bluuebunny/crossref_metadata_2025 huggingface dataset:
Reverberation characteristics in shallow water with a strong thermocline
Authors: Zhou Ji-Xun , Zhang Xue-Zhen , Jin Guoliang
Published: July 2002

The first joint China–U.S. ocean acoustics experiment was conducted in the summer of 1996 in a far offshore area in the Yellow Sea with strong thermoclines. The water depth was about 76 m with a flat seabed. The sediments in the area consisted of silty sand with mean grain diameter of 0.0643 mm. Shallow-water reverberation data were collected by using a 32-element vertical array that spanned the water column. Explosive sources of 1 kg were detonated both above and below the thermocline. The Yellow Sea ’96 reverberation data exhibit strong receiver and source depth dependence. Reverberation intensity level (RL), received in the thermocline, shows a regular interference structure with increasing time (distance). This can be explained by the R-mode theory. In general, seabottom scattering dominated the Yellow Sea ’96 reverberation process. Therefore, the seabottom scattering strength was derived, by inversion, from the reverberation and propagation data. A resonant volume-scattering source in the water column was also observed in the measurements. This demonstrates that water column effects (scattering from internal wave packets, fish groups, etc.) may also be significant for the shallow-water reverberation at some frequencies. [Work supported by ONR.]
High-frequency scattering from heterogeneous marine sediments
Authors: Ivakin Anatoliy N.
Published: July 2002

A model is presented for high-frequency acoustic scattering from marine sediments with continuous and discrete heterogeneities. The process of penetration into the sediment is described in terms of a combined wave–ray approach which gives a simple expression for the sound intensity within sediment taking into account main contributions of both ray and lateral components of the full-field solution. The process of volume scattering is described in terms of the scattering cross section per unit volume defined for continuous and discrete types of sediment heterogeneity. In the case of a continuous medium, it is defined through the spatial spectra of fluctuations of acoustical parameters. In the case of discrete heterogeneity, the scattering cross section per unit volume is expressed through the size distribution and individual scattering functions of discrete scatterers. Existing data on sediment heterogeneity are analyzed to provide inputs for the seabed scattering model. Angular-frequency dependencies of the backscattering strength are calculated and comparison with available experimental results is presented and discussed.
Sea-surface generated noise dependence on wind speed and white cap coverage
Authors: Cato Douglas H.
Published: July 2002

Breaking waves are an important source of noise in the ocean, and evidence from laboratory measurements indicates that the noise is generated by bubbles formed in wave breaking. Measurements at sea, however, have found that the noise correlates better with wind speed than any property of the surface waves. The relationship between noise intensity I and wind speed U is usually of the form I=aUn (where a is a constant), but values of n vary between studies over the range of 1 to 3. Measurements of noise near Australia show that, where other components of noise are low, the result is consistently n=3 for a wide range of conditions. It is suggested that lower values of n result where non-wind-dependent noise contributes significantly to the levels at lower wind speeds, so decreasing the slope of the dependence on wind speed. Studies of white cap coverage have found a similar dependence on wind speed, with observed values of n being close to 3, thus providing a link between noise, wind speed, and wave breaking. Some preliminary results of noise measurements concurrent with measurements of white cap coverage to test this link are discussed.
Inversion of reverberation data for rapid environmental assessment
Authors: Preston John R.
Published: July 2002

From 1996 through 1998 SACLANTCEN participated in three rapid environmental assessment (REA) trials, including experiments for bottom reverberation. Eight sites were visited: near Sicily, in the Ionian Sea, and near the Straits of Gibraltar. SUS charges were used as sources. The receivers were horizontal arrays (four apertures) spanning a wide frequency range. Sets of nearly monostatic recordings were analyzed in frequency bands from 80 to 4000 Hz. Previous results by the author [Berlin ASA meeting (1999)] showed polar plots of the beam time series superimposed on bathymetric charts, revealing a number of scattering features not on the charts and that directional reverberation measurements are a useful remote-sensing tool. Another objective of the reverberation experiments was to quickly invert for estimates of scattering and geo-acoustic parameters that can be used in a wider variety of conditions. A manual inversion procedure was originally used to obtain at-sea results. New work uses a simulated annealing algorithm giving more formal inversion results. The horizontal array data are compared with the generic sonar model (GSM) predictions for both the manual and automated inverse schemes. A summary of the estimated geo-acoustic parameters using both methods is presented. [Work supported by ONR and DREA.]
Geoacoustic properties of sediments determined from measurements of head waves
Authors: Berger Thomas K. , Buckingham Michael J.
Published: July 2002

