bluuebunny/crossref_metadata_2025 huggingface dataset:
Saltus-type boundary conditions for the modeling of rough interfaces in acoustic wave problems
Authors: de Hoop Adriannus T. , de Vries Sijtze M. , Miller Douglas
Published: October 2005

The method of moving volume averages is used to derive boundary conditions of the saltus or jump type for the modeling of acoustic wave interaction across a rough interface between two media. For this purpose, a smooth boundary layer is constructed that contains the rough interface in its interior. The medium in this layer is considered as a mixture of the two media present. On the scale at which the acoustic wave motion is analyzed, the mixture is assumed to have acoustically linear macroscopic properties. The resulting saltus-type boundary conditions express the jumps in the basic quantities that describe the wave motion (pressure or stress and particle velocity) across the boundary layer in terms of the limiting values that these quantities attain at either side of the layer in a linear manner. Conditions of this type are worked out for a rough interface between (a) two fluids, (b) two solids, and (c) a fluid and a solid. In all cases, full anisotropy, including the one that is induced by the interface geometry, is taken into account.
Arctic ambient noise mechanisms
Authors: Dyer Ira
Published: October 2005

The study of ambient noise ca n be divided into two categories, one dealing with the correlation of averaged noise with the slow evolution of environmental parameters, and the other concentrating on details of the ice fracture processes that ultimately give rise to individual noise events. Recent progress in both categories, especially at low frequencies (3–100 Hz) where significant results appear to be at hand, is reviewed. Thoughts on higher frequencies (100–3000 Hz) are also given, for which it seems likely that the environmental correlates and detailed source mechanisms are of a different character than at low frequencies. Finally, distinctions are drawn between pack ice of the central Arctic and low-concentration ice of the marginal ice zone, with respect to their likely mechanisms of noise generation. [Work supported by ONR, Arctic Program Office.]
The movie palace as performing arts center
Authors: George Peter J.
Published: October 2005

Many movie theaters in downtown neighborhoods have been saved from demolition by their renovation and recycling as performing arts centers. While these spaces often have physical characteristics that are deemed acoustically desirable, there are often many features that are detrimental to a good acoustical performing environment. This paper describes typical attributes and deficiencies with methodology to improve the latter.
The female voice—Experiments and overview
Authors: Fant Gunnar , Gobl Christer , Karlsson Inger , Lin Qiguang
Published: October 2005

Results from recent experiments at the KTH directed to the study of aerodynamics and voice source flow will be presented. These include simultaneous recordings of glottal airflow and supraglottal pressure from a Rothenberg mask. A number of females served as subjects producing isolated syllables and, in one instance, complete sentences. For one subject, the subglottal pressure was also recorded. Typical temporal profiles of these measures, including glottal leakage, will be discussed. In a separate study, data were collected on glottal flow waveforms from inverse filtering of the speech pressure wave. A parametrization and resynthesis in terms of the four-parameter LF model has been undertaken, which allows a comparison with a set of male voices. Theoretical studies of source-vocal-tract interaction effects provide a basis for interpretation of results and modeling of female specific characteristics. Finally, a review is presented of accumulated insight in the properties of female speech including factors other than source mechanisms.
Glottal airflow and pressure measurements for female and male speakers in soft, normal, and loud voice
Authors: Holmberg E. B. , Hillman R. E. , Perkell J. S.
Published: October 2005

Measurements on the inverse filtered airflow waveform (the “glottal waveform”) and of estimated average transglottal pressure and glottal airflow were made for production of syllable sequences in soft, normal, and loud voice by 20 female and 25 male speakers. Statistical analyses showed that, while there was no significant female-male difference in pressure within any of the loudness conditions, there were significant female-male differences in the glottal waveform parameters that should be relevant to differences in voice source characteristics. In normal and loud voice, female waveforms indicated lower vocal fold closing velocity, lower ac (modulated) flow, and proportionally shorter closed phase of the cycle, suggesting a steeper spectral slope for females. In soft voice, female ac flow was significantly lower than males', but there were no significant differences in female-male closing velocity or relative length of the closed portion, suggesting more similar spectral slopes. The dc (unmodulated) flow did not differ significantly between females and males. Possible implications of the results for female and male voice quality are discussed. [Work supported by NIH.]
Acoustic correlates of breathiness: First harmonic amplitude, turbulence noise, and tracheal coupling
Authors: Klatt Dennis H.
Published: October 2005

A selected sample of reiterant speech has been collected from ten female speakers and six male controls in order to quantify acoustic correlates of perceived breathiness of the female voice, and to contrast these measures with comparable data from males. Two sentences with differing stress patterns were spoken by replacing each syllable by [hV] and by [ʔV], where V = [a,i,ae,o,rr]. Detailed analysis of the [a] data reveals (1) wide variation in the strength of the first harmonic (relative to first formant amplitude), with an average increase of about 6 dB for females relative to males; (2) a greater tendency for the third formant to be excited by noise rather than voicing harmonics in the female population; and (3) indications of tracheal poles and zeros in the spectra of vowels adjacent to voiceless consonants in utterances produced by both genders. These three measures of breathiness tend to be greatest in unstressed syllables and toward the end of an utterance. The acoustic data will be correlated with perceived breathiness of utterances from individual talkers in a preliminary attempt to determine which measure is perceptually most salient; future research using synthesis will systematically investigate perceptual salience. [Work supported, in part, by an NIH grant.]
Profile analysis with time-varying stimuli
Authors: Green David M. , Nguyen Quang T.
Published: October 2005

