bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrasonic and low-frequency vocalizations from Siberian and Bengal tigers
Authors: von Muggenthaler Elizabeth
Published: July 2012

Tigers have many vocalizations including chuffling, growling, prusten, gurgling, grunting, and roaring. It has been well documented that the tiger’s high-amplitude, low-frequency roars, which are thought to be territorial in nature [C. Packer and A. E. Pusey, Sci. Am. 276, 52–59 (1997)] transmit for miles. It has been suggested that because some tigers inhabit dense jungles with limited visiblity, the capacity to hear low frequency may be beneficial for sensing and locating prey [G. T. Huang, J. J. Rosowski, and W. T. Peake, J. Comp. Physiol. A (2000)]. In an effort to understand more about these low-frequency vocalizations and to provide data to other researchers testing hearing in anesthetized felids, 22 tigers, both Siberian and Bengal, are being recorded. A portable system can record from 3 Hz to 22 kHz. On-site real-time analysis of vocalizations is performed using a portable computer. Real-time and edited playback of sonic and infrasonic tiger vocalizations is facilitated by car audio speakers capable of producing frequencies from 10 Hz–22 kHz. Initial findings have documented fundamental frequencies of some roars at 17.50 Hz. Other vocalizations, including chuffling, have fundamental frequencies of 35 Hz ±5. Playback of both real-time and edited vocalizations appear to illicit behavioral responses, such as roaring, from male tigers.
On the sound of snapping shrimp: The collapse of a cavitation bubble
Authors: Versluis Michel , von der Heydt Anna , Lohse Detlef , Schmitz Barbara
Published: July 2012

Snapping shrimp produce a snapping sound by an extremely rapid closure of their snapper claw. They usually occur in large numbers providing a permanent crackling background noise, thereby severely limiting the use of underwater acoustics for active and passive sonar, both in scientific and naval applications. Source levels reported for Alpheus heterochaelis are as high as 220 dB (peak-to-peak) re 1 μPa at 1 m distance. Recent ultra-high-speed imaging of the snapper claw closure [Versluis et al., Science (in press)] revealed that the sound is generated by the collapse of a cavitation bubble formed in a fast flowing jet of water forced out from between the claws during claw closure. In this work, we develop a theoretical model for a bubble under such conditions. The dynamics of the bubble radius and the emitted sound can be described by the Rayleigh–Plesset equation. The calculated results are compared with the experimental data. The model fully reproduces the bubble dynamics and it quantitatively accounts for the time dependence of the bubble radius and for the emitted sound. a)Also at Dept. of Physics, Philipps-Univ. Marburg, Renthof 6, 35032 Marburg, Germany.
The effect of internal wave time dependence on ray chaos
Authors: Vera Michael , Flatté Stanley M.
Published: July 2012

A range-dependent field of sound speed in the ocean can give rise to chaotic instabilities in acoustic ray paths. A model of internal waves is used as a range-dependent effect on the speed of sound in numerical simulations. These simulations, performed over a 1000-km range, demonstrate the sensitivity of ray paths to slight changes in the sound-speed field or the initial conditions of their launch. Previous work [Simmen et al. (1999)] has shown the effect on arrival depth of slightly shifting the launch angle of each ray. The focus of this work is the effect of internal wave time dependence. Comparisons are made between simulations using a time-dependent medium and those using a time-independent (‘‘frozen’’) medium, and between simulations with different geophysical starting times. The resulting arrival depth differences are compared to those induced by launch angle shifts. The structure and magnitude of these differences are considered in the case of two different sound-speed profiles: a Munk canonical profile and a profile from the Slice89 experiment.
One-path scintillation method for transverse current monitoring
Authors: Fuks Iosif , Charnotskii Mikhail , Naugolnykh Konstantin
Published: July 2012

A sound wave passing through the inhomogeneous fluid is modulated producing the intensity fluctuations or scintillations at the receiving plane. These fluctuations evolve as the intervening medium changes. If the fluctuations in the medium are produced by the advection of frozen fine-structure field, then the evolution of the scintillation pattern can be linked to the motion of the ocean medium [S. Clifford and D. Farmer, J. Acoust. Soc. Am. 74, 1826–1832 (1983)]. This method of the ocean current registration can be realized by the measurement of correlation of the signals transmitted from the source to two separated in space receivers and can be respectively considered as space-domain scintillation method. However, it is possible to register the transverse flow by sounding ocean along the one path using the multifrequency signal [J. Fuks, Radiotechn. Electron. (in Russian) 3, 515–524 (1975)]. The coherence of frequency-spaced signal fluctuation is related to the advection of the inhomogeneous medium through the sound path, thus providing a basis for the current velocity measurement. The sensitivity of this method in application to flows in straits and narrow channels is considered and the accuracy of the current velocity measurement is estimated.
Low-frequency acoustics of bubble plumes formed in fresh water and salt water
Authors: Berger Thomas K. , Buckingham Michael J.
Published: July 2012