As part of the SAX 99 experiments, head wave signals have been analyzed to determine geoacoustic properties for the sandy sediment at the shallow water site near Destin, FL. A small-aperture (2.33 m), vertical array of four hydrophones was deployed at mid-water depth over the sea floor, where the water column is 20 m deep. Transient signals were generated by an airgun, at a fixed location, resting on the ocean bottom. At a range of approximately 1 km from the source, the array was allowed to drift to vary its position; the location was measured with DGPS equipment. Two estimates of the compressional wave speed in the sandy sediment were obtained from the incoming signals: a spatially averaged value over the track between the source and receiver, determined at a single sensor from the difference in arrival times between the head wave and the water-borne wave; and a localized value, computed from the critical angle derived from the vertical directionality of the received head wave signals. A comparison of the independent local and spatially averaged estimates provides a useful consistancy check, and establishes the spatial variation of the sediment more completely than by either purely averaged or local measurements alone.
Introduced song replaces existing song in east Australian humpback whale population
Authors: Noad Michael J. , Cato Douglas H. , Bryden M. M.
Published: July 2002

Observations of humpback whale song in various parts of the world have shown that the song is a complex sequence of sounds that at any time is stereotyped within a geographical stock but differs between stocks. The song changes with time at a variable rate, usually in a gradual and evolutionary fashion. This paper reports observations of song change that differ from anything previously observed. A completely new song appeared spontaneously in a small number of singers in the east Australian stock, increasing in prevalence to completely replace the original song within two years. The two songs coexisted in the population for this period but individual singers generally produced one song or the other, with few occurrences of an intermediate variety. The new song was found to be the same as that observed off Western Australia. Previous comparisons have shown the east and west coast songs to be unrelated despite a small amount of interchange between the two stocks. The rapid rise to dominance of an introduced song indicates that song change is not necessarily evolutionary, gradual, or internally driven.
Geoacoustic inversion results from the modal mapping experiment
Authors: Becker Kyle M. , Frisk George V. , Rajan Subramaniam D.
Published: July 2002

The modal mapping experiment (MOMAX) was conducted in March 1997 off the New Jersey coast in about 70 m of water [G. V. Frisk et al., J. Acoust. Soc. Am. 103, 3028(A) (1998)]. A cw source emitting several discrete tones in the frequency range 50–175 Hz was used to excite the acoustic pressure field, which was measured using an array of freely drifting hydrophone buoys equipped with GPS navigation and radio telemetry. The wave-number content of the spatially varying pressure field was extracted using a Hankel-transform-based method. The discrete portion of the resulting spectrum was used as input data to a perturbative inversion algorithm for inferring the geoacoustic properties of the seabed. Results are shown as depth-dependent sound-velocity profiles in the sediment. Comparisons are made among profiles obtained in different locations, highlighting the effect of variations in wave-number content on the inferred geoacoustic properties. [Work supported by ONR.]
Adaptive transmit focusing by numerical backpropagation of ultrasonic waveforms
Authors: Lacefield James C. , Waag Robert C.
Published: July 2002

Physical aspects of adaptive transmit-focusing algorithms that model an inhomogeneous medium as a time-shift screen distant from the aperture are described. Exact restoration of an ideal focus by numerical backpropagation of a time-shifted field to the aperture followed by physical propagation of transmitted waveforms requires an aperture that is sampled at greater than twice the highest spatial frequency in the field and occupies an area larger than the nonzero region of the field. Time-shift screens that are estimated from backpropagated pulse–echo data include oscillations at outer sample positions. The oscillations are caused by edge waves diffracted from the aperture boundary. Simulations performed using point-reflector data acquired through a distributed aberration phantom with a two-dimensional array system demonstrate that nonidealities from spatially windowed data increase the peripheral energy of the compensated focus compared to the ideal case at levels below −20 dB. Omission of the outer time-shift estimates and apodization of the time-shifted field reduce the significance of these nonidealities. For biomedical applications in which pulse distortions more severe than simple time shifts are observed, compensated foci produced using the backpropagation method nevertheless exhibit lower peripheral energy than foci produced after time-shift compensation in the aperture.
An energy-based method for the experimental determination of electrostrictive coefficients on polyurethane films
Authors: Guillot Francois M. , Jarzynski Jacek
Published: July 2002

A new method for measuring electrostrictive coefficients on thin plastic films is presented. This method is applied to polyurethane samples, whose large electrostriction makes them interesting new transduction materials. The experimental part of the technique involves a small sample to which both an ac voltage and a large dc bias voltage are applied in the thickness direction. The sample is encapsulated in a soft silicone rubber and its electric field-induced deformations are optically measured in three perpendicular directions by a laser Doppler vibrometer. These data are input into a Rayleigh–Ritz energy minimization program implemented symbolically in mathcad. The program outputs the second-order electromechanical coupling coefficients M3311, M3322, and M3333 which represent the variations of the dielectric constant of the material with respect to stress. These are true electrostrictive coefficients, in the sense that they are material properties of the polyurethanes, independent of the mechanical boundary conditions imposed to the sample and of the second-order effect resulting from Maxwell stress. A first-order version of this method applied to piezoelectric polymers was validated numerically and experimentally. Experimental values of the electrostrictive coefficients are presented here for several types of structurally different polyurethane samples.
The philosophy of electronic room enhancement
Authors: Poletti Mark A.
Published: July 2002

