bluuebunny/crossref_metadata_2025 huggingface dataset:
Environmental factors governing shallow-water active sonar
Authors: Cable Peter G. , Carey William M.
Published: July 2002

Recent experiments have measured the broadband sound transmission, coherency, reverberation and bottom backscattering strength in a variety of shallow-water environments with sand-silt bottoms. Ancillary range and time-dependent conductivity and temperature versus depth along with bathymetry were also obtained. The measurements were performed with especially designed impulsive sources, and vertical and horizontal receiving arrays. This paper presents key results on the spatial coherency of the received signals, the frequency dependence of the effective attenuation factors and the frequency dependent backscatter strength coefficient. The broadband coherency measurements, although variable from site to site, were found to be consistent with lengths of 30–35 wavelengths at 400 Hz at 40-km range. The frequency-dependent effective attenuation factor varied as frequency to a fractional power ranging between 0.15–0.25 dB/km at 100 Hz and 0.4–0.55 dB/km at 1 kHz. Bottom backscattering strengths at grazing angles on the order of 10 deg were found 10–15 dB lower at 200 Hz as compared to 1 kHz. The results are shown to be consistent with those of other investigators and are shown to place realistic limits on shallow-water sonar parameters. [Work supported by DARPA.]
Feature localization and classification from echolocation constraints with navigation uncertainty
Authors: Leonard John J. , Feder Hans Jacob S.
Published: July 2002

This talk will describe techniques for the classification and localization of simple geometric features from sonar data in the presence of navigation uncertainty. The goal is to recover the geometry of one or more unknown objects, the location of the object(s) in the global reference frame, and the trajectory of the sensor via combination of echolocation constraints obtained from multiple positions. The sonar is assumed to be a single transducer with a wide beam, which yields accurate range information but provides only weak angle constraints. Previous research has considered this problem without navigation uncertainty or using multi-element sonar array configurations [J. Leonard, J. Acoust. Soc. Am. 93, 2340(A) (1993); L. Kleeman and R. Kuc, Int. J. Robotics Res. 14(4) (1995)]. Echolocation constraints serve as input to a concurrent mapping and localization algorithm that performs both discrete (number and type of features) and continuous (location of features and sensor) estimation. Experimental results will be presented using a 675-kHz underwater mechanically scanned profiling sonar mounted on a large workspace robotic positioning system in a testing tank at MIT.
New organs in new spaces: A discussion of acoustical considerations from the organ builder’s perspective
Authors: Pike David C.
Published: July 2002

Thoughtful planning for new pipe organs in different architectural environments and in a variety of acoustical conditions is a crucial part of organ design. Organs, perhaps more than any other musical instrument, rely on their surroundings for their ultimate success or failure. The organ builder must take into account many factors, some of which are not under his or her direct control, in formulating optimum organ placement, case design, facade arrangement, interior layout, tonal design, pipe scaling and construction techniques, and voicing. Meaningful dialogue with an acoustician at an early stage in a project can have tremendous ramifications for the completed room and organ. C. B. Fisk, Inc., has much recent experience with large concert and recital hall instruments. The Fisk organs installed during this decade at the Meyerson Symphony Center in Dallas, Texas, Minato Mirai Hall in Yokohama, Japan, and in particular, Edythe Bates Old Recital Hall at Rice University in Houston, Texas, provide valuable case histories for both organ builder and acoustician. Each features the work of a different acoustical consultant. In all three cases the final result reflects the degree to which the acoustics were specifically optimized for the pipe organ.
Optimum organ acoustics reconciled with other hall uses
Authors: Klepper David Lloyd ben Yaacov Yehuda
Published: July 2002

Providing optimum acoustics for a large musical instrument, the organ, to insure good sound distribution and proper times of arrival for performer and audience is a formidable task, involving consideration of reverberation times over the frequency range, initial time delay gaps, early to reverberant ratios, and energy frequency balance. To coordinate these parameters for the organ and also maintain them near optimum for chamber groups, orchestras, and choruses, adds further complications. Some guidelines in architechtual design are presented, and examples drawn from buildings built over a period of 36 years are shown, with the improtant role of adjustability, in suspended sound-reflecting panels, stage-enclosure elements, stage floors on elevators, and even the organ itself, emphasized. One important example using electronics for music is shown, and provision of high-speech intelligibility through sound systems is also summarized for each example. The case studies are from work performed by the acoustical consulting firms of Bolt Beranek and Newman, and Klepper Marshall King, although the author has moved to independent practice in Jerusalem. George Izenour was Theatre Consultant for several projects shown.
Microcalcifications and high-performance breast ultrasound
Authors: Anderson Martin E. , Trahey Gregg E. , Soo Mary S. C.
Published: July 2002