Experiments aimed at comparing the acoustics of bubble plumes formed in salt water and fresh water were performed in a laboratory tank and natural bodies of water. The plumes were generated as a vertical stream of water, with a diameter of millimeter order and velocity ranging to about 10 m/s, penetrated a free water surface. The acoustic signals were measured with hydrophones in different positions, amplified, and digitally sampled. The measured power spectra revealed well-defined, nonuniformly spaced resonance peaks at frequencies below about 1 kHz. A theory based on a conical bubble plume, with a nonuniform sound speed profile acting as a resonant cavity, predicts the frequencies of the resonance peaks and shows remarkable agreement with the experimentally measured values for both salt water and fresh water bubble plumes. Though the bubbles contained in the salt water bubble plumes are much smaller than those in the fresh water plumes, the resonance frequencies are largely unaffected, consistent with the observation that the plumes in both cases are nearly identical in size and geometry for the same incoming velocity and air-entrainment rate. The acoustic levels in salt water were lower, indicating possible differences in attenuation or driving mechanisms. [Work supported by ONR.]
Acoustic propagation measurements in the surf
Authors: Stroud John S. , Commander Kerry W. , McDonald Robert J. , Wilbur Jo Ellen
Published: July 2012

As a follow-on experiment to the 1999 Near Shore Acoustic Network Experiment, the 2000 Surf Zone Acoustic Test Experiment (SZATE) was conducted off of the Scripps Institute of Oceanography pier in La Jolla, CA. In this experiment, measurements were conducted in a very shallow water/surf zone (VSW/SZ) region to investigate acoustic propagation and sound channel stability in the coastal area. These measurements utilized two receivers and a broad band source. The data to be presented were acquired by a computer controlled system designed and operated by Grant Deane of Scripps Institution of Oceanography. This system provided for 12 18-min data acquisition periods per day. The probative transmissions consisted of a variety of linear frequency modulated (LFM) and binary phase shift keyed (BPSK), as well as 4-ary frequency shift keyed (FSK) signals. Each of the types of signals was used during each data acquisition period, providing a record of propagation throughout the tidal cycle. Results of this acoustic measurement for select pulse types will be reported. [Work supported by ONR Code 321OE.]
Optimal transmit beam synthesis for coded-excitation pulse–echo imaging
Authors: Ebbini Emad , Jeong Mok-kun
Published: July 2012

The use of code-fed arrays for pulse–echo ultrasonic imaging is gaining increased attention in medical applications. One of the most important applications is true real-time 3-D cardiac imaging where parallel processing of multiple-image lines is required to meet the stringent real-time constraints. The key to this approach is transmitting multiple codes to illuminate the region of interest (ROI), producing independent echo waveforms from different directions. We have examined several different scenarios in which the transmit aperture is divided into focused subapertures. Each subaperture is excited by one code and focused appropriately based on the definition of the ROI. For example, a 128-element array can be driven by eight independent codes on eight 16-element subapertures to illuminate a 6° ROI with f number of 2. The optimal solution is a sparse array pattern for each transmit subaperture (i.e., the subapertures overlap). Significant improvement in both lateral and range sidelobes of the system point-spread function (PSF) were achieved (compared to random transmit code selection). In this paper, we describe a new optimal synthesis of coded excitation transmit patterns. Examples of pulse–echo PSFs for the imaging system along with image reconstructions from a speckle-generating tissue-mimicking phantom will be given.
International calibration comparisons: Who benefits?
Authors: Wong George S. K.
Published: July 2012

The mutual acceptance of acoustical calibrations and measurements between industrial countries is essential for international trade and the removal of no-tariff trade barriers. For example, the sound level or sound power emitted by a machine measured at the country of manufacture with certified instruments and methods in accordance with international standards, should be acceptable by the importing country without the requirement to duplicate the measurements. To achieve this mutual recognition, it is necessary for the exporting country to have proven capabilities via international comparisons and an unbroken chain of traceability from their national metrology institute to the machine shop level. Under the umbrella of the Bureau International does Poids et Mesures (BIPM), the Consultative Committee on Acoustics, Ultrasound and Vibration (CCAUV) has arranged international calibration comparisons, involving over 15 countries. The above comparisons require a lot of effort from each participating country. One may ask the question: Who is the beneficiary of international comparisons? The detailed answer is rather complex. In general, the results of International Calibration Comparisons provide confidence in the measurement capabilities of the participants. In the long term, the consumer is the ultimate beneficiary.
Key elements of mutual recognition arrangements
Authors: Brinkmann Klaus
Published: July 2012