The acoustic design of rooms involves the determination of surface materials to provide a desired reverberation time, loudness, and diffusion. These acoustic properties are similar for sources and receivers throughout the room, and are therefore global. They are derived from the later part of room impulse responses. Reflecting surfaces are typically included to direct early energy from the stage area onto the audience areas. They operate locally for sources in the stage area, and produce more localized effects at different receiving positions. The acoustic effects are determined from the early part of room impulse responses. This paper argues that the design of electronic room enhancement systems should follow a similar philosophy to that of passive rooms. Those properties that are global, such as the reverberation time, should be enhanced using a system which can maintain this global property. This is ensured by using non-in-line systems which use microphones spaced throughout the room. Local properties are most effectively controlled using in-line systems which use microphones close to the stage area. A review of non-in-line and in-line enhancement systems will be presented, and a hybrid system introduced which aims to provide both global and local control of room acoustics.
Development of auditory sensitivity in budgerigars
Authors: Brittan-Powell Elizabeth F. , Dooling Robert J.
Published: July 2002

We examined the course of vocal development in budgerigars from hatch to 4 weeks postfledging. During this period, calls undergo dramatic changes that culminate in a stereotyped FM patterned food-begging call by the time of fledging. A shortened version of this call becomes the bird’s first adult vocalization. Auditory feedback influences the development of these vocalizations, but little is known about nestling hearing. The present study tracked the development of auditory sensitivity in nestling budgerigars using the auditory brain stem response (ABR). Adult ABR audiograms are similar in shape to behavioral audiograms but are elevated by 20–30 dB. Thresholds for week-old nestlings are above 90 dB pSPL for tones and clicks, but improve markedly approaching adult levels by fledging. ABR waveform shape also changes dramatically over development. Because budgerigars use auditory feedback to learn and modify their calls throughout life, knowing how the auditory system develops and what and when the animal hears provides insights into the role that hearing plays in the development of different types of vocalizations. [Work supported by Grants DC-00046 from NIDCD to E.F.B.-P. and DC-00198 from NIH to R.J.D.]
Cyclic variation of the Doppler power from porcine blood under pulsatile flow in tubes of varying compliance
Authors: Paeng Dong-Guk , Shung K. Kirk
Published: July 2002

The cyclic variation of the Doppler power backscattered from porcine whole blood and red blood cell suspensions was investigated under pulsatile flow in a mock flow loop of varying compliance. Experiments were performed using five different hematocrit values at four different stroke rates. A significant cyclic variation of Doppler power was measured in all experiments but the pattern of the cyclic variation was different. At high stroke rates (40 beats/min or more), the cyclic variation of the Doppler power showed a small peak during acceleration of flow and reached a minimum at peak systole and another peak was observed during deceleration. This minimum power phenomenon during peak systole became more prominent as the stroke rate was increased up to 60 beats/min. At a low stroke rate (20 beats/min), the Doppler power increased during early systole and remained the same until late diastole. The cyclic variation using whole porcine blood and red cell suspension showed the same pattern and suggested that aggregation of RBC did not affect the pattern of the cyclic variation. In addition to these general features, the differences for different experimental scenarios (whole blood versus red cell suspensions, and rigid tube versus compliant tube) are discussed.
Quantitative measurement of cavitation activity during red blood cell lysis and sonoporation
Authors: Chen Wen-Shiang , Porter Tyrone M. , Mourad Pierre D. , Chang Peter H. , Hadley Maile , Crum Lawrence A.
Published: July 2002

Ultrasound contrast agents have proven to be an effective agent for producing cavitation-associated bioeffects. A comparative analysis of the strength and duration of cavitation activity and the lifetime of nucleation sites during red blood cell (RBC) lysis and sonoporation was performed. The RBCs were treated with 1.1-MHz tone-burst ultrasound in the presence of contrast agents and analyzed for hemoglobin release and the uptake of FITC-dextran (MW= 4 kD). Pulse durations ranged from 100 to 10000 ms and the total number of bursts for each pulse duration was selected to ensure a constant exposure. The extent and duration of cavitation activity during treatment was monitored using a passive cavitation detection system. The collected cavitation-activity data was analyzed quantitatively and correlated with the percent of hemolysis and the ratio of fluorescent cells to total cells treated.
Internal noise in miniature electret microphones
Authors: Thompson Stephen C.
Published: July 2002