Breast microcalcifications (MCs) are small crystals of calcium phosphate which are in some cases the only evidence of malignancy. Thus MCs serve as important diagnostic indicators, despite the fact that mammography has a low specificity in cases where MCs are the only suspicious feature. The overall sensitivity and specificity of mammography is also reduced in the radiographically dense breast. While the adjunctive use of breast ultrasound continues to expand with advances in the state of the art, ultrasound is currently not considered a reliable means to visualize MCs. Their improved visualization under ultrasound would be of significant clinical benefit, particularly in the dense breast. The findings to date of ongoing studies of the in vivo acoustic properties of MCs and breast tissues are reviewed. These include investigations of the scattering properties of MCs and breast tissue as well as direct measurements of in vivo phase aberrators and mean tissue sound speed using MCs as in vivo point scatterers. These studies suggest that MCs have elastic acoustic properties, and that gross sound speed error and tissue backscatter are the most significant factors limiting the visualization performance of ultrasound, among those studied. [This work is supported by NIH Grant Nos. RO1-CA43334-01 and R01-CA76059-01.]
A model for elastic wave propagation in tissue
Authors: Szabo Thomas L.
Published: July 2002

Data for attenuation in tissue fit a power law form: frequency raised to an exponent y which is typically between 1 and 2. A new self-consistent comprehensive causal model for elastic wave propagation in tissues with this type of loss has been derived based on the assumption that the loss per wavelength is small. The model agrees well with data and has the following features: (1) This model is in the form of a time domain wave equation with convolution operators for loss and phase velocity that depend on the value of y. (2) The frequency domain solution is expressed as a material transfer function that includes a velocity dispersion term which is maximum for y=1 and zero for y=0 or y=2. (3) The time domain solution is a material impulse response which can be used to predict broadband pulse propagation in tissues.
Bubble-mediated hyperthermia in an instrumented tissue phantom
Authors: Edson Patrick , Holt R. Glynn , Roy Ronald A.
Published: July 2002

The coagulation of blood by ultrasound, a procedure termed acoustic hemostasis by us, involves the contributions of several physical and biophysical effects. To investigate these effects, experiments have been undertaken involving rapid hyperthermia in an instrumented tissue phantom. Previously, the authors have reported a sharp increase in the rate of heating with increasing peak negative insonation pressure [J. Acoust. Soc. Am. 103(A) (1998)]. This increase occurs at a well-defined pressure, a threshold effect not unlike that observed at the onset of inertial acoustic cavitation. It was postulated that this effect may be the result of such cavitation activity leading to bubble-enhanced heating. The results of experiments in which the temperature rise and cavitation activity are monitored simultaneously are reported. The results will be interpreted in the light of the aforementioned cavitation effect, as well as competing explanations such as the excess absorption associated with the formation of nonlinearity in the pressure profile. [Work supported by DARPA.]
Time-domain analysis of nonlinear transducer networks
Authors: Warren Daniel M.
Published: July 2002

The existence of computer methods for the construction of network system equations from a netlist description and numerical methods for the solution of initial-value problems in mixed differential-algebraic equations (DAE’s) allow the time-domain analysis of networks containing nonlinear elements. This paper will demonstrate these techniques in application to electromechanical transduction systems exhibiting small- and large-signal nonlinear behavior. Nonlinear constitutive equations defining electromechanical elements in transducer networks will be developed in the proper form for inclusion in a modified nodal formulation. It will be shown that consistent sets of initial conditions can be determined from a modified netlist under limited circumstances, but these limitations do not significantly constrain the utility of method in this application. In fact, this approach opens the method up to elements with static behavior, such as permanent magnets or electrets. Time-domain behavior of the system is numerically derived from the descriptor equations by a backward difference formula (BDF) DAE integrator appropriate for stiff systems.
Patents and noise cancellation
Authors: Hiney James W.
Published: July 2002

This presentation will initially center on a brief overview of the Patent Law as it now exists after the 1995 and subsequent changes including patent term, Patent Cooperation Treaty enlarged membership, changes in prosecution, trends in the courts interpretation of patents, and proposed changes. A discussion of the patentability of algorithms in acoustic software will be made with illustrations. The presentation will then deal with some developments in acoustics and recently awarded patents which may prove to be of significance. To illustrate the importance of patents to growth of companies within the acoustics field, the current status of patents in the field of noise cancellation or sound attenuation will be addressed and examples shown of various positions of companies within the field and their focus. Specifically, the patent holdings of several companies within the field will be analyzed and the pattern of concentration of each company illustrated. To conclude, an analyses of expiring patents in the noise cancellation field will be presented to show opportunities for companies to expand into new areas now open for competition.
Advanced modeling of active control of fan noise for turbofan engines
Authors: Hutcheson Florence V. , Fuller Chris R. , Burdisso Ricardo A. , Dunn Mark H.
Published: July 2002