Mutual recognition arrangements in the field of metrology are concluded between equal partners to promote the acceptance of each other’s calibration certificates and test reports in order to facilitate global trade (‘‘one-step-testing’’). Acoustics is affected by this development both on the level of national metrology institutes, cooperating in organizations of the Metre Convention, and on the level of accreditation bodies and their accredited calibration and testing laboratories, cooperating in the International Laboratory Accreditation Cooperation (ILAC). Both arrangements are equivalent in the sense that they are based on mutual confidence between the partners, established mainly by the results of interlaboratory comparisons, uniform implementation of International Standards and peer assessments or accreditations.
Reference values for the sensitivity of standard accelerometers used in intercomparisons
Authors: Evans David J. , Leigh Stefan D. , Payne Beverly F.
Published: July 2012

The National Metrology Institutes (NMIs) of five countries in North America and South America participated in an interlaboratory comparison involving the calibration of the magnitude of the sensitivity of three standard accelerometers. This comparison was performed by laboratories within the framework of the Interamerican Metrology System (SIM). One of the key values to be obtained in any interlaboratory comparison is an estimate of the reference values for the artifact being calibrated. Three statistical methods have been used to obtain candidate reference values and associated uncertainties from the SIM intercomparison data: an average of means method; a method based on the ISO Guide to the Expression of Uncertainty in Measurement; and a maximum likelihood method. Reference values and associated uncertainties obtained using the three methods are presented and compared, as well as useful graphical displays with resulting qualitative conclusions.
Model-based method for improvements in the calibration of ultrasonic power measurements at low-power levels
Authors: Wu Lixue
Published: July 2012

The measurement uncertainty in the calibration of ultrasonic power measurements at low-power levels was reduced by a model-based signal-processing method. The ultrasonic power measurement system is based on the radiation force balance method according to IEC 61161. Outputs of an electronic balance and the excitation voltage were simultaneously sampled and recorded. A computer-controlled coaxial switch that utilizes data lines of the parallel port of a desktop computer was used for power-on and power-off control. Power-on and power-off intervals were finely controlled by the desktop computer. The Electroacoustic radiation conductance, defined as the ratio of the ultrasonic power of a transducer and the square of the rf voltage at its input, was calculated from the recorded data. During data processing, a simple model for drifting and switching was proposed and a least-mean-squares algorithm was used to estimate parameters of the model. Good measurement reproducibility was also observed that resulted in the reduction of total measurement uncertainty.
Chinese string instruments 400 B.C.–200 A.D
Authors: Lawergren Bo
Published: July 2012

When the tomb of Marquis Yi of Zeng (deceased 422 B.C.) was opened in 1978, a large number of musical instruments came to light. Many of those have since been well studied—in particular the bronze and stone chimes—but the string instruments (various types of zithers) have not. This year the author published the first Western language study of the zithers from Zeng and contemporary Chinese sites (B. Lawergren, ‘‘Strings,’’ in Music in the Age of Confucius, edited by J. F. So, Washington, DC), and it forms the basis of this survey. Some types of Zeng zithers were precursors of instruments (qin and zheng) that became important during the last two millennia of Chinese music. Other types (se and the zhu) died out after some centuries. The most interesting precursor is that of the classical qin. The latter has been held in highest esteem since at least 200 A.D., imbued with deep philosophical meaning, and considered an indigenous invention par excellence. But several features of the precursor appear to be foreign, probably from central or western Asia. A reproduction will be used to demonstrate sounds, tuning systems, and concepts of the Zeng qin.
The Burmese harp: Its scale and tunings
Authors: Williamson Robert M.
Published: July 2012

The 16 strings of the Burmese horizontal, arched harp are tuned in pentatonic octaves over a range of two-and-a-half octaves. A brief description of the harp, its history, and examples of its classical music will precede a discussion of the results of pitch measurements of harp tones recorded in Mandalay in the mid-20th century of the late Muriel C. Williamson [The Burmese Harp (Southeast Asia Press, DeKalb, IL, 2000)]. Prior to about 1960, the seven-tone Burmese harp scale could be accurately described by the notes CDE*( E ) F G A *( A ) B*, where the starred notes were about a quarter tone (50 cents) lower than the corresponding Western notes. The pitches of the notes E* and A* could be varied when they occurred as stopped tones of the harp. The distinctive Burmese notes became Western within a few decades. The remarkably precise tunings of master harpists sometimes showed octaves stretched by about 15 cents. Previous measurements of Burmese fixed-pitch instruments show them to have had somewhat tempered version of the harp scale. a)Present address: 1189 Pond Cypress Drive, Virginia Beach, VA 23455.
How are two tones produced simultaneously in throat-singing?
Authors: Adachi Seiji , Yamada Masashi
Published: July 2012

