: July 2002

As the output of diagnostic ultrasound equipment increased during the past decade, so did the potential for producing significant temperature elevation. The introduction of equipment features for real-time display of an estimated upper limit to the temperature rise is proving helpful to informed users. In obstetrical applications it is particularly important to know whether teratological effects could be produced under the operating conditions being used. While there is an extensive body of literature on defects produced in progeny of laboratory animals exposed to heat during pregnancy, its specific relevancy to clinical ultrasound situations is unclear. Most exposures were done by placing pregnant animals in heated chambers. Although the temperature of the medium (air or water) surrounding the animal was maintained constant during the time of an experiment, the temperature rise experienced by the fetus increased during most or all of that time. In contrast, when an ultrasound beam is focused on fetal bone, it is expected that the temperature will rise to its steady-state value relatively rapidly. An approach based on reaction rate theory is proposed as an approximate method for relating effects of the two kinds of exposures.
Mechanical index: The influence of nonlinear propagation in water and tissue
Authors: Cahill Mark D. , Humphrey Victor F.
Published: July 2002

Safety indices for diagnostic ultrasonic scanners are calculated from measurements made in water, which are derated to account for the attenuation of tissues. Shock waves are expected to form more readily in water than in tissue, because of water’s lower intrinsic attenuation. The resulting increase in the attenuation of high-amplitude waves leads to the possibility that amplitudes might be underestimated from water-based measurements. By considering idealized models of scanners involving a rectangular source with two focal planes, the effect of such nonlinear propagation on the mechanical index has been investigated. As expected, it was found that the mechanical index is greatly reduced from that which would be predicted by a linear extrapolation from low-amplitude measurements. However, under most circumstances considered, the reduction of the analogous index in tissue was commensurate with that in water, partly because of the weaker frequency dependence of attenuation in tissue, which promotes the formation of shocks. The evaluation of mechanical index at the location of peak-derated intensity did, however, result in an underestimation of the peak negative pressure by about 10%, and even greater errors resulted when the gain and operating frequency were raised.
Review on the viability of mammalian cells in ultrasonic standing wave fields
Authors: Doblhoff-Dier Otto , Gaida Theo , Burger Wolfgang , Trampler Felix , Gröschl Martin , Benes Ewald , Piret James M. , Woodside Steven M.
Published: July 2002

Ultrasonic standing waves have been used in a number of applications for the separation of suspended particles, such as the separation of animal cells in fermentation processes. This technology has led to the development of high cell density, continuous perfusion fermentation systems with increased volumetric productivity. The ultrasonic separation device additionally can be used for controllable selective retention of viable cells and selective removal of cell debris. A key issue with this technology is the question if the ultrasound fields applied can be stressful to animal cells growing in suspension, thereby decreasing cell viability or impeding metabolic functions. This issue is also of interest to regulatory bodies concerned with quality assurance and quality control of pharmaceuticals derived from animal cell culture. Available data concerning cell viability, productivity, and metabolic activities will be reviewed and put into perspective to regulatory and fermentation technological concerns, such as product identity and purity, biological activity, consequences for subsequent protein purification procedures, long-term continuous production strategies, etc. [Work supported in part by the European Commission, Contract No. ERBFMRXCT970156.]
Sounds that are not what they sound: The unrecognizability of piano sounds transformed due to string preparations
Authors: Hettergott Alexandra
Published: July 2002

Three different performances of John Cage’s, Sonatas and Interludes for Prepared Piano (1946–1948), each of which is a recent CD recording, were analyzed in relation to a common notational model. Though following the same lines regarding the preparations of the grand piano by means of screws, bolts, nuts, rubber, and/or plastic, applied to the double and triple piano strings, realizations of the same piece may differ from one another in almost all musical parameters: not only in aspects of tempo and dynamics, but also with respect to the respective spectral distribution, as pitch strength and tone color, and also in the perceived pitches themselves. The course of a tone sequence in one performance perceptually may completely be changed relating to the other. Cage’s preparations, though detailed up to a certain point, thus allow one to take interpretative liberties. The performances were compared referring to both their spectral and temporal characteristics, each of them yielding a completely different sound quality. Differences and factorial common facts will be shown in multicomponent features derived from; in addition, several sound examples will be given.
Harmonic and unharmonic components of violin tones in dependence on playing techniques
Authors: Moravec Ondřej , Štěpánek Jan , Syrový Václav
Published: July 2002

