bluuebunny/crossref_metadata_2025 huggingface dataset:
Toward a design methodology for equipment emulators in the shock testing of large structures
Authors: DuPont Pierre , McDaniel J. Gregory
Published: July 2002

In a variety of situations, an undesired shock excitation is applied to a master structure which supports shock-sensitive equipment. Often, one wishes to design and test a master structure which transmits the least amount of shock energy to the attached equipment. In scaled testing of new designs, a major task is to design and construct ‘‘equipment emulators,’’ inexpensive mechanical systems which approximately mimic the dynamic behavior of the actual full-scale equipment as seen by the master structure. This presentation will present new methodologies for designing equipment emulators, assessing their fidelity, and interpreting test data taken in the presence of imperfect emulators. Starting with frequency-domain impedance descriptions of the master structure and actual equipment at the attachment points, this work develops sensitivity metrics which directly relate the fidelity of the emulator to its structural complexity. These ideas may provide a path by which experimentalists can efficiently arrive at conceptual designs of emulators which promise a specified degree of fidelity in terms of system velocities and their associated shock spectra. The ideas are illustrated on simple examples and applied to the emulation of commercial-grade electronic cabinets for the testing of novel ship deck structures. [Work supported by ONR.]
Three questions for a theory of speech
Authors: Liberman Alvin M.
Published: July 2002

On reviewing my 50 years of research, I see that in trying to head theory in the right direction I have been led ever more compellingly by the need to find plausible answers to three questions: (1) What is the basis for the parity between primary motor and perceptual representations that explains how, in the evolution of speech, production and perception managed to proceed in lock step, thus allowing the parties to each two-way exchange to communicate, then as now, in a common code? (2) How does speech meet the requirement, unique to its combinatorial mode, that discrete, invariant, categorical, and distinctly linguistic segments be produced and perceived in strings at rates as high as 20 segments per second? (3) What biological and psychological properties account for the vast difference in the difficulty of acquisition and use between speech and the reading or writing of its alphabetic transcription? Two theories of speech—one quite conventional, the other much less so—provide answers that differ greatly in their plausibility.
The impact of system latency on dynamic performance in virtual acoustic environments
Authors: Wenzel Elizabeth M.
Published: July 2002

Engineering constraints that may be encountered when implementing interactive virtual acoustic displays are examined. In particular, system parameters such as the update rate and total system latency are defined and the impact they may have on perception is discussed. For example, examination of the head motions that listeners used to aid localization in a previous study suggests that some head motions may be as fast as about 175°/s for short time periods. Analysis of latencies in virtual acoustic environments (VAEs) suggests that: (1) commonly specified parameters such as the audio update rate determine only the best-case latency possible in a VAE, (2) total system latency and individual latencies of system components, including head-trackers, are frequently not measured by VAE developers, and (3) typical system latencies may result in undersampling of relative listener-source motion of 175°/s as well as positional instability in the simulated source. To clearly specify the dynamic performance of a particular VAE, users and developers need to make measurements to average system latency, update rate, and their variability using standardized rendering scenarios. Psychoacoustic parameters such as the minimum audible movement angle can then be used as target guidelines to assess whether a given system meets perceptual requirements.
Criteria for accurate acoustic emulation
Authors: McGrath David
Published: July 2002

The technique of auralization was pioneered by acoustics researchers in the field of concert hall simulation, where an accurate rendering of the acoustics implied that all characteristics of an acoustic space were reproduced, wherever possible. As the convolution technology is pushed into more cost-effective implementations, the broader potential for this technology is being realized. Now the criteria for acoustic emulation must be reevaluated to take into account a number of new factors. This paper explores many relevant criteria for repeatability testing and characterizing the performance of equipment in the presence of realistic three-dimensional noise fields and complex acoustic environments. Such an acoustic system can be accurately emulated using real-time simulation hardware, if a complete characterization of the system can be obtained. This paper discusses methods that are appropriate for the implementation of accurate acoustic emulation, with the emphasis on real world problems and solutions. It is shown how the entire acoustic signal path can be replaced by an appropriate low latency FIR filter, defined using new techniques for impulse response measurement.
Experimental investigation of matched-field processing in a wedgelike shallow-water environment
Authors: Baxley Paul A.
Published: July 2002

Underwater acoustic propagation in shallow-water wedgelike environments will experience ‘‘bending’’ out of the vertical plane containing the source and receiver. Consequently, the time for the energy to travel from the source to the receiver will be altered, or some paths may miss the receiver altogether. Localization estimates from array processors will be in error if this horizontal multipath propagation is ignored. This phenomenon is investigated experimentally via the analysis of vertical-line-array source-tow data recorded in a steep wedgelike environment near San Clemente Island during the fourth Shallow Water evaluation cell Experiment (SWellEX-4). The source-tows examined were approximately in the cross-slope direction. The objective of this study is (1) to observe the horizontal ‘‘refraction’’ effects via an examination of the matched-field localization errors resulting from a neglect of that phenomenon, and (2) to study the feasibility of including modeled horizontal refraction effects into the matched-field processor to enhance localization performance. Geo- acoustic parameter inversion was performed at short range so that mismatch in this parameter would not be misinterpreted as a horizontal ‘‘refraction’’ effect. A three-dimensional Gaussian beam program was used to generate replica fields, and to perform investigative simulations for the experimental environment. [Work supported by ONR/SPAWARSYSCEN San Diego.]
Modern measurements, optimized diffusion, and electronic enhancement in a large fan-shaped auditorium
Authors: O’Keefe John P. , Cox Trevor , Muncy Neil , Barbar Steve
Published: July 2002