An advanced model of active control of fan noise for turbofan engines is being developed using the ducted fan noise prediction code TBIEM3D [M. H. Dunn, NASA/CR-97-206232, Sept. 1997]. An engine fan surrounded by a duct of finite length and cylindrical profile, translating in its axial direction with a uniform speed, is considered. A collection of spinning line sources located inside the duct are used to simulate the fan noise. Control sources modeled by point monopoles are placed along the duct inner wall to generate the secondary field that destructively interferes with the fan noise. A feedforward active noise control algorithm is simulated. Test cases were performed to demonstrate the feasibility of the model to perform active noise control studies. First- and fourth-order circumferential modes generated at a blade passage frequency of 1000 Hz were generated and targeted for control using far-field and inlet error sensors combined with a rigid or lined duct inner wall. Interference between inlet and outlet radiation, as well as the reflection from the duct openings and near-field effects were included. This model was found to be accurate, fast, and versatile. [Work supported by NASA Langley Research Center.]
Active control of structural intensity in an infinite elastic plate
Authors: Hayek Sabih I. , Won Jungyun , Kim Giman
Published: July 2002

In this study, the active control of active vibrational structural intensity (SI) in an infinite elastic plate is discussed. The plate is excited by mechanical noise sources, which generate a vector active SI field in the plate. A set of control actuators made up of point forces and point moments are located judiciously on the plate. The vibrational active SI-vector components are quadratic functions of the mechanical noise sources and control actuators magnitudes and phases. Thus the magnitude-squared active vector-SI at a sensor point is an expression with up to fourth power in the sources and actuators magnitudes and phases. An algorithm is developed to minimize the active SI using steepest descent on the gradient of the magnitude-squared total SI to obtain optimum values for magnitudes and phases of the control point actuators. Test cases are discussed to exhibit the influence of excitation structural wavelength, relative location of the control actuators to the mechanical noise source region, the orientation of the point moments, and the optimum combination of point forces and moments to minimize the total intensity in the near and far field. An attempt is made to explore actuators configurations that result in efficient local or global control. a)Currently Visiting Scholar at Penn State.
Noise control of structures with dipole acoustic cell devices, an analytical study
Authors: Kitts Zachary T. , Burdisso Ricardo A.
Published: July 2002

A new passive surface treatment has been developed to attenuate low frequency radiated noise from large structural surfaces. The acoustic treatment consists of an array of weak radiating cells that covers the structure’s surface. Each cell is a mechanical device that has two surfaces. The cells are driven by the motion of the structure and designed such that the two surfaces operate nearly out-of-phase, effectively creating dipole acoustic sources. Preliminary experimental results for nine cells applied to a simply supported plate driven by a white noise input show a 10 dB of sound power reduction over a frequency range of 100–1600 Hz. An analytical model is used to gain physical insight on noise control properties of the cells-plate system. Interaction effects of the system such as mass loading, damping, and dynamic coupling of the cells and plate are also investigated. The model is also utilized in design optimization studies of the weak radiating cells for beam and plate structures subjected to broadband inputs.
An interactive user interface for selecting optimal listening conditions
Authors: Rankovic Christine M.
Published: July 2002

An audio-visual interface was developed to allow listeners to hear a range of different conditions and convey their preferences. Feasibility for selecting optimal listening conditions was assessed for eight normal-hearing listeners. The visual display was a 4-by-4 matrix with the x and y axes representing two different manipulations of the frequency-gain characteristic. For a speech-in-noise condition, the axes represented low-frequency gain and broadband gain. For a filtered-speech condition, the axes represented high-pass cutoff frequency and bandwidth. Subjects altered the amount of processing applied to the ongoing speech (or speech in noise) by moving a screen pointer from cell to cell. Selections were compared to percent-correct scores for lists constructed from the same speech items (nonsense syllables), and to articulation indices (AIs). It took approximately 2 min to select, and selected conditions typically had AIs within 0.10 of the highest AI in the matrix. A potential application is determining settings for nonlinear hearing aids. [Work supported by NIDCD.]
On the light emission from a collapsing laser-induced cavitation bubble
Authors: Ohl Claus-Dieter , Lauterborn Werner
Published: July 2002

The collapse of laser-induced cavitation bubbles is accompanied by the emission of light. A detailed experimental study of the properties of the luminescence is presented. The dependence of the luminescence duration on the size of the bubble and on its sphericity prior to collapse is investigated. In aqueous sodium solutions line emission is found. The shape of these lines varies with the sphericity of the collapse. Also, differences in the emission spectrum in the case of spherical and aspherical collapse have been found.
Sound-induced cuticular vibrations in the atympanate bladder grasshopper Bullacris membracioides
Authors: Robert Daniel , van Staaden Moira J. , Roemer Heiner
Published: July 2002

