bluuebunny/crossref_metadata_2025 huggingface dataset:
Modulation detection interference measured with a new procedure
Authors: Yost William A.
Published: October 2005

A new selective attention procedure was used to measure modulation detection interference (MDI) in which listeners determined if a sinusoidally amplitude modulated probe tone (500 ms and 4000 Hz) had a depth of modulation (ten modulation depths were used) greater than or less than a cue tone (the same as the probe) presented with a depth of modulation of −15 dB (20 log m). Four conditions were tested: (1) probe alone (PA)−probe presented in isolation, (2) unmodulated masker (UM)−an unmodulated 1000-Hz masker presented simultaneously with the probe, (3) modulated masker (MM1)−masker modulated at different rates and with the same envelope phase as the probe, and (4) MM2 condition−masker modulated with an envelope 180° out of phase with that of the probe. In the MM conditions, the modulated masker was presented with the same ten depths of modulation as the probe. The probe and masker were simultaneously presented, each modulated with one of the ten depths of modulation randomly chosen from trial to trial. The data were analyzed in terms of the weight given to the masker tone while the listener determines probe modulation depth. A weight of 1.0 indicates a synthetic listener in that he/she is unable to hear out the modulated probe in the presence of the modulated masker, and a weight of zero indicates an analytic listener in that he/she can hear out the modulated probe. The results will be discussed in terms MDI and the perceptual grouping of spectral components based on common patterns of amplitude modulation. [Work supported by a Program Project grant from The National Institute on Deafness and Other Communication Disorders, NIDCD.]
Possible uses of submarine canyons in acoustic thermometry
Authors: Denner Warren W. , Lashkari Khosrow , Miller James H. , Chiu Ching-Sang
Published: October 2005

High-power sources and high-gain receivers are used in long-range ocean acoustic thermometry. Because of power supply and data telemetry the sources and receivers are often placed near coastal facilities. There may be some significant benefits associated with taking advantage of natural terrain features to protect the sources and receivers from fisheries, and to optimize certain aspects of their performance. Sources and receivers are generally moored in deep water, in the axis of the sound channel, on the order of 100 to 1000 m. The shortest distance from shore to deep water is frequently associated with submarine canyons. For example it is less than 15 km from Point Pinos to water depths in excess of 2000 m in Monterey Submarine Canyon, less than half the distance along continental borders without submarine canyons. Fishermen do not fish inside the canyon walls for fear of rapid depth changes. Therefore, the canyons provide a natural barrier to the threat of fishing activity to moored sources and receivers. It is obvious that the canyon restricts the ray paths between a source or receiver in the canyon. However, if the source and receiver geometry is carefully selected this may not be a significant limitation. Oceanic noise arrivals in a submarine canyon can be restricted to those in the direction of deep water. If for example the canyon opens at an angle of 30 deg from the receiver and if the noise is omnidirectional at the axis of the array, the terrain barrier restricts noise to that 30-deg window.

This would provide an optimum noise reduction of 7.8 dB. On the source side of the problem, placing the source in the canyon will limit the high-intensity blast to the energy going out the canyon mouth into deep water. In this way, marine mammals in the area of the source would be shielded from the direct blast unless they happen to be in a restricted direction from the source, or very near the source. If the source could be made so that it was directional, the volume of the direct blast would be even more restricted. Certainly, there are some possible downsides to placing sources and receivers in submarine canyons. These will be explored in the presentation.
Acoustic models and target strengths of the Atlantic cod (Gadus morhua)
Authors: Clay C. S. , Horne John K.
Published: October 2005

Acoustic models should realistically represent the fish body form. To display the form, anesthetized Atlantic cod were soft x rayed to image inflated swimbladders and skeletal elements. The fish lengths ranged from 177 to 804 mm and the corresponding mass range was 48 to 4700 g. The x rays give good images of the swimbladder and skeleton. The fish images were projected at the same length to compare the relative shapes of their bodies and swim bladders. The relative shapes of the 177- to 412-mm cod were about the same. The maximum fish body heights and widths were about 0.18 and 0.13 of total length. The relative swimbladder lengths were about 0.25 of the total fish lengths and the maximum diameters were about 0.05 of the total lengths. The swimbladder of the 804-mm cod had a relative length of 0.16 and maximum diameter of 0.07 total length. From the shapes of the fish, it was evident that simple bent cylinders were not adequate. The integration of the scattering amplitudes over length [in C. S. Clay, J. Acoust. Soc. Am. 89, 2168–2179 (1991)] was replaced by a summation over a finite number of cylinders. One set of cylinders represents the fish flesh and another set represents the swimbladder. All of the computations were done numerically. Interactions between the swimbladder and fish body were ignored. The scattering amplitudes S(f) were converted to target strengths by using the 10 log[S(f)S*(f)]. [Work supported by the Office of Naval Research and the Memorial University of Newfoundland.]
Tidal signals in basin-scale acoustic transmissions
Authors: Spiesberger John L. , Headrick Robert H. , Bushong Paul J.
Published: October 2005