The Hummingbird Centre in Toronto Canada, formerly known as the O’Keefe Centre, is a 3000 seat fan-shaped auditorium, typical of the postwar era. Since it opened in 1960 it has been plagued by complaints about its acoustics. A LARES electronic enhancement system was proposed for the building and a feasibility study was carried out. Modern acoustical measurements lend credence to the years of complaints. Among other interesting findings, late energy (Glate) is 10–20 dB lower than a traditional shoe-box-shaped concert hall. Such low levels of late energy explain, in part, the image shift and echoes that are found throughout the hall. A side wall echo threatened to compromise the proposed enhancement system. In an effort to reduce the echo, a crescent-shaped diffuser was developed using a BEM optimization routine. Four LARES mainframes are employed in the enhancement system with more than 280 front ported two-way loudspeakers, each of which can be addressed individually. The renovated acoustics have been well received by the owners, users, and patrons.
Calculation and measurement of acoustic factors for the Kirishima International Concert Hall
Authors: Nakajima Tatsumi , Ando Yoichi
Published: July 2002

The Kirishima International Concert Hall was designed by architect F. Maki with Ando’s acoustic design theory. It opened on July 22, 1994. The 770 seat main hall which has a volume of 8475 m3 was primarily designed for chamber music. Computer simulations made it clear that the acoustical design of the main hall would be an optimum solution with a plan like a leaf shape and a cross section like a bottom of a ship. These were solutions which satisfied requirements for both acoustical and architectural design concepts of the main hall. Getting a low IACC sound field at the front seat was most important. In order to get a low IACC, sound reflections from the stage to the audience floor were examined and studied in the early design processes. Calculation and measurement of acoustic factors of the sound fields in the main hall show: (1) the calculated and the measured IACCs are good in agreement, (2) IACCs tended lower values of about 0.1 than the calculated ones throughout the seats, and (3) the number of reflections needed for predicting IACC is recommended to be about 40 for the practical method of IACC calculation at the design stage of a hall.
Design of a circular hall improving the subjective preference at each seat
Authors: Takatsu Akio , Sakai Hiroyuki , Sato Shin-ichi , Ando Yoichi
Published: July 2002

The circular type of the medium-sized (400 seats) multipurpose event hall in Kobe Fashion Plaza, which was named Orvis Hall, was designed based on Ando’s theory of subjective preference. Acoustic problems caused by such a circular plan were minimized by means of ceiling diffusion panels, side-wall-reflective panels, and a small room at the back wall preventing echo-disturbance created by the long-path echo or ‘‘Whispering Gallery’’ effects. One of the most remarkable systems of this hall is controlling the subsequent reverberation time through blending architectural acoustics and electrical acoustics by use of a hybrid system with both a reverberation control room and a digital reverberator. Therefore the total scale value of subjective preference at each seat is maximized by the four acoustic factors, namely, the delay time of first reflection, the listening level, the subsequent reverberation time, and the IACC. After construction of this hall, four factors at each seat were measured, and results are presented.
ESWL—The evaluation of a revolution
Authors: Chaussy C. G.
Published: July 2002

After 6 years of experimental research at the Departments of Urology and Surgical Research of the Ludwig—Maximilian University in Munich, extracorporeal shock-wave lithotripsy (ESWL) was introduced for clinical use in 1980. Uniquely successful and increasingly requested by stone patients, the method soon became widespread. Currently more than 2000 lithotriptors are in operation worldwide and over 5 000 000 treatments have been carried out successfully. Clinical experience in all centers has proven the safety, reliability, and reproducibility of the method. Currently approximately 70% of nonselected stone patients are eligible to receive ESWL treatment and, when combined with endourological procedures, more than 95% of patients can benefit from this method and thus avoid open surgery.
Effects of lithotripter fields on biological tissues
Authors: Dalecki Diane
Published: July 2002

