bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrations of circular and noncircular cylindrical shells
Authors: Jelatis George J. , Rossing Thomas D.
Published: October 2005

In order to better understand the vibrational modes of Chinese two-tone bells [Rossing et al., J. Acoust. Soc. Am. 83, 369–373 (1988)], the vibrational modes of capped and uncapped cylinders with circular and nearly elliptical cross sections have been studied. Mode doublets in the noncircular cylinders replace single modes in the circular cylinders. The higher frequency mode in each doublet, in both the capped and uncapped cylinders, generally belongs to the mode that has a node where the curvature is greatest. The frequency ratio of the doublet pair appears to decrease with increasing m (number of wavelengths around the circumference) but to increase with n (number of nodal circles). The splitting increases with eccentricity, as expected.
Vibrational modes and damping in a snare drum shell
Authors: Fystrom Dell O. , Rossing Thomas D.
Published: October 2005

The lowest modes of a cylindrical snare drum shell, described by the number n of nodal circles and the number of m of nodal lines around the circumference, have been identified by means of holographic interferometry, scanning the nearfield sound with a microphone, and by attaching a small accelerometer to the shell. The modal decay rate in the free shell increases rapidly with modal frequency. In a complete snare drum, on the other hand, the normal modes of vibration are determined mainly by the motion of the drumheads. The modal decay rates are strongly dependent on the manner in which the drum is supported, being least when the drum is supposed on elastic cords. This indicates that a considerable amount of vibrational energy is transmitted to the shell of the drum as the heads vibrate.
Asymptotic series for disparate mixtures
Authors: Gillette Gregory
Published: October 2005

The term “disparate mixture” here refers to a physical mixture composed of two distinct phases, where the physical properties of the phases are very dissimilar. It might be formed, e.g., from two immiscible gases or fluids, or from a soil-water compound. The calculation of fields in such a mixture is discussed, leading to the development of a pair of coupled asymptotic series (corresponding to the field point in one or the other of the phases). The specific problem of acoustic wave fields due to a point source in a two-fluid mixture illustrates the procedure. Questions of interest are: How does the mixture behave away from the limiting case, i.e., when the property ratio of the phases is very small but nonzero? How are successive terms in the series related to geometric length scales in the mixture (connectivity scales, inclusion size scales, matrix “gap” scales)? Preliminary results of applying the method to the reflection of plane waves from a flat interface are presented, and extensions to additional layered mixture models are indicated.
Anomalous ultrasonic behavior of hydrogen-bonded liquid binary systems containing Ortho Chlorophenol
Authors: Ramamurthy Janjanam S.
Published: October 2005

Ultrasonic absorption and velocity have been measured in a number of binary hydrogen-bonded liquid systems of which Ortho Chlorophenol forms a common constituent. The composition and temperature dependence of absorption and velocity bear a remarkable similarity to those observed in aqueous hydrogen-bonded liquid binary systems. Pronounced absorption peaks, maxima in velocity, and negative excess compressibilities followed by peaks of shear viscosity and liberation of considerable heats of mixing are attributed to the formation of a metastable intermediate state with a sound sensitive structural equilibirum. A modified two-state model is proposed for quantitative interpretation of results.
Properties of gallstones and their relationship to destruction mechanisms in acoustic lithotripsy
Authors: Everbach E. Carr , Gracewski S. M. , Vakil N.
Published: October 2005