Travel times of acoustic signals were measured between a bottom-mounted source near Oahu and five bottom-mounted receivers located near Washington, Oregon, and California in 1988 and 1989. At three out of five receivers, observed travel times at M2 and S2 periods agree with predictions from a barotropic tide model to within 30 deg in phase and a factor of 1.6-in. amplitude. The discrepancies at the fourth and fifth receivers can be removed, to first order, by including predicted effects of phase-locked baroclinic tides generated by guyots in the Moonless mountains. A simple model is used to estimate the conversion of energy from barotropic to baroclinic tides by the world’s seamounts. At M2, the conversion amounts to about 4% of the total dissipation at M2. Although this estimate is very approximate, it is similar to other published values.
Nonlinear dynamics of wind waves: Multifractal phase/time effects
Authors: Mellen R. H. , Leykin I. A.
Published: October 2005

Recent analyses of the phase/time behavior of wind waves have shown self-similarity, the power spectra of the phase fluctuations having no characteristic frequency scale. This has suggested fractal properties and a fractal dimension of D≊1.4 has been estimated from data obtained at sea and in the laboratory [R. Mellen and I. Leykin, J. Acoust. Soc. Am. 91, 2319 (A) (1992)]. However, analyses of a broad range of natural phenomena have demonstrated multifractal properties [S. Lovejoy and D. Schertzer, ‘‘Multifractals in Geophysics,’’ AGU/CGU/MSA, 1992 Spring Meeting]. The theory considers, not simply the second moments, but relations between moments including nonintegral. This provides a quantitative link with the nonlinear dynamics of the process involved. Analysis of laboratory wave data is reported here and the results suggest that the phase fluctuations are ‘‘hard multifractal’’-like turbulence. Implications for backscattering from ocean waves are considered.
Electric micromotors on silicon
Authors: Mehregany Mehran
Published: October 2005

A review of micromotor technology will be presented and micromotor design, fabrication, and operational characteristics will be discussed. Micromotors are submillimeter actuators capable of unrestrained motion in at least one degree of freedom. The micromotors described in this presentation are actuated by attractive electrostatic forces. For micromotor fabrication, silicon surface micromachining is used to create freely moving parts held to the surface of the silicon wafer with bearings. In this process, heavily phosphorus-doped polysilicon is used for the structural parts, deposited silicon dioxide is used for the scarificial layers, and silicon-rich silicon nitride is used for electrical isolation. Layers of the structural and sacrificial materials are deposited and patterned in a manner that the structural polysilicon parts (e.g., the rotor) are appropriately encapsulated by the sacrificial oxide layers. At the final stage of fabrication, the sacrificial oxide is selectively removed in hydrofluoric acid to free the micromotor structural parts. Operational rotary, variable-capacitance, salient-pole, and harmonic (or wobble) side-drive micromotors have been fabricated with two different bearing designs and typical diameters of 100- to 130-μm, rotor/stator gaps of 1.5 μm, and a rotor thickness of 2.2 μm. Electrical operation of the salient-pole and harmonic side-drive micromotors have been demonstrated in a number of gaseous environments including room air, oxygen, argon, and nitrogen, and in insulating liquids such as silicone lubricating oil and deionized water.

Minimum operating voltages differ with the environment but can be as low as 30 V. Extended operation (i.e., beyond 100 h) of the micromotors in gaseous environments and in silicone lubricating oil has been demonstrated. Operational speeds of up to 15 000 and 1000 rpm have been achieved in gaseous environments for the salient-pole and harmonic side-drive micromotors, respectively. In silicone lubricating oil, the maximum operation speed has been below 125 rpm for both micromotor types. [The presentation reflects the results of a collaborative micromotor research program with Professor J. H. Lang and Professor S. D. Senturia of MIT. This research program is funded by the National Science Foundation.]
Electrothermal microactuators using PVDF-TrFE
Authors: Rashidian Bizhan , Allen Mark G.
Published: October 2005

There is currently application in micromachining technology for a spin-on, organic piezoelectric material that could be used for microactuation. One material that possesses these properties and is currently being studied actively is the copolymer of vinylidene fluoride and triflouroethylene, PVDF-TrFE. It has been found that this material also exhibits a strong electrothermal effect; i.e., it can be locally heated by application of voltage in the MHz frequency range. This heating is sufficient to allow electrothermal actuation of released micromachined structures fabricated using this material. Using bulk micromachining, several released bridges and cantilever beam structures have been fabricated, ranging in length from tens of microns to a few millimeters. The structures are bimorphs, consisting of a layer of PVDF-TrFE (sandwiched between two metal electrodes) on top of a layer of polyimide. The structures were tested by applying 0-16-V peak rf signal with frequencies up to 50 MHz and observing the resultant deflection. The deflection was a function of both frequency and amplitude of the applied signal. To verify that the heating of the sample was due to the dielectric loss of PVDF-TrFE, the induced temperature change was measured by measuring the IR radiation of the structures. These measurements clearly show the expected linear dependence of the film temperature with the square of rf signal amplitude (i.e., the applied power). Deflections exceeding 900 μm have been observed. The structures can also be made to vibrate up to about 50 Hz by gating the input rf signal.
Fabrication and performance of a silicon micromachined hydrophone
Authors: Evans Patrick J. , Jerman J. Hal
Published: October 2005