Biological effects resulting from exposure to lithotripter fields include hemorrhage in soft tissues, such as the kidney, lung, and intestine, the production of premature cardiac contractions, malformations in the chicken embryo, and killing of Drosophila larvae. Pulsed ultrasound can produce similar bioeffects at comparable pressure thresholds. Tissues that contain gas bodies, either naturally or after the addition of ultrasound contrast agents, are particularly susceptible to damage from low-amplitude lithotripter fields. Lung and intestine contain gas naturally and are hemorrhaged by exposure to lithotripter fields on the order of 1 MPa. After the introduction of an ultrasound contrast agent into the vasculature, many organs and tissues, such as the bladder, kidney, fat, muscle, and mesentery, show extensive hemorrhage after exposure to lithotripter pressures less than 2 MPa. Tissues near developing bone are also selectively susceptible to damage from exposure to low-amplitude lithotripter fields. The thresholds for hemorrhage in tissues near developing bone, such as the fetal head, limbs, and ribs, are all less than 1 MPa for exposures with a piezoelectric lithotripter. Cavitation and purely mechanical forces have been investigated as possible mechanisms for these biological effects of lithotripter fields.
Sonar simulation and display techniques
Authors: Guo Yuhong , Liu Hong , Hui Junying
Published: July 2002

This paper describes techniques used in the simulation and display of a passive sonar system. The sonar and its environment models, including target, channel, noise background, and array, and a complete sonar signal processing chain are developed in the simulation system. Based upon the simulation system, different display techniques are studied. Modeling for performance assessment of a colored brightness mode sonar display is difficult because of its relation to human visual psychology and physiology. A concept of ‘‘visual threshold’’ is proposed in the paper; based on it, as well as the statistical model of display data, detection performance of the sonar display system can be analyzed quantitatively and theoretically. The second-decision method, based on the statistical property of LOFAR display, and a four-dimensional display technique are presented in the paper.
A new accurate model-based music synthesis technique by using recurrent neural networks
Authors: Liang S. F. , Su Alvin W. Y.
Published: July 2002

Reproduction of the tones generated by playing a particular musical instrument electronically remains an open and difficult problem. An accurate model-based analysis/synthesis approach with respect to plucked-string instruments by using recurrent neural networks is proposed. The procedure is described as follows. A recurrent neural network corresponding to the physical model of a musical string is first configured. The vibration of a plucked string is measured and used as the training data of the neural network. The backpropagation-through-time method is used to train the network such that output of this network can be matched to the measured data as close as possible. The well-trained neural network is then used as our synthesis model for this particular string. Since the characteristics of a string keep changing over the period of vibration, it is also necessary to update the parameters of the neural network during the synthesis process. In our experiments the synthesized tones and the real tones sounded almost identical. These results will also be demonstrated during the presentation in ICA/ASA 98 if this paper is accepted. [This Work is supported by both NSF, Taiwan and Computer/Communication Lab. ITRI, Taiwan.]
Modeling Chinese musical instruments
Authors: Horner Andrew B. , Ayers Lydia
Published: July 2002

Chinese instruments include a range of colorful instruments with distinctive characters. For example, the dizi is the most common Chinese flute, and it has a bright buzzing quality produced by a rice paper membrane glued over a hole. This paper describes models for more than 20 Chinese traditional and folk instruments using group additive synthesis with genetic algorithm-optimized parameters. Other types of Chinese flutes modeled include the xiao (vertical flute), paixiao (panpipes), and xun (ocarina). The sheng is a mouth organ with a ring of bamboo pipes attached to a wind chamber, and dates back to 1500 BC. A folk version of the sheng, called the lusheng, has also been modeled, as well as the bawu and hulusi, folk instruments that sound similar to the clarinet. The player’s mouth completely covers the bawu’s blowhole, which has a vibrating reed cut into a copper strip covering the hole. The hulusi has a playing tube and multiple drone tubes. Several pitched percussion and plucked string instruments have also been modeled. The presentation will show the acoustic instruments, their sound, their spectra, and resynthesized excerpts of music written for these instruments.
Supportive sound environments in building research
Authors: Berglund Birgitta , Hojan Edward , Furmann Anna
Published: July 2002

The aim of this research is to create good sound environments in rooms of ordinary buildings (schools, dwellings, offices, hospitals) for people with hearing deficits. If the deterioration of hearing with age is considered, this group of people may represent a majority rather than a minority of the population. From the many evaluation criteria of natural sounds, both stationary and nonstationary and in room environments, used by subjects, the authors have identified independent ones. These criteria may be named attributes and primarily define the ‘‘quality’’ of the sound-perception space in rooms. New experiments involving perceptual evaluation of sound and environments by 40 randomly chosen subjects and the use of multidimensional data analysis confirm in part our earlier results regarding the particular evaluation criteria applied [Furmann et al., J. Acoust. 4, 535–551 (1991)]. According to Stevens’ argument, it seems that the relationship between the values of the evaluation scale and the perceptions are identical for people of normal and impaired hearing although their perceptions may differ.
Conditions during multibubble sonoluminescence
Authors: Suslick Kenneth S. , McNamara William B. , Didenko Yuri
Published: July 2002

