bluuebunny/crossref_metadata_2025 huggingface dataset:
Synchronization of musical sound and visual images: Issues of empirical and practical significance in multimedia development
Authors: Lipscomb Scott D.
Published: July 2002

In recent years, there has been a significant number of investigations into the interaction between auditory and visual systems in a multi-modal context, e.g., film, animation, and multimedia software. The author will report results of his own research, confirming a subject preference for alignment of audio-visual (AV) accent structures, i.e., combinations resulting in perceived AV synchronization. A revised version of a model of Film Music Perception [Lipscomb and Kendall (1994)] will be presented, explicating a dynamic relationship between stimulus complexity and significance of AV synchronization in the determination of subject preference ratings. Using these findings as a starting point, the author will illustrate the practical importance of musical sound and its temporal placement within a multimedia context. Multimedia software and technologically enhanced course materials created by the author will provide examples of the effect of combining musical sound and visual images. The presentation will illustrate that the combinatorial effect of such multimedia presentations far surpasses the effect of either auditory or visual stimuli in isolation, resulting in an improved aesthetic experience for the audience and an enhanced learning environment for the student.
Update on the structureborne noise standard structures
Authors: Carroll Gerard , Cuschieri Joseph M. , Burroughs Courtney B.
Published: July 2002

In 1994 the authors, along with a number of interested parties, established a set of structures of increasing complexity intended to be used as standards for investigating structureborne noise prediction techniques. The structures are: a T-beam, a ribbed panel and an acoustic enclosure. This activity was jointly sponsored by Technical Committees of the Institute of Noise Control Engineers (Prediction and Modeling) and the Acoustical Society of America (Structural Acoustics and Vibration). With the assistance of funding from the Structural Acoustics Branch of the NASA Langley Research Center, these structures have been built and experimentally characterized by various interested parties with the intention of providing a baseline check for the various analytical methods. This paper will introduce the structures and present the results which have been obtained thus far in this investigation, thereby creating the framework for viewing the more recent work to be presented by other authors within this session.
Finite-element predictions and experimental measurements of aircraft fuselage panel dynamic response
Authors: Buehrle Ralph D. , Fleming Gary A.
Published: July 2002

Results from an analytical and experimental study of the dynamic response of an aircraft fuselage panel are presented. The ability to predict the dynamic response of a complex stiffened panel into the kilohertz region using finite-element methods is examined. Beam and plate element models of the stiffeners are evaluated with numerous mechanisms for attaching the stiffeners to the plate elements representing the panel skin. The analytical models are validated with an extensive database of Scanning Laser Doppler Vibrometer (SLDV) data acquired by the Naval Research Laboratory and Electro-Optic Holography (EOH) measurements. For both measurement techniques, forced response data were acquired with soft springs supporting the panel to simulate free–free boundary conditions. The analytical results were obtained from a normal mode analysis of the various panel finite element models with free–free boundary conditions. The finite element models are described and comparisons between the analytical and experimental results are presented.
Perceptual learning of synthetic speech
Authors: Francis Alexander L. , Nusbaum Howard C.
Published: July 2002

Over the course of a lifetime, listeners are likely to encounter many unfamiliar talkers speaking the listeners’ native language. Despite the fact that talkers may differ radically in the way they sound, listeners normally learn to understand the novel speech patterns of unfamiliar talkers without difficulty. Part of learning to understand an unfamiliar talker speaking a familiar language is learning to relate novel acoustic patterns in the unfamiliar speech to existing mental representations of familiar phonetic categories. This process has frequently been described in terms of modifying an existing psychological ‘‘space’’ of mental representations by shifting the focus or weight of attention to linguistically useful aspects of the speech signal. In the experiment reported here, native English listeners were trained to better understand an unfamiliar talker—a computer speech synthesizer. Training to recognize and transcribe English words resulted in a significant increase in listeners’ abilities to understand words and to identify consonants. Training also strongly influenced the distribution of attention to particular features of the speech signal, as indicated by changes in listeners’ judgments of the similarity of consonants after training. Implications for theories of perceptual learning and phonetic categorization will be discussed.
Perception of English vowels by native speakers of Japanese
Authors: Nozawa Takeshi
Published: July 2002

Japanese children and adults living in the United States took the English Vowel Perception Test. Fourteen vowel contrasts were chosen. All the subjects heard the digitized stimuli through headphones, which were tokens of English vowels spoken by multiple talkers. American children and adults also took part in this experiment as control groups. A′ scores were computed for each vowel contrast. A′ scores for Japnese subjects were significantly lower in all contrasts but one (/i/ vs /ε/), and for Japanese subjects significant difference in A′ scores among vowel contrasts were found. It was expected that Japanese children would do it better than adults, but their A′ scores were no better than adult Japanese. Since American children did as well as American adults, the poor performance of those Japanese children was not attributed to the experiment design. To see if and how the exposure to English changed those Japanese subjects’ perception of English vowels, Japanese teenagers who had never lived out of Japan were brought in. Though some subjects were exceptionally good, no significant difference was observed in A′ scores between Japanese living in the United States and those who study English in Japan.
Comparison of transmission loss for underwater sound pulses measured using matched filters and integrated received power
Authors: Hutt Daniel , Theriault James
Published: July 2002