The most remarkable characteristic of throat-singing is that one singer simultaneously produces two distinct tones—drone and melody. The drone has a low and sustained pitch, and is sung with a pressed voice. The melody has a whistlelike tone, whose pitches are much higher than the drone. It was conjectured that the production of the melody was caused by the resonance of the vocal tract, but has never been proved. This study clarifies that the high melody pitch is produced by the pipe resonance of the rear cavity in the vocal tract. This is derived from acoustic investigations on a throat-singer’s vocal tract measured by magnetic resonance imaging. Four different shapes of the vocal tract are examined, with which the melody pitches of F6, G6, A6, and C7 are sung along with the F3 drone of a specific pressed voice. The second formant frequency calculated from each tract shape is close to the melody pitch within an error of 36 cents. Sounds are synthesized by convolving a glottal source waveform with transfer functions calculated from the vocal tract shapes. Two pitches are found to be successfully perceived when the synthesized sounds are listened to.
Thermoacoustic oscillation around a plate in a nonlinear standing wave field
Authors: Dongtao Huang , Qing Guo , Zhichi Zhu
Published: July 2012

A stack of plates is a most basic and important component of thermoacoustic engines and thermoacoustic refrigerators. Analysis of thermoacoustic oscillation around a plate is a basis of analysis of the mechanism of these machines, but only the works in a linear standing wave field were published. On the other hand, it is shown from some experiments that the thermoacoustic efficiencies of these machines will be increased in the nonlinear standing wave field, but any quantitative result has not been found yet. In this paper a numerical simulation of thermoacoustic oscillation around a plate in a standing wave tube where the sound-pressure level of the sources is from 90 to 170 dB has been presented in order to discuss the nonlinear effects quantitatively. Two conclusions have been obtained: (1) thermoacoustic efficiencies are increased with the increase of the source slowly below 150 dB, moderately from 150 to 160 dB, and rapidly above 160 dB. (2) There exists a rule of multiplying growth of high-order harmonics of oscillation temperature level, which is very similar to the rule of multiplying growth of high-order harmonics of oscillation sound-pressure level in a nonlinear standing wave tube.
A unified method for free vibrations of elastically restrained plates arbitrarily loaded with springs and masses
Authors: Li W. L. , Daniels M.
Published: July 2012

A simple and unified Fourier series method is presented for the vibration analysis of a class of plates that are simply supported along a pair of opposite edges and elastically restrained along the others. The plates can also be arbitrarily loaded with springs and masses. The transverse displacements of the plates are expressed as the superposition of a Fourier sine series and a simple cubic polynomial. The polynomial is introduced to take care of all the discontinuities with the original displacement and its relevant derivatives along the edges so that the Fourier series now simply represents a residual (or conditioned) displacement which is continuous and has at least three continuous derivatives. The excellent accuracy and convergence of the current method are demonstrated through various numerical examples.
Weak and strong couplings between a master oscillator and a set of satellite oscillators
Authors: Maidanik G.
Published: July 2012

The distribution of resonance frequencies of the satellite oscillators in situ is imposed. This imposition demands that the stiffness control term in the satellite oscillator’s impedance and the stiffness control term in the coupling, of this oscillator to the master oscillator, be supplemental. Moreover, the distribution is aligned in ascending order; namely, ωr≤ωq; q=(r+1); 1≤r≤(R−1), where (ωr) and (ωq) are the resonance frequencies of the (r)th and (q)th satellite oscillators, respectively, and (R) is their number. In addition, the numbers of resonance frequencies of the satellite oscillators, on either side of the resonance frequency (ωο) of the master oscillator, are rendered equal. The couplings are assigned mass, stiffness, and gyroscopic control terms. Examples of the influence that the satellite oscillators collectively have on the response of the master oscillator, under various coupling forms and strengths, will be cited.
On the use of Ritz series as an alternative to field equations for modal analysis of continuous systems
Authors: Ginsberg Jerry H.
Published: July 2012

Mathematical analysis of a continuous system’s transient response commonly relies on modal properties obtained as an eigensolution of the field equations. Such solutions become cumbersome if the system has attached springs, masses, or substructures, in which case the eigenvalue problem requires mathematically connecting subdomains of the continuum with continuity conditions and Robin boundary conditions. Derivation of the modal orthogonality conditions, knowledge of which is required for implementing the expansion theorem, is quite intricate in such cases. The Rayleigh–Ritz method is a widely used alternative for identifying modes. Representing the displacement field with a Ritz series in conjunction with Hamilton’s principle, which is commonly known as the method of assumed modes, offers a generalization of the Rayleigh–Ritz method that can also be employed to analyze forced response. The present paper will demonstrate that if one appropriately alters their viewpoint, and performs a few minor intermediate steps, it is possible to use the Ritz series formalism to obtain the same results (mode functions, orthogonality properties, and the expansion theorem) as those obtained by solving field equations. Such a derivation solely requires knowledge of the kinetic and potential energy functionals, and therefore is much easier to implement for multiply connected systems.
Test stand for measuring the vibration of impact-type hand-held tools
Authors: Reynolds Douglas , Markle Jeff
Published: July 2012