As part of an investigation of the mechanisms of gallstone destruction in extracorporeal shockwave lithotripsy, the effectiveness of lithotripsy has been examined as well as the form of the resulting damage to simulated and biological concretions as a function of several physical properties of the stones: air content, hardness, fracture toughness, flaw size distribution, chemical composition, and crystal structure. Measurements on plaster suggest that increasing air content tends to promote damage suggestive of a cavitation mechanism of destruction, while degassing promotes rearsurface damage (spalling) suggestive of a stress-fracture mechanism. It has been found that some human gallstones contain air in vivo, that all gallstones that have been allowed to dry contain significant quantities of air, and that during lithotripsy stones containing air break up more easily and into finer pieces than fully hydrated stones. The measured hardness of gallstones is roughly ten times smaller than that of kidney stones; this finding suggests that a ductile, rather than brittle, mechanism of fracture or crack growth may be responsible in gallstone lithotripsy. Most gallstones exhibit a preferred radial pattern of crystal orientation, which may have implications for strain-wave propagation within the stone material. [Work supported by the F. V. Hunt Postdoctoral Fellowship of the Acoustical Society of America and the National Institute of Health through U.S.P.H.S. Grant No. DK 39796.]
On the nucleation of transient cavitation from stabilized microbubbles
Authors: Roy Ronald A. , Calabrese Adam , Church Charles C.
Published: October 2005

In recent years, powerful techniques have been developed for the detection of acoustic cavitation produced by short pulses of high-frequency ultrasound. However, quantitative agreement between the measured and theoretically predicted cavitation threshold pressures is poor, presumably because of the lack of a priori knowledge of the mechanism for cavity nucleation. Microbubbles stabilized by human serum albumin have attracted considerable attention as echo-contrast agents in ultrasonography. By seeding clean water with these microbubbles, it is possible both to establish and to control the nucleation mechanism, and thus obtain threshold measurements that can be compared directly with theory. Results from experiments performed at 1 and 2.5 MHz in water seeded with Albunex® stabilized microbubbles (1–1μm in diameter) are presented and compared with theoretical predictions based on a “dirty” bubble model [C. C. Church and R. A. Roy, J. Acoust. Soc. Am. Suppl. 1 86, S41 (1989) ]. [Work supported in part by the ONR and the NIH under Grant No. 2-RO1-CA 39374-04A1.]
Brownian motion of a stable microbubble used to measure viscosity of a fluid
Authors: Clark Jerome , Wu Junru , Nyborg Wesley
Published: October 2005

Brownian motion of a stable microbubble in a fluid can be observed under a microscope and registered automatically by a computer. By analyzing data stored in the computer, viscosity of the fluid can be calculated. By using this method, viscosities of water and human albumin were measured. There were reasonable agreements with the accepted values. [Work supported by NIH via Grant No. 42947.]
Equivalent threshold levels for TDH-49 earphones and ER-3A insert earphones
Authors: Goran Vickie F. , Frank Tom
Published: October 2005

Equivalent threshold sound-pressure levels were obtained for 24 normally hearing adult subjects from 125 to 8000 Hz using TDH-49 earphones in P/N 51 cushions and ER-3A insert earphones having a modified foam earplug inserted into the ear canal so that the outer edge was flush with the floor of the concha. Test versus retest thresholds within and across test sessions were not clinically significant for each earphone type at each frequency. The threshold difference between the TDH-49 and ER-3A and the ER-3A threshold levels at each frequency, referenced to an HA-1 (2-cc) coupler, were in very good agreement with the ER-3A proposed reference threshold sound-pressure levels at each frequency as reported by Wilber et al. [J. Acoust. Soc. Am. 83, 669–679 (1988)].
Attenuation provided by audiometric earphones
Authors: Goran Vickie F. , Frank Tom
Published: October 2005

The attenuation provided by TDH-49 earphones in P/N 51 cushions and ER-3A insert earphones using modified foam earplugs was determined for 24 subjects using a real-ear attenuation at threshold paradigm (ANSI S3.12-1984). The TDH-49 earphones were fitted on each subject as normally done for audiometry and the ER-3A earplugs were inserted into each subject's ear canals so that the outer edge was flush with the floor of the concha. Compared with the TDH-49, the ER-3A provided about 18 dB more attenuation for the lower (125–500 Hz) and about 15 dB more attenuation for the higher (1000–8000 Hz) frequencies. Implications concerning the use of TDH-type earphones and ER-3A insert earphones in reference to permissible ambient noise levels for audiometry (ANSI S3.1-1977) will be discussed.
Bone conduction thresholds for different mastoid placement sites
Authors: Wright Diana C. , Frank Tom
Published: October 2005