Acoustic cavitation results in extraordinary transient conditions inside the collapsing bubble. In addition to interesting chemical effects (sonochemistry), cavitation also produces light emission. Such sonoluminescence from cavitating clouds of bubbles [‘‘multibubble sonoluminescence’’ (MBSL)] in room-temperature liquids closely resembles flame emission. Effective emission temperatures have been obtained for MBSL from excited state metal atom emission (from sonolysis of several volatile metal carbonyls). From the relative intensities of multiple line emissions from Cr, Mo, and Fe, emission temperatures have been calculated and are all in close agreement with each other. The effects of bubble contents can alter the observed temperatures and this has been now directly observed for the first time. In addition, effective pressures can be estimated from line broadening and line shifts of the metal atom emission. The effective transient conditions formed during cavitation of bubble clouds are roughly 5000 K, 500 atm, which implies heating and cooling rates in excess of 1e10 K/s. Temperatures reached during single bubble sonoluminescence (SBSL) are likely to be very much higher.
Predictions for stable sonoluminescence in nonaqueous liquids
Authors: Brenner Michael P. , Hilgenfeldt Sascha , Lohse Detlef
Published: July 2002

The oscillation behavior of single sonoluminescing bubbles, and therefore their stability and the intensity of light emission, depends on a multitude of material parameters, including viscosity, surface tension, and liquid vapor. It is shown in analytical and numerical computations how substitution of water by nonaqueous fluids affects the domain for stable and unstable sonoluminescing bubbles in parameter space.
The effect of spectral resolution on speech perception in a multitalker babble background
Authors: Kwon Bom Jun , Turner Christopher W.
Published: July 2002

Does finer spectral resolution always have an advantage for speech recognition? In this experiment, speech was divided into separate bands within which spectral information was removed by replacing the fine structure with noise; the temporal envelope cues of each band remained intact. Normal-hearing subjects identified consonants in a/C/a for speech and babble processed with 1, 2, 4, and 8 bands, in addition to the unprocessed speech and babble, for a range of signal-to-babble ratios. For high S/B ratios our results agree with earlier results, in that performance improved with increases in the number of bands, and higher transmission of information was observed for voicing and manner than place of articulation [Shannon et al., Science 270, 303–304 (1995)]. However, as S/B decreased, the advantage of better spectral resolution was reduced. This suggests that for speech in a competing babble background, increased spectral resolution not only increases the saliency of speech, but at the same time makes background babble a more effective distracter. Thus the benefit provided by fine spectral resolution depends upon the task and S/B ratio. [Work supported by NIDCD.]
Protective effects of magnesium on noise-induced hearing loss: Animal studies
Authors: Scheibe Fred , Haupt Heidemarie
Published: July 2002

Magnesium (Mg) deficiency was found to increase noise-induced hearing loss in laboratory animals. This paper reports both prophylactic and therapeutic effects of Mg on the acoustic trauma produced by a high-level impulse noise series (Lpeak 167 dB, 38 min, 1/s). Hearing loss was tested by auditory brainstem response audiometry at frequencies between 0.5 and 32 kHz. Permanent hearing threshold shifts (PTS) were measured 1 week after the exposure. For the prophylaxis experiments, anesthetized guinea pigs with either a physiologically high or low Mg status, produced by different diets, were used. For the therapy experiments, animals with the low Mg status received (immediately after exposure) either Mg injections combined with a Mg-rich diet or saline as a placebo. Total Mg concentrations of perilymph, cerebrospinal fluid, and plasma were analyzed to test the Mg status of the animals. The PTS was found to be significantly lower in the high-Mg group than in the low-Mg group. This also applies to the PTS found between the therapy and the placebo groups. There was a good correlation between the PTS and the perilymphatic Mg. The intracochlear Mg level seems to play an important role in the acoustic trauma. [Supported by German Defence Ministry.]
Vibrational power transmission in asymmetric framework structures
Authors: Horner Jane L.
Published: July 2002

When attempting to control the vibration transmitted from, say, a machine into and through the structure upon which it is mounted, it is desirable to be able to identify and quantify the vibration paths in the structure. Knowledge of transmission path characteristics enables procedures to be carried out, for example, to reduce vibration levels at points remote from the source, perhaps with the objective of reducing unwanted radiation of sound. One method for obtaining transmission path information is to use the concept of vibrational power transmission. Many machines are installed on frameworks constructed from beamlike members. By using the concept of vibrational power it is possible to compare the contributions from each wave type. Wave motion techniques are used to determine the expressions for vibrational power for each of the various wave types present. The results from the analysis show the amount of vibrational power carried by each wave type and the direction of propagation. Consideration is given to the effect on the vibrational power transmission of introducing misalignment of junctions in previously symmetric framework structures. Unlike other techniques using vibrational power to analyze frameworks, the model keeps the contributions from each of the various wave types separate.
The effect of shear thinning in vocal fold tissues—or why we can phonate over two octaves in pitch
Authors: Titze Ingo , Chan Roger
Published: July 2002