Modern miniature electret microphones normally include an internal amplifier to buffer the very high electrical impedance of the electret motor. This amplifier, usually an FET source follower circuit, generates a part of the noise in the microphone output signal. The electrical noise originates in the semiconductor and in the resistive components of the electrical circuit. Recent developments have reduced the electrical noise considerably so that it is no longer the dominant source. The other noise sources are the resistive components of the mechanical and acoustical impedances within the microphone. This paper describes recent work and special measurement methods that have helped to identify and reduce the acoustical noise components.
Speech/nonspeech discrimination in reverberant teleconferencing environments for acoustical source location
Authors: Alvino Christopher V. , Grove Deborah M. , Kleban James T. , Sathyanarayana Shashank
Published: July 2002

A real-time acoustical source location system implemented at the CAIP Center at Rutgers University presently tracks all sounds within a room. The system aims a video camera and audio sensors at the determined sound source for transmission of video and audio information to a remote teleconferencing location. It is desired to only direct attention to speech and to ignore nonspeech such as the shuffling of feet or the moving of papers. Speech detection is implemented to allow the system to aim sensors only at talkers. Present detection methods depend upon energy levels and the pitch present in voiced sounds to detect speech. In a reverberant environment the accuracy of speech detection degrades. Speech detection accuracy in reverberation is tested. Measures of false acceptance of nonspeech signals and false rejection of speech signals are used to determine which speech detection methods are optimal in different reverberant rooms. Speech and nonspeech in reverberant rooms are simulated using impulse responses generated by CATT-Acoustic. The test environments range from anechoic to heavily reverberant. A look-back buffer and adaptive tracking of energy and zero-crossing levels are used to allow speech detection to work optimally with the current source location system.
Modeling stiffness in virtual bowed-string instruments
Authors: Serafin Stefania , Smith Julius O.
Published: July 2002

Physical models of bowed-string instruments have achieved a degree of completeness that enables understanding and simulation of most of the phenomena that appear in real instruments. Moreover, improvements in hardware technology and the development of efficient signal processing algorithms enable the implementation of these models in real-time platforms, including also improvements and refinements which were not possible before. One of these elements is the stiffness of strings, whose main effect is to disperse the sharp corners that characterize the ideal Helmholtz motion. In this paper, a method is proposed for estimating numerical filters that model dispersion in strings. The phase dispersion of the string is modeled using allpass filters whose coefficients are obtained by minimizing the L-infinity norm of the error between the internal loop phase and its approximation by this filter cascade. This algorithm, which turns out to be a nonlinear version of the Remez exchange algorithm, can successfully design filters of low order which are suitable for real-time implementation, and also accurate enough to model strings of different materials.
The effect of time-averaged velocity on boundary layer species separation
Authors: Waxler Roger
Published: July 2002

Recently, Swift and Spoor observed acoustically induced separation of the components of a gas mixture. To explain their observations, they developed a theory by estimating the second-order time-averaged mass fluxes of each component, assuming the second-order time-averaged velocity to be zero. Here, the effect of the second-order time-averaged velocity is estimated.
Neural substrates for presbycusis: Anatomy, chemistry, and neuroimaging of the central auditory system
Authors: Frisina Robert D.
Published: July 2002

Overall, loss of hearing with age involves at least two main components: Reductions in sensitivity to sounds, starting with the high frequencies, and a decline in the ability to understand speech in the presence of background noise. The former is intimately linked to the age-related loss of: sensory cells, stria vascularis metabolic activity, and auditory-nerve fibers. The latter is affected by these peripheral changes, as well as by the pathologies of the central auditory system that occur with age. Recent findings concerning age-related plasticity in the structure, chemistry, and functional anatomy of the central auditory system will be presented to shed light on changes in the brain that may underlie the physiological and perceptual deficits in the processing of biologically relevant sounds presented by the other speakers of this session. Some changes include: declines in central auditory pathway connectivity, changes in the presence of calcium-binding proteins critical for intracellular calcium regulation and optimal neural functioning, reductions in GABA neurochemistry at the midbrain level, and changes in activity of the human brain during the processing of speech in background noise as seen in PET imaging experiments. [Work suported by NIA–NIH, and the International Center for Hearing & Speech Research, Rochester, NY.]
Measurement of the backscatter from two pressure-release spheres using a near-field measurement system
Authors: Logan Thomas , Prasse Brian , Rogers Peter
Published: July 2002