Properties of harmonic and unharmonic spectral components of violin tones played nonvibrato using different bowing techniques (naturale, sul ponticello, sul tasto) and dynamics of playing (p, mf, f) were studied by means of suitable analytical methods. The tones from the whole violin range were recorded in an anechoic room. The shape of the spectral envelope, harmonicity, and amplitude relations among harmonic components were observed. Unharmonic components were investigated in three frequency bands separated by fundamental frequency of the tone and by the frequency of the highest ‘‘well pronounced’’ harmonic. Specific analytical tools and describing quantities were used in each part of the spectrum. The dependence of the spectrum on playing techniques, dynamics, and tone pitch was discussed.
Reduction of road traffic noise: The legislature’s point of view
Authors: Stenschke Reiner , Jaecker Michael
Published: July 2002

Measures to improve motor-vehicle technology play an important role in the reduction of road traffic noise. Therefore, appropriate noise control regulations must ensure that all possibilities for reducing noise levels through technical vehicle-related measures are exploited. An important basis for achieving this is the introduction of a test method for motor vehicle type approval that depicts the driving and operating modes occurring in real traffic as closely as possible, so as to ensure that future noise limit value reductions will influence noise emissions in real traffic more effectively than has been the case to date. Furthermore, there is the need for a separate noise emission regulation for tires that ensures that tires introduced to the market satisfy ambitious noise criteria. In addition, it must be ensured that low-noise road surfaces are used when road surface renewal work is carried out on noisy streets in particular. An essential requirement for reducing road traffic noise is that noise control regulations are complied with by all vehicles throughout their lifetimes. To this end, a concept for improving the efficiency of compliance monitoring must be developed. The contribution will present available results and report on planned activities in this field.
How to reduce tire/road noise: Chances and limits
Authors: Gauterin Frank
Published: July 2002

Tire/road noise is an important sound source for traffic noise. Measures for tire/road noise reduction are reviewed and discussed concerning chances and limits for a traffic noise reduction. Vehicle layout, tire construction, road specification, and legal requirements are taken into account.
A numerical method to predict sound propagation for realistic road environments
Authors: Gauvreau Benoît , Bérengier Michel C.
Published: July 2002

When dealing with traffic noise propagation over large distances, models assuming flat and homogeneous grounds and homogeneous atmosphere are not sufficient to have an accurate prediction. A first improvement was obtained by many authors who worked on new theoretical approaches individually dealing with the influence of mixed grounds, stratified atmosphere, noise barriers, etc. on sound propagation. Thus, many models were built. In order to predict sound pressure levels for complex conditions representative of realistic traffic noise situations, a model based on the resolution of the wave equation through a parabolic approximation has been developed. The problem is numerically solved for various conditions including mixed grounds, upward and downward refracting turbulent atmospheres, and the presence of noise barriers producing a variation of the sound celerity profile along the propagation path between the source and the receiver, over several hundred metres. The numerical approach is based on the split-step Padé technique mainly developed and recently improved by the acoustic group of the Ecole Centrale in Lyon, France [Chevret et al., J. Acoust. Soc. Am. 100, 3587–3599 (1996)]. Interesting comparative results with other theoretical approaches and experimental data have been obtained and will be widely developed in the paper.
A theoretical tire model based on the general field equations
Authors: Larsson Krister , Kropp Wolfgang
Published: July 2002

Most of the models for the structure-borne sound behavior of tires are designed for the low-frequency range (i.e., below 300–400 Hz) and often contain the geometrical details of the tire. Above this frequency range the curvature of the tire can be omitted while the internal structure (i.e., multilayers of steel and rubber) increases in importance. For this higher-frequency range, a model has been developed based on the general field equations. The model consists of a double-layered thick plate, representing the tire belt, which is prestressed due to the internal pressure in the tire. An elastic bedding supports the plate, in order to take into account the compression of the air inside the tire cavity and also to take into account the influence of the side walls on the belt. Both the radial and the tangential motions in the belt are included, since the model is based on the general field equations. The model also incorporates the effect of the local deformation of the soft rubber surface. Results from the model are compared with results from other models from the literature and with measurements.
Reply to “Comment on ‘Enhancement of the transient-evoked otoacoustic emission produced by the addition of a pure tone in the guinea pig’ ” [J. Acoust. Soc. Am. 105, 919–921 (1999)]
Authors: Yates Graeme K. , Withnell Robert H.
Published: July 2002