Transmission loss (TL) may be found from the amplitude of a matched filter correlation applied to a pulsed acoustical signal. Use of matched filters to determine TL is advantageous because the technique can be applied continuously in real time without previously determining the pulse arrival time. However, distortion of the transmitted waveform by scattering, multiple path propagation, and Doppler frequency shift reduces the amplitude of the matched filter output thus increasing the TL determined in this way. The conventional TL calculation involves filtering the signal and integrating the received power for the duration of the pulse which yields a TL based on total received energy. This method must be applied after data is collected because the time of arrival of the pulses must first be determined. TL measurements derived using both methods were compared for data gathered during two trials in the Gulf of Mexico in both shallow and deep water environments. The transmitted waveforms were linear frequency-modulated pulses with a frequency range of 10 Hz, centered at 1055, 1225, and 1395 Hz. Results of the comparison will be presented.
Large-signal characterization of prestressed PMN-PT-Ba and PMN-PT-Sr at various temperatures
Authors: McLaughlin Elizabeth A. , Janus Robert S. , Gittings Kim D. , Ewart Lynn
Published: July 2002

Quasistatic (10-Hz) electromechanical measurements were made of two relaxor ferroelectrics, PMN–PT–Ba (90 mol% lead-magnesium-niobate, 10 mol% lead-titanate, doped with 3% barium) and PMN–PT–Sr (88 mol% lead-magnesium-niobate, 10 mol% lead-titanate, 2 mol% strontium, w/2500 ppm iron oxide) under high electric fields (0–1.5 MV/m) and high mechanical prestresses (0–41.4 MPa) over a temperature range (−5–40 °C). The measured quantities—the piezoelectric constant, d33, the permittivity, ε33T the Young’s modulus, Y33E the electromechanical coupling factor, k33, and the energy density, U—are found for both small and large ac signal conditions. These measurement conditions and material properties are of great interest for applications in high-power Navy sonar transducers to material manufacturers. Material property trends with increasing prestress, temperature, and electric field are identifieid. The PMN–PT–Sr is shown to have better properties for sonar transducers than the PMN–PT–Ba. Compared to Navy type-III PZT piezoelectric ceramic, the energy density of PMN–PT–Sr at 5°C and 41.4 MPa is nearly 11 dB higher and the coupling 23% lower.
Optimization of fiber optic acoustic transduction for neutrally buoyant accelerometers
Authors: Brown David A. , Arinov Boris , Reinhart Lawrence , Cheng Lan , Jim Hardiman
Published: July 2002

It is desirable to maximize both the sensitivity and bandwidth of fiber optic accelerometers used for acoustic motion, accelerometer, and pressure-gradient sensor applications. Designs and figures-of-merit for centrally and peripherally supported flexural disks and compressional type accelerometers will be presented and compared. The optimization of optical fiber coils, coating diameter, materials properties, and packaging will also be discussed. [Work supported by ONR, NUWC, and the UMass Dartmouth Ph.D. Program.]
Matched field processing photoacoustic signals to localize small gas leaks
Authors: Yönak Serdar H. , Dowling David R.
Published: July 2002

Leaks from devices that are filled with pressurized gases and liquids are not only costly to consumers and manufacturers but may also be harmful to the environment. Detecting these leaks and determining their location is a critical process. Previous results have shown that a gas leak small enough to fill a thimble in 5 days could be detected and localized by using photoacoustic signals, two microphones, and Bartlett matched field processing. The present work considers the impact of using the broadband characteristics of the photoacoustic source, adaptive matched field processors, and four microphones. Photoacoustic sound is generated by rapidly scanning a carbon dioxide laser tuned to 10.6 μ over the suspected leak area. Sulfur hexafluoride is the tracer gas. A comparison is made between two-microphone and four-microphone results. Advantages and disadvantages of the adaptive matched field processors when compared to the Bartlett processor for the problem at hand are discussed. Leak location uncertainty due to microphone directivity and microphone placement error is also discussed. Experimental results are presented. [Sponsored by Ford Motor Company.]
Underwater measurements and modeling of a sonic boom
Authors: Desharnais Francine , Chapman David M. F.
Published: July 2002