The backscattering of sound by two pressure-release spheres was studied using a near-field measurement system (NFMS) based upon the near-field calibration array (NFCA) concept developed by Trott and Van Buren. The NFMS consists of a planar near-field transmit array (NFTA) consisting of 34 real-shaded line elements comprised of 26 hydrophones and a synthetic cylindrical aperture near-field receive array (SA-NFRA) consisting of a single line element comprised of 26 hydrophones. The line elements of the NFTA were shaded to obtain a volume of plane wave uniformity of 1 m3 in front of the NFTA. The synthetic aperture was formed by moving the single line element with a precision positioning system. The total acoustic pressure field was measured by the SA-NFRA. Since the incident pressure and the scattered overlapped in the time domain, background subtraction was used to obtain the scattered pressure. Far-field scattered beam patterns for the SA-NFRA were formed using the NFCA concept to extrapolate near-field measurements to the far field. Three configurations of pressure-release spheres were studied: a single sphere, two spheres arranged perpendicularly to incident field, and two spheres arranged parallel to the incident field. Experimental and numerical model results will be presented as well as NFTA uniformity measurements.
Lumped-element analysis of a fluid-loaded pipe-hull coupling
Authors: Caspall Jayme J. , Yoda Minami , Rogers Peter H.
Published: July 2002

This research addresses the question: how much acoustic energy is coupled into the fluid and the structure at the end of a fluid-filled pipe connected to an externally fluid-loaded shell? As a first approximation, the hull is modeled as a flat elastic plate with an infinite acoustic medium on one side and a vacuum on the other side. The pipe is modeled as a lumped mass with finite rotational inertia attached to the hull and founded on imaginary fixed points by torsional and linear springs. Energy transmission through the simple structure to the far field is examined by allowing one of the fixed foundation points to move while applying a force at that point. The radiated acoustic power is calculated as a function of frequency. The effect of the simple structure on the radiated power spectrum is determined by comparing the results to the response of a point driven plate. [This work was supported by the ONR Structural Acoustics Program under Grant No. N00014-98-1-0851.]
Development of pitch perception and memory of general psychological abilities in children speaking tonal languages. A comparative approach
Authors: Castro-Sierra Eduardo , Romero-Garibay Dinorah , Gomez-Gama Marha
Published: July 2002

The development of pitch perception and memory in language and music among 6- to 15-year-old Otomi-speaking children of either sex and Zapotec-speaking children of the same age and of either sex was studied. These languages are characterized by the use of lexical tones. For the analysis of musical abilities, Bentley’s Tests of Pitch Discrimination and of Tonal Memory were employed; for that of language abilities, special tests were devised that measured the perception and memory of tonal changes in either Otomi or Zapotec words. Results showed that development of abilities in music in Otomi-speaking children followed a course that was parallel to, although significantly below, that obtained by Bentley in his original study of 1966 in England. In the Otomi-speaking group, the course of development of abilities in language was above that of those in music. On the other hand, the same tests in Zapotec-speaking children provided data that were very irregular and further below the average obtained by the Otomi-speaking children. Interestingly, the application of Raven’s Progressive Matrices and Koppitz’s Test of Human Figure Drawings to these two groups of subjects indicated that, generally, Zapotec-speaking children had a higher cognitive level than Otomi-speaking children. [Work supported by Fondo de Neurologia, Hospital Infantil de Mexico.]
Coarticulation and stress across word boundaries in Russian
Authors: McCoy Priscilla
Published: July 2002

There is a rule in Russian phonology that can be stated as follows: /i/ > [-i] / C——. [/i/ is realized as [-i] (barred i) in the environment after a nonpalatalized consonant.] This rule holds true word internally (e.g., prefixation), at prepositional boundaries, but shows significant variation across word boundaries, particularly when stress and timing are considered. Phrases focusing on two-word sequences were recorded by six speakers, where the timing of the phrases was varied by fast or careful speech. The constituent structure of these phrases is illustrated below ( . - slight pause). (A) Stressed V1: 1. Eto moj brat ‘‘Igor.’’ This my brother Igor. fast –[t-i]; careful –[t.i] 2. Vot idet ‘‘Ira.’’ There goes Ira. fast –[t-i]; careful –[t.i] . (B) Stressed V2: 3. brat Iv‘ana brother of Ivan fast –[t-i]; careful –[t-i]. (4) idet Ir‘ina goes Irina fast –[t-i]; careful –[t-i]. Formants of [i] versus [-i] were measured to examine coarticulation, as evidenced by a barred i in the phonetic realization of /i/. Results showed that (A) stressed V1 of the final word has no coarticulatory effects in careful speech, whereas (B) stressed V2 adhered to the rule.
Fast, nonperturbative, transmission inverse scattering, quantitative imaging with laboratory and simulated acoustic data
Authors: Johnson Steven A. , Borup David T. , Wiskin James W. , Berggren Michael J. , Guillerum Thierry , Olsen Scott C.
Published: July 2002