Detecting a change in spectral shape, when the change occurs at a single spectral locus, requires a simultaneous comparison of the unchanged part of the spectrum with the altered or “signal” part. What are the temporal parameters of the stimulus that influence such comparisons? To consider this question, a complex of 21-equal-amplitude components was used, ranging from 200–5000 Hz, with equal logarithmic spacing between components. The signal was an increase in level of one component of the multicomponent spectrum. Overall level of the sound varied randomly over a 20-dB range. The signal component and the 20 nonsignal components were amplitude modulated separately. The relative phase of the two modulators was manipulated so that the signal and nonsignal components waxed and waned either in-phase or out-of-phase. For modulation rates faster than about 40 Hz, the thresholds in the two conditions are nearly the same. Thus, for slower rates of modulation, the data suggest that the temporal structure of the spectrum is important, while above 40 Hz, only the power spectrum of the stimulus is critical. [Research supported by the National Institute of Health and the Air Force Office of Scientific Research.]
Phase has no effect on simultaneous or forward masked thresholds
Authors: Weber Daniel L.
Published: October 2005

Thresholds for sinusoidal signals at 0.5, 2.0, and 6.0 kHz were measured in a variety of masking conditions using a two-interval, forced-choice procedure. All conditions were performed in the presence of a diotic, white, broadband noise with a spectrum level of 20 dB SPL. All sinusoidal stimuli were presented monaurally in the listener's left ear; all fixed level components were presented at 65 dB SPL. In a determination of the Weber fraction for a 295-ms signal masked by a sinusold of the same frequency and temporal characteristics, the threshold varied with the phase between masker and signal, as one would predict from the assumption that the task depends only upon the detection of a difference in power (or related dimension) between masker and masker plus signal. In these data, the detection of phase differences, per se, appeared to have no effect on threshold. These data provided a reference for a second condition, in which the 295-ms signal interval was preceded and followed by 295-ms presentations of a sinusoid at the signal frequency. These “fringe” components had the same phase on all presentations; the signal was added to the masker in quadrature. Signal threshold was measured as a function of the phase angle between the fixed fringe components and the masker. In nonsignal intervals, the masker and signal were replaced by a presentation of the fringe component. Presentation of the signal thus produced a change in both phase and level compared to the fringe components. However, thresholds were not improved by the presence of the phase change. Both of the above conditions were repeated for a 20-ms masker and signal, and again showed no evidence that a change in phase improves detection performance. With this shorter signal, it was possible to examine threshold as a function of the phase angle between the signal and a 295-ms forward masker. In forward masking, phase had no effect on signal threshold. [Research supported by NSF.]
Forced-choice procedures can yield contaminated thresholds: Masker response bias
Authors: Spiegel Murray F.
Published: October 2005

Early measurements of human performance were plagued by response biases, such as a preference for choosing “yes” in a yes/no signal-detection task, or a tendency to choose the second of two sounds as louder, longer, or higher. Signal detection theory, as well as forced-choice and adaptive procedures, have largely eliminated the influence of response biases while also streamlining the data collection process. These procedures are adequate when the set of maskers are indistinguishable. However, adaptive procedures, when combined with forced-choice methods, are sensitive to response bias when the various maskers are distinguishable. The response bias is a preference for particular maskers, when maskers are randomized within a trial. Thresholds can be seriously contaminated; depending on the magnitude of the bias, subjects can appear to be responding perfectly to inaudible signals. Procedures that avoid the problem resulting from this form of response bias are not as efficient as adaptive, forced-choice procedures, and often entail more traditional methods of testing.
A context-free rubber band model of scaling auditory dimensions
Authors: Pollack Irwin
Published: October 2005

Auditory signals varying in frequency, duration, and/or amplitude were presented to listeners. The listener's task was to mark a linear scale to rate the relative position of one sound on a scale demarked by the other two. The signals that defined the ends of the scale were varied from trial-to-trial. The ratings are well-predicted by assuming that the ratio of scale distances is invariant with the particular sounds that define the scale. Stated otherwise, the rating scale is conceived in terms of positions upon a rubber band. Different scales, defined by different end stimuli, result in local compression and extension of the band, but relative distances among intermediate ratings are unchanged by scale changes. The model's apparently excellent performance may simply result from the powerful constraint of monotonicity in the scaling of unidimensional signals.
A satellite classroom for advanced acoustic studies
Authors: Stern Richard
Published: October 2005