The shear modulus and viscosity of vocal fold tissues was measured with a rheometer in the frequency range of 1–30 Hz. Extrapolation to phonation frequencies was possible. As in most biological tissues (and for polymers in general), the shear modulus was found to be roughly constant and the viscosity varied inversely with frequency. This makes the damping ratio only a weak function of frequency in phonation. Since self-oscillation of the vocal folds is critically dependent on this damping ratio, it is reasoned that large F0 ranges (on the order of two octaves) are possible only because of this decrease in viscosity, an effect known as shear thinning. A molecular interpretation is given for this effect. [Work supported by NIDCD, Grant No. P60 DC00976.]
Beyond current medical ultrasonic imaging: Opportunities for advanced signal processing
Authors: Miller James G.
Published: July 2002

This keynote address will illustrate some aspects of current medical ultrasonic imaging and attempt to identify areas in which advanced signal processing may be able to contribute to the enhancement and extension of clinical ultrasound. Examples will be drawn primarily from echocardiography, in part because of challenges specifically associated with imaging the beating heart. The presentation will address the goals and needs of the (medical) user in order to avoid approaches which are technically elegant but clinically irrelevant. One feature peculiar to medical imaging, which limits the effective resolution to far less than the expected theoretical limit for the few hundred micrometer wavelength imaging systems in current use, is the subtle variation of elastic properties of soft tissue and the corresponding local variation in the speed of sound. Both random and systematic (for example, anisotropic) variations contribute to degradation in image quality, including the effect known as speckle. Opportunities for advanced signal processing may include not only approaches designed to enhance image resolution but also contributions to areas such as contrast agents and tissue characterization. The talk is designed to provide a broad overview which might serve as a common reference point for subsequent presentations.
The evolution of medical ultrasonic imaging systems
Authors: Reid John M.
Published: July 2002

A limit to effective soft tissue imaging is set by the acoustic properties of tissue. The attenuation is roughly proportional, and the size of a resolution element inversely proportional to frequency. Thus the number of resolution elements per image is fixed. Accordingly, acoustic frequencies from about 1 to 50 MHz are required. Effective imaging has required the development and application of innovative high-frequency hardware; particularly the transducers. These have progressed from single element types to 512 element arrays in production, with two-dimensional arrays having 1282 elements in development. The electronics now require many more channels with a dynamic range exceeding 100 dB and, with the introduction of digital methods, even multiple very fast A/D converters in the beamformer. Display devices have gone from WWII CRT’s with 200 spots per radius to digital image stores on CRT’s with thousands of spots available. These can now do image processing with software. The earlier systems survive in some applications that require them. The single element types are still used in high-frequency catheters, for example. The wideband transducers have opened up new methods, enhanced Doppler, contrast and tissue imaging that use a wider range of frequencies than previously possible. The single element types are still used in high-frequency catheters, for example.
Beneficial effects of notched noise on intensity discrimination in the region of the “severe departure”
Authors: Plack Christopher J.
Published: July 2002

Intensity discrimination for a 6-kHz sinusoidal pedestal was measured in quiet and in the presence of a noise background. In the first experiment, the level of a 30-ms pedestal was fixed at 45 dB SPL and presented in the temporal and spectral center of a 110-ms notched noise. For a noise spectrum level of between 0 and 15 dB the noise produced a substantial reduction in the Weber fraction, i.e., an improvement in detectability, compared to the condition without the noise. The second experiment showed that, unlike the situation with notched noise, narrow-band noise produced no performance improvement, suggesting that the effect is dependent on noise frequency components outside the critical band of the pedestal. The third experiment showed that the improvement also occurred for a 6-ms pedestal presented in a 10-ms gap between two bursts of notched noise. The experiment rules out an explanation for the effect of the noise in terms of suppression on the basilar membrane. Finally, the effect was shown to decrease as the gap between the noise bursts was increased, in a manner at least broadly consistent with the decay of the temporal excitation pattern. It is suggested that the improvement in intensity discrimination in notched noise is due to an across-frequency comparison mechanism similar to “profile analysis,” perhaps operating on a temporally smoothed central representation of the stimulus.
Computation of T-phase coda
Authors: de Groot-Hedlin Catherine D.
Published: July 2002

T-phases result from the conversion of seismic to acoustic energy at the seafloor in the vicinity of an earthquake epicenter. The time-frequency characteristics of T-phase coda are observed to be strongly dependent upon the bathymetry of the ocean floor in the source region; thus earthquakes from the same geographic area generate similar T-phase coda. In this study, detailed bathymetry and sound speeds computed from the Levitus atlas are used to simulate the T-phase amplitudes which would be recorded at distances of several thousand kilometers from these natural sound sources. It is hypothesized that seismic/acoustic coupling occurs over a distributed region of the ocean floor, with seismic energy being scattered into low-order modes in shallow water. Comparison with observed coda indicates that T-phase onset times and durations are modeled quite accurately with this simple method. The feasibility of using this method to determine accurate source times and locations for small suboceanic earthquakes, given natural ocean variability, is examined in this study. Contributed Papers
Internal wave effects on single-frequency coherence, matched field processing, and adiabaticity
Authors: Heaney Kevin D. , Mikhalevsky Peter N. , Freese Herb , Kuperman W. A.
Published: July 2002