A packaged hydrophone based on silicon micromachining technology has been developed. The device is a pressure-balanced, variable-gap capacitor that features a corrugated, bossed, movable diaphragm and a novel, vented backplate design with a pattern of channels to limit viscous resistance. The device is designed for better-than-ambient-limited signal-to-noise performance well down into the infrasonic band (5 Hz) and for reasonably flat frequency response to 1 kHz. The device can be packaged in 3 cm3, including a reservoir for the compliant, pressure-balancing fluid and preamplifier electronics. Due to the pressure-balancing feature, the device survives and retains sensitivity, within several dB, down to the deepest ocean depths. Design criteria include low-cost manufacturability. This paper discuses the theory of device operation, design rationale, and techniques used in piece-part fabrication. Comparisons between design predictions and laboratory measurements of several performance parameters are made. Last, opportunities for design improvements based both upon these measurements and upon theoretical considerations are discussed, for example ac biasing for super-sensitive transducers, useful in short dipoles and other applications. [The research reported here was sponsored by the Naval Air Warfare Center, (NAWC), Aircraft Division, Warminister, PA, under Contract No. 62269-90-C-0526.]
Electron tunneling sensors
Authors: Kenny T. W. , Kaiser W. J. , Rockstad H. K. , Reynolds J. K.
Published: October 2005

Many physical sensors operate by coupling the signal of interest to deflection of a sensor component, and utilizing a displacement transducer to produce an electrical signal. The development of miniature high-performance sensors have been limited by the availability of small, sensitive transducers. A novel accelerometer has been designed that utilizes an electron tunneling transducer to detect the relative motion of a suspended proof mass. The sensitivity of the tunneling transducer allows miniaturization of the device with resolution near 10−8 g/√Hz from 10 Hz to 1 kHz. Thermal noise in the positions of sensor components is important for high-resolution miniature accelerometers, and is the dominant factor in selection of design parameters. Thermal noise for this dual element system will be discussed and compared with other noise sources. A simple closed-loop electronic feedback system that is used with these sensors will also be described. Preliminary test results will be described. This system offers improved resolution, compact geometry, low mass, and low cost relative to present miniature accelerometers or acoustic sensors. A wide range of possible applications exist including underwater acoustics. [Work supported by NAWC, and SDIO/IST.]
A two-component Arctic ambient noise model
Authors: Greening Michael V. , Zakarauskas Pierre
Published: October 2005

Short-term Arctic ambient noise spectra over the frequency band 2–200 Hz are presented along with a two-component noise model capable of reproducing these spectra. The model is based on the measured source spectrum and the spatial, temporal, and source level distributions of both active pressure ridging and ice cracking. Modeled ambient noise levels are determined by summing the input energy of the distributions of ice cracking and pressure ridging events and removing the propagation loss. Both modeled and measured spectra show that below 40 Hz, the ambient noise is dominated by a single or few active pressure ridges at ranges of tens of kilometers. Above 40 Hz, the ambient noise is dominated by a large distribution of thermal ice-cracking events with over 50% of the total noise level produced by events within 6-km range and over 80% produced by events within 30-km range.
Treatment of early and late reflections in a hybrid computer model for room acoustics
Authors: Naylor Graham
Published: October 2005

The ODEON computer model for acoustics in large rooms is intended for use both in design (by predicting room acoustical indices quickly and easily) and in research (by forming the basis of an auralization system and allowing study of various room acoustical phenomena). These conflicting demands preclude the use of both ‘‘pure’’ image source and ‘‘pure’’ particle tracing methods. A hybrid model has been developed, in which rays discover potential image sources up to a specified order. Thereafter, the same ray tracing process is used in a different way to rapidly generate a dense reverberant decay. In this paper the computational model is described. Particular attention is paid to alternative methods of implementing the reverberant tail, and to the problems that arise when joining early and late parts of a reflectogram generated with different algorithms. A companion paper presents the features of the model as implemented.
Room acoustic prediction and auralization based on an extended image source model
Authors: Dalenbäck Bengt-Inge , Svensson Peter , Kleiner Mendel
Published: October 2005

During the 1980s, an exciting new technique was developed that put great demands on prediction methods. This new technique, called ‘‘auralization’’ in an analogy to visualization, enables the designer of a concert hall to get an aural impression of the hall before it has been built. By the calculation of highly detailed octave-band echograms, the use of signal-processing techniques and measured head-related transfer functions, a binaural room impulse response can be synthesized. This response is convolved with anechoically recorded music to give an impression of how the music would sound in the completed hall. This paper describes auralization using the image source model. This model, as well as others, has its share of short comings. In an attempt to compensate for some of these, the basic model has been extended. The two most important extensions are the treatment of scattering and the use of ray tracing to estimate the late part of the echogram. The combined method enables reasonably fast calculations, highly detailed early parts of the echograms, and smooth transitions to the late parts. The predicted measures compare well with measurements and the aural impressions created sound natural.
Multiple source auralization progress report
Authors: Prince David , Talaske Rick
Published: October 2005