During a sea trial on the Scotian Shelf, acoustic signals from a sonic boom were recorded on several hydrophones of a vertical array. The array spanned the lower 50 m of the water column above a sand bank at 75-m water depth. The source of the sonic boom was deduced to be a Concorde supersonic airliner traveling at about Mach 2. The water-borne waveform was observed to decay as an evanescent wave below the sea surface, as expected. The very calm weather resulted in low ambient noise and low self-noise at the hydrophones, resulting in good signal-to-noise ratio on the upper hydrophones; however, the decreased signal amplitude is more difficult to detect towards the lower part of the water column. The period of the observed waveform is of the order 0.25 s, corresponding to a peak frequency of about 4 Hz. The shape of the measured waveform differs slightly from the theoretical N-shape waveform predicted with Sawyers theory [J. Acoust. Soc. Am. 44, 523–524 (1968)]. A simple shallow ocean geoacoustic model suggests that this effect may be caused by seismo-acoustic interaction of the infrasonic waves with the elastic sediments that form the seabed.
SR-71 sonic boom propagation experiment
Authors: Haering Edward A. , Ehernberger L. J. , Murray James E.
Published: July 2002

SR-71 sonic boom signatures were measured to validate sonic boom propagation prediction codes in support of the High Speed Research Program. An SR-71 aircraft generated sonic booms from Mach 1.25 to Mach 1.6, at altitudes of 31 000–48 000 ft, and at various gross weights. An F-16XL aircraft measured the SR-71 near-field shock waves from close to the aircraft to more than 8000 ft below, gathering 105 signatures. A YO-3A aircraft measured the SR-71 sonic booms from 21 000–38 000 ft below, recording 17 passes, including booms reflected off the ground. Three types of ground sensors were deployed to three station locations near the aircraft ground track, recording 172 signatures. Signatures of the F-16XL were also gathered. Atmospheric data were recorded for each flight. These results show that shock wave patterns and coalescence vary with SR-71 gross weight, Mach number, and altitude. This paper describes the design and execution of the flight research experiment, including instrumentation and flight maneuvers of the three aircraft. A guide to the entire digital database of sonic boom signatures, flight conditions, and atmospheric properties is included.
Sonic boom environmental impact prediction methods and issues
Authors: Garrelick Joel , Martini Kyle , Ting Carina
Published: July 2002

Concerns over the environmental impact of sonic booms include their effect on humans, other animals, and fabricated structures. Over the past few years, CAA has been involved in a number of projects focusing on the latter two concerns. Specifically, working with Hubbs Sea World to supplement previous empirical studies, an analytical model was developed for estimating the sonic boom induced response of fertilized tern eggs and evaluated the potential for damage. Working with Wyle Laboratories, Inc., both direct and reciprocal structural-acoustic testing techniques were developed for simulating structural responses in order to assess damage. These methods were validated by comparison with data from actual flyovers. Curently, with Marine Acoustics, Inc., the authors are involved in a project to assess testing and other issues associated with predicting the subsea penetration of sonic booms for assessing marine mammal impacts. Here at issue are those physical processes that may transform from second to first order in light of the evanescent attenuation of the typically subsonic, ‘‘primary’’ acoustic wave that penetrates to depth. These three projects are reviewed in this talk. Particular attention is given to idealizations in the prediction process, the associated uncertainties, and their effects on the overall impact evaluation process. [Work supported by The Armstrong Laboratory of The U.S. Air Force.]
Generation and measurement of laboratory scale focused sonic booms
Authors: Welle Richard P. , Kwok Munson A.
Published: July 2002

Development of an accurate modeling code for rocket-generated, focused sonic booms requires experimental verification. Opportunities to make field measurements of shock waves from rocket launches are rare and unpredictable because of launch delays and last minute trajectory modifications. Laboratory simulations of accelerated supersonic trajectories have been hampered by the difficulty of accelerating laboratory scale projectiles in supersonic flight. This difficulty can be overcome by using acoustic reflectors with constant speed projectiles to create virtual projectiles with accelerated trajectories. A supersonic projectile, such as a bullet, moving past a curved acoustic reflector will generate shock waves which, after reflection, will appear to be coming from a bullet following a curved, accelerating trajectory. A simply curved reflector can shape the virtual trajectory of a M=1.2 projectile to closely simulate the portion of a typical rocket launch trajectory which generates a focused sonic boom incident on the surface. For proper scaling to full size vehicles, laboratory scale measurements require microphones with well-characterized frequency responses up to at least 1 MHz. The results obtained with a custom fabricated device based on an earlier design [E. P. Cornet, ARL-TR-72-40, Applied Research Laboratories, University of Texas (1972)] will be reported.
Simulation results of loudness-based active noise control
Authors: Sommerfeldt Scott D. , Samuels Timothy O.
Published: July 2002