A set of PE calculations at various frequencies (10, 30, 75, and 150 Hz) through internal wave realizations was performed. To examine the range/frequency limits of coherent processing, the coherence against the range-independent PE was calculated every km out to 3000 km. The coherence between with and without internal waves drops to 0.8 (−2 dB) at ranges of 3000, 1800, 500, and 200 km for the 10, 30, 75, and 150 Hz, respectively. The sidelobe structure of matched-field processing results confirms these as range/frequency limits of matched-field processing. Vertical coherence as a function of range and frequency will be presented. The decomposition of the full field into normal mode amplitudes will be presented, as well as range limits for the adiabatic approximation. The validity of the first-order perturbation theory correction to the adiabatic approximation will be examined.
High-frequency bottom backscattering from a homogeneous seabed
Authors: Briggs Kevin B. , Stanic Steve
Published: July 2002

High-frequency acoustic backscattering was measured from a sandy site located in very shallow water (8 m) off Tirrenia, Italy, at a range of frequencies and grazing angles. Concomitant measurements of the seabed indicated that the very fine sand was well sorted, relatively uniform with respect to vertical and horizontal distribution of compressional wave velocity and attenuation, and depleted with respect to biological activity. Bottom scattering strengths were very low and variability of sediment parameters was exceptionally low. Coefficients of variation determined for sediment compressional wave velocity and attenuation were 0.29% and 7.2%, respectively. These data compare with previously recorded minima of 0.30% and 14.8% for the same respective parameters, in nearshore, mobile fine sands from the Gulf of Mexico and the Pacific Ocean. Lack of variability in sediment sound velocity and density concurrent with low acoustic bottom scattering strength measurements would endorse recent modeling approaches that predict scattering from sediment impedance fluctuations. Acoustic data are compared with predictions from the composite roughness model (modified for inclusion of sediment volume scattering parameters) at various frequencies and grazing angles in order to test the model’s response at minimal perturbation of seabed properties.
Time/frequency spread for bistatic geometries
Authors: Culver R. Lee , Link Christopher J.
Published: July 2002

The overall goal of this work is to develop a functional characterization of, and empirical models for, high-frequency, broadband acoustic propagation through a shallow ocean channel. One important aspect of this characterization is the time/frequency spread, which quantifies how much signals spread in time and frequency as they propagate. Because time and frequency spread are random quantities which vary from pulse to pulse, time/frequency spread must be characterized using a second-order statistic, e.g., the scattering function, which is the expected value of the mean-square spreading function. The scattering function has been measured in the following ocean environments: sandy gravel bottom, isovelocity sound speed profile (SSP); rough rock bottom, slightly downward-refracting SSP; and mud bottom, upward-refracting SSP. A statistical model for the scattering function is being developed for these environments based upon radial basis function decompositions of the scattering function estimates. The ultimate use of a scattering function model will be with simulation to assess and optimize acoustic receiver performance. [Work is sponsored by the Office of Naval Research Ocean Acoustics Program.]
Nonlinearity, complexity, and the sounds of musical instruments
Authors: Fletcher Neville H.
Published: July 2002

Musical instruments can be treated to a first approximation as linear harmonic systems, but closer examination shows that they are, almost without exception, nonlinear and inharmonic. Sustained-tone instruments such as violins and clarinets can be characterized as ‘‘essentially nonlinear’’ and owe their deceptively simple behavior to mode locking due to strong nonlinearity. When the nonlinearity is weakened, the behavior becomes complex, with inharmonic and multiphonic sounds that are sometimes exploited in modern music. In contrast, impulsively excited instruments, such as guitars, pianos, gongs, and cymbals, may be described as ‘‘incidentally nonlinear.’’ They would function quite acceptably if the nonlinearity were to be eliminated but, when it becomes strong, they exhibit physically and aurally interesting behavior such as period doubling, frequency multiplication cascades, and chaotic oscillation. This paper will explore some of these phenomena and demonstrate both their physical origins and musical utility.
Classroom acoustics IV: Speech perception of normal-hearing and hearing-impaired children in classrooms
Authors: Crandell Carl C. , Siebein Gary W. , Gold Martin A. , Hasell Mary Jo , Abbott Philip , Lehde Mitchell , Lee Hee Won
Published: July 2002