In terrestrial animals, detection of sound waves over long distances conventionally requires the presence of tympanal ears. Although it lacks tympana, the South African bladder grasshopper Bullacris membracioides (Orthoptera, Pneumoridae) is endowed with an acute sense of hearing. Long-range acoustical communication is mediated by duets in which the males loud song (1.7 kHz, 98 dB SPL at 1 m) is answered by the females milder reply (at 4 kHz, 60 dB SPL), allowing the male to locate her. Males present a conspicuously inflated abdomen that constitutes a resonant sound radiator. Both males and females harbor six pairs of mechanosensory organs attached to the wall of abdominal segments A1–A6 that are involved in sound reception [M. van Staaden and H. Roemer, Nature 394, 773]. Using microscanning laser vibrometry to investigate the mechanics of atympanate hearing, sound-induced vibrations were shown to differ between male and female in their deflection shapes and amplitudes. Male cuticular vibrations culminate at 1.7 kHz, confirming the resonant nature of their abdominal wall. In both sexes, vibrations at the points of sensory insertions indicate that conventional tympana do not constitute a necessary condition for highly sensitive auditory function. [Work supported by the Austrian and the Swiss Science Foundations.]
The anecoicity phenomenon in a live room
Authors: Arau Higini
Published: July 2002

The radius of reverberation must be obtained by iteration of the following equation: Q/r2=312(T/V)e−0.04r/T. The phenomena of the anecoicity are noticed when the radius of the reverberation does not exist because the sound direct curve never intercepts the sound reverberant curve; because of that the sound reverberant field is not a constant, as it was assumed in the classical formulation. In this case it is known [M. Barron and L. J. Lee, J. Acoust. Soc. Am. 84, 618–628 (1988)] that the reverberant function is dependent on the distance through an exponential function. Therefore a minimum distance of reverberation will exist among both curves, which are very near. This distance is obtained by finding the minimum of the function: e0.04r/T/r2=312T/QV. This minimum distance is rmin=50T. Also, a minimum directivity factor of the source is determined, including rmin:  Qm=105561.5209T3/V. This Q[m] expresses the minimum directivity factor, for a determinated T and V, that must have the sound source because the sound direct field never intercepts the reverberant sound field. With this it will be possible to establish a direct dialog source-receptor without the liveness of the room being damaged.
Threshold condition for traveling wave excitation in an annular prime-mover
Authors: Le Polles T. , Job S. , Bailliet H. , Lotton P. , Bruneau M. , Gusev V.
Published: July 2002

The threshold condition for thermoacoustic instability in an annular prime-mover is derived. The region of spatially inhomogeneous temperature distribution (due to the presence of a stack and hot and cold heat exchangers) is assumed to be acoustically thin. The interaction of acoustic waves with the stack is assumed to be quasiadiabatic. Theoretical approach (based on the transformation of differential wave equation into Volterra integral equation, which is solved by iterative procedure) is valid for arbitrary spatial temperature distribution. Nevertheless, it was found that the threshold for the excitation of a traveling acoustic wave does not depend on the details of temperature spatial distribution but just on the ratio of the temperatures of hot and cold heat exchangers. Moreover, the critical temperature ratio does not depend on the thickness of the stack if the acoustic losses inside the heated region are negligible in comparison with acoustic losses in the rest part of the annular system. In this important limiting case critical temperature ratio diminishes when the dimensions of the system are scaled up. [Work supported by DGA.]
Frequency-angle selectivity under conditions of 3-D antenna motion
Authors: Gorban Igor I. , Volkovetsky Sergey P.
Published: July 2002

Common estimation of frequency-angle signal parameters under conditions of complicated 3-D antenna motions with angle rotations around the space axes is researched. A program package for modeling has been developed. The package calculates Fisher informative matrix and Cramer–Rao estimates of frequency-angle signal parameters. Research showed that (1) frequency-angle selectivity essentially depends on parameters of motion. Common estimates may be essentially better for systems with complicatedly moving antennas than for systems with static antennas or antennas moving with constant velocity; (2) a constant component of velocity makes the common estimates of frequency-angle signal parameters worse and variable components make them better; (3) angle selectivity is mainly determined not by size of array, as for static antenna, but by sizes of area where there is antenna motion (especially periodical motion); (4) in conditions of complicated antenna motion, increasing of angle selectivity takes place even if frequencies of the signal or Doppler’s shift are unknown; (5) by correctly taking into consideration complicated antenna motion, there is often a real possibility to increase common frequency-angle selectivity of the systems.
The influence of internal waves on signal fluctuation in the Yellow Sea
Authors: Sun Zhenge , Zhang Renhe , Yan Jin
Published: July 2002