For many active noise control applications, the desired result is to reduce the noise perceived by a human listener. Typical active noise control systems operate in a manner that reduces the sound pressure level at the location of one or more error sensors. However, it has been shown that decreasing the sound pressure level at a location does not guarantee a similar decrease in the perceived loudness at that location. In fact, in some cases it is possible to reduce the overall sound pressure level of a signal, but have the perceived loudness increase. In this work, the filtered-x algorithm that is commonly used for active noise control has been modified to incorporate the approximate response of the human auditory system. This was done to see if improved subjective results could be obtained when minimizing a signal that approximates the loudness rather than the sound pressure level. It has been found that the effectiveness of this technique is largely dependent upon the nature of the input noise signal, as well as on the number of coefficients used in the controller. Simulation results will be presented to illustrate where this technique may be useful.
Improved performance of output active structural acoustic control using collocated strain-based transducers
Authors: Vipperman Jeffrey S. , Clark Robert L.
Published: July 2002

A simple method of greatly improving performance of direct rate feedback (DRFB) control of piezostructures is presented. Piezostructures are not generally amenable to application of DRFB control since the compliance of the piezostructure generally increases with increasing frequency due to the structural differentiation performed by the transducers. Some improvement can be gained through selecting the width and position of the piezoceramic patch such that certain groups of modes will cancel from the response. However, a more drastic improvement is gained by increasing the size of the rectangular aperture to cover at least 50% of the structural demension(s). It is shown that the rectangular aperture of the piezoceramic acts as a low-pass filter with corner frequency inversely proportional to the transducer aperture size. Using a large aperture results in better coupling into lower-frequency modes targeted by the control system as well as decreased control effort. Analytical open and closed loop results for an acoustically radiating simply supported plate piezostructure are presented.
Electroelastic nonlinearities in piezoelectric transducers and their effect on vibratory energy transmission, transduction, and dissipation in structural systems
Authors: Royston Thomas J. , Lee Soon-Hong
Published: July 2002

Though all structural dynamic systems are inherently nonlinear, the majority of analyses are typically based on the assumption of linearity. While vibration of passive systems is often reasonably described by linear system theory, particularly in the audio and ultrasonic frequency ranges, the vibrations of systems employing integrated actuators fabricated from smart materials often are not, whether they be based on piezoelectric, electrostrictive, or magnetostrictive technologies, etc. Nonlinearities can affect the system performance through a loss of actuation authority, stability, and/or system functionality. Recognizing this, some researchers have included nonlinearities in their formulations for the constitutive equations of the smart material. Typical nonlinear operators are either in the form of higher-order polynomial expressions or various hysteresis operators involving the electrical (magnetic), elastic and/or electroelastic (magnetoelastic) relations. An important fundamental issue is how the different types of nonlinearities affect the smart material in its role as source, conduit, transformer and/or receiver/dissipator of vibroacoustic energy in a smart structure. This is the principle focus of this study in which a generic active vibration isolation application is considered. The effect of different types of nonlinearities with respect to how vibratory energy flows throughout the smart structural system is investigated. [Work supported by NSF.]
An auditory-feedback-based model of speech production in the developing child
Authors: Callan Daniel E. , Kent Raymond D. , Vorperian Houri K. , Guenther Frank H.
Published: July 2002

The purpose of this project is to demonstrate that self-produced auditory feedback is sufficient to train a mapping between auditory target space and articulatory reference space under conditions in which the structures of speech production are undergoing considerable developmental restructuring. One challenge for competing theories that propose invariant constriction targets is that it is unclear what teaching signal could specify constriction location and degree so that a mapping between constriction target space and articulatory reference space can be learned. It is predicted that a model trained by auditory feedback will accomplish speech goals, in auditory target space, by continuously learning to use different articulatory configurations to adapt to the changing acoustical properties of the vocal tract during development. The Maeda articulatory synthesis part of the DIVA neural network model [Guenther et al., Psych. Rev. (in press)] was modified to reflect the development of the vocal tract by using measurements taken from MR images of children. The model accurately produced English vowels during development using various auditory target spaces. Stable constriction patterns were maintained throughout development using differing articulatory configurations to accomplish the same speech goals demonstrating that auditory feedback is sufficient to accommodate speech production development. [Work supported by NIHCD.]
The integration of discriminative and maximum likelihood distance measures for a vowel articulation training aid
Authors: Zimmer A. Matthew , Zahorian Stephen A.
Published: July 2002

Improvements to the vowel articulation training aid described in a previous paper [Zimmer, Zahorian, and Auberg, J. Acoust. Soc. Am. 101, 3199(A) (1997)] have been made. The system uses a standard Windows 95/NT compatible sound card on a multimedia PC to provide continuous feedback about articulation for ten American English monopthong vowels in two modes: an F1/F2 style ‘‘ellipse’’ display and a vowel bargraph display. Neural network discriminative classifiers are used to produce the display outputs based on 12 features. Though testing showed that the system provided useful output for most voiced speech sounds, the network would classify some out-of-category sounds (e.g., nonvowel sounds, ambient noise) as belonging to one of the ten vowel categories. Experimental tests indicate that the inclusion of a generalized Euclidean distance measure to compare the feature values of an utterance with the average feature values for the vowel category specified by the neural network output help to greatly reduce the number of out-of-category sounds improperly classified as ‘‘correct’’ responses. The paper will describe the processing in more detail and summarize experimental results from vowel classification tests. [Funded by NSF, Grant No. NSF-BES-9411607.]
A review of diffusor design over the past two decades
Authors: D’Antonio Peter , Cox Trevor J.
Published: July 2002