Inverse scattering provides an ultimate method for acoustic imaging for medical and other fields of application (because it is quantitative and is self-correcting for refraction, absorption, and diffraction artifacts). E. Wolf showed that, with plane wave incident excitation, spatial distributions of inhomogeneous acoustic speed of sound and absorption within bodies could be reconstructed under the Born approximation by use of a simple back propagation algorithm operating in spatial frequency space (k-space). This approach, as extended to include the Rytov approximation and/or to real-space, is known as ‘‘diffraction tomography’’ (DT). However, DT fails at frequencies above 1 MHz, for objects with the size and contrast of the human female breast. We have extended DT by replacing its approximate wave equations with an exact wave equation. We present for the first time images of laboratory objects (agar cylinders, excised tissue, etc.) made by inverting transmission data. Present algorithms are at the boundary of real time operations or for 3D imaging with PC level computer networks. We discuss problems characteristic of inverse scattering such as multiple minima solutions and the need for receiver and transmitter element beam patterns. Input of these images for computer aided diagnosis is discussed.
Travel time bias in 2D modeling of 3D sound propagation
Authors: Godin Oleg A.
Published: July 2002

Limitations of the available mathematical models and/or computational resources often require invoking the so-called uncoupled azimuth approximation and substituting the 3D problem of sound propagation in horizontally inhomogeneous ocean by a set of 2D problems. In this paper, it is demonstrated that such approximation leads to a systematic error in ray and mode travel times. True travel times of ray arrivals as well as phases of cw adiabatic normal modes are less than those predicted within the uncoupled azimuth approximation. The travel time bias and its dependence on environmental gradients and propagation range are studied for random and deterministic inhomogeneities and evaluated under conditions of recent experiments in deep and shallow water. A simple criterion is suggested that allows one to assess applicability of the uncoupled-azimuth approximation for given environmental conditions and propagation geometry, without performing 3D propagation modeling. Moreover, explicit corrections to modal travel times and amplitudes due to horizontal refraction are derived in terms of range-averaged cross-range environmental gradients that enable a significant extension of the domain of validity of the 2D modeling of the acoustic fields in the horizontally inhomogeneous waveguide. [Work supported by NRC.]
Sound system and acoustic design for arena-sized performance venues
Authors: Janssen Craig
Published: July 2002

The rapid rise of ‘‘mega’’ churches in the USA over the last decade has led to the construction of numerous arena-sized church auditoriums seating over 7000 people. The programmatic usage of these spaces generates inherent design conflicts between the need for acoustics to support congregational singing, while at the same time supporting high-power concert quality sound reinforcement. These design challenges have precipitated the development of new design approaches for both room acoustics and the sound reinforcement system. A case study of a 7200-seat church will be presented to illustrate these core design approaches and techniques. The presentation will include discussion of specular versus reverberant field intelligibility predictions, the usefulness or lack of usefulness of early reflections, loudspeaker system design options, creation of a useful left, center, right loudspeaker system, and other related issues.
Acoustics of political conventions—A review
Authors: Randorff Jack E.
Published: July 2002

The acoustical challenges encountered in recent political conventions is reviewed. Examples are drawn from The 1992 Republican National Convention in the Astrodome in Houston, The 1996 Republican National Convention in the San Diego Convention Center, and the siting study prepared for The 2000 Republican National Convention scheduled for Philadelphia. The acoustical needs of the delegates and the broadcast audience are discussed. The technical performance requirements of convention sound reinforcement and media network broadcast feed are outlined. The necessary technical and performance tradeoffs are enumerated with respect to the physical constraints, schedule requirements, budget limitations, and planning committee expectations.
Acoustocyclone filter concept for soot retention in automotive diesel engines
Authors: Hoffmann Thomas L.
Published: July 2002

Fine-particle soot emissions are an intrinsic problem of diesel-powered vehicles. A number of car manufacturers have already begun marketing diesel vehicles with particle emission control equipment in an effort to address the problem. While technical solutions exist to reduce the number of fine diesel exhaust particles, these systems tend to be bulky and poorly resistant to high mechanical stresses and high temperature operation. Filters tend to get blocked, causing unwanted pressure increases in the exhaust line and an eventual loss of engine power and fuel efficiency. The concept study presented here focuses on a compact particle retention device that will generate only a small pressure drop, while efficiently filtering fine and coarse particle exhaust emissions. Based on a technology developed for coal-fired power plants, the new filtration unit will make use of a two-stage collection system consisting of a conventional cyclone and an acoustic aerosol agglomerator. The approach will build on the concept of aerosol preconditioning to improve the retention efficiency of a conventional cyclone. This improvement will be achieved through initial agglomeration of the fine particles with larger soot particulates, and subsequent filtration of the preconditioned aerosol in a cyclone collector.
Perception of shape and material from contact sounds
Authors: Pai Dinesh K. , Klatzky Roberta L. , Krotkov Eric P.
Published: July 2002