The present investigation examined the speech-perception abilities of normal-hearing and hearing-impaired children in a number of classroom environments. Speech perception was assessed as a function of teacher location, background noise levels, early sound reflections, reverberation time, and signal-to-noise ratio. Specific acoustical measurement procedures are described in Classroom Acoustics I and II. Speech perception was assessed by nonsense syllables, monosyllabic words, and sentences. Normal-hearing populations included children, aged 5–17 years, who are progressing normally in school; learning-disabled children; children with central auditory processing deficits; articulatory- and/or language-disordered children; children with developmental delays and/or attention deficits; and children for whom English is a second language. Hearing-impaired populations consisted of children with minimal-to-severe degrees of bilateral and unilateral, sensorineural or conductive hearing loss. Data will be discussed in view of developing appropriate classroom acoustics for normal-hearing and hearing-impaired pediatric listeners.
Absorption characteristics of a double-leaf membrane with an absorptive layer in its cavity
Authors: Sakagami Kimihiro , Uyama Toru , Kiyama Masakazu , Morimoto Masayuki
Published: July 2002

Absorption characteristics of double-leaf membranes with an absorptive layer in the cavity are theoretically analyzed. The double-leaf membrane is modeled as two infinite membranes with a cavity between them, which consists of three layers of arbitrary media. The theory also includes the effect of permeability of the interior leaf. The effects of parameters of the absorptive layer on the absorption characteristics are discussed through numerical examples. The absorption characteristics of an impermeable double-leaf membrane are characterized by a mass-spring resonance peak at low frequencies. This peak becomes larger and shifts to lower frequencies as the thickness of the absorptive layer increases. The absorption characteristics are, in permeable cases, similar to those of the conventional porous absorbents; the absorption is low at low frequencies and higher at high frequencies. As the thickness of the absorptive layer increases, the absorption becomes higher at all frequencies. The change in position of the absorptive layer affects the absorption characteristics of the double-leaf membrane. This effect is related to the standing-wave sound field in the cavity. The flow resistance of the absorptive layer has an optimum value to maximize the absorption of a double-leaf membrane.
The application of wideband signals in fisheries and plankton acoustics
Authors: Ehrenberg John E. , Torkelson Thomas C.
Published: July 2002

Over the last 30 years, there have been considerable improvements in techniques developed for acoustic assessment of fisheries and plankton populations. Techniques have evolved from analog echo integrators used to obtain crude abundance estimates to digital multiple-beam techniques for measuring in situ target strength, location, and velocity of individual targets. These advancements have been largely due to digital signal processing techniques applied to signals at the output of an echo sounder. Constant-frequency sine wave (CW) pulses have been used with nearly all plankton and fisheries assessment systems. The same digital signal processing technology used to improve post-processing is now finding its way into biological assessment echo sounders that use FM slide/chirp signals. Systems with time-bandwidth products of up to 50 have been developed and implemented to provide a signal-to-noise advantage in excess of 15 dB when compared to CW pulse signals with the same spatial resolution. This paper describes the implementation and application of FM slide/chirp signals for echo integration and target strength measurement. Practical implementation issues, such as the use of pulse shaping for range side-lobe control, are discussed. Recent data collected with a multifrequency acoustic assessment system developed for WHOI are presented.
Wideband fisheries sounder. From individual echoes analysis to classification of schools at sea
Authors: Zakharia Manell E.
Published: July 2002

Several works have been carried out in the last decade concerning wideband fisheries systems and their ability to discriminate fish species. The paper will first review previous work showing the relevance of wideband systems for fisheries acoustics (analysis of individual echoes). A short description of a wideband prototype (20 to 80 kHz) will then be given showing the technological issues. An emphasis will be made on the analysis of fish schools either in a controlled situation (lakes) or at sea. Wideband echo processing was based on autoregressive modeling of individual pings (modeling of spectrum resonances). This modeling concentrates the information contained in the wideband echo in a reduced set of parameters that could be used for classification. A neural network was trained to recognize several fish species. Ground truth was achieved by species identification, at sea, using associated trawling. For the construction of an echo data base, only monospecific schools were considered. Classification results at sea using only the spectral signature of the echoes were as high as 75% from a single ping. Lake tests have shown that the use of several pings (ten and above) could increase the recognition rate to more than 90%.
Multifrequency acoustic assessment of fisheries and plankton resources
Authors: Torkelson Thomas C. , Austin Thomas C. , Wiebe Peter H.
Published: July 2002

The range of target species encountered in marine biological resource assessment and the inability to obtain a broad view of these resources by direct physical sampling techniques has lead to the utilization of various indirect measurement techniques. Among these techniques is the use of acoustics (sonar) to determine biomass distribution through integration and target strength measurements. WHOI is using a multifrequency acoustic system to obtain more accurate measurements of target species on the Georges Bank. The system uses advanced acoustic techniques to enhance detectability at the lower trophic levels and uses an advanced towing technique to enable sampling over the water column to depths in excess of 200 m. This presentation discusses the challenges encountered with indirect acoustic sampling and the techniques implemented to meet them. The system to be discussed operates at frequencies between 38 kHz and 2 MHz, using either FM slide (chirp) or traditional CW acoustic pulses.
Full-wave modeling of lithotripter fields
Authors: Steiger Eckard
Published: July 2002