Bone conduction thresholds were obtained from 250 to 4000 Hz by placing the bone vibrator on the mastoid as done for audiometry and at mastoid sites initially judged to produce the loudest perception of a 250-, 500-, and 1000-Hz pure tone and white noise using 30 normally hearing adult subjects. The bone conduction thresholds were found to be variable across placement sites and test frequencies. However, the placement site judged to be the loudest with white noise generally resulted in the lowest thresholds. Implications for bone conduction audiometry, including normal air-bone gaps, and reference equivalent threshold force levels will be discussed.
Possible observation of acoustic emission precursors to catastrophic delaminations in composites
Authors: Tittmann B. R.
Published: October 2005

Measurements are reported of the elastic properties of carbon—carbon (C/C) composites during pyrolysis. This heat treatment is the first critical step during the processing of C/C components and constitutes the most frequent source of component failure, because of delaminations. Here, the use of active (Lamb wave) and passive (AE) acoustic sensors to study the various stages of microstructural evolution of C/C during pyrolysis is reported. The results of several experimental runs are presented in which AE precursors to delaminations were found. In some of the runs the precursors were used as indicators to slow down the time-temperature profile of the run and the delaminations were avoided. In other runs, the time-temperature profile was not changed and the components delaminated. The apparatus, sensors, and the technique of recognizing the precursors are described. A physical model is discussed for the source of the precursors based on the chemical and physical changes in the C/C component and their consequences on the microstructure as studied by micrographical and ultrasonic techniques. [The author acknowledges help from F. Montgomery of General Atomics in the measurements and the support of Rockwell International Science Center under a contract from the Office of Naval Research Contract N00014-87-C-0724.]
New quasistatic model for ultrasonic wave interaction with imperfect solid-solid interface
Authors: Rokhlin S. I. , Wang Y. J.
Published: October 2005

A new model for prediction of ultrasonic reflection and transmission on a partially contacting interface between two solids is considered. A thin anisotropic layer with effective elastic properties is introduced to simulate the interface conditions. The effective elastic constants of the anisotropic layer and its thickness are selected based on a micromechanical theory of multiphase inhomogenous media. For an interface layer thin relative to wavelength an asymptotic expansion of the transfer matrix for the anisotropic layer is performed. At normal incidence this approximation is equivalent to a solution based on the spring model. The advantage of the solution suggested here appears at oblique incidence when nondiagonal transverse stiffness elements appear naturally as corresponding elements of the transfer matrix for the anisotropic layer. On the basis of the transfer matrix technique the reflection and transmission coefficients on the interface are calculated for both longitudinal and transverse incident waves at oblique incidence. The reflection and transmission coefficients predicted by the suggested model are compared with the results given by the spring model and elastodynamic scattering theory.
Efficient anechoic tank linings
Authors: Reader Wayne T. , Megill Robert W.
Published: October 2005

Viscoelastic polymers containing gas-filled voids are frequently used to fabricate anechoic linings for water-filled tanks. Shaped sheets or wedges of the polymer can be employed to provide efficient linings—efficiency being measured in terms of the degree and frequency bandwidth of the acoustical reflectivity; and in terms of cost of the installed treatment. Acoustical efficiency results by virtue of the gradual transition from the impedance of water to a highly dissipative region. Pecuniary efficiency results from minimization of the volume of polymer required to fabricate the treatment. However, neither acoustical nor pecuniary efficiency can be realized without the use of a viscoelastic polymer whose moduli and loss factor are appropriate for the frequency and temperature regions over which the tank is to operate. A geometric transition concept and a family of polymers is described that provide the versatility to design anechoic tank linings capable of providing 10 dB or more reflection loss over several decades of frequency and water temperatures ranging between freezing and boiling.
Measurements of the complex dynamic shear compliance and loss tangent of pilot whale blubber and the role of blubber in flow-noise reduction
Authors: Fitzgerald James W. , Fitzgerald Edwin R.
Published: October 2005