Vibration from hand-held impact tools is a major cause of hand-arm vibration syndrome (HAVS) in industrial workers. Evaluating the effectiveness of engineering methods for reducing tool vibration in impact tools has been hampered because of the inability to measure the impact vibration of the working end of the tools. A test fixture has been developed that can be used to measure the impact vibration at the working end of a hand-held impact tool. These measured values can be used to determine whether or not the claimed vibration reduction of a tool is related to an effective engineering modification to the tool without reducing the productivity of the tool. Measurements were made on a rivit hammer to determine the effectiveness of a vibration-reducing mechanism applied to the tool attachment section at the working end of the tool. This mechanism reduced the vibration at the handle of the tool by 80%.
Cable strum self-noise cancellation for sonar towed arrays
Authors: Premus Vincent E.
Published: July 2012

Nonacoustic self-noise observed on marine seismic streamers and towed sonar arrays represents a serious problem for acoustic source detection at low frequency. Towed array self-noise, also known as cable strum, consists of mechanical vibrations induced by vortex shedding. Transverse vibrations in the array body subject each hydrophone pressure head to local accelerations. The resultant acoustic response can be several orders of magnitude stronger than the water-borne acoustic signals of interest. In this paper, a beamspace, time-domain adaptive signal processing architecture for the coherent rejection of broadband nonacoustic self-noise is presented. The approach is based on the recognition that most vibrational modes of a towed array propagate at phase speeds substantially less than those of acoustic signals in the water column. This property supports the formation of a signal-free, strum reference using the same sensor that samples the acoustic data. The approach removes the need for additional measurement channels, such as accelerometers or strain gauges, to independently sense the undesirable distortions introduced by cable strumming. The phenomenology underlying flow-induced self-noise for towed arrays is discussed and characterized using k-w analysis. An overview of the method is presented and cancellation performance is demonstrated using snapshots of passive sonar towed array data. [Work sponsored by the Department of the Navy, under Air Force Contract F19628-95-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the U.S. Air Force.]
Articulatory gestures in the motor theory
Authors: Mattingly Ignatius G.
Published: July 2012

According to Alvin Liberman’s motor theory, the objects of speech perception are ‘‘articulatory gestures.’’ But, what is an articulatory gesture? In early statements of the theory, this phrase seems to mean simply the movements of a single articulator, as idealized in traditional impressionistic-phonetic terms such as ‘‘tongue raising.’’ But, the notion of the articulatory gesture was greatly enriched over the years as Liberman and his colleagues took account of evidence from experiments in both speech perception and speech production. In the most recent statements of the motor theory, the articulatory gesture has become a temporary modification of the geometry or the excitation of the vocal tract, typically involving more than one articulator, often global rather than local. To Liberman and his colleagues, the human ability to distinguish and identify various such gestures from the available acoustical and optical data, despite extensive temporal overlap, appeared more remarkable than ever.
Inversion methods for ultrasonic travel-time tomography
Authors: Berryman James G.
Published: July 2012

Ultrasound travel-time tomography in a laboratory setting, where data can be collected without limited views in 2-D and/or 3-D imaging, has many advantages over seismic travel-time tomography in the earth. When samples to be imaged have relatively high contrast, some new methods that might be called ‘‘velocity spectroscopy’’ and ‘‘smart backprojection’’ become viable for fast and accurate imaging of any number of inclusions, as long as they are not too small and not too dense in the imaging plane. For low contrast, some simple methods have also been developed for ray bending analyses that are relatively quick and more accurate than straight ray methods, such as filtered backprojection. Applications of these methods to synthetic and real data will be discussed.
Recent developments in 3-D SAFT reconstruction applied to laser-ultrasonics
Authors: Levesque Daniel , Blouin Alain , Neron Christian , Monchalin Jean-Pierre
Published: July 2012

The Synthetic Aperture Focusing Technique (SAFT) has been used to improve both the detectability and the lateral resolution of conventional ultrasonics. This method has recently been applied to laser-ultrasonics, an ultrasonic technique based on the generation and detection of ultrasound with lasers. Actual 3-D SAFT reconstruction is still considered computationally intensive and the pseudo-3-D SAFT, stacking line SAFT images together, is more commonly used. A recent development in 3-D SAFT reconstruction is toward improvements of frequency domain SAFT. In addition to increasing speed, the improved method (F-SAFT) includes temporal deconvolution to enhance both axial and lateral resolutions, con-trol of the aperture to improve signal-to-noise ratio, as well as spatial interpolation in subsurface planes. These last two features also allow a reduction in the sampling requirements to further decrease both data acquisition time and processing time, therefore making the technique more attractive for industrial use. All the above operations are well adapted to the frequency domain calculations and embedded in the F-SAFT processing. The performance of F-SAFT reconstruction will be illustrated using laser-ultrasonic data taken from test samples with flat-bottom holes.
Optimal source distribution for virtual acoustic imaging
Authors: Takeuchi Takashi , Nelson Philip A.
Published: July 2012