This paper studies the signal fluctuation due to the tide and internal waves in the Yellow Sea. The spread of internal waves appears to be the fluctuation of the thermocline in summer time. As a result, the characteristics of normal modes including their wave numbers and group velocities vary with this fluctuation. This leads to the signal fluctuations since the receiving signals are actually the interference results of arriving modes. The influence of internal waves on normal modes and signal fluctuation was examined in an experiment in the Yellow Sea in 1998. In the experiment, an ADCP and thermistor chain were used to observe the internal waves, while a vertical array with 32 hydrophones was used to receive CW and FM acoustic signals. The CW signals provided the measurement of amplitude fluctuation at several frequencies from 450 to 650 Hz. The FM signals were used to get the mode arriving structure by means of pulse compression and mode filtering technique. The variation of mode group delay between the 3800-Hz signal and the 450-650 Hz signal was also measured.
Temporal coherence of broadband acoustic signals in the presence of internal waves in shallow water
Authors: Yang T. C. , Yoo K.
Published: July 2002

Ocean medium fluctuations reduce the temporal coherence of acoustic signals. At low (e.g., 500 Hz) frequencies, temporal coherence limits the time duration of a replica field used for matched-field source localization in a random ocean. At mid (e.g., 10 kHz) frequencies, temporal coherence of the acoustic signal dictates the update rate for the channel equalizer for a phase coherent communication scheme. In this paper, the temporal coherence of broadband acoustic signals is studied at low- and mid-frequencies in a shallow-water environment which includes both the linear and nonlinear (solitary) internal waves. The internal wave model is constructed based on the measured (average) sound-speed profile and sound-speed variance collected during the SWARM-95 experiment. A broadband pseudorandom (PRN) signal is used at low- and midfrequencies. The signals are propagated using a PE model through the internal wave perturbed sound-speed profiles which evolve in time according to the internal wave equation of motion. Temporal coherence at 400 Hz is shown to agree with experimental observations based on the SWARM-95 measurements. Implications for midfrequency communications will be discussed. [This work is supported by the Office of Naval Research.]
Directional hearing in grasshoppers: Biophysical mechanisms and animal performance
Authors: Holderied Marc , Schul Johannes , v. Helversen Dagmar , v. Helversen Otto
Published: July 2002

Grasshopper hearing organs are pressure difference receivers: two tympana are connected by air-filled tracheal sacs. Sound reaches a tympanum’s outer surface directly and its inner surface through these sacs. Recently, Michelsen and Rohrseitz determined the transfer function of these sacs and developed a biophysical model to predict directional hearing. Tympanal nerve recordings made in Erlangen revealed that this model can predict hearing even for complex stimulus situations with two sound sources emitting pure tones of varying phase and amplitude. Behavioral tests using broadband grasshopper songs showed that a 1-dB intensity difference between two lateral sound sources is sufficient for correct lateralization. It is, however, difficult to predict actual interaural intensity differences for broadband noise by model calculation. A direct method to determine the actual interaural intensity difference necessary for correct lateralization is to decouple the two tympana. For this purpose, light magnetomechanical earphones for free-moving grasshoppers were developed. Lateralization performance using earphones was similar to acoustic stimulation. The possible influence of coherence in broadband signals to the model is discussed.
Fisheries and plankton acoustics: State of the art and beyond
Authors: MacLennan David N.
Published: July 2002

Acoustical methods are well established as a means of remotely observing aquatic organisms. The range of applications reported in the literature is wide, from studies of isolated animals to populations extending over large areas. The geometric scale of target organisms is similarly huge, from microscopic plankton to the largest of marine mammals. The information required from acoustical investigations may be simple quantities like abundance estimates, or more descriptive output like species identification. In each case, there are different problems to be considered. The multi-disciplinary nature of acoustical techniques is important. Success depends on a combined appreciation of scattering physics, animal physiology, statistics, and sonar technology to mention just some of the contributing fields. The historical context is explained, leading to a critical review of recent developments. To a large extent, the driving force has been new technology, especially the rapid growth of computing power. It is important to ensure that appropriate scientific research is done to achieve the benefits of new technology, in acoustics as in other fields, for a better understanding of the living resources in the sea and fresh waters.
Measurements and models of small-scale surface roughness effects at audio-frequencies in air
Authors: Attenborough Keith
Published: July 2002

Surface roughness has been found to have an important influence on outdoor ground effect. Indoor and outdoor measurements of roughness effects are reported together with developments of analytical boss theories and numerical predictions using boundary elements. Although the Twersky boss theory including incoherent scatter is found to lead to reasonable agreement with data, it fails to predict measured diffraction grating effects and, overall, the BEM results are in better agreement.
Binaural assessment of loudness of environmental noise
Authors: Preis Anna
Published: July 2002

Loudness of time-varying environmental noises (two types of car noise and aircraft noise) presented under dichotic and diotic stimulation was investigated via headphones. The stimuli were combinations of signals with increasing and decreasing SPL. The objective was to discover if there is a difference between the noise assessment of these signals presented in diotic and dichotic conditions. The results are compared with previous research, where it was found that for combinations of tone/noise and noise/noise, there was no difference between binaural loudness perceived in diotic and dichotic listening conditions. In the case of stimuli that consist of two tones of different frequency, those presented diotically were perceived to be louder than those presented dichotically.
Evaluating sequences of environmental noise using the method of absolute judgment in laboratory and outdoor situations. Some methodological considerations
Authors: Hellbrueck Juergen , Zeitler Alfred
Published: July 2002