The Graduate Program in Acoustics, Penn State University, is offering a Master of Engineering Degree in Acoustics via satellite to the Navy Undersea Weapons Engineering Station (NUWES), Keyport, Washington. The program will take 2 years to complete and consists of both televised and on-site instruction. Progress of the program and lessons learned will be discussed.
Graduate continuing education by satellite
Authors: Baldwin Lionel V.
Published: October 2005

Progress in telecommunications technologies presents the engineering profession with exciting new ways to integrate advanced study with the job. Ten years ago the U.S. colleges of engineering that operate regional ITV systems started planning for a common goal: to increase the national effectiveness of continuing education of engineers. Two new institutions, the National Technological University (NTU) and the Association for Media-Based Continuing Engineering Education (AMCEE) that coordinate credit and continuing education programs, respective]y, are now accelerating the introduction of linkages between engineering faculty and engineers at work via a satellite. Both NTU and AMCEE began regular satellite delivery of advanced technical education in August 1985. As we enter the third year of operations, NTU will serve more than 3200 enrollees for academic credit instruction during 1987–1988; AMCEE will provide over a thousand hours of noncredit, live-and-interactive programming. The service operates in GSTAR-I with a modern Kuband transponder, which broadcasts two channels of full-motion, color video throughout the day and evening of each workday. Eighteen universities currently operate uplinks to provide live programming over the networks and, in addition, three corporate studios have uplinks and regularly originate instruction.
Optimizing the performance of piezoelectric drivers using stepped horns
Authors: Bangviwat A. , Finch R. D.
Published: October 2005

An analysis is presented for the design of piezoelectric transducers, in a sandwich configuration using a stepped horn as particle velocity amplifier. The condition for maximum power delivery to the load impedance is established in terms of the parameters of the horn and the piezoelectric material. Analytical solutions can be found readily if one of the horn lengths is chosen. If this is done, then there are two area ratios that satisfy the maximum power condition. The method of false position that is suitable for finding solutions numerically in a general case by using a computer is also described.
Interpreting piezoelectric oscillator dissipation effects in terms of the underlying materials viscoelastic relaxation phenomena
Authors: Smith R. Lowell
Published: October 2005

Equivalent circuit modeling has long been recognized as a valuable tool for describing transduction processes and the behavior of transducers. The formalism has been generalized to represent distributed properties, mode coupling, and the implications of structural complexity, mechanical loading, and electrical tuning. Dissipation or loss phenomena can also be accommodated by equivalent circuit methods. It is generally recognized that interpreting all relevant elastic, dielectric, and piezoelectric coefficients as complex numbers is an appropriate way to represent losses. All too often, the scope of this approach discourages the development of detailed results. This paper analyzes the dissipation modeling problem in terms of relaxation processes, a phenomenological approach that gives algebraic form to certain groupings of the electromechanical coefficients. The implication is that sound speed, coupling coefficients, materials moduli, etc., are frequency dependent. A mass-loaded longitudinal vibrator with a segmented piezoelectric cylinder is analyzed as an example of this model-parameter dispersion problem. Of particular interest is the effect of the adhesive joints on the oscillator admittance spectrum over a wide range of frequencies.
Development of spherical and cylindrical polarization for three-dimensional piezoelectric finite elements
Authors: Tiecee P. , Anifrani K. , Debus J. C. , Decarpigny J. C. , Boucher D.
Published: October 2005

Three-dimensional analysis of spherical or cylindrical transducers with axially or radially polarized piezoelectric ceramics is rather difficult because it needs a large number of classical elements to take into account the correct polarization. A new type of piezoelectric finite element has been developed in the ATILA code [J. N. Decarpigny et al., J. Acoust. Soc. Am. 78, 1499 (1985)] to obtain a good representation of the polarization. This paper describes these elements and analyzes the results (in air resonance modes, electrical characteristics, and mode shapes) obtained on some examples.
Use of special waveforms for optimum efficiency of high-intensity sound sources
Authors: Pla Frederic G. , Reethof Gerhard
Published: October 2005

High-intensity sound sources, such as sirens, have received much attention in the recent past due to renewed interest in industrial applications of high-intensity acoustics. As a result of the very high sound pressure levels required (155–165 dB), finite amplitude effects must be taken into account in the design of sound generators. A time domain solution of the second-order nonlinear wave equation is used to predict the behavior of initially nonsinusoidal plane waves, and is compared with a frequency-domain approach. Results for initially sinusoidal, rectangular, and inverse-shock waves are presented. It is shown that the shock formation distance for an initially inverse shock wave is π times the shock formation distance for an initially sinusoidal wave, and that the wave distortion actually results in an amplification of the fundamental, thus increasing the efficiency of the sound generation process. The consequences of wave distortion on several practical high-intensity sound sources is discussed.
The distortion spectrum of the fractionally addressed digital oscillator
Authors: Hartmann W. M.
Published: October 2005