In a recent paper [J. Acoust. Soc. Am. 104, 344–399 (1998)] suggested that the TEOAE might be comprised of significant quantities of intermodulation distortion energy, based on a series of suppression experiments involving the measurement of the TEOAE with the addition of a pure tone. [J. Acoust. Soc. Am. 105, 919–921 (1999)] have suggested an alternative explanation for our experiments, wherein a pure tone produces a local impedance change in the nonlinear mechanical properties of the basilar membrane: emission energy at frequencies below the frequency of the pure tone is suggested to arise from reflections at this impedance discontinuity. In this Letter, a response to their hypothesis is given, arguing that it is not consistent with experimental findings, and that, in fact, the TEOAE is comprised predominantly of intermodulation distortion energy [Yates and Withnell, Assoc. Res. Otolaryngol. Abstr. 21, 5 (1998)].
Modification of electrodynamic loudspeakers for 3-D spatialization
Authors: Evreinov E. Grigori , Agranovski V. Alexander
Published: July 2002

The modification of electrodynamic loudspeakers was developed on a separation base of management cues by spatial and acoustic sound attributes. A loudspeaker has a single diaphragm and segmented surround, because a diaphragm embodiment in a kind of several adjacent parts evokes the losses and distortions at a sound reproduction of low frequencies. Surround’s segments have an electrical control by their mechanical properties (a density). It allows the regulation of a velocity of the diaphragm fluctuations in appropriate zones. Thus a redistribution of a sound pressure (or of an acoustic energy) in the near-field or in the immediate neighborhood of pinna occurs according to the changes of spatial coordinates of sound objects. Offered construction provides a spatial localization of sound objects in the near field, even with using a single loudspeaker.
A sound transducer with a flat, flexible diaphragm working with bending waves
Authors: Manger Daniela L.
Published: July 2002

From the time of the idea to the finally working sound transducer, a period of over 20 years was necessary. The time has been needed for development and research in manufacturing and materials. It took a long time until new synthetic and magnetic materials were available with their best fitting mechanical behaviors. Nowadays it is possible to present a wideband sound transducer working from 100 Hz up to 35 kHz. It follows time precise without any mechanical energy storage the incoming signal. The special structure of the flat and flexible diaphragm works concentrically only with bending waves. A simple mechanical model, theoretical equations and measurements will be presented in comparison to the omnipresent Rice–Kellogg piston loudspeaker. The advantages in perception and hearing will be shown with regard to physiological behaviors of the hearing sense.
Sound production of flue organ pipes
Authors: Miklos Andras , Angster Judit
Published: July 2002

For understanding the sound production of flue organ pipes, the acoustic properties of the two main components, the acoustic resonator and the air jet generator at the labium (flue + upper lip), have been investigated separately. It was found that the formant structure of the stationary sound spectrum is mostly determined by the geometry of the pipe, including the location, size, and shape of the openings (mouth and open end), while the attack is strongly influenced by the air jet generator. An influence of the wall vibrations on the stationary sound has been also found, but this effect could be neglected until the wall is not too thin. The spectra of the stationary sound radiated by the openings are markedly different. The analysis of their formant structures implies that the source of the radiation is the acoustic flow at the openings. Experiments performed on labium models and pipes with damped acoustic resonators show that an edge tone with characteristic spectrum appears first during the attack. Its sound field may excite the acoustic resonator purely acoustically, preceding the development of the coupling between jet and acoustic oscillations. This assumption has been supported by the experiments discussed in the paper.
Sound production in flue instruments: A review
Authors: Fabre Benoit , Verge Marc-Pierre , Hirschberg Avraham
Published: July 2002

The introduction of computer implementation of numerical methods, 40 years ago, has opened the way towards quantitative modeling of the sound production in flue instruments. This has induced a first wave of new research initiated in the late 1960s by the precursor work of Bechert, Cremer, Ising and Coltman. The breakthrough of real-time sound synthesis in the last decade has allowed the judgment of models on the basis of the sound which they produce. With this breakthrough ‘‘verbal’’ modeling such as the controversy between Helmholtz and Rayleigh about the nature of the sound source at the labium (volume source or dipole) is now a historical curiosity. However, it has became clear that lumped models as used in sound synthesis will remain semi-empirical caricatures. It has appeared that direct numerical simulation of the details of the flow including the effect of turbulence is still impossible. One observes, therefore, a shift back towards experimental studies such as that of jet response to acoustical excitation, the effect of nicks, the effect of chamfers, the influence of materials, Coanda effect induced by turbulence, etc. A review of these recent studies will be presented.
Some comments on the artificial blowing of the reed woodwind instrument
Authors: Idogawa Tohru
Published: July 2002