It has been shown that the perceived average loudness of a noise sequence can be predicted from the Leq [S. Namba and S. Kuwano, J. Acoust. Soc. Jpn. (E) 1, 99–106 (1980)] or the percentile loudness N4 [e.g., H. Fastl, Contributions to Psychological Acoustics. Results of the Fifth Oldenburg Symposium on Psychological Acoustics (1991), pp. 205–216]. While most of the experiments have been conducted in laboratory situations, there is lack of evidence that the results can be transferred to noise situations outside of the laboratory. Context factors and psychological frames of reference play an important role, when environmental noises are rated in real noise situations. Category scaling based on the method of absolute judgment is regarded to be a natural scaling procedure which is inherently associated with psychological theories of frames of reference. Current results of empirical studies on the evaluation of longer periods of traffic noise have proved the applicability of category scales. The method has been used in outdoor settings as well as in laboratory situations, and yielded reliable results in both cases. Therefore, it is proposed to use measurements which are familiar to the subjects, such as absolute judgments, thus having direct access to individuals’ perceptions.
Effects of helicopter and aircraft interior noise and vibration on passengers’ comfort sensation and subjective well-being
Authors: Quehl Julia , Schick August , Mellert Volker , Schulte-Fortkamp Brigitte , Remmers Hermann
Published: July 2002

Apparently passengers’ sensation of comfort and subjective well-being are key concepts in the research on user acceptance of helicopter and aircraft systems. The design and development of advanced air transportation technologies require a fundamental, theory-based understanding of these concepts. From the passengers point of view, helicopter and aircraft interior noise and vibration are primary physical factors underlying the perception of comfort and well-being. In various judgmental contexts the influence of exposure to combined interior noise and vibration in helicopters and aircrafts will be analyzed by means of combined psychoacoustical, socioacoustical, and psychological research methods: Field experiments in a flight simulator and during real flight situations as well as laboratory experiments using a sound and vibration reproduction system will be carried out in order to examine the interactive effects of noise and vibration. The aim is to develop a passenger comfort or well-being index for helicopter and aircraft interior environments. The index will be based on the integration of physical predictors for the flight situation and psychological predictors for the passengers’ sensation of comfort and well-being.
Vibration characteristics of bone-conducted sound
Authors: Stenfelt Stefan , Hȧkansson Bo , Tjellström Anders
Published: July 2002

A dry skull, prepared with a layer of damping material in the brain capsule, was used to investigate the vibratory pattern of bone-conducted sound. Three orthogonal vibration responses of the cochleas were measured, by means of accelerometers, in the frequency range 0.1 to 10 kHz. The exciter was attached at different points in the temporal, parietal, and frontal bones. The results revealed a profound low-frequency antiresonance (attenuation) in the ipsilateral transmission path, which was psychoacoustically shown to yield a distinct lateralization effect. It was further shown that the direction of excitation coincides with that of maximum response at the ipsilateral cochlea. No dominating response direction was found for frequencies above the first skull resonance at the contralateral cochlea. An overall higher response level was achieved at the ipsilateral cochlea when the transducer was attached close to the posterior semicircular canal compared with the other excitation points of the skull, for the energy transmission in general and specifically for the direction of excitation. Transcranial attenuation between the cochleas was found to be highly frequency specific, with a maximum of 40 dB in a single direction. Transcranial energy attenuation was less than 10 dB for the investigated frequency range.
Three-dimensional measurements of a physical full-size model of the human middle ear
Authors: Taschke Henning , Weistenhofer Christian
Published: July 2002

Complete systematical investigations of the vibrational properties of the human middle ear are impossible to carry out by means of temporal bone measurements of a single specimen because of post-mortem changes (time variance), damages to the object to be measured, and the irreversibility of manipulations. Measurements of physical models offer the facility for examining the properties of the human middle ear regardless of the above problems. The quality of the scientific findings obtained from the physical models depends on how good the properties of the real middle ear are reproduced by the elements, forms and materials chosen. A physical full-size model of the human middle ear was developed that allows the use of measurement instrumentation which is applied for real ear measurements. One- and three-dimensional measurements of the physical full-size model will be presented. The quality of the model will be judged by comparisons with real ear measurements and model predictions. The fields of application of the model resulting from this will be discussed.
Computed optical emissions from a star in a jar
Authors: Moss William
Published: July 2002