When binaural sound signals are presented with loudspeakers, the system inversion involved gives rise to a number of problems such as loss of dynamic range and a lack of robustness to small errors in control performance. Regularization, often used to design practical filters, also results in poor control performance around ill-conditioned frequencies. These problems for such systems are investigated and this has resulted in the proposal of a new system concept. The system overcomes these fundamental problems by means of a conceptual pair of monopole transducers whose span varies continuously as a function of frequency. The underlying theoretical principle is described in detail. The significance is that all of the above problems that are associated with the multi-channel system inversion are solved by using this principle. The limitations with this principle are also made clear in terms of the operational frequency range. Several examples of practical solutions that can realize a variable transducer span by discretization are also described. The discretization expands the operational frequency region to be used with only a little decrease in performance. This principle is extremely useful and practical because a single transducer which can cover the whole audible frequency range is not currently available.
High-frequency propagation modeling with the parabolic equation
Authors: Fromm David M. , Collins Michael D. , Norton Guy V.
Published: July 2012

It is generally believed that the parabolic equation method rapidly becomes impractical above a few hundred Hertz for ocean acoustics problems. Results will be presented to illustrate that the split-step Padé algorithm [J. Acoust. Soc. Am. 100, 178–182 (1996)] is practical out to ranges of tens of kilometers for frequencies up to at least on the order of 10 kHz. The presentation will include a discussion of modifications to the parabolic equation model to handle effects that are usually neglected at lower frequencies, such as rough surfaces, internal waves, and volume attenuation in the water column. The examples will involve propagation in surface ducts and interaction with the seafloor. [Work supported by the Office of Naval Research.]
A wide-angle parabolic equation for advected acoustic waves
Authors: Lingevitch Joseph F. , Collins Michael D. , Dacol Dalcio K. , Rogers Joel C. W. , Siegmann William L.
Published: July 2012

Parabolic equations are derived by factoring operators in elliptic equations. For acoustics problems involving an ambient flow, the elliptic equation contains two depth operators that do not commute with each other. Due to this difficulty in factoring the operator, the parabolic equations that have been derived for this problem are limited to small grazing angles (i.e., energy that propagates nearly horizontally). A wide-angle parabolic equation for advected waves will be described and examples will be presented to demonstrate its accuracy. As in previous investigations of this problem, the Mach number is assumed to be small. The derivation is based on the introduction of a new dependent variable that is related to the acoustic pressure by an amplitude operator that can be implemented using either of two approximations. A zeroth-order approximation (in Mach number) is useful in some cases since the error is local in range. Greater accuracy can be achieved using a first-order approximation, which can be expressed in terms of the derivative of an operator with respect to a parameter and implemented using a difference formula. [Work supported by the Office of Naval Research.]
A new stable formulation of an elastic parabolic equation
Authors: Jerzak Wayne , Siegmann William L. , Collins Michael D. , Lingevitch Joseph F.
Published: July 2012

The parabolic equation method can be used to model acoustic-wave propagation in elastic media. Current implementations do not accurately match the shear stress between two elastic layers, for which the expression involves a second-order depth derivative. This inaccuracy could be large in range-dependent problems. A reformulation of the elastic equations in terms of new variables permits all interface conditions to be handled accurately since no expressions contain second- or higher-order depth derivatives. However, the implementation in the new variables is found to be unstable because some evanescent modes are allowed to grow. Higher-order evanescent modes can be suppressed using a rational approximation to the depth operator with a polynomial in the denominator having a higher degree than the numerator. The lower-order evanescent modes can be controlled by imposing constraints on the choice of coefficients in the approximation. Examples are presented to show the accuracy and stability of the new parabolic equation in shallow-water environments. [Work supported by ONR.]
Computation of the acoustical wave-fronts in a phase space
Authors: Maltsev Nick E.
Published: July 2012

The computation of acoustical wave-fronts in 2-D and 3-D coordinate space can be performed by the computation of rays and approximation of the fronts between the rays by some interpolation formula. The amount of neccessary rays increases with distance and rapidly exhausts memory and performance of the computer. It happens due to the extremely sophisticated and unsmooth nature of the ray picture. Due to the fact that trajectories of a dynamic system do not intersect in phase space, appropriate rays and fronts surface in phase space is smooth and can be easily approximated by a smaller number of rays, and this number increases very slow with distance. This number can be reduced by involving equations in variations, which generate tangent vectors to this surface. Formally, dimension of phase space is a doubled dimension of coordinate space. Using some properties of ray equations, the dimension of the phase space in the 2-D coordinate case can be reduced from 4-D to 3-D and in 3-D coordinate case from 6-D to 5-D. This approach opens new ways of fast global and local estimates of sound field and for inverse problems in underwater acoustics. This report produces a set of numerical and analytical examples.
Wave-front modeling
Authors: Tindle Chris T.
Published: July 2012