In the later 1970s Manfred Schroeder suggested using number theory sequences to approximate uniform angular scattering. Today tens of thousands of these diffusors are in use in almost every type of architectural acoustic application. Schroeder’s work has been a catalyst, enabling the design of numerous new diffusor types. D’Antonio employed additive modulation, in the form of a self-similar fractal diffusor to minimize the lobing associated with periodic arraying and to extend the frequency bandwidth. Angus suggested multiplicative spread spectrum modulation and orthogonal modulation to minimize lobing. Angus has suggested binary reflection-absorption amplitude gratings, which D’Antonio has used for 2-D planar binary amplitude diffusors. Cox used numerical optimization and boundary element prediction techniques to optimize the performance of number-theory diffusors, stepped diffusors, curved and fractal shapes. Cox and D’Antonio are developing optimized aperiodic shapes to form aesthetically pleasing diffusing acoustical sculpture. Shape optimization has significantly expanded the choice of available diffusors. Today, diffusors can be designed for a specific appearance, specified scattering coverage, given source and receiver positions and a desired frequency bandwidth. All of these surfaces developed over the past two decades comprise an expanded palette of scattering surfaces. These complement contemporary architecture in the way that statuary and relief ornamentation blended with classical architecture.
Precision and accuracy estimation based on round robin field testing—A case history
Authors: Sachs Felix Z.
Published: July 2002

A standard method for field measurement of in-situ noise lacked precision and accuracy information. A relatively straightforward round robin test organizes to provide data brought to light several problems and considerations. The initial test objective was to select experienced participants, hand them the written standard measurement procedure and collate the results. Problems arose in noise source and background noise variation, procedure interpretation among participants, instrumentation usage, and in the procedure itself. After a retest the standard deviation among participants was 0.7 dB for A-weighted and 1.8–4.1 dB for individual octave bands. Considerations and lessons learned will be discussed including instrumentation (one set for all participants or separate sets), noise source monitoring for uniformity, reported statistical quantity, approaches for adjustments to variables held constant, data recording, and logistics. [The opinions or assertions contained herein are the views of the author and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.]
Influence of low-frequency content on rate of growth of annoyance of high-energy impulsive sounds
Authors: Fidell Sanford , Silvati Laura , Pearsons Karl S. , Howe Richard R. , Lind Stephen J.
Published: July 2002

Various ‘‘corrections’’ have been suggested to measures of high-energy impulsive sounds to account for their seemingly anomalous annoyance, some on the basis of the findings of studies that may not have accurately reproduced the low-frequency content of high-energy impulses. The present study measured rates of growth of annoyance of impulsive and nonimpulsive sounds by adaptive paired comparisons of the annoyance of five variable level signals and 29 impulsive and nonimpulsive fixed level signals. All test sounds were presented for judgment in a specially designed low-frequency test facility. When the annoyance of an aircraft flyover was compared to that of a low-frequency band of noise and of sonic booms accompanied by rattle, the relative rates of growth of annoyance were not much different from 1:1. When the annoyance of sonic booms that were not accompanied by rattle was compared with that of sounds containing more higher-frequency energy (an aircraft flyover and an octave band of noise centered at 1 kHz), the relative rates of growth of annoyance were nearly 2:1. These differences in relative rates of growth of annoyance of impulsive and nonimpulsive sounds are as plausibly attributed to their relative low-frequency content, as to impulsiveness per se.
Effect of plate vibration on sound absorption of the micro-perforated elastic plate
Authors: Tanaka Manabu , Takahashi Daiji
Published: July 2002

Perforated plates have long been used as sound absorbers, and many studies have been done on their acoustic characteristics. In these studies, the effect of plate vibration caused by the incident sound wave is neglected. This is reasonable for the perforated plate of ordinal design [D. Takahashi, Appl. Acoust. 51 (1997)]. However, if the ratio of perforation decreases, e.g., in case of the micro-perforated plate, the effect of plate vibration is considered to be distinct, because the flow resistance of the plate is relatively large in this case. In this study, a new theoretical model for predicting the acoustic characteristics of the micro-perforated elastic plate (MPEP) is presented. This model includes the effect of plate vibration caused by the pressure difference between both surfaces of the plate. Numerical experiments are also carried out with this model. From the results, it may be said that the plate vibration occurs when the surface porosity of the perforated plate is roughly under 1%. This model can be applied to the perforated plates of any flow resistance, i.e., from the ordinarily perforated plate to nonperforated plate throughout.
Toward a global in situ method for materials acoustic impedance assessment at very low frequencies using evolution strategy
Authors: Dutilleux Guillaume J. A. , Kristiansen U. R.
Published: July 2002