The technique of fractional addressing permits one to construct a digital oscillator with arbitrarily high frequency resolution. However, the technique introduces distortion. The distortion power spectrum may be calculated exactly by borrowing mathematical methods from crystallography, such that the crystallographic unit cell length equals the denominator of the irreducible fractional part of the address increment. The calculation exhibits remarkable mathematical symmetries, which lead to simple closed-form expressions for the levels of the components in the distortion spectrum and for the total rms distortion. The expressions show how the distortion may be minimized or possibly employed as an alternative to digital FM in the synthesis of complex tones. [Work supported by the NIH.]
On the nature of acoustic singularities arising from the coincidence of flow and sound sources
Authors: Campos L. M. B. C.
Published: October 2005

The coincidence that flow and acoustic sources can occur in important acoustic problems, e.g., a spherical wave in a conical duct containing an incompressible mean flow, is an example of flow and sound sources colocated at the vertex of the cone; the cone is the particular case n = 1 of the power-law ducts of cross-sectional area S(x) ∼ x2n, which exhibit, for all real n, coincidence of flow and sound sources or sinks at x = 0 or x = ∞ It is shown that the coincidence of flow and sound sources can lead, for the power law ducts, to algebraic singularities for the phase, and essential singularities for the acoustic field; a transformation involving the solution of a particular Ricatti equation is used to account for the essential singularity, and regularize the acoustic problem. Exact solutions are obtained for sound in parabolic and hyperbolic nozzles, and these are used to study the acoustic field in the ray, asymptotic and compactness approximations, compare acoustic velocity and pressure, discuss equipartition and biasing of kinetic and compression energies, and conservation and nonconservation of wave action. The duality principle for horns [R. W. Pyle, J. Acoust. Soc. Am. 37, 1187 A (1965)] is shown to fail, and have no simple extension, for nozzles.
Whispering gallery resonances on solid elastic spheroids
Authors: Nagl A. , Werby M. F. , Überall H. , Dickey J. W.
Published: October 2005

Using tbe NORDA T matrix code, backscattering amplitudes versus frequency have been calculated for the axial incidence of a plane acoustic wave in water on solid tungsten carbide spheroids with a large variety of aspect ratios. Besides the usual series of broad Rayleigh wave resonances, series of narrow whispering gallery resonances are observed and investigated. The dominant mode number of each of these resonances is identified by an interpretation of the bistatic scattering pattern. For increasing aspect ratios, it is noted that an increasing number of the lowest-order whispering gallery resonances fail to be excited. A possible explanation of this phenomenon is discussed, based on phase matching arguments for the circumferential propagation of surface waves.
Review of studies on the effects of man-induced noise on marine mammals of the Bering, Chukchi, and Beaufort Seas and how the results have been applied to federal offshore oil and gas management decisions
Authors: Imm Jerry L. , Cowles Cleveland J.
Published: October 2005

The U.S. Minerals Management Service has been funding and managing studies of the potential effects of man-induced noise on marine mammals, particularly endangered cetaceans, in the Bering, Chukchi, and Beaufort Seas since 1978, and has expended approximately $5,000,000 toward those efforts. The purpose of such studies is to provide information needed for informed decision making pertaining to environmentally sound leasing and management of offshore oil and gas development on the Alaska OCS. Many of the noise/marine mammal interaction studies have been used to establish or modify lease terms or regulations for offshore operations in federal lease areas. Also, these results have been important in resolution of litigation pertaining to OCS oil and gas leasing/exploration. Specific case examples of how results have been applied will be presented and projection of future Alaska information needs in this discipline will be discussed.
Reactions of bowhead whales to drilling and dredging noise in the Canadian Beaufort Sea
Authors: Richardson W. John , Würsig Bernd , Greene Charles R.
Published: October 2005

Behavioral reactions of bowhead whales, Balaena mysticetus, to seven 30- to 40-min underwater playbacks of recorded drillship and dredge noise were determined in 1982–1984. Water depths were 10–150 m with little or no ice. Some (but not all) bowheads oriented away when received noise levels and spectra resembled those several kilometers from actual drillships and dredges. During some playback tests, call rates decreased, feeding ceased, and cycles of surfacing, respiration, and diving changed. Sensitivity of various whales to noise differed. Roughly half responded to received noise levels of about 115 dB re: 1 μPa broadband, or about 110 dB in one 13-oct band (20–30 dB above ambient). Such levels occurred 3–11 km from a drillship and dredge in the Canadian Beaufort Sea. Bowheads occasionally were seen less than 5 km from actual drillships and dredges, where received noise levels were at least as high as during brief playbacks. Thus some bowheads may habituate to prolonged noise exposure. Alternatively, only the least-sensitive individuals may occur less than 5 km from drillships and dredges. [Work supported by U.S. Minerals Management Service.]
Using sounds to control the movements of sea otters
Authors: Davis R. W. , Awbrey F. W. , Williams T. M.
Published: October 2005