Important results were obtained by artificial blowings of the reed woodwind instruments: Many states of air column vibrations can be excited under a fixed fingering and a fixed embouchure; these states have their respective regions of blowing pressure in which frequency and waveform of the air column vibration change slightly and continuously as the blowing pressure is varied; a sudden transition from one state to another takes place irreversibly at a blowing pressure, the upper (or lower) boundary of the state, when blowing pressure is increased (or decreased) gradually. It will be presented that the above-described results are not necessarily valid for a conical brass pipe (0.63 m long), which has the same apex angle as that of the bassoon, blown by the mouthpiece of the soprano saxophone. One of the vibratory states excited has changed to another state without transition. When a cylindrical brass pipe, which has about the same length as that of the clarinet, has been artificially blown with the clarinet mouthpiece, the reed has been easily broken, which has rarely been observed for the clarinet.
Acoustic performance of finite-length apertures using finite-element analysis
Authors: Lyons Richard , Macey Patrick C. , Horner Jane L.
Published: July 2002

There is a wide range of published literature covering ducts of infinite or semi-infinite length and to a lesser extent there are studies on apertures having restricted dimensions. The work presented in this paper is taken from recent research into the characterization of acoustic devices in finite-length apertures, which may need to allow for a flow of fluid. Results of a finite-element solution for a short duct between two half spaces are presented, along with a closed-form solution [K. H. Jun and H. J. Eom, J. Acoust. Soc. Am. 98, 2324–2327 (1995)] as a validation of the finite-element method. Further results of more complicated aperture geometry, which are not easily amenable to such forms of solution, have also been investigated and are presented.
Scattering of sound in a stratified moving atmosphere
Authors: Ostashev V. E. , Goedecke G. H. , Wood R. C.
Published: July 2002

An equation derived recently for the sound-scattering cross section per unit volume in a stratified moving atmosphere is presented. The dependence of the temperature and wind velocity contributions to the cross section on the scattering angle is studied in detail analytically and numerically for different stratifications of temperature and wind velocity. Such studies are important for acoustic sounding of the atmosphere by sodars since the equation for the sound scattering cross section is a theoretical basis for this remote sensing technique. It is shown that both temperature and wind velocity fluctuations contribute to the backscattering signal if the wind velocity is not zero at the height of scattering. This means that a signal received by a monostatic sodar is a linear combination of the structure parameters of both temperature and wind velocity fluctuations, while it has previously been assumed that this signal is proportional only to the structure parameter of temperature fluctuations. The new results obtained should be taken into account in existing techniques of acoustic remote sensing of the atmosphere. [This material is based upon work supported by the U.S. Army Research Office under Contract Nos. DAAG55-98-1-0463 and DAAG55-97-1-0178.]
On acoustic sounding of large-scale turbulence in the middle atmosphere
Authors: Kulichkov Sergey N.
Published: July 2002

The possibilities of the bistatic acoustic method to measure sound turbulence with vertical and horizontal scales equal to 10–1000 m and 1–100 km correspondingly in the middle atmosphere (z=20−80 km) are discussed. More then 60 surface explosions with yields of 20–70 tons realized in different seasons during 1989–1991 were used as sources of the initial acoustic pulses. The receivers were placed at distances of 300 and 310 km toward the West and the North from the sources, respectively. Infrasound signals scattered from large-scale turbulence in the middle atmosphere and recorded on the ground surface in the geometric shadow of explosions were analyzed. The theoretical approach was based on the theory of Fresnel reflection of sound from anisotropic acoustic refractive index irregularities in the approximation of a local-layered structure. It was found that intense turbulence exists in the middle atmosphere during all seasons, with the maximum in July. Vertical gradients of the effective sound velocity in the middle atmosphere are characterized by great values, which earlier were observed only in the atmospheric boundary layer. Samples of the profiles of those obtained for different seasons are presented.
Marking the starting and ending points of auditory apparent motion: Effect of timing, spatial separation, and azimuth
Authors: Strybel Thomas Z. , Guettler Diane L.
Published: July 2002