The problem of accurate spatial representation of large orchestras in binaural auralizations is attacked by convolving anechoic recordings of individual instruments with the room impulse responses simulated from each instrument location to a single listener location and subsequently mixed. Instrument directivity and power, orchestra member effects, individual pinna transfer functions, and headphone transfer functions are considered. Progress, techniques, limitations, and problems of this current research will be discussed. [Research supported by The Talaske Group, Inc.]
Generation and dispersion of near-surface bubble densities
Authors: Su Ming-Yang , Cartmill John
Published: October 2005

In four ocean experiments conducted in 1985, 1991, and 1992, extensive near-surface microbubble densities were obtained by both optical and acoustical techniques. The bubble radius (r) range for the former is 8–200 μm and the range for the latter is 34–1200 μm. Detailed analyses of the temporal variations (both on the order of 10 and 60 s) of these bubble densities reveal some common characteristics existing in all four sets of independent field measurements. Two maxima appear in the bubble density with the first one near r1=100–150 μm and the second one near r2=20 μm. The r1 peak occurs immediately when a fresh breaking wave plume is generated near the measuring sensor, while the r2 peak is more or less unchanged during the entire measurement period. These two peaks essentially divide the bubble density into two distinct radius ranges: the first range is 100<r<1200 μm with the power law of r−3, and the second range is 30<r<80 μm with a power law of r−4. It is speculated that the first and second range are, respectively, controlled by generation and subsequent dispersion of bubble plumes initially generated by wave breaking. [Work supported by ONR Acoustical Reverberation SRP.]
Low-frequency oscillations of bubble plumes
Authors: Koller D. P. , Shankar P. M.
Published: October 2005

The collective oscillations of bubbles in a plume are believed responsible for the portion of the ocean noise spectrum that is roughly less than 1 kHz. The plume due to its dimensions and change in speed of sound from that of pure water acts as a resonating cavity. Since a plume may have a relatively complex shape, making it difficult to predict resonant frequencies, theoretical and experimental work is being carried out on simpler geometric models. The initial model has been created to predict the resonance of a cylindrical bubble cloud assuming a uniform void fraction throughout. The theory predicts an oscillatory pressure field described by Bessel functions [Jn( )] inside the cloud an an evanescent field described by modified Bessel functions [Kn( )] outside of it. Once the dimensions of the cloud are fixed, the only parameter that is varied is the void fraction. A relatively simple characteristic equation was obtained that was used to predict the resonant frequencies. Experimental work was carried out in a pool 3 m in diameter and 1 m deep. The cylindrical bubble cloud was created by passing compressed air through an annular array of hypodermic needles. Void fractions were altered by changing the flow rate to the bubble maker, and they were measured by determining the local speed of sound; the two are related by a simple expression if the frequency propagating through the cloud is less than the resonant frequency of the bubbles which compose it. Experimental measurements appear to verify the theoretical model. The model was then adapted to account for a gradient in the void fraction as a function of radius. The cloud was approximated to be four concentric cylinders with different void fractions. This is a more realistic model of a bubble plume in an ocean environment. The void fraction in each ring was estimated through the local speed of sound measurements. There was reasonable agreement between theory and experiment. [Work supported by ONR.]
Acoustic scattering from elemental Arctic ice features: Laboratory modeling results
Authors: Fricke J. Robert , Unger Gladys L.
Published: October 2005

Analytic and numerical modeling calculations predict that fluid and elastic ice floes produce distinctly different scattered fields at low frequency (10–100 Hz): dipolar and quadrupolar, respectively. This led to the hypothesis that first-year ridges, which are loose aggregations of ice blocks, behave like fluid structures, while multi-year ridges, which are frozen solid, behave like elastic structures. Ultrasonic laboratory experiments were conducted at a scale of 1000:1 to test this hypothesis by actually measuring the difference in the scattered field from these two types of structures. Polypropylene with ρ=0.9 kg/m3, Cp=2650 m/s, and Cs=1300 m/s was chosen as a surrogate for ice. Floes were modeled two ways using the polypropylene; a half-cylinder modeled the elastic floe, and an aggregation of chips modeled the fluid floe. The scattered field for each case is estimated by subtracting the field measured for a free-surface experiment from the field measured for the scatterer experiment. Experimental results show that loose aggregations of chips produce a dipolar scattered field and that the elastic half-cylinder produces a quadrupolar scattered field. These results support the notion that first-year and multi-year ridges in the Arctic produce distinctly different scattered fields and that scatter from first-year ridges is the dominant scattering loss mechanism in long-range Arctic propagation. [Work supported by ONR and Doherty Foundation.]
Ray acoustic fields of submerged thin elastic shells under on- and off-surface source excitation: The cylindrical prototype
Authors: Ho Jin-Meng
Published: October 2005