The complex dynamic shear compliances and loss tangents of pilot whale blubber (BLB), pork-belly fat (PBF), and beef-belly fat (BBF) have been measured over a frequency range of ≃ 45 to 4500 Hz, using the Fitzgerald apparatus [E. R. Fitzgerald and J. D. Ferry, J. Colloid Sci. 8, 1–34 (1953)]. Representative values at 100 Hz for J* and tan ζ PBF, J* = 3 × 10−9 cm2/dyn, tan ζ = 0.5; BLB, J* = 2 × 10−6 cm2/dyn, tan ζ = 0.7; BBF, J* = 2 × 10−8 cm2/dyn, tan ζ = 0.1. Thus beef-belly fat is ≃ 100 times stiffer (less compliant) and pork-belly fat is ≃ 15 times less stiff (more compliant) than whale blubber. The general shape of the compliance curves are similar except for a frequency shift in the peak values. The broad peak in J* and tan ζ implies a relaxation mechanism in all three fats. The high loss tangent in blubber and its intermediate value of compliance suggests that it plays a role in reducing flow noise by acting as a “matched load” to the boundary layer “turbulence generator.” A polyvinyl gel, with dynamic shear properties closely matched to those of blubber, is proposed as a “synthetic blubber: for studies of turbulent flow over compliant surfaces.” [Work had fragmentary support from NUSC/NLON.]
The damping of panels by thick layers of elastic porous media
Authors: Shiau N.-M. , Wahl T. J. , Bolton J. S.
Published: October 2005

In this paper a technique is presented for calculating the response of a panel to a line force input when loaded by both a finite-depth layer of elastic porous material and a heavy fluid. Damping theories normally require that an attached damping layer be thin compared to the flexural wavelength in the base panel. Here this requirement is avoided by allowing explicitly for wave propagation within the damping layer. Specifically, the porous damping layer is modeled using a theory derived by Biot that allows for the existence of two dilatational waves and a transverse wave. Conditions required to couple the porous medium to the panel and an adjacent fluid will be discussed. A formal solution for the plate response may be obtained easily in the wavenumber domain. Although it is not possible to obtain the spatial response analytically in this instance, it will be shown that under practical circumstances the required inversion integral may be evaluated efficiently and “exactly” by using the fast fourier transform algorithm. Results will be given illustrating the damping potential of thick layers of porous materials.
Static and dynamic moduli measurement and temperature dependence for elastomers and composites
Authors: Serocki J. , Beaton B. L. , Wetterskog K. , Brown D. A. , Garrett S. L.
Published: October 2005

Castable elastomers are currently being evaluated for use in fiber-optic interferometric acoustic sensors. The sensitivity and depth tolerance of elastomer-based hydrophones are functions of the Young's modulus (E), the shear modulus (G), and the yield strength of the material. The moduli are a function of temperature. This presentation will describe the methods used, materials tested, and results obtained to date. The dynamic moduli measurement method employs a resonant technique with electrodynamic transducers attached to a rod of circular cross section placed in a magnetic field. This method allows continuous measurement of the moduli over temperature. Here, E determined from the dynamic technique was one-fourth to one-half of that determined from static test methods (ASTM638). Of the 17 material samples tested to date, the most promising is a glass-filled epoxy that has 0.35%/°C moduli changes [(1/E)(∂E/∂T) = (1/G)(∂G/∂T)] at 1500 Hz. The worst temperature-dependent material is an unfilled polyurethane (URALITE™ 3130) with a 3.1%/°C change in shear modulus at 250 Hz and a 2.1%/°C change in Young's modulus at 30 Hz. [Work sponsored by Naval Sea Systems Command and the Naval Postgraduate School Direct Funded Research Program.]
The reflective properties of compliantly coated uniform panels
Authors: Maidanik G. , Dickey J.
Published: October 2005