Wave-front modeling offers a direct method of finding pulse waveforms in both deep and shallow water. The wave-front is found by tracing rays to a fixed range and finding the ray depth as a function of starting angle. Interpolation on the wave-front provides the amplitude and arrival time at the receiver depth. Phase is determined by the ray history. The expressions for the phase and amplitude are derived directly from the wave equation using WKB approximations for solutions to the depth-separated equation. Caustics are handled by treating rays as pairs and involve Airy functions which describe the smooth transition between insonified and shadow regions. On the shadow side of a caustic the rays have complex angles and travel times. Ray-tracing for complex angles can be avoided and waveforms in the shadow can be found approximately by fitting the phase function near the caustic.
Evaluation of schemes for interpolating eigenray properties between updates in acoustic propagation modeling
Authors: Clark Joseph A.
Published: July 2012

Acoustic simulators can model the propagation of sound in the ocean by computing a set of eigenrays between sources and receivers. A matrix of features characterizing each eigenray is computed using environmental data. The eigenray matrices are then used to modify the source signals received by each receiver. Temporal variations, introduced into the eigenrays by motions of the sources and receivers, require that the eigenray matrices be updated. Some form of interpolation between updates is needed in order to avoid the introduction of artifacts into the simulated signals. Doppler effects must also be appropriately reproduced in the data. This talk describes a method for evaluating interpolation schemes by performing transient analyses of the simulated signals. Graphical displays used to examine the data streams will be shown. Visual and aural indications of artifacts produced by poor interpolation schemes and difficult modeling conditions will be identified. Evaluations of some improved interpolation schemes will be presented.
Simulation of underwater intensity vector measurement: Effect of errors and noise
Authors: Hutt Daniel L. , Hines Paul C. , Young Victor W.
Published: July 2012

Pressure and pressure-gradient signals from an array of hydrophones can be processed to yield the three-dimensional sound-intensity vector of an acoustic field. In underwater applications, the technique may prove useful for near-field measurements of acoustic intensity and characterization of ambient noise fields. Unfortunately, the accuracy of the magnitude and direction of the calculated intensity vector is degraded by many factors including: fluctuations in the received signal, the presence of ambient noise, system noise, phase error, and errors in channel sensitivity. To investigate the effect of these errors, a numerical simulation of the pressure field due to signal sources and ambient noise was developed. The model is used to calculate the variance of intensity measurements under different noise conditions and to simulate the effects of channel gain and phase imbalance. The results are found to be in good agreement with theoretical expressions. The simulation was also used to compare the performance of a six-element orthogonal intensity array and a four-element tetrahedral intensity array in terms of gain against noise and variance in estimated direction to a sound source.
Spectral integral representations of multistatic scattering from sediment volume inhomogeneities
Authors: Schmidt Henrik , LePage Kevin D.
Published: July 2012

A perturbation approximation for multistatic scattering from sediment volume inhomogeneities has been developed using a Fourier–Bessel spectral integral representation of the source and receiver Green’s functions. This approach is particularly efficient for modeling scattering from horizontally isotropic, three-dimensional distributions of scatterers in waveguides with arbitrary horizontal layering, and is accurate for scatterers in fast bottoms near the critical angle and for scatterers in layers with background sound-speed gradients. The theory has been implemented in the oases code and the model has been exercised over broad bandwidths in order to explore the temporal and angular evolution of bistatic scattering for a variety of environmental and experimental scenarios. Examples show that the scattered field received on a bistatic vertical line array shows a distinct evolution in time and angle which can be simply related to the source–receiver geometry and the location of the contributing scatterers at any given time. Similarly, the horizontal angular evolution of bistatic scattering shows a time-angle trajectory which may be easily interpreted using similar geometrical arguments. [Work partially supported by ONR.]
Outdoor concert sounds—Searching for acceptability criteria for communities adjacent to amphitheaters
Authors: Cavanaugh William J.
Published: July 2012

Most municipal, state, and federal codes and regulations are inadequate for protecting residential communities adjacent to concert amphitheaters from annoyance due to sound of high-level amplified music, as well as from other concert-related sounds. From numerous consultations involving siting of new and evaluating existing amphitheaters, the author has evolved a criterion which appears to predict with sufficient accuracy the likely response of residential occupants to amphitheater sounds. This experience suggests that if the intrusions represented by the 1-percentile A-weighted levels are not more than 5 dB above the pre-existing (i.e., nonconcert) background represented by the 90-percentile levels, the intrusions are sufficiently immersed in and masked by the normal background and most communities are satisfied. However, some neighbors find the mere audibility or detectability of amphitheater sounds objectionable and measurement is at best difficult where the sound levels are of the same order of magnitude as the normal community background sound. The experience in developing and applying this signal-to-noise based criterion to several amphitheater projects, one of which has been in operation for over 15 years, is reviewed.
Community noise reduction through sound system renovation, a case study
Authors: Marsh David E. , Randorff Jack E.
Published: July 2012