Field tests were conducted in Prince William Sound, Alaska, to determine whether the playback of artificial sounds, killer whale calls, or sea otter pup calls could be used to control the movements of sea otters (Enhydra lutris). Tests were conducted on three groups of five adult otters that were captured and placed in an enclosed lagoon (180 m long × 40 m wide). Sounds were broadcast in air and underwater from a platform in the center of the lagoon. The behavior and distance of the otters from the platform were determined from video recordings obtained from a remote-controlled video camera overlooking the lagoon. The results showed that sea otters were not repelled by loud (SPL = 120 dB at 1 m), obnoxious sounds in air such as a warble tone (frequency-modulated sinusoid centered at 1 kHz) or air horns and narrow-band pulses at frequencies of 500 Hz–20 kHz projected underwater. However, the otters were attracted to the aerial playback of sea otter pup calls and repelled by the aerial and underwater playback of killer whale calls. Psychoacoustic stimuli appear to have the best chance of influencing the movements of wild sea otters. [This research was supported by Minerals Management Service, Contract No. 14-12-0001-30256.]
Effects of aircraft noise on Pacific black brant and other geese in Alaska
Authors: Ward David H. , Derksen Dirk V. , Schomer Paul D.
Published: October 2005

In 1987, a study of the effects of aircraft noise on the behavior, distribution, and habitat use of Pacific black brant, Canadian geese, and emperor geese was initiated on the Alaska Peninsula and on the North Slope of Alaska. The objectives were to: (1) describe the behavioral responses of geese as an effect of noise from aircraft overflights; (2) record and examine noise associated with experimental overflights of fixed- and rotary-wing aircraft and specific altitudes, airspeeds, and environmental conditions; (3) secure baseline noise levels for routine flights of nonexperimental aircraft; and (4) provide recommendations to government agencies for reduction or mitigation of any adverse impacts associated with aircraft noise to these populations of geese. Behavior of geese was monitored from remote locations prior to, during, and following level overflights along prescribed routes. Concurrently, 13-oct sound exposure and maximum A-weighted and sound levels of each aircraft were measured with a real time analyzer. Here, the design and preliminary results of the first of a multiyear study will be discussed.
Adaptive reuse of existing auditoria
Authors: Jaffe J. Christopher
Published: October 2005

The adaptive reuse of existing auditoria is an extremely cost efficient way for communities to create contemporary “state of the art” performance facilities. The key to the successful culmination of such a facility is a clear definition of the program use of the space and an understanding between the client and the consultant that all available acoustic techniques can be utilized to achieve final design goals. This paper will discuss the adaptive reuse of a number of buildings as diverse as a library, a union hall, a WPA built art deco music hall, and a three theatre/film complex.
Theories for sound propagation in rigid-framed porous materials
Authors: Attenborough Keith
Published: October 2005

An historical overview of the development of theories for sound propagation in rigid-framed porous media is offered. Phenomenological and microstructural theories are contrasted. Microstructural approaches may start either from specifications of the geometrical form of the solid frame or from specifications of the geometrical form of the pores. The former approach is particularly useful for describing acoustical properties of fibrous materials. The latter approach has the longest history, the wider application, and is the basis of many recent developments in the dynamic theory of poroelasticity. In one form of the pore-based theory, consideration is given to the incorporation of dynamic effects of pore shape and irregularity and steady flow tortuosity. An alternative form results from a more rigorous approach to the effects on viscous drag and thermal interaction with pore walls of the inclination of pore axes to the macroscopic pressure gradient, i.e,, dynamic tortuosity effects. By comparing theoretical predictions with experimental data for sand, lead shot, glass heads, and snow, both the usefulness and the current limitations of theories that use microscopic pore-based descriptions and their various approximations are explored.
Recommended seismic zonation for Hawaii
Authors: Adams W. M. , Furumoto A. S. , Herrero-Bervera E.
Published: October 2005

The state of Hawaii has both volcanic and tectonic earthquakes: The volcanic earthquakes are confined to the Big Island of Hawaii with the tectonic earthquakes occurring at all the major islands, from Hawaii to Kauai. The historical seismicity is relatively high, as might be expected from the presence of active volcanoes and the transection of the Hawaiian archipelago by the Molokai Fracture Zone. For the past 120 years, the extreme seismic intensity varies island to island: Kauai, IV; Oahu, VII; Molokai, VIII; Maui, VIII; Lanai, IX; and, for Hawaii, XII [H. D. Wood, J. Bull. Seismol. Soc. Am. 4, 169–203 (1914)]. This information suggests that an appropriate seismic zonation for building design is: zone 1 for Kauai and Niihau; zone 2 for Oahu; zone 3 for the islands of Maui, Lanai, and Molokai; and zone 4 for Hawaii. By estimating the loss distribution suitable for a particular location, one can derive risk functions useful for setting insurance levels [C. A. Williams and R. M. Heins, Risk Management and Insurance (McGraw-Hill, New York, 1985)].
A new method of ocean acoustic tomographym—“Phase tomography.”
Authors: Shang E. C.
Published: October 2005