The perception of sources of percussive sounds, as a function of variables that govern sound synthesis, was investigated. In the first set of experiments, perception of the source’s material was investigated. Two types of experiments were conducted. In the first, subjects judged similarity with respect to material and length. The sounds corresponded to modal vibrations of struck clamped bars. They varied in fundamental frequency and frequency-dependent rate of decay. Differences between sounds in both decay and frequency affected similarity judgments, with decay playing a substantially larger role. In the second type of experiment, subjects assigned sounds to one of four material categories. Decay parameters for each category were estimated and found to correlate with measurements reported in the literature. The second set of experiments investigated perception of contact location on the object. Subjects were presented with pairs of sounds produced by striking a string at two locations. Two strings with different fundamental frequencies were used. In one experiment, subjects judged the distance between the strike points, and in another, judged which point was closer to the point of attachment. The results confirm that subjects are sensitive to the interstrike distance and can judge which point is closer.
Experimental instability study in a thermoacoustic prime-mover
Authors: Bretagne Emmanuel , François Maurice-Xavier , Delbende Ivan
Published: July 2002

First, the stability properties of a linear thermoacoustic prime-mover are determined experimentally. For different values of the mean pressure between 0.5 and 10 bars, the damping rate is carefully obtained as a function of the temperature gradient |∇T| enforced along the stack, up to the instability onset at |∇T|c. These results are then confronted with the predictions of a numerical model based on Rott’s theory used with complex frequencies, in which the prime-mover is seen as a feedback loop in the electrical analogy. The experimental results are found to comply with Rott’s theory as soon as the mean pressure exceeds 2 bars. Below this value, which pertains to the merging of facing stack boundary layers, substantial discrepancies are found, as confirmed by the work of Yazaki. Second, the saturated wave amplitude has been measured as a function of |∇T|−|∇T|c for fixed pressure above the instability onset. The bifurcation to the nonlinear saturated wave may be subcritical, although thermal inertia effects make it look supercritical.
Quantifying the influence of dynamic intensity on changes in pitch
Authors: Neuhoff John G.
Published: July 2002

Previous work has shown that dynamic continuous changes in intensity can influence judgments of pitch change in ways that are not predicted by classic equal-pitch contours derived with static stimuli. Rising intensity can elicit judgments of rising intensity even at frequencies where static increases in intensity yield judgments of lower pitch [J. G. Neuhoff and M. K. McBeath, J. Exp. Psychol. Human Percept. Perform. 22 (1996)]. However, the effects thus far have been measured in arbitrary perceptual units. Thus, we know relatively little about the absolute amount that one dimension influences the other in physical terms. In the current work, listeners heard tones that were simultaneously modulated in both frequency and amplitude at the same rate (2 Hz). When frequency and amplitude modulation were in phase, frequency was judged to change more than when frequency and amplitude modulation were 180 degrees out of phase. To quantify the effect in physical terms, pitch change in the experimental trials was compared to a control condition in which tones were only frequency modulated. The findings have implications for sonification and auditory display as well as structural modeling of pitch and loudness. [Work supported by NSF Grant No. 9905266.]
Methods for calculating the response of structures to inhomogeneous turbulent flows
Authors: Glegg Stewart , Devenport William
Published: July 2002

Problems involving the response of structures to turbulent flows are usually modeled using a linear approach. The incoming turbulence is described using a Von Karman or Liepmann spectrum using typical turbulence velocity and length scales. However, these models only apply to homogeneous turbulence and so inhomogeneous flows can only be treated in an approximate manner. This paper will describe an alternative approach in which the turbulent flow is decomposed into a set of uncorrelated modes using proper orthogonal decomposition. The response of the structure to each mode can then be considered independently and the results summed incoherently to give the complete response. However, to obtain the proper orthogonal modes the flow must be measured in great detail. It will be shown that this requirement can be reduced if measurements are limited to the most energetic parts of the flow.
Noise generated from a flexible and elastically supported structure subject to turbulent boundary layer flow excitation
Authors: Allen Michael J. , Vlahopoulos Nickolas
Published: July 2002

A numerical methodology based on the finite-element and boundary-element methods is presented for computing the noise radiated from a structure subject to boundary layer excitation. The new algorithm utilizes the fluctuating wall pressure in order to define the excitation on the structural acoustic system. The developments target wind-noise prediction for the sound radiated by the side glass window of an automobile. The glass-seal assembly is modeled as a flexible plate mounted on a foundation with stiffness and damping characteristics. Numerical predictions are compared successfully to wind-tunnel test data. Parametric analyses are performed in order to identify the characteristics of the seal that can lead to noise reduction. [Work supported by Ford Motor Co.]
A probabilistic particle view of a propagating pulse
Authors: Cohen Leon
Published: July 2002

When time-frequency analysis is applied to a dispersive propagating pulse an interesting view is obtained. We will show how the Gram/Charlier/Edgeworth of standard probability theory can be generalized to time-frequency distributions and applied to study pulse propagation. Explicit expressions are given for the evolution of the pulse which appear to be more accurate than the standard asymptotic approximation, at least that is the case for some exactly solvable problems. Also, explicit expressions are given for the low order conditional moments and the spread of a pulse and we show that a very simple probabilistic particle model emerges that explains these results.
When wavelet/scale processing is useful
Authors: Young Randy K.
Published: July 2002