Noise intrusions from the Miller Outdoor Theater in Houston, Texas caused recurring complaints from the surrounding upscale community. Measurements confirmed that events at this performing arts venue regularly produced levels of 75 dBA and above at residents homes approximately 1,300 ft from the proscenium stage. The project goals were to provide the theater with a high-quality sound system, capable of producing nominal levels of 95 dBA at the audio mixing console and 85 dBA at the farthest lawn seats (340 ft from the stage) while not exceeding levels of around 55 dBA in the nearby neighborhood. These goals were met through loudspeaker selection (including some customization) along with careful loudspeaker zoning, elevation, and aiming. Two different computer-based programs were used for acoustical modeling—one to design and predict the sound systems coverage throughout the seating area and another to predict noise propagation from the theater into the community. Both programs were used to produce maps indicating sound levels as color contours which simplified presentation of these data to the client.
The acoustics of the outdoor Shakespeare theater—Rutland, UK
Authors: Mapp Peter A.
Published: July 2012

The outdoor Shakespeare Amphitheatre at Tolethorpe (Rutland, UK) is an unusual form of theater in that the actors perform in the open air while the audience is enclosed in a lightweight Teflon fabric auditorium. This unique format produces some unusual acoustic properties and problems. The early reflection patterns from and around the stage are quite different from a normal enclosed proscenium theater. The Teflon walls and roof, while effectively acoustically transparent at low and lower midfrequencies, become highly reflective at high frequencies. This not only impacts the transmission of sound through the structure but also speech transmission and intelligibility within the auditorium. The hyperbolic curved-roof surfaces and flat parallel walls were found to cause undesirable sound focusing and reflections detrimental to speech intelligibility. The acoustics of the space was investigated by means of both directional and binaural time-domain spectrometry techniques as well as more traditional acoustic measures. The paper presents the results of these measurements and outlines the remedial treatments adopted.
Recent developments in biomedical ultrasound
Authors: Crum Lawrence A.
Published: July 2012

Biomedical ultrasound has seen remarkable advances in recent years. By utilizing the properties of nonlinear acoustics, diagnostic ultrasound has shown increased applicability to a wide number of clinical conditions and pathologies. Techniques such as harmonic imaging and the use of ultrasound contrast agents (stabilized microbubbles) have enabled such long-sought goals as noninvasive determination of myocardial perfusion to be clearly within our grasp. Advancements in semiconductor miniaturization have led to the construction of ultrasonic scanners that are now hand-held, and together with telemedicine techniques, it is now reasonable to expect that diagnostic ultrasound will soon be the doctor’s stethoscope. An even more promising future is seen for therapeutic ultrasound. Although the mechanism is not yet clearly understood, ultrasound can transiently permeabilize cell membranes, thus permitting the delivery of therapy to specific sites within the body; indeed, together with drug-carrying ultrasound contrast agents, ‘‘site-specific drug delivery’’ is now in clinical trials. Finally, the application of High Intensity Focused Ultrasound can induce coagulative necrosis at well-controlled sites within tissue. When imaging and therapy are combined, ‘‘image-guided, transcutaneous, bloodless surgery’’ devices are now under development. With acoustics, ‘‘Star Trek medicine’’ is just around the corner.
Recent studies of the lip reed: Low-tech experiments and stroboscopic observations
Authors: Ayers R. Dean
Published: July 2012

There are currently three basic models for the brass player’s vibrating lips: (1) Helmholtz’s outward-striking or swinging door model, (2) a sliding door model, with motion that is transverse to the air stream, and (3) a hybrid, two-dimensional model that combines those two motions. Time-domain computer simulations of these models have been carried out by S. Adachi and M. Sato [J. Acoust. Soc. Am. 97, 3850–3861 (1995); 99, 1200–1209 (1996)]. The experience of brass players agrees qualitatively with the behavior of the hybrid model. Feedback is optimized near each peak of the input impedance curve, and from there it is easy to drop the playing frequency but not to push it upward. (Buzzing on an isolated mouthpiece yields the same behavior, even though there is no regime of oscillation.) A graph of playing frequency versus an operationally defined ‘‘lip frequency’’ is obtained by using a side hole in the backbore. Agreement with results from the hybrid model is good for the first few modes but not the higher ones. Stroboscopic images of Rayleigh waves on the upper lip suggest that a more advanced model should have at least two masses performing orbital motion. Demonstrations will be included. [Work supported in part by the Scholarly and Creative Activities Committee at CSULB.]
Sounds of ancient Korean bells
Authors: Kim Yang-Hann
Published: July 2012

This paper reviews the sounds of bells cast during the Shilla Dynasty. One unique characteristic of Korean bells is that they create beats. The beats of various ancient bells are summarized and analyzed with regard to mass, and other geometrical dimensions. Other interesting and unique features of the old Korean bells are that they have sound pipes on top and hollows below the bells. The types of pipes and hollows are also studied and reported. In fact, the pipe is a high-pass filter so that it dissipates high-frequency sound as fast as it can, and the hollow is a resonator that can somehow sustain a beating sound. Bells cast during the Shilla and Korea Dynasty and their sound characteristics are investigated and summarized.