The ray travel time has been used as the basic measurement for inversion of the sound speed structure in the conventional ocean acoustic tomography. There are cases where the ray theory is neither applicable nor convenient, especially for lower frequency and axial propagation in the ocean sound channel. In the present paper, a new method of ocean acoustic tomography has been developed; it is a full-wave approach based on the adiabatic normal mode theory. Instead of the ray travel time, the modal phase difference perturbations are used for inversion—we call it “phase tomography.” The method is suitable for lower frequency, and it is also suitable for axial propagation; moreover, the range-dependent sound-speed structure can be obtained from the vertical slice inversions. The mathematical derivation will be presented and some possible ways of implementation will be discussed.
Scattering from thin elastic screens
Authors: Audoly Christian
Published: October 2005

The characteristics of acoustical materials are often determined by standard panel tests. To improve low-frequency measurements, the scattering effects due to the finite size of the panels are investigated. A theoretical model, based on the Helmholtz integral equation and its derivative form, is used to calculate the scattering of acoustic waves from rigid, soft, and elastic screens in water. The cases of the infinite strip (2-D space) and of the rectangular plane screen (3-D space) are considered. In both cases, it is assumed that the thickness of the screen is small compared to the wavelength. The calculations are made up to ka = 10 (k, wavenumber; a, characteristic dimension). The results are compared to experiments on soft material and steel screens, and to the infinite plane model. It is shown that in this frequency range, the scattering effects due to the finite size of the screens are important, mainly for the steel panel.
The use of numerical optimization techniques in the design of acoustic horn loudspeakers
Authors: McLean James , Hixson E. L.
Published: October 2005

The use of numerical optimization techniques in the design of acoustic horn loudspeaker systems is considered. Conventional synthesis techniques (i.e., stepped impedance transformer or nonuniform line) are inadequate for horn loudspeaker design due to the frequency-dependent nature of the radiative load at the mouth and the complex behavior of the driver. In this paper, the horn is modeled as an n-section commensurate stepped impedance transformer terminated in a one-port network that represents the complex frequency-dependent radiation impedance. The driver is modeled as a linear two-port transducer using measured data as described in an earlier presentation [J. S. McLean and E. L. Hixson, J. Acoust. Soc. Am. Suppl. 1 79, S90 (1986)]. The entire horn/driver system is optimized to exhibit equiripple frequency response using the characteristic impedances of the individual transformer sections as the optimization variables. The system is optimized as a singly terminated filter in order that it may be driven by a low-impendance power amplifier. The optimized horn/driver system exhibits a bandpass response. This differs from previous horn designs which were high pass in nature. In the optimized design, the bandwidth of the system may be increased by allowing a higher ripple level and vice versa.
Influence of ground reflection on measurements involving bands of noise
Authors: Noble John M. , Bass Henry E. , Raspet Richard
Published: October 2005

It has been shown [L. C. Sutherland and H. E. Bass, J. Acoust. Soc. Am. 66, 885–894 (1979)] that frequency-dependent atomospheric absorption can lead to a propagation loss for a band of noise that is much different from that for a pure tone at band center. In the presence of a ground surface, interference can also cause the sound amplitude to vary rapidly with frequency. When this occurs, the level measured for a pure tone can differ dramatically from that measured for a band of noise. Accurate treatment of this difference requires integration over the bandpass of the fractional octave band filter used in the measurement. Example calculations have been performed for a typical filter. These examples form a basis for general guidelines to be used when comparing theory to measurements.
Sum and difference frequency generation in sound radiation from a vibrating planar boundary
Authors: Foda Mosaad A.
Published: October 2005

An earlier study [J. H. Ginsberg, J. Acoust. Soc. Am. 69, 60–65 (1981); 69, 929–936 (1981)] of sound radiation from a vibrating planar boundary considered the case of monochromatic excitation. That work featured perturbation analysis combining asymptotic integration and the renormalization version of the method of strained coordinates. The present analysis initiates an extension of those techniques to the case of a two-frequency excitation. These frequencies are considered arbitrary; hence, the results for a parametric array (closely spaced frequencies) can be obtained as a special case of the present analysis. Using the Fourier transform in its conventional complex function form to describe the linearized signal leads to fomulation of the second-order potential in terms of complex functions. A coordinate straining transformation describing the full spectrum (propagating and evanescent) is deduced. Accordingly, uniformly accurate expressions for the acoustic pressure and the velocity components are obtained.
Scratchpad II: A computer algebra language and system
Authors: Jenks Richard
Published: October 2005

The Scratchpad II system represents a new generation of systems for doing symbolic mathematics, based on modern algebra and abstract data types. A large number of facilities are provided, for example: symbolic integration, “infinite” power series, differential operators, Cartesian tensors, and solution of nonlinear systems. Scratchpad II has been designed from the outset to be extendible. The system introduces a new data abstraction notion, the “category,” to express intricate interrelationships between data types. The result design permits the compilation of algorithms described in their most natural mathematical setting. The use of categories guarantees user defined types and packages are compatible with each other and with built in facilities. This system provides a single high-level language with an intepreter and compiler. The language can be used by the naive user for convenient interactive mathematics calculations and by the advanced user for the efficient implementation of algorithms. Scratchpad II is built on Lisp/VM and runs on IBM/370 class mainframes. An implementation of the system on the RT/PC is expected soon.
Creation of experiment-oriented materials to enhance a nonlab acoustics elective
Authors: Elder S. A. , Korman M. S.
Published: October 2005