The ray-acoustic formulation developed previously for a thin elastic cylindrical shell [Felsen etal., J. Acoust. Soc. Am. 87, 554–569 (1990)] is subject to extensive numerical tests for both on- and off-surface sources, i.e., plane waves, which incidence may be normal or oblique to the axis of cylinder, and phased line sources located on or near the shell surface. The Fresnel transition function is employed to account for the saddle point-near-pole effect which arises when the incidence angle is close to the mode angle. As functions of frequency, the amplitude and phase of the pressure field are computed in the range of κa=2 to 50, where κ is the transverse component of the acoustic wavenumber and a is the shell radius, at particular observation angles; whereas the field pattern, parametrized by κa, is established along the azimuthal direction. The ray field agrees well with the reference solution (normal modes) in both cases. Furthermore, the constituent ray-acoustic components, especially shell-guided modes of different types such as compressional and shear waves, are also shown individually so as to identify their imprint on the total field, and the coupling coefficients for the supersonic leaky and subsonic trapped flexural waves are numerically compared, thus quantifying the excitation mechanisms of structural waves.
Ray acoustic fields of submerged thin elastic shells under on- and off-surface source excitation: The spherical prototype
Authors: Ho Jin-Meng
Published: October 2005

This is a counterpart of the companion paper above, with the additional complexity that is introduced by the spherical focusing. It is based on the previous ray formulation for a thin elastic spherical shell [J. M. Ho and L. B. Felsen, J. Acoust. Soc. Am. 88, 2389–2414 (1990)], again augmented by the Fresnel integral to accommodate the transition region. The shell guided wave field is focused near the backscatter direction, or the polar axis, according to the zeroth-order Bessel function, which may be approximated by Debby asymptotics when away from the focusing regime, thus leading to the regular region where the two counter-circumnavigating surface waves are distinguishable from one another. The excellent agreement between the ray field and the reference solution (normal modes), as achieved in the spherical as well as the cylindrical case, supports that the ray-acoustic technique is effective for evaluation of sound scattering and radiation from submerged elastic shells in the mid- and high-frequency ranges. The successful numerical implementation also helps understand, and extract, wave objects dominant on the structure, which can then be generalized to describe more practical geometries with increased confidence.
Virtual environments: Introductory remarks
Authors: Durlach Nat
Published: October 2005

Virtual environments are now receiving a great deal of attention by the R & D community, government agencies, industrial firms, and the press. Although much of this attention can probably best be classified as ‘‘hype,’’ there are in fact some truly interesting problems, ideas, and research efforts associated with the creation and application of such environments. These introductory remarks will provide some basic definitions, a brief overview of some of the more important research problems and application areas associated with virtual environments, and an introduction to the four special sessions on virtual environments that are scheduled for this ASA meeting.
Perceptual consequences of engineering compromises in synthesis of virtual auditory objects
Authors: Wightman Frederic , Kistler Doris , Arruda Marianne
Published: October 2005

The aim of most attempts to synthesize a virtual auditory environment is duplication of the acoustical features of a real auditory environment. In other words, the sound pressure waveforms reaching a listener’s eardrums in the virtual world should be the same as they would have been in a real world. This goal is currently reachable only in certain laboratory conditions. Thus, production of usable virtual sound systems involves a number of compromises. For example, error-free synthesis of an auditory object at an arbitrary point in space requires knowledge of the free-field-to-eardrum transfer functions (HRTFs) for both ears at all sound incidence angles. Since it is impossible to measure HRTFs at all sound incidence angles, some interpolation is required, and how best to accomplish it is a difficult question. In addition, HRTFs vary considerably from listener to listener, but it is not feasible to measure HRTFs from each potential use of a virtual sound system. Either a single HRTF must be chosen or some kind of average HRTF computed. Interpolation and use of nonindividualized HRTFs are two of the many compromises that must be made in order to produce a usable virtual sound system. These compromises produce error, the significance of which can only be assessed in psychophysical experiments. The experiments described here require listeners to judge the apparent positions of virtual auditory objects that are synthesized so that the error introduced by interpolation and other compromises is systematically manipulated. The perceptual consequences of the manipulations are evaluated by examining the variance in apparent position judgments, the discrepancy between apparent position and intended position, and the frequency of front-back and up-down confusions. [Work supported by NIH and NASA.]
Auditory space modeling and simulation via orthogonal expansion and generalized spline model
Authors: Chen Jiashu , Van Veen Barry D. , Hecox Kurt E.
Published: October 2005