A sonoluminescing bubble has been modeled as a thermally conducting, partially ionized plasma. The model accounts for most of the observed experimental trends, including (i) the asymmetric pulse shape; (ii) the temperature and driving pressure dependence of the pulse width and intensity; and (iii) spectral shapes, in particular, the 300-nm peak in the spectrum of xenon sonoluminescence. The agreement between the calculations and the data, as well as the models predictions of almost every experimental trend, leave little doubt that the spectral and temporal properties of the emissions of a single sonoluminescing bubble are due to adiabatic- or shock-initiated thermal emission from a cool dense plasma. [Work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.]
Multibubble sonoluminescence at 2 MHz: Optical spectral data and attempt at interpretation
Authors: Lepoint T. , Hankenne E. , Lepoint-Mullie F. , Vogelet N.
Published: July 2002

In order to obtain information on the physical conditions created by transient cavitation bubbles imploding at acoustic frequencies (fac) of therapeutic interest, the UV–visible spectral distribution of multibubble sonoluminescence at 1.7 MHz is focused on. Original optical spectra (wavelength range: 220–950; resolution: 0.24 nm) will be reported for aqueous solutions containing various alkali-metals chlorides and dissolved noble gases. Special emphasis will be put on the profile of D1 and D2 lines associated with the reduced metals [i.e., (i) their blending toward the red zone (much less than for fac 20 kHz); (ii) the absence of measurable shift and broadening; (iii) the absence of fusion of the D lines]. Several scenarios for (i) the reduction of the cation and (ii) the surrounding of the emitting metal atoms will be discussed. [The present authors—particularly T.L. and F. L-M.—are very grateful to Dr. J-L. Domanchain and G. Nivez (Jobin-Yvon I.S.A.).]
Nonlinear amplification in the cochlea—Implications of a computer model
Authors: Steurer Martin
Published: July 2002

In the cochlear amplifier the output is fed back to the input. Namely, the contraction of the outer hair cells (OHCs) is believed to be controlled by the deflection of the ciliary bundle caused by the movements of the tectorial membrane. The contraction of the OHCs leads to an intensified movement of the basilar and tectorial membrane, and by this closing the loop. Such a model implies minimal response time of up to 300 ms to reach the steady state of amplification and even more time to return from maximum amplification to zero movement (except thermal movement). These time limits can be reduced when accepting intensity-dependent optimal frequencies of the cochlea amplifiers. The optimum frequency defined by best phase shift at a certain place of the basilar membrane starts nearby the characteristic frequency of the basilar membrane and increases with increasing intensity. Therefore, the peak amplification for a fixed frequency moves in the apical direction with increasing intensity. The results of this model simulated on a computer show improved time responses and explain how to control phase shifts for the optimum frequency in the cochlear amplifier.
Speech intelligibility in real and virtual adverse auditory environments
Authors: Vause Nancy L. , Grantham D. Wesley
Published: July 2002

The purpose of this investigation was to examine the effects of real and virtual adverse conditions on speech intelligibility. The experiment was designed to examine the effect of presentation method on speech intelligibility in conditions of noise and reverberation as signal-to-noise ratio was systematically varied. Additionally, this investigation evaluated the influence of talker gender on speech intelligibility in anechoic and reverberant environments as a function of signal-to-noise ratio and presentation method. Speech intelligibility scores were obtained from 21 normal hearing subjects using a nonsense syllable test. The syllables were recorded in three environments (diotic anechoic, virtual anechoic, and virtual reverberant) with three signal-to-noise ratios (0, 5, 9 dB) using two simultaneous masking sources. The findings indicate that (a) traditional diotic presentation of these stimuli degrades speech intelligibility compared to virtual presentation and may not accurately represent real-world performance; (b) the signal-to-noise ratios did not influence performance trends between presentation modes, as intelligibility improved with increasing SNR; (c) reverberation decreased intelligibility although the effects were not as dramatic as expected; and (d) using these stimuli, the female talker tokens were more easily identified than male talkers in a virtual presentation, but not generally for diotic presentation. [Work supported by NICDC and U.S. Army.]
Auditory spatial attention influences discrimination of interaural time differences: Evidence from a probe-signal paradigm
Authors: Sach Andrew J. , Hill Nicholas I. , Bailey Peter J.
Published: July 2002

Performance on a same–different ITD discrimination task was used as a metric for auditory spatial attention. In several variants of a probe-signal procedure, attention was directed as detailed below. In all experiments, performance was better for signals lateralized on the expected side of the head. In experiment 1, a lateralized auditory cue preceded the signal. Lest this functioned not simply as an attentional cue but also as a spatial landmark, experiment 2 used no cue but manipulated expectation by presenting trials more frequently on a particular side. To establish whether the effects in experiment 2 generalized to all sounds within the spatial focus or were attributable simply to greater familiarity with the expected stimulus, a rove was incorporated in the pitch (experiment 3) or the timbre (experiment 4) of the signals on each trial. Experiment 5 introduced trial-by-trial visual cueing which, necessarily endogenous, provided evidence for top–down attentional control. Further work established whether analogous effects are seen on a frequency discrimination task, and when sounds are lateralized by IID. [Work supported by UK BBSRC.]
Acoustic weapons? Sources and propagation of strong sound
Authors: Altmann Jürgen
Published: July 2002