Two acoustics courses are offered by the Naval Academy Physics Department. One is a physics major elective course in physical acoustics with a weekly 2-h lab; the other, a sonar course, is basically a service course for other departments. On account of the large attendance for the latter, and the limited space available, it has not been possible to make lab work a routine part of the course. Since it is believed that some lab experience is essential to good physics teaching, materials are being created to be used by students outside of class time that will address this need. Among ideas being considered are computer-graphic homework assignments, special project-type lab setups, video-cassette instructional aids, and sonar games. Current materials and experience will be described.
Measurement of acoustical cavitation in liquid 4He
Authors: Nissen Joel A. , Bodegom E. , Brodie L. C. , Semura J. S.
Published: October 2005

A piezoelectric hemispherical transducer was used to focus high-intensity ultrasound into a small volume of liquid helium. The transducer was gated at its resonant frequency of 566 kHz, with gate widths less than 1 ms, in order to minimize the effects of transducer heating and acoustic streaming. The onset of cavitation was detected with small-angle scattering of laser light from the cavitation zone by microscopic bubbles. In the superfluid, the pressure amplitude at the focus was calculated based upon the acoustic power radiated into the liquid, the geometry of the transducer, and the nonlinear absorption of sound. Above the lambda point, this method is complicated by the scattering of sound by bubbles present in the liquid and on the surface of the transducer, and so a calibration curve for the diffracted light intensity at different pressure amplitudes and temperatures was obtained in the superfluid. The diffracted light intensity was then used to determine the acoustic pressure and extend the cavitation measurements to the normal fluid. [Work supported by NSF.]
Propagation of ultrasound in skin
Authors: Riederer-Henderson Mary Ann , Olerud John E. , Odland George F. , Forster Fred K. , Steiger Dianne L. , O'Brien William D.
Published: October 2005

The scanning laser acoustic microscope (SLAM) at 100 MHz and backscattering acoustic technique (BAT) at 10–40 MHz were used to examine canine skin. Specimens from four animals and from four locations on the animal were analyzed biochemically and morphologically as well as acoustically. The mean collagen and water concentrations were 20% ± 2% and 60% ± 3%, respectively. An analysis of variance of the SLAM data and the biochemical data showed significant animal to animal differences and some differences due to location on the animal. At 100 MHz the mean ultrasonic speed obtained with the SLAM was 1632 ± 34 m/s and the mean attenuation coefficient was 57 ± 10 dB/mm. Using BAT the mean integrated attenuation coefficient was 11 ± 3 dB/mm at 25 MHz (midfrequency range). While the speed values fall within the range of values previously reported for skin, the values for the attenuation coefficient using either SLAM or BAT are considerably higher than would be predicted from literature values at 1–10 MHz. Thus the attenuation coefficient is a stronger function of frequency that the data at lower frequencies would suggest. [Work supported by NIH and RR&D of the Veterans Administration.]
Ultrasonic propagation properties of articular cartilage at 100 MHz
Authors: Agemura D. H. , O'Brien W. D. , Olerud J. E. , Chun L. E. , Eyre D. R.
Published: October 2005

A pilot study on articular cartilage assessed the contribution of individual matrix components to ultrasound propagation. The influence of collagen fibril orientation and collagen crosslinking was also assessed. Sections of adult bovine articular cartilage taken both parallel and perpendicular (cross sections) to the articular surface were examined using the scanning laser acoustic microscope (SLAM) operating at an ultrasonic frequency of 100 MHz. A set of samples was evaluated that had been sequentially treated by enzymes to (1) remove 85% of the chondroitin sulfate; (2) remove remaining GAGs, glycoproteins, and other noncollagen proteins, leaving only the collagen fibril network; and (3) disrupt the collagen intermolecular crosslinks. Two striking observations were made: a profound effect of the “preferred” collagen fibril orientation on acoustic wave speed and a marked increase in attenuation coefficient when intermolecular crosslinks were broken in the collagen. [This work was supported by NIH Grants AM21557, CA36029, and AR36794 and Rehabilitation Research and Development Services of the Veterans Administration.]
Comments regarding the two-scale expansion for the fourth moment of waves propagating in random media
Authors: Patton R. S. , Codona J. L.
Published: October 2005