A two-stage model that establishes a mathematical representation of auditory space is developed. The first stage of the model consists of a low-dimensional subspace representation for the free-field-to-eardrum transfer functions (FETF’s). The bases of this subspace are complex-valued eigentransfer functions (EF’s) obtained from the Karhunen–Loeve expansion of the measured FETF’s covariance matrix. Each FETF is represented as a weighted sum of the EF’s. The second stage of the model is a functional representation for the weights, termed spatial transformation characteristic functions (STCF’s), applied to the EF’s. The STCF’s are functions of azimuth and elevation. A generalized spline model is fitted to each STCF derived from measurements. The spline model filters out noise and permits interpolation of the STCF between measured directions. The FETF’s for an arbitrary direction is synthesized by weighting the EF’s with the smoothed and interpolated STCF’s. Using FETF’s sampled uniformly over the upper 3/4 sphere for one KEMAR ear, it is shown that 99.9% of the energy in the measured FETF’s is contained in a 16-dimensional subspace. The relative average mean-square error between 2320 measured and simulated FETF’s is found to be less than 0.25%. [Raw data provided by Dept. of Neurophysiology, University of Wisconsin−Madison.]
Acoustic validation of an ‘‘in ear’’ system for recording the head-related transfer functions (HRTFs) in the human
Authors: Pralong Daniele , Phillips John R. , Carlile Simon
Published: October 2005

An inherent problem in accurately measuring HRTFs is the use of recording systems placed in the ear canal that may interfere with the sound field. A simple earprint and electroplating method is described for making customized, ultra-thin (0.2-mm) holders, which can be used to position a small (1.25-mm-diam) polyethylene probe coupled to a miniature microphase deep within the auditory canal. Acoustic recordings using the system on a model ear equipped with a microphone in place of the eardrum show that (1) spectral notches created by standing waves within the canal can be used to precisely place the probe relative to the eardrum; (2) the system does not significantly affect the sound spectrum as it is transformed from the free-field to the eardrum (±1 dB from 0.2 to 12 kHz, ±3 dB from 12 to 14 kHz); (3) it does not introduce direction-dependent spectral components; and (4) successive insertions of the set produce highly repeatable recordings. Finally, the system was used to test the reproducibility of headphones placement, a crucial element in the high-fidelity simulation of auditory space. [Work supported by the Swiss National Science Foundation, the Foundation for the 450th Birthday of the University of Lausanne, the McDonnell–Pew Centre for Cognitive Neurosciences, the Beit Foundation, and the Wellcome Trust.]
Localization in a virtual echoic environment
Authors: Hafter E. R. , Saberi K. , Jensen E. R.
Published: October 2005

Virtual auditory environments are generally created by filtering stimuli through head-related transfer functions that mimic reflections and resonances of the shoulders, head, and external ears, and then presenting the sounds through earphones. Here, a different approach has been adopted in which multiple loudspeakers are used in an anechoic chamber to create virtual sources and echoes in space. Individual digital filters are used to equalize the loudspeakers and the computer/interface system allows for creation of multiple virtual sources and echoic surfaces. The locations of sources and echoic surfaces can be roved from trial to trial over a wide range of distances and over the eight separate azimuths allowed by the apparatus. Spatial discrimination is measured with two-alternative forced choice psychophysics while, for localization, subjects use a laser pointer to indicate the directions of apparent sources. For wideband clicks (cf=4 kHz), these results show that the presence of single echoes increases spatial thresholds by a factor of about 2 across the range of source azimuths from 0° to 90°. The pointing data show that apparent locations of the sources are moved toward those of the echoes by about 4° to 5°, a result that is unaffected by the magnitudes of the source–echo separation in either azimuth (8° to 40°) or delay (1 to 30 ms). At longer delays, subjects sometimes report double images, one near the direction of the source and the other near that of the echo.
Recent studies of human response to sonic booms
Authors: Shepherd Kevin P. , Sutherland Louis C.
Published: October 2005

The National Aeronautics and Space Administration, in conjunction with major aerospace companies, is investigating the technical and economic feasibility of a new generation of supersonic transport airplanes. Efforts are being devoted to an examination of the feasibility of designing and operating a supersonic transport that will yield a sonic boom acceptable to the affected population. This work is focused on sonic boom signatures that differ from the classical N wave. The presentation will discuss the results of a series of studies conducted using a sonic boom simulator at the NASA−Langley Research Center in which human subjects assessed a wide range of shapes of sonic boom signatures. Various psychophysical scaling techniques were employed and the results were examined in terms of their relationship with several calculated noise measures. For the situation in which people are exposed to sonic booms while indoors, building vibration and rattle are potentially important factors in need of consideration. Structural response to sonic boom is reviewed and compared with human vibration response criteria. A review of existing data is used to determine the acceleration required to induce rattle of wall-mounted objects.
JAMSTEC’s ocean tomography method
Authors: Nakano Iwao , Tsuchiya Toshio , Amitani Yasutaka
Published: October 2005

Two one-way transmission experiments (1989) and one reciprocal transmission experiment (1991) have been conducted by JAMSTEC. These experiments were in the 200–300 km range and were less than 4 days in duration. The data of mooring motions were not available in the experiments. This tomography method, which can work well with the limited data, is made up as follows. The reference data are constructed with the data supplied by JODC. The ray-tracing code based on the generalized ray theory [H. Weinberg, J. Acoust. Soc. Am. 58, 97–109 (1975)] is range independent. The identification of multipaths is accomplished by means of linear ray identification. The bias component in travel times is corrected using a linear tomography inversion. The covariance function of sound speed is a Gaussian [Chiu etal., J. Geophys. Res. 92, 6886–6902 (1987)]. The estimator is constructed by the simple stochastic inverse theory. The map is a 1-D and 2-D time series of a sound-speed anomaly and a temperature anomaly. The three-dimensional tomography method is now under consideration.
Errors in tomographic imaging of scalar and vector fields from underdetermined data
Authors: Wilson D. Keith
Published: October 2005