Acoustic weapons are under research and development in a few countries. Reliable information is scarce; allegations, mainly in the military press, have stressed the infrasound region. By means of a literature review and own analysis potential strong sources from infra- to ultrasound were identified. Speakers with horns, sirens, and whistles can produce acoustic powers of kilowatts to tens of kilowatts. Explosive blasts have no upper limit. Repetitive explosions, e.g., of a fuel–air mixture, might produce powers on the order of megawatts. Most sources would be too large to be handheld. Propagation of strong sound to some distance meets several problems, however. Diffraction impedes or prevents directed propagation, in particular at low frequencies. Sound of high intensity propagates nonlinearly, deforming into shocked waves with strong attenuation. The level at a given distance depends in a complicated way on details, such as source level, source size, frequency, wavefront form, and humidity. Keeping certain sound-level limits, e.g., at the ears of targeted people, would require very complex processing and automatic control. Acoustic weapons may turn out cumbersome and may not add important new options for the military; this could facilitate preventive limits up to a ban.
Sensor proximity error in the conformal near-field acoustic holography and its solution by using the nonsingular boundary integral equation
Authors: Ih Jeong-Guon , Kang Sung-Chon
Published: July 2002

In the conformal near-field acoustic holography (NAH) using the boundary element method (BEM), the transfer matrix relating the vibro-acoustic properties of source and field depends solely on the geometrical condition of the problem. This kind of NAH is known to be very powerful in dealing with the sources having irregular boundaries. When the vibro-acoustic source field is reconstructed by using this conformal NAH, one tends to position the sensors as close as possible to the source surface in order to get rich information on the nonpropagating wave components. The conventional acoustic BEM based on the Kirchhoff–Helmholtz integral equation has the singularity problem in the very-near field of the source surface: computation error increases very rapidly as approaching from the far field. This problem originated from the singular kernel of the fundamental solution of the BIE and can influence the reconstruction accuracy. In this paper, the holographic BIE is reformulated to remove the singularity by introducing an additional propagating plane wave. Reconstructed results by the conventional and the nonsingular BIE are compared for a simple radiator model. It is observed that the nonsingular formulation can yield accurate vibro-acoustic transfer matrix and thus improve the resolution of the reconstructed source field.
A distributed active vibration absorber for sound radiation and vibration control
Authors: Fuller C. R. , Cambou P. E.
Published: July 2002

This paper discusses the analytical and experimental development of a distributed active vibration absorber (DAVA) designed to reduce sound radiation and vibration over extended areas of elastic structures. The distributed vibration absorber, in contrast to the classical vibration absorber, consists of a continuous active elastic layer covered with a continuous mass distribution. The distribution of the mass layer can be optimally designed to reduce either sound radiation or vibration over selected areas or frequency bands for particular structures. The paper first discusses an analytical model of the DAVA based upon variational techniques and used in conjunction with a genetic algorithm to design the mass distribution optimally. Simulated results on vibration and sound radiation control for a vibrating beam are presented and are compared to experimental realizations of the DAVA. The analytical and experimental tests confirm that the DAVA can passively attenuate vibration and sound radiation through an extended area and over an extended frequency range. The DAVA is shown to outperform the classical point vibration absorber significantly. The introduction of an active signal to the DAVA is seen to provide significant additional sound and vibration reduction. The DAVA is demonstrated to provide effective passive and active vibration and sound control in a conformal, compact, skin treatment. [Work funded by the ONR, Dr. Kam Ng, Technical Monitor.]
Non-natives’ production of vowels in conversational speech
Authors: Piske Thorsten , Flege James E. , MacKay Ian R. A. , Meador Diane
Published: July 2002

The aim of this study was to determine if native speakers of Italian can ever learn to produce accurately English vowels not found in Italian. A recent study [J. E. Flege, I. R. A. MacKay, and D. Meador, J. Acoust. Soc. Am., under review], in which native Italian subjects were asked to repeat real words presented via a loudspeaker, showed that early but not late bilinguals produced English /ɪʊɚ/ accurately. None of the subjects, however, did so when asked to repeat nonwords. But what about the most crucial evidence—conversational speech? Here a new technique with satisfactory experimental control ws developed to assess vowels produced in conversational speech. Speech samples were obtained from the same 90 subjects who participated in the earlier study. The subjects’ production of /ɪʊɚ/ (not found in Italian) and /i æ o/ was evaluated auditorily by native English-speaking listeners. Preliminary results indicate that early bilinguals can learn to produce /ɪʊɚ/ accurately in conversational speech, but that only a declining proportion of subjects do so as the age of learning English increases. High scores for /o/, which is much like an Italian vowel, were obtained. This suggested that listeners are not unduly influenced by overall degree of foreign accent in the samples examined.