Cladding a panel with various layers designed to achieve radiative, reflective, and transmissive properties that are substantially different from those of the bare panel is a common noise control procedure. The achieved changes in these properties are often assessed on the basis of changes that occur in uniform panels on components that are normal to the surface of the panels. In this paper the practice of this kind of assessment is examined. In particular, a specific anomaly in the reflective property of a compliantly coated panel is presented and discussed. The relevance of the anomaly in the assessment of the reflective property at angles of incidence other than normal is also discussed.
The prediction of shock structure in noncircular jets using conformal mapping with a pseudospectral hybrid scheme
Authors: Bhat T. R. S. , Morris P. J.
Published: October 2005

Broadband shock associated noise, in supersonic jets operating off-design, is generated by the interaction of large-scale structures in the jet mixing layer and the quasiperiodic shock cell structure of the jet. In this work, the shock cell structure of supersonic jets with noncircular exit geometry is modeled using a linear analysis. The analysis requires the solution of the equations of hydrodynamic stability for zero frequency. The model takes into account the finite thickness of the jet shear layer using realistic velocity and density profiles. The effects of the shear layer turbulence are included by incorporating eddy-viscosity terms. The numerical method involves the transformation of the cross section of a given jet to a rectangular computational domain using a series of conformal mappings. A pseudospectral hybrid scheme is used in the computational domain to set up the finite-differencing scheme. The variation of the pressure fluctuation with downstream distance is given for an elliptic jet of aspect ratio 2. Comparisons with experimental data are made, where possible. This work is an extension of earlier work [P. J. Morris, T. R. S. Bhat, and G. Chen, J. Sound Vib. 132(2), 199–211 (1989)], where the shear layer was approximated by a vortex sheet. [Work supported by NASA Langley Research Center under NASA Grant NAG-1-657.]
High-quality wideband audio coding
Authors: Brandenburg Karlheinz , Johnston James D.
Published: October 2005

Coding of CD-quality wideband digital audio signals at low bit rates (e.g., 64–128 kbits/s per audio channel) is a rapidly evolving research topic. Although considered impossible only a few years ago, recent results have demonstrated this capability, and these coding algorithms are now a topic for standards committees including the International Standards Organization (ISO). This technique promises reduction of the bit rate needed for digital transmission and digital storage of CD-quality sound by a factor of 6 to 10. This is achieved while maintaining transparency of the coding and decoding process even to the most critical listener. The most advanced coding algorithms in this field employ models of the masking properties of the human auditory system to “hide” the inevitable quantization noise under the masking threshold. The best results have been obtained using frequency domain techniques. As known from speech coding, the input signal is decomposed into subsampled spectral components using either an overlapped transform or a tree-structured filter-bank. This paper will present examples of both transform and subband coders. It will focus on the use of knowledge from psychoacoustics in these “perceptual” coders. Demonstrations of the capabilities and the weak points of the currently existing wideband audio coders will be given.
Surface impedance measurements as a function of moisture content in porous glass beads
Authors: Sabatier James , Prasad Shyam , Kasim Fauziah
Published: October 2005

The effects of moisture content on the acoustic surface impedance of outdoor soil has received recent attention [A. J. Cramond and C. G. Don, J. Acoust. Soc. Am. 82, 293–301 (1987)]. This work indicated dramatic effects of moisture content. A measurement apparatus for measuring the moisture content in a synthetic soil (100-μm spherical glass beads) and the acoustic surface impedance is being constructed. The apparatus consists of a cylindrical soil column that attaches to the sample end of an impedance tube. The moisture content in the soil column can be varied by applying a suction to one end of the column where a porous plate is positioned. Water is caused to flow in and out of the soil column through the porous plate. The acoustic surface impedance is measured using a phase gradient technique. [Work supported by DOA.]
Boundary layer flow noise—The direct radiation
Authors: Lauchle Gerald C. , Brungart Timothy A.
Published: October 2005