The usual error maps computed for underdetermined tomographic images can be very misleading for two reasons. First, the spatial correlation function of the actual field usually differs from the correlation function used to solve the inverse problem. Second, the effect of smoothing by the projections is neglected. Numerical examples are used to demonstrate these points, and methods for improving the inverse reconstructions are suggested. Tomographic imaging of flow fields is also discussed. Although it can be proven that the irrotational part of the flow that is interior to the array is invisible to the measurements, this is shown not to be a fundamental impediment for flow tomography using the methods usually applied by geophysical tomographers, largely because they assume apriori statistics of the spatial structure.
Broadband PE propagation through mesoscale perturbations
Authors: Smith Kevin B.
Published: October 2005

When acoustic ray paths are computed in a range-dependent environment with mesoscale perturbations, the behavior of the smaller angle, axial rays has been shown to be chaotic−imposing a limitation on ray predictability to within the first few thousand km [Smith etal., J. Acoust. Soc. Am. 91, 1939–1959 (1992)]. This may be indicative of nonadiabatic behavior. A manifestation of this may be observable in the SLICE-89 data set [Cornuelle etal., SIO Reference Series 92-17 (1992)], which displays a broad, late arrival in depth of acoustic energy, as opposed to a narrow region of late arrivals at the sound channel axis as predicted by range-independent models. A broadband version of the parabolic wave equation is implemented for both a range-independent and range-dependent (consisting of a superposition of baroclinic Rossby waves) deep ocean environment. The results are compared qualitatively with experimental data. Acoustic mode coupling due to mesoscale ocean structure is addressed and the effects on long-range acoustic tomography is discussed.
Molecular relaxation effects on sonic boom waveforms: A tutorial survey
Authors: Pierce Allan D.
Published: October 2005

Although molecular relaxation has a dominant effect on the attenuation of sound in the audio frequency range, it was largely ignored in the early work on sonic boom propagation, until Hodgson and Johannesen circa 1971 brought the phenomena to the attention of sonic boom researchers. Although interest in the overall subject waned somewhat with the March 1971 decision to indefinitely postpone the SST program in the United States, the intriguing physics involved and its fundamental importance for atmospheric sound propagation in other contexts sustained the interest of researchers, especially Bass and Raspet, who sought a better quantitative understanding of relaxation effects on shock waves in the atmosphere. The present author and his students, spurred in more recent years by the revived interest in a possible US high-speed civilian transport, extracted a simple approximate formulation, which captured the essential physics and which predicted the detailed, albeit local, waveform shape at a shock in terms of peak overpressure and atmospheric humidity. The present paper discusses the basis of this theory, its predictions, its use to substantiate the claim that turbulence is typically more important than molecular relaxation, and the progress that has recently been made to understand its limitations. [Work supported by NASA−LRC and by the William E. Leonhard endowment to Penn State Univ.]
Flight test measurements of the effect of turbulence on sonic boom peak overpressure and rise time
Authors: Willshire William L. , Garber Donald P. , DeVilbiss David W.
Published: October 2005

Sonic boom bow shock amplitude and rise time statistics from a sonic boom propagation flight test experiment are presented. The experiment consisted of flying two types of aircraft, the T-38 and F-15, at speeds of Mach 1.2 to 1.3 over a ground-based microphone array with concurrent meteorological measurements. Bow shock overpressure and rise time distributions measured under low and moderate atmospheric turbulence conditions for the same test aircraft are quite different. The peak overpressure distributions are skewed positively, indicating a tendency toward positive deviations from the mean. Standard deviations of overpressure distributions measured under moderate turbulence were slightly larger than those measured under low turbulence. Under moderate turbulence conditions the mean rise time was larger by a factor of 3.7 and the standard deviation was larger by a factor of 3.2 from the low turbulence values. These changes resulted in a transition from a peaked appearance of the low-turbulence rise time distribution to a flattened appearance for moderate turbulence rise time distributions.
Acoustic telemetry of RDI Doppler current meter data−A real time acoustic link
Authors: Duchesney John , Chappell Steve , Pettigrew Neal , Sprenke James
Published: October 2005