Participants identified the path of auditory apparent motion (AAM), produced by the appropriate timing (burst duration and stimulus onset asynchrony, SOA) of two successive noise bursts (high-pass A-weighted noise at 55 dB). Three burst duration/SOA combinations were tested: 100/50 ms, 400/100 ms, and 400/600 ms. The first two combinations produce AAM; the last was a nonmoving control. The stimulus sequence was presented through two loudspeakers selected from a horizontal array so as to produce two spatial separations (16 and 33°) and three midpoint locations (−23, 0, and 23° azimuth). The actual starting and ending locations were jittered around each midpoint. Participants faced a large cloth screen having a grid pattern and were instructed to identify the cells corresponding to the starting and ending points of the stimulus sequence. At timing values producing motion, the path of motion was displaced in the direction of the motion with the greatest direction effect occurring at 100/50 ms. However, the midpoint between the loudspeakers also affected the path of AAM. At −22° azimuth, the path was displaced toward the left, regardless of motion direction. At 22° azimuth the path was displaced toward the right. This midpoint effect was obtained only at timing values producing AAM.
Effects of the spatial distribution of competing sounds on speech reception thresholds
Authors: Culling John F. , Hawley Monica L. , Litovsky Ruth Y.
Published: July 2002

The experiment tested whether listeners can suppress competing sound from several different locations simultaneously. Speech reception thresholds were measured adaptively in anechoic virtual auditory spaces with a target voice directly ahead and competing sounds in four spatial configurations. Three concurrent competing sounds were distributed on the horizontal plane among consecutively numbered positions at 30-degree intervals, position 4 being directly ahead, 1 far left, and 7 far right. The competitor configurations were 444, 367, 567, and 777. Four types of competing sound were used: speech (same voice), reversed speech, speech-shaped noise, and speech-modulated, speech-shaped noise. The patterns of results across spatial configurations were similar for each type of competitor, although binaural advantage (777 vs 444) was 2–3 dB greater for speech competitors than for noise. Speech gave thresholds 3 dB higher than reversed speech throughout, suggesting linguistic interference effects. Most notably, however, 567 and 777 always gave similar thresholds (7–10 dB lower than 444). The multiple source locations of 567 produce a sound field with relatively low interaural coherence, but binaural unmasking experiments indicate that masking release demands maskers of high within-channel interaural coherence. Multiple competing sources on both sides (367) were more difficult to suppress. [Work supported by MRC and NIH.]
Performance of children on the Multisyllabic Lexical Neighborhood Test as a function of the number of channels of stimulation
Authors: Dorman Michael , Loizou Philip , Svirsky Mario , Kirk Karen
Published: July 2002

When monosyllabic words are processed in the manner of cochlear implant signal processors and are presented to adult, normal-hearing listeners for identification, 4 channels of stimulation allow mean scores of 48% correct, 6 channels allow 71% correct, 8 channels allow 87% correct, and 12 channels allow 89% correct. When patients fit with cochlear implants are tested with the same material, only 7% of the patients achieve scores in the range of scores for normals with 8 channels, 28% achieve scores in the range of 6 or more channels, 61% achieve scores in the range of scores for 4 or more channels and 39% achieve scores below that of normals with 4 channels. The aim of the research to be reported was to collect, for both normal-hearing children and children with cochlear implants, scores on the Multisyllabic Lexical Neighborhood Test. The results will provide a window on the effective channels of stimulation delivered to children who use cochlear implants with 8–20 physical channels of stimulation.
Determination of Young’s modulus and internal friction coefficient from flexural wave in thin bars
Authors: Guo Qiushuang , Brown David A.
Published: July 2002

The flexural wave equation including internal friction and the correction due to rotatory inertia and shear deflection for thin bars is solved. The system response of the forced-free bar excited in flexural vibrations is obtained. Corrections for rotatory inertia and shear deflection have to be included for a best fit. The numerical factor representing the correction effect of shear deflection is smaller than previous results which means that shear deflection has a greater correction contribution than previously thought. At low-frequency range, the Young’s modulus obtained from flexural modes is different from that from longitudinal modes. This may suggest that more correction effects need to be included for the flexural system. [Work supported by the Ph.D. Program and the Strategic Environtechnology Partnership (STEP) through the Advanced Technology Center at the University of Massachusetts Dartmouth.]
A clamped beam, images solution
Authors: Brunskog Jonas
Published: July 2002