‘‘When wavelet/scale processing is useful’’ identifies specific acoustical problems where these tools is beneficial. The emphasis is on time-varying linear system modeling with a wavelet domain system representation. Systems that involve motion are emphasized. Both acoustic scattering and transmission problems will be presented and the unique features offered by wavelet/scale processing will be demonstrated. Time-frequency and wavelet/scale processing will be compared.
Effect of transverse solitons on acoustic transmission
Authors: Houk Gareth M. , Wolf Stephen N. , Badiey Mohsen
Published: July 2002

Effects of solitary internal waves (solitons) on acoustic signals propagating transversely to the solitons were studied by transmitting 60- to 200-Hz LFM pulses along a 15-km path in shallow ocean water during periods of high and low internal wave activity. The data were collected as part of the SWARM95 experiment on the New Jersey continental shelf. Acoustic normal-mode analysis reveals amplitude fluctuations in the received acoustic modes in the presence of a series of transverse internal waves. Contemporaneous measurements without transverse solitons lack such fluctuations. The acoustic environment and internal wave field were modeled using data from thermistors, CTDs, a high-frequency acoustic flow visualization system, and ship-borne radar images. Theoretical studies [J. C. Preisig and T. F. Duda, IEEE J. Ocean Eng. 22(2), 256–269 (1997)] predict that 2D range- and depth-dependent models are insufficient to describe the mode amplitudes for acoustic scattering by highly transverse waves. In order to test this prediction, the data are compared to 2D and 3D parabolic equation solutions in data-driven simulated environments. [Work supported by ONR.]
Shallow-water acoustic propagation experiments in the Florida Straits—Sensor installation and environmental data
Authors: Williams Neil J. , DeFerrari Harry A. , Nguyen Hien B. , Venezia William A.
Published: July 2002

Measurements of shallow-water acoustic transmissions from a moored acoustic projector to a fixed triaxial array of acoustic hydrophones have begun off the southern coast of Florida in 145 m of water. The projector transmits M-sequence coded signals at frequencies ranging from 100 to 3200 Hz. Source-to-receiver ranges from 10 to 100 km in 10-km steps are planned. The receiving array is powered from shore and linked via a fiber-optic cable. It contains two 500-m-long sections deployed on the bottom and a third moored vertically with a pressure sensor to monitor hydrophone depth. Each section contains 32 hydrophones spaced in a nonlinear distribution to facilitate acoustic coherence measurements. Linux computers control the projectors and process data from the arrays. The computers can be accessed via TCP/IP connections and programmed from shore. Two environmental monitor moorings were deployed along the path from source to receiver. They contain arrays of temperature, conductivity-temperature, and temperature-pressure recorders. An extensive set of CTD casts was also made. Detailed geophysical measurements are planned for the spring—including cores and high-resolution bottom and sub-bottom profiling. A companion paper will discuss the acoustic data collected and preliminary results. [Work supported by ONR.]
Shallow-water acoustic propagation experiments in the Florida Straits—preliminary results
Authors: DeFerrari Harry , Williams Neil , Nguyen Hien , Venesia William
Published: July 2002

Acoustic propagation experiments have begun on a newly developed shallow-water range off the south Florida coast. The measurements are concerned with fluctuations and coherence of signal and reverberation fields for ranges out to 100 km and for frequencies from 100 to 3200 Hz. The centerpiece of the experimental site is a set of three receiver arrays, two horizontal, 500 m in length, and one vertical array that is suspended in 148 m of water. A total of 96 hydrophones are processed in situ and data are transmitted to a shore station via fiber optics cable. The arrays are used to receive transmissions from a multifrequency moored source that transmits broadband M-sequences at each of six center frequencies from 100 to 3200 Hz. A first source deployment at a range of 10 km is complete and data were collected continuously for 28 days along with detailed measurements of sound-speed profile, bathymetry, and geoacoustic properties of the bottom and sub-bottom along the propagation path. Subsequent source moorings at longer ranges are underway. Results from the 32-element vertical array are presented here and compared with model predictions. Coherence and fluctuations of the signal and reverberation fields are computed and discussed. [Work supported by ONR.]
Acoustical design of learning spaces
Authors: Tan Paul
Published: July 2002

Learning spaces in the past 100 years have evolved from chalkboards and printed media to real-time digital distant learning centers equipped with the latest in communications and multimedia technologies. As a result, the modern learning space bears little semblance with its archetypal shoe-box classroom most are accustomed to. What are the criteria for designing a fully integrated learning environment, wherein human factors and technological systems function symbiotically within a carefully optimized space? This paper will seek to explore the impact of room acoustics, sound isolation, building systems, and equipment noise on the functionality and success of the modern learning environment through selected design cases.