As the current in situ absorption measurement methods are both local and based on time-domain processing, the time-frequency uncertainty relationship limits their ability to measure at low frequencies, leaving the building engineer with an uncovered frequency range. The complementary approach proposed here is to work in the frequency domain instead and to consider the measurement problem as an inverse and optimization one. A critical assumption for practicality is that very few measurement points should be necessary to define the pressure field without ambiguity. As the optimization problem is clearly not local, a global algorithm is necessary in combination with a forward model of the room giving the pressure field from the boundary conditions. A numerical study is given concerning a 2-D rectangular room modeled by the finite-difference method. Each wall has a specific impedance. An evolution strategy is used as a global optimization tool, both alone and in combination with a local search method, to find the boundary conditions of an imaginary room. Good results are obtained over the 100–250-Hz frequency range, with only as many measurement points as unknown variables.
A refined room acoustical simulation algorithm based on free path distribution
Authors: Schmitz Oliver
Published: July 2002

Eyring’s or Sabine’s formula gives good results in rooms with a diffuse field. However, when long, flat, or coupled rooms, for example, are investigated, these formulas do not describe the decay correctly. The error has its reason in the assumption of an exponential decay with just one exponential coefficient calculated from the mean free path length and an averaged absorption coefficient. A new approach to calculate decay curves and reverberation time, already introduced by Vorländer [‘‘A fast room acoustical algorithm based on free path distribution’’ ICA 98] has been further refined. This method uses statistical results obtained by a short ray-tracing simulation. Free path length and absorption coefficient are statistically recorded for each reflection during this simulation. The recorded data represent the geometry of the room under investigation. In the next step several processes, each defined by an exponential function, are generated using this information, which are superposed to give a better approximation for the decay curve of the room. Some additional steps must be introduced to these processes to give reasonable results. This lecture will present the refined algorithm and some results.
Nonlinear saturation of thermoacoustic instability
Authors: Karpov Sergey , Prosperetti Andrea
Published: July 2002

In earlier work [Watanabe et al., J. Acoust. Soc. Am. 102, 3484–3496 (1997)] a quasi-one-dimensional nonlinear model for thermoacoustic devices was developed. The model reduces exactly to the well-known Rott theory upon linearization, but numerical work has shown that it is also able to predict nonlinear features in agreement with experiment. In this work, a weakly nonlinear analysis of the model is carried out for conditions close to the linear stability threshold. The level at which the amplitude of the linearly unstable perturbation is predicted to saturate compares favorably with numerical calculations and experiment. On the basis of the result, the effect of several design variables such as nonuniformity of the resonator cross section, stack plate spacing, and others is explored. [Work supported by the Office of Naval Research.]
Sound radiation from a line forced perforated elastic sandwich panel
Authors: Abrahams I. David
Published: July 2002

Composite barriers, consisting of thin plates separated by light matrix structures, are widely used for fuselage construction in the aircraft industry, and in partitions in the building trade. The acoustical properties of such materials can vary considerably by altering the interior geometry, and perforations can be added to one or both sides. With perforations the interior cavities can act as Helmholtz resonators, causing a substantial modification to the overall transmission and reflection properties of such barriers. Leppington [Proc. R. Soc. London, Ser. A 427, 385–399 (1990)] devised an effective boundary condition for a perforated sandwich plate structure, valid in the limit of low frequency (acoustical waves long compared with the typical dimensions of the hole/cavity construction), and obtained transmission and reflection coefficients for infinite planar structures. This article investigates the radiation properties of perforated sandwich plates by examining a simple infinite one-dimensional model (employing Leppington’s effective boundary condition) which is loaded by a line force or moment. The radiated far field, and unattenuated subsonic plate wave coefficients, are found explicitly, and are plotted over a range of frequencies for two physical configurations, namely an aluminum plate in water and in air. It is revealed that, unlike the usual thin plate equation, the model discussed herein has two bi-directional unattenuated plate waves, and for the structure in air the two waves are of similar magnitude over most frequencies. Surprisingly, these amplitudes are shown to become very large at a frequency below that of the structure’s Helmholtz resonance frequency. Further, the field radiating into air is also significantly modified by the cavity/perforations well away from the Helmholtz frequency.
Optimized image processing for multi-beam/multi-aspect sidescan sonar application
Authors: Hoelscher-Hoebing Ursula , Kraus Dieter
Published: July 2002