Datasonics has developed and tested a two-way acoustic telemetry link with software/firmware for command, control, and recovery of data from an (RDI) acoustic Doppler current profiler (ADCP) instrument. In operation, the acoustic link is quasitransparent to the system operator. Standard ADCP user command protocol allows PC-generated commands to be buffered and transmitted from a surface acoustic modem to a subsurface modem, which is connected by RS-232 interface cable to the ADCP. The acoustic down link command signals are reformatted in the subsurface modem and passed on to the ADCP. Data are transmitted over the up-link in 4096-byte packets at a data rate of 1200 bits/s. The self-contained subsurface acoustic telemetry modem (ATM) is housed in an aluminum pressure housing 5 in. o.d.×33 in. long. Connectors are provided for RS-422 I/O to the ADCP and for external power input for long-term insitu deployments. A choice of directional or omni directional acoustic transducers is available. The system was tested in the Piscatagua River in Portsmouth, NH and will be installed in Tampa Bay as part of NOAA’s PORTS program, which offers shipping traffic access to current profiler data in near real time. The operating software protocol will be discussed and results from both the New Hampshire tests and Tampa Bay operations will be presented.
Long-range probing of the ocean by a parametric source
Authors: Naugol’nykh Konstantin A.
Published: October 2005

Experimental investigations of the performance of a parametric transmitting array (PA) in the deep and shallow ocean are presented in the present paper. The array to produce the two primary waves consisted of two parts, each 2×3 m in size, with a total acoustic power of up to 24 kW. The two primary frequencies were in the band 1.9 to 3.9 kHz, the difference frequency in the band up to about 1 kHz. Three sets of experiments were made: (1) an investigation of the formation of the PA field in the homogeneous deep ocean; (2) PA performance in shallow water; and (3) directivity pattern measurements in the inhomogeneous deep ocean. The possible application of parametric arrays for long distance ocean probing is discussed.
Test of nonperturbative ocean acoustic tomography inversion
Authors: Jones R. Michael , Georges T. M. , Ehret Laura
Published: October 2005

This work is part of an effort to compare various ocean acoustic tomography inversion methods given the same hypothetical sound-speed field (specified in a 1000- by 1000- by 5-km region). To test the WPL nonperturbative inversion method [Jones etal., NOAA Tech. Memo. ERL WPL-217 (1991)], the authors simulated tomographic data using ray tracing, performed an inversion, and compared the results with the sound-speed field provided. The simulation sampled the region in several vertical slices, and the inversion yielded the range average of the symmetric part of the sound-slowness profile for each slice.
Teaching acoustic cues of nasal resonance
Authors: Andrews Cathy
Published: October 2005

Acoustic coupling between the oral and nasal cavities results in the addition of pole-zero pairs to the vocal-tract transfer function, which interacts with variations in vocal-tract shaping across different vowels and speakers. Presentation of the myraid of acoustic features associated with nasalization based on vocal-tract models can confuse students with little mathematical background. One successful approach allows students to discover a few established cues via waveform and spectrographic analysis. Broadband spectrograms of students’ productions of ‘‘bead–bean’’ clearly illustrate a nasal murmur (200–300 Hz) and the attenuation of formant frequencies is the nasalized vowel compared to the oral vowel. Another broadband spectrogram is made of the tape-recorded speech of a female speaker of Texan English, exhibiting extreme attenuation in the F1 region. The decreased intensity of the nasalized vowel in ‘‘bean’’ (compared to the oral vowel in ‘‘bead’’) is seen as rounded waveform cycles with lower amplitude using waveform-editing software. Changes in vowel quality due to nasalization can be heard as the students proceed screen-by-screen through the waveform.
Auditory profile analysis of harmonic complexes
Authors: Zera Jan , Green David M.
Published: October 2005

Spectral shape discrimination of a variety of harmonic complexes was investigated. The signal was an increment in a single component of an otherwise equal-amplitude complex. The focus in these experiments was to determine how the frequency of the signal, the number of components in the complex, and the phases of the components influenced signal detectability. The fundamental frequency was 100, 200, or 400 Hz in spectra ranging up to 6000 Hz. Thresholds increased by almost 30 dB at the highest signal frequencies. These results are understandable because more components fall within the same critical band at the higher frequencies. Thus, the signal caused a lesser change in the output level of a single critical band as more and more nonsignal components were added to the channel. A simple transformation of data were applied to remove the effects of the nonsignal components. The corrected thresholds have a bowl-like shape similar in appearance to that seen in previous studies of spectral shape discrimination where the components of the complex were spaced in frequency at equal logarithmic intervals. [Research supported by AFOSR and the Hays–Fullbright Foundation.]
Noncontact ultrasonic spectroscopy technique for the measurement of elastic moduli and ultrasonic attenuation of solids
Authors: Schwarz R. B. , Kuokkala V.-T.
Published: October 2005

A novel method and apparatus for measuring the elastic moduli and ultrasonic attenuation of small samples (millimeter dimensions) over a wide temperature range is described. In the most general case, a nonmagnetic sample is coated with a thin film of a magnetostrictive material. The film performs both as a driving transducer and as a receiving transducer. An alternating magnetic field of variable frequency generates a periodic stress in the film and drives the sample into mechanical resonances. The permeability of the film changes when the sample is resonating and allows the detection of the resonances. The operation of the system and the mathematical procedures to deduce the elastic moduli and ultrasonic attenuation are exemplified with measurements on amorphous and crystalline alloys. [Work supported by the U.S. Department of Energy.]