Over recent years, the method of two-scale expansions has been applied with a great deal of success to the problem of the fourth moment of waves propagating in random media. Specifically, the method yields a remarkably simple expression for the two-point intensity correlation that is valid in both strong and weak scattering and both high and low spatial frequencies. Unfortunately, of the published derivations, there is no clear presentation of the physical content of the method nor a straightforward approach for finding either corrections to the approximation or generalizations for treating waves in arbitrary refracting media. The clearest approach would appear to be based on standard configuration-space path integrals [B. J. Uscinski, C. Macaskill, and M. Spivack, J. Sound Vib. 106, 509–528 (1986)]; however, that derivation appears to have (at the minimum) a different physical content from the other, moment equation based, derivations. The nature of the approximation is discussed in the context of both configuration-space and phase-space path integrals. The two-scale approximation is found to be a simple interpolating formula between a high spatial-frequency approximation (found by considering high-frequency asymptotics in phase space) and the low spatial-frequency behavior from the standard Born approximation. Looking at the approximation from this perspective lends both physical insight and simplifies the derivation to the point where it becomes quite simple to write expressions for refracting environments and correction terms.
Non-Kirchhoff elastic wave scattering from rough interfaces
Authors: Schmidt Henrik , Kuperman W. A.
Published: October 2005

An earlier developed solution technique for seismoacoustic scattering by stochastically rough interfaces [W. A. Kuperman and H. Schmidt, J. Acoust. Soc. Am. 79, 1767 (1986)] has been modified to treat the scattering without applying the Kirchoff approximation. This is accomplished by including the rotation of the boundary conditions in the perturbation formulation and by numerically evaluating the scattering integrals, allowing the roughness correlation lengths to be finite. It is demonstrated that the effect of the scattering on the mean (coherent) field can be accounted for in a self-consistent manner by solving the unperturbed problem with modified boundary conditions. As was the case for the Kirchhoff approximation, the non-Kirchhoff formulation has been implemented in the seismoacoustic SAFARI code [H. Schmidt and F. B. Jensen, J. Acoust. Soc. Am. 77, 813 (1985)], allowing for simultaneous treatment of multiple rough interfaces. The model is applied to analyze the effect of scattering from a rough shallow water sea bed as well as from an Artic ice canopy. By comparing these results to the Kirchhoff results for the same problems, it is demonstrated that the non-Kirchhoff theory predicts significantly higher losses, in particular for acoustic wavelengths of the same order of magnitude as the roughness correlation length. [Work supported by NRL.]
Rough surface scattering using the phase-perturbation technique
Authors: Broschat Shira L. , Thorsos Eric I. , Ishimaru Akira
Published: October 2005

There is a need for a solution to the problem of wave scattering from rough surfaces that is accurate when both the classical field perturbation and Kirchhoff (physical optics) approximations are not. In this work, the validity of the phase perturbation technique is examined for a region in parameter space when the two classical solutions fail. Numerical results for the phase perturbation scattering strength are compared with exact numerical results for one-dimensional pressure-release surfaces having a Gaussian roughness spectrum and Gaussian height and slope distributions. Exact results are obtained using a Monte Carlo technique. It is found that in the region considered the phase perturbation results agree with the exact results over all scattered angles away from low grazing for a fixed angle of incidence. Furthermore, in many cases it is found that exchanging incident and scattered angles in the phase perturbation equations gives an alternate phase perturbation solution whose numerical results are in excellent agreement with exact results. [Work supported by ONR.]
Integral equations for the rough surface scattering amplitude
Authors: DeSanto John A.
Published: October 2005

The rough surface scattering amplitude can be written as a surface integral over the boundary values of the field and its normal derivative on the surface. A general procedure is described to derive Lippmann-Schwinger integral equations in k space on these scattering amplitudes for Dirichlet, Neumann, and interface or transmission problems. The procedure is valid for arbitrary incident fields. It yields a multiple scattering description of the scattering process in terms of a fundamental surface interaction function that describes the scattering primarily as a phase modulation due to the roughness. Simple examples of single and double scattering for a one-dimensional surface will be presented. Also included are comments on the diffraction and scattering problems that arise when treating unbound surfaces. [Work supported by ARO.]
Ultrasonic propagation properties of canine aorta at 100 MHz
Authors: Chu Felice , Riederer-Henderson Mary Ann , Olerud J. E. , Riederer-Henderson Mary Ann , O'Brien William D.
Published: October 2005

A pilot study examining canine aorta investigated the ultrasonic propagation properties as a function of location and orientation along the aorta. Longitudinal, circumferential, intimal, and adventitial sections of canine aorta were taken at seven locations along the aorta from the aortic arch to the iliac bifurcation. Aortic media consists of circumferentially oriented elastin fibers interspersed with a randomly oriented network of fibrils. Over the distance from the heart to the abdomen, the elastin concentration decreases as the collagen concentration increases. The speed is shown to be statistically significant with respect to location and correlates strongly with orientation. The 28 speed values ranged from 1610–1859 m/s with the average being 1662 m/s. On the other hand, the attenuation coefficient is not shown to be statistically significant with respect to orientation but does correlate strongly with respect to location. The 27 attenuation coefficient values ranged from 48.5–131.8 dB/mm with an average of 91.2 dB/mm. [This work was supported by NIH Grants AM21557, CA36029, and AR36794 and Rehabilitation Research and Development Services of the Veterans Administration.]