The farfield sound radiation due to the transitional and turbulent boundary layer flow over a rigid, finite body of revolution is addressed quantitatively. Three statistically independent sources of flow noise are analyzed; namely, the intermittent laminar-to-turbulent transition zone that occurs near the nose, the fully developed turbulent boundary layer that covers nearly all of the body surface, and the unsteady trailing edge flow that occurs on the body stabilizer fins. The modeling is used to predict the radiated noise spectra measured in a deep lake along the trajectory of a test body that was released from the bottom and propelled by buoyancy. These experimental data are from the Huddle and Skudrzyk [J. Acoust. Soc. Am. 46, 130–157 (1969)] flow noise experiments. In these experiments the radiated noise was found to be independent of the body composition (both metal and wooden units were used) and the authors concluded that flow unsteadyness was the primary source of farfield radiation. The predictions presented here support that conclusion in that the transition zone and trailing edge flows are very unsteady and their acoustic emissions are significantly more intense than those from the relatively stable turbulent boundary layer flow. [ Work supported by Applied Research Laboratory under contract with U. S. Navy.]
Measurement of flexural and longitudinal vibration intensity by a two-channel laser vibrometer
Authors: McDevitt Timothy E. , Burroughs Courtney B. , Koopman Gary H.
Published: October 2005

In the flexural farfield, vibrational intensity can be measured by using the cross spectrum of two accelerometer signals. However, accelerometers can mass load a structure and they can impede the process of mapping intensity over the surface. Consequently, the use of a scanning two-channel laser Doppler vibrometer was investigated for flexural intensity measurements. Results from vibrometer cross-spectral intensity measurements on a small aluminum beam are given and compared with results obtained by other (one-dimensional) approaches. An investigation was also conducted into measuring longitudinal intensity using the vibrometer in the differential Doppler mode. Results are given and comparisons made with one-dimensional longitudinal methods.
Visualization of instantaneous energy transfer from three point sources
Authors: Gaumond Charles F. , Woo Sheila
Published: October 2005

The instantaneous energy density, as well as pressure and velocity components, were computed for the case of three point sources treated earlier [J. A. Mann, J. Tichy, and A. J. Romano, J. Acoust. Soc. Am. 82, 17-30 (1987)]. The behavior of the pressure field and the transport of energy through regions denoted active intensity vortices will be shown in a video generated on an IRIS-4D color graphic superworkstation.
Measurement of the vibrational isolation characteristics of an underwater transducer element mount by laser vibrometery
Authors: Zintel Harold , Hughes W. Jack , Pechersky Martin J.
Published: October 2005

For the purpose of vibration isolation, underwater transducer elements are often mounted on a constrained layer base plate. The mass of the constraining plate in conjunction with the compliance of the damping layer adds an additional degree of freedom to the axial response of the element at low frequencies. A laser vibrometery system is used to measure the vibrational characteristics of the element and its isolation mount. This technique eliminates erroneous results caused by the added mass of an accelerometer. Three element configurations are studied—the transducer directly glued to the base plate, the transducer mounted with a syntactic foam isolation ring, and the transducer with the isolation ring supported by a constrained layer damped base plate. The ratio of the output voltage of the transducer to the velocity of the base is reported for each configuration in frequency ranges from 70 Hz to 16 kHz. The experimental results are compared to an analytic model.
Aircraft laser sensing of sound velocity in water: Brillouin scattering
Authors: Hickman G. Daniel , Kattawar George W. , Fry Edward S.
Published: October 2005

This study shows that it may be feasible using state-of-the-art pulsed lasers, coupled with a novel technique for maintaining laser line stability, to design, construct, and operate an airborne laser system to remotely measure sound velocity in water. This system should be capable of yielding range-resolved (3-m bins) sound velocity in water to depths of 75 m to an accuracy of 1 m/s. Flying at aircraft speeds of 300 mi/h and operating at a laser repetition pulse rate of 10 pps, vertical sound profiles would be obtained every 44 ft. Such upper-ocean high-vertical-resolution profiles of sound speed would be useful to various Naval applications. They could serve as stand-alone data sets or combined with other real time and/or historical data sets to yield improved acoustic and oceanographic prediction models. [Work supported by NOARL.]
The use of linear and nonlinear activation in neural networks developed for field reconstruction
Authors: Beran Mark J. , Steinberg Ben Zion
Published: October 2005