In the development of future sonor systems, computer-aided classification (CAC) becomes increasingly important. Adequate processing of the multidimensional image data is one important component in a multi-beam/multi-aspect sidescan sonar CAC system. Because the target strength of an object varies with aspect angle, the sonar echo and its representation in a sidescan image is rather random. To make sure that a maximum echo strength is gained, in multi-beam/multi-aspect sidescan sonars overlapping bottom areas are insonified by temporal successive pings, giving the echoes of the target under different aspect angles. Taking advantage of the multi-aspect echo structure in the images of successive pings, they are fused to one sidescan image. Existing image fusion algorithms now require an operator to set threshold values distinguishing target and shadow zones from bottom reverberation zones. An unsupervised method is proposed here for segmentation and optimal fusion of multidimensional images. Its basic steps are image segmentation by means of the EM algorithm; clustering of image segments applying the Markov random field approach; and fusion of successive pings images following a minimum/mean/maximum strategy according to the results of image segmentation and clustering.
Broadband inversion of shallow-water range-dependent acoustic data using a genetic algorithm
Authors: Simons Dick G. , Snellen Mirjam
Published: July 2002

In October 1997, shallow-water experiments were carried out on the Bank of Adventure southwest of Sicily. The purpose of this trial was to obtain acoustic data in range-dependent environments for testing and further developing matched-field inversion methods to determine geoacoustic properties of the sea floor. On one track of the experiments, an acoustic source was towed over a sloping bottom with a water depth varying from 100 m at the vertical receiving array to 75 m at the end of the 7-km track. The array comprises 64 hydrophones and covered the central 62 m of the water column. At several source-receiver ranges, the source (towed below the thermocline) transmitted a multitone signal in the band 50–300 Hz. Detailed sound-speed profiling of the water column and seismic profiling of the bottom were performed along the track. Broadband inversion of the acoustic data was done using a genetic algorithm as the global search method. The forward model uses standard adiabatic mode theory. Inversion results are shown for different geoacoustic models with different complexity concerning sediment layering. The bottom parameters obtained agree well with the results of the seismic analysis and its geological interpretation.
Acoustic intensity and phase variability caused by time-evolving internal wave fields
Authors: Finette Steven , Orr Marshall , Turgut Altan , Wolf Stephen , Pasewark Bruce , Apel John
Published: July 2002

Relationships between time-evolving internal wave fields in a shallow-water environment and both acoustic intensity and phase variability are explored through a computer simulation model developed from experimental data acquired on the continental shelf off the New Jersey coast [Apel et al., IEEE J. Ocean. Eng. 22, 465–500 (1997)]. From an analysis of SWARM (Shallow Water Acoustics in a Random Media) data, single realizations of the acoustic field are computed at an array located approximately 42 km from sources emitting at 224 and 400 Hz. Using a wide-angle parabolic equation, the acoustic field is computed in 1-min intervals over a 12-h time window during which both spatially diffuse and spatially localized internal wave fields propagate through the water column. Results include time-evolving modal power and scintillation indices, and can be interpreted in terms of mode coupling. The ability to locate a source using phase-coherent techniques such as matched field processing will also be addressed. [Work supported by ONR.]
Sound production in wasps and ants (Hymenoptera)
Authors: Tschuch Gunther , Brothers Denis J.
Published: July 2002

Some species of ants (Formicidae) and stinging wasps (some Sphecidae, Bradynobaenidae, Rhopalosomatidae, and all species of Mutillidae) possess stridulatory organs without resonance structures. The stridulatory organs occur in both sexes between the 3rd and 4th, 4th and 5th, or 5th and 6th abdominal tergites. The sphecid wasp Pseudoplisus phaleratus makes use of all three positions. The main part of the stridulatory organ is an area of 60 to 200 very regular ripples with species-specific ripple distances of 1.2 to 5 μm. To prevent mechanical destruction of the ripples during sound production, the force is spread over a width of more than 100 μm. The signals are optimized to serve as warning signals. Frequently wasps and ants present the acoustical signals together with optical (aposematic coloration) and chemical signals (allomones). The potential predators (e.g., lizards, mammals) are phylogenetically very diverse. Therefore the acoustical signals must have a broad frequency spectrum. The mechanisms used for the production of such spectra were investigated by laser vibrometry. The signals were analyzed by cepstrum and by an adaptive optimal-kernel time-frequency representation [D. L. Jones and R. G. Baraniuk, IEEE Trans. Signal Process. 43, 2361–2371 (1995)]. [Work supported by DFG.]
The target strength of the northern right whale (Eubalaena glacialis)
Authors: Miller James H. , Potter David C. , Weber Thomas , Felix James
Published: July 2002