The method of images is a well-known idea in theoretical physics, but not often used in structural acoustics. When considering the problem of obtaining Green’s function for a general bounded domain, the reflection is described by an image source, and position and sign of the image is chosen to fulfill the boundary conditions. The Green’s function can then be found as the superposition of the free Green’s function for the two sources. Consider now a finite beam, clamped at the boundaries and driven by a point force. In order to make use of periodicity, expand the region along the x axis. To the original force an infinite number of image sources were added. The image expansion is even, and the clamped boundaries convert to simply supported edges. The reforcing supports are introduced in the equation as infinite sums. The system is now infinite, implying Fourier transforms to be used on the spatial coordinate. The transformed displacement and inverse transform are solved for formally. The support forces are related to the beam displacement, so that the yet-unknown reaction forces are solved for. The resulting infinite sums are given explicitly using the Poisson sum formula and the contour integration.
A boundary controller for realistic double-panel partitions; Feasibility and experimental validity
Authors: Jemai B. , Ichchou Mohammed N. , Lezequel L.
Published: July 2002

The double-panel partitions are often used in noise control engineering because of their high attenuation capacity of noise. In the literature, simply supported panels with thick fluid cavities are considered to investigate the physical phenomena governing the vibro-acoustic behavior. In this study, a realistic partition is considered. It is a set of two flat rectangular and glass panels and three rubber bands and a frame. The panels are fixed to each other and to the frame using the rubber bands as separators at the edges. A numerical model taking into account possible motion of the panel’s boundaries and the fluid–structure interaction is developed. The influences of the rubber stiffness and the panel’s mass-to-stiffness ratio and the fluid cavity thickness on the pumping mode are considered. The study shows that a double-panel partition where rubber band rigidity is higher than the equivalent rigidity of the fluid cavity is not interesting because it behaves as a single panel. However, the partition with lower rubber rigidity provides higher attenuation in all the frequency domain except near the mass–air–mass mode where an active structural control is shown possible by partial piezoelectric sheets at the panel’s boundaries. A comparison with an experimental study is proposed in this work.
Combined damping treatments
Authors: Nikiforov A.
Published: July 2002

At present, to decrease a vibration of engineering structures three main types of damping treatments are used: (i) layer of hard viscoelastic plastic with sublayer of hard light plastic; (ii) layer of soft viscoelastic plastic or rubber, constrained by thin hard layer; and (iii) layer of thickness viscoelastic material. All these treatments ensure effective vibration damping at a limited frequency range. Structures of combined damping treatments uniting properties of some of the above-mentioned ones are proposed. Damping effectiveness of proposed treatments is essential at more wide frequency range. Formulas to estimate the loss factor of combined treat- ment are given. Measured loss factor of one of the proposed treatments is shown. Data of an experiment and an estimation are close to each other.
An overview of the fan active noise control effort at NASA, Lewis
Authors: Heidelberg Lawrence J.
Published: July 2002

NASA, Lewis began an effort, several years ago, in the area of fan tone active noise control. This effort was part of the Advanced Subsonic Transport Program. The effort consists of two parts: (1) building a test facility (the active noise control fan) to allow proof of concept testing, and (2) a contract effort to bring several concepts to the test phase. This paper will describe the test facilty and its unique capabilities such as a continuously rotating rake to measure the complete modal structure of the fan tones. Concepts tested will be described and the test results will be briefly discussed. All the concepts involve modal control. The concepts range from a single wall actuator array to control a single radial mode order, to multiple orders in both inlet and exhaust ducts using active vanes. In addition, a hybrid system (active+passive elements) and active treatment system will be presented. The performance of these systems will be discussed in terms of mode and tone total power reduction.
A modal concept for active noise control in circular or annular ducts
Authors: Zhang Yanchang , Enghardt Lars , Neise Wolfgang
Published: July 2002

A new active noise control strategy is presented which is aimed at reducing circumferential as well as radial acoustic modes in circular and/or annular ducts as used, for example, in aircraft engines. The azimuthal mode structure of the duct sound field is measured by using circumferentially spaced sensors in several axial planes which are mounted flush with the inner duct wall. No attempt is made to control the entire primary sound field, but only the dominant azimuthal modes which are propagational in the duct. With this procedure, the number of control variables is greatly reduced. The radial modes are reduced in an indirect way, i.e., the exact radial mode structure of the primary sound field in the duct need not be known for this purpose. a)Now with LUK GmbH & Co., Industriestrasse 3, 77815 Buehl, Germany.