The propagation of extracorporeal shock wave lithotripter pressure pulses is considered. A computational modeling must account for the effects of diffraction, nonlinear steepening and generation, and propagation of shock waves. Some commercial lithotripters are reflector focusing systems. Therefore, reflections at curved boundaries have to be considered. For specific interests in the propagation through and the interaction with human tissue structures, refraction, absorption, and scattering must be included. A full-wave model based on a set of nonlinear acoustic time domain equations is applied. This system is discretized to obtain a finite difference representation of broad bandwidth and low dispersive character. To enable an accurate shock wave computation an algorithm that modifies the temporal and spatial resolution adaptively is developed. Exemplary a reflector focusing lithotripter is modeled. To validate the model resulting computed wave profiles are compared with measured ones. The measurements are performed using a fiber-optic probe hydrophone. Excellent agreements show the method to provide an accurate and flexible tool for field predictions of complex devices. Characterizing parameters like −6-dB focal regions and energy quantities can be obtained, too. A human tissue model is applied to obtain predictions of the relevant parameters inside the human body.
Acoustic shock-wave induced cavitation: A comparison of theory and experiment
Authors: Coleman Andrew J. , Cahill Mark D.
Published: July 2002

A calibrated membrane hydrophone has been used to make measurements of pressure in a cavitating field generated in water by a single 30-μs duration ultrasound pulse with a 0.2-MHz center frequency and a peak negative pressure (p−) variable from 0.5 to 5 MPa as employed in clinical lithotripsy. The acoustic emission from cavitation in the vicinity of the hydrophone is identified as the high-frequency (>1 MHz) component of the waveform. This ‘‘cavitation component’’ is compared with theoretical predictions of the pressure radiated by a bubble made using the Gilmore model [C. C. Church, J. Acoust. Soc. Am. 86, 215–227 (1989)]. The model was run for initial bubble radii of 1–100 μm using the measured pressure waveform to drive the radial dynamics of the bubble. The theory predicts a transition from completely driven dynamics at p− below 3 MPa to largely undriven dynamics above 3 MPa. This transition, which is substantially independent of bubble size, is experimentally observed and occurs at a measured p− of 3±0.4 MPa. The time between the pressure pulse and the first undriven inertial collapse is predicted to increase approximately twice as rapidly with increasing amplitude as is measured. A mechanism resulting in shorter than predicted collapse times is discussed. [Work supported by the Medical Research Council, UK.]
A short water-filled pulse tube for the measurement of the acoustic properties of materials at low frequencies
Authors: Kenney Debra M. , Rogers Peter H.
Published: July 2002

A method of measuring the acoustic properties of materials at low frequencies in a water-filled pulse tube, which was a fraction of a wavelength long, was investigated. The method employed active sound cancellation at the end of the tube opposite from the sample, and signal processing of two hydrophone signals to separate the signal incident on the sample from its reflection. Two analytical models were developed and an experimental tube was built to examine the feasibility of such measurements. The results from the simulation and experiment suggest that the short water-filled pulse tube would be useful for measuring compliant materials at moderately low frequencies (down to 300 Hz), but not for measuring high impedance materials or for making measurements at very low frequencies. The simulation and experiment showed that the thicker the sample, relative to a wavelength, the lower the sensitivity to experimental errors. Fortunately, many of the materials of interest in underwater acoustics are compliant materials with relatively slow phase velocities and consequently shorter wavelengths. The impedance of the backing behind the sample also influences the sensitivity of results to errors in the measurements. [Work supported by ONR and NSF.]
Analytical results for the conditions of shock formation inside SBSL bubbles
Authors: Guenther Ralf
Published: July 2002

The mechanism of light emission during single-bubble sonoluminescence is still an unresolved question. Of central importance in this respect is whether a converging shock forms inside the bubble. Using an expansion of the fields inside the bubble, a set of dimensionless equations is derived, which allows exact solutions as well as perturbative treatment during different stages of the bubble collapse. The transition from nonshock to shock solutions is obtained as a function of dimensionless con- stants characterizing the dynamics. The explicit form of spatial distributions of temperature, velocity, and density is derived and consequences for the light emission are discussed.
Shock formation in a sonoluminescing gas bubble
Authors: Yano Takeru
Published: July 2002

Whether a shock is formed or not in a sonoluminescing gas bubble is a fundamental problem in the sonoluminescence study. The problem is numerically studied by solving Euler equations of gasdynamics in conjunction with an approximate equation of Keller type for the motion of the bubble radius. A high-resolution TVD upwind finite-difference scheme is used for Euler equations and a fourth-order Runge–Kutta method for a Keller-type equation. The result shows that, owing to the strong nonlinearity of the bubble motion, a slight increase of the driving pressure over a critical value makes the maximum collapse speed of a bubble wall supersonic, and hence the gas behavior changes from a nearly incompressible and adiabatic flow to a compressible one including a shock wave. The relation between the critical driving pressure and other parameters (the driving frequency, the initial bubble radius, etc.) is analyzed. The maximum temperature and pressure attained in the bubble are compared with those in earlier theoretical and numerical works.