The greatest cause of anthropogenic mortality in great whales is ship strikes. Avoiding collisions, which are almost exclusively with baleen whales, may be critical to the survival of the northern right whale (Eubalaena glacialis). A potential solution to this problem is the use of an active forward-looking obstacle avoidance sonar. This sonar could alert the ship’s crew of the presence of the whales or other obstacles at useful maneuvering ranges. The prediction of these detection ranges depends on the reflectivity of the whales. The focus of this study is the determination of target strength of the right whale. In May and September of 1998, a prototype phased-array sonar was mounted on the bow of a 25-m research vessel to collect these measurements. The sonar used a CW ping with a frequency of 87 kHz, a duration of 2 ms, a source level of 175 dB re: 1 μPa at 1 m. The receive array consisted of an 8×8 element array with BD wavelength spacing. The frequency was chosen to be inaudible to the baleen whales. Target strengths were also collected for humpback whales (Megaptera novaeangliae), and compare well with previously published data. [Work supported by NMFS and NSF.]
Status and distribution of the dolphins in the Black Sea—By the acoustically improved line transect sampling technique
Authors: Gucu Ali C.
Published: July 2002

Although dolphins are an endangered species, until 1983 they had been harvested in the Black Sea. Due to severe ecological changes taking place in this sea, the fish stocks experienced a decline within the last decade. The dolphins preying upon fish stocks were adversely affected and their population size was shrunk due to food shortage. But there is an ever growing lobbying on the government for legalizing dolphin fishery, because fishermen believe that the dolphin population has increased since the ban of dolphin fishery, resulting in an increased predation over the fishes by dolphins, causing fishery to collapse in 1989. The aim of this study is to assess dolphin population size within the Turkish EEZ. One of the best techniques to assess the population size of dolphins is the line transect sampling. Being a direct visual census method, the major disadvantage of this technique is the probability of detection, which is not a uniform unity; as far as the eye can see is the basis of the line transect sampling. This disadvantage was eliminated acoustically by using fisheries’ acoustic devices, and the sounds of the dolphin recorded by a scientific echosounder were used to detect the existence of the animals on the transect.
Schools and clusters: Interannual variability in the aggregative behavior of North Sea herring from acoustic surveys
Authors: Aukland Richard , Reid David
Published: July 2002

Commercially exploited pelagic fish species have a strong tendency to aggregate together. Individual fish aggregate into schools of varying sizes and schools will also tend to aggregate into clusters of many schools. If the stock abundance changes, it is expected that the pattern of these aggregations will change. The numbers, sizes, densities of the schools, and clusters may be expected to change with changing stock level. Such changes will in turn influence the conduct of both fishing and survey activities. A knowledge of fish aggregation patterns and the processes involved should improve the reliability of stock monitoring techniques and provide an understanding of the impact of exploitation on dynamically changing populations. Using image processing techniques a database of schools has been developed from data recorded during acoustic surveys for herring in the NW North Sea between 1993–1998. Positional, morphometric, environmental, and energetic descriptors have been computed for each school. The paper will present the results of the analysis of this database, giving particular attention to variation in schooling and clustering patterns, and the spatial distribution of these aggregations, in relation to the changing herring stock size in the period 1993–1998.
Assessing the relationships between oceanographic parameters and fish distribution: Methodological access and potential problems
Authors: Schneider Patrick
Published: July 2002

The management of living resources, such as fish, is depending on the information available on the interrelationships between these resources and other factors—biotic or nonbiotic—prevailing in the system of interest. As far as the impact of oceanographic parameters on the distribution of pelagic fish is concerned, little is known. A profound understanding of distributional patterns of fish, of shifts in distribution, and the interactions between environmental factors and distribution requires at first the simultaneous acquisition of both acoustic and oceanographic data. Haul data and hydroacoustic data, gathered on five small scale surveys in two Mediterranean areas simultaneously with data for temperature, salinity, sigma-t, and currents, was compared visually and statistically to reveal possible interrelations. As new methods needed to assess the interrelations between environmental and acoustic data are still being developed or adapted from other applications within the scientific community, methodological problems related with this approach are discussed and preliminary results and implications for further investigations and survey designs are presented. Further, new techniques for visualizing survey data are presented and discussed with the objective to open new insights in well-known data. [This work has been financed by the European Commission under Contract No. FAIRGT950139.]
Silicon micromachined microphone chip at Siemens
Authors: Dehé Alfons , Bever Thomas , Schmitt Stephan , Michaelis Sven , Timme Hans-Jörg , Pettenpaul Ewald , Oppermann Klaus , Aigner Robert
Published: July 2002

Applications ranging from hearing aids over communication to noise cancellation open up a high volume market for low-cost, batch producible and reliable microphones. To obey these conditions, a single-chip capacitive microphone has been developed at Siemens, utilizing a modified standard CMOS process with adjacent bulk micromachining. In a first step, the microphone is integrated with a source follower, enabling low output impedance of the signal. The technology allows for the future integration of advanced circuitry. The microphone consists of an acoustically sensitive polycrystalline silicon membrane and a highly perforated back-plate as the counter electrode. To achieve highly sensitive devices, special emphasis was given to the stress of the polycrystalline silicon membrane, which should be slightly tensile. Another key issue during the fabrication and in operation is to prevent stiction of the sensitive membrane. Since the overall chip size is below 3-mm side length, surface mounting in low-cost SMD packages is possible.