The inverse problem which is used to determine the source location or source intensity distribution from field or coherence measurements is considered. The conditions under which a linear perceptron model is adequate for this problem are shown and its performance is compared to a nonlinear perceptron. Also discussed are the cases in which it is necessary to use a nonlinear perceptron and possibly multilayer models.
Effects of environmental degradation on higher-order correlation detectors for deterministic signals
Authors: Pflug Lisa A. , Ioup George E. , Ioup Juliette W. , Barnes Kenneth H. , Field Robert L. , Leclere James H.
Published: October 2005

Higher-order correlation detectors are investigated using essentially band-limited deterministic finite energy signals. These signals have been propagated through a simulated range-dependent ocean environment using a time domain parabolic equation model. The detectors are analyzed using receiver operating characteristic (ROC) curves. Correlation coefficients [R. L. Field, J. H. Leclere, and E. J. Yoerger, submitted to J. Underwater Acoust.] and limiting signal-to-noise ratios for which the detectors exhibit good performance are given. Previously reported results for undegraded signals [J. Acoust. Soc. Am. Suppl. 1 86, S118 (1989)] are extended to include rectification [W. B. Moseley (private communication)] as part of the bicorrelation detection scheme. The bicorrelation detector not only benefits from rectification, but rectification permits its use in cases where it might otherwise be inapplicable. [Work supported by the Naval Oceanic and Atmospheric Research Laboratory through the U. S. Navy-ASEE Summer Faculty Research Program and through Grant No. N00014-89-J-6002.]
Active sonar and transient detection using polyspectra
Authors: Sullivan Edmund J. , Hinich Melvin J.
Published: October 2005

The detection of transients is a special case of nonstationary time series. It encompasses the detection of transient sonar signals, including active sonar returns. The detection of active sonar returns is generally treated as a matched-filter problem. The matched filter requires total a priori knowledge of the signal which, ideally, is stored in the receiver in the form of a “replica.” Since both the sonar target and the propagation channel distort the signal, and the time of arrival is usually not known, this replica of the signal is never known exactly, and therefore the matched filter is always applied suboptimally in practice. In this paper, the application of polyspectra to the general problem of the detection of a deterministic transient signal in stationary but not necessarily Gaussian noise is examined. It is applicable to both transient and active sonar detection since the exact configuration of the signal does not need to be known a priori. This, coupled with the fact that there is no need to assume Gaussianity on the part of the stochastic part gives the method great power. Detection statistics are computed for the method and compared to those for the matched filter. Also, results using synthetic data will be shown.
Ocean medium and platform effects on synthetic aperture sonar
Authors: Rolt Kenneth D. , Schmidt Henrik , Milgram Jerome
Published: October 2005

Synthetic aperture methods have been extensively used in radar ground mapping and imaging since the 1950s. They have also been discussed and occasionally used in biomedical and nondestructive testing ultrasound, and in hydrographic sonar since the late 1960s. A recent example of a synthetic aperture sonar (SAS) is that of Gough and Hayes [J. Acoust. Soc. Am. 86, 2328-2333 (1989)]. In order for SAS to form sharp images, both the amplitude and phase content of a collection of sequential echo histories of a target, for example a point target on the ocean bottom, must be known. The collection of echo histories represent data taken over the length of a synthesized aperture, usually from a sonar platform moving at a known speed. If the phase is not accurately measured over the synthesized length, the image resulting from the signal processing will be blurred or even absent. Medium instability, multipath effects, and uncorrected platform motion may all contribute to phase errors that lead to blurred images. This paper will discuss SAS and these related ocean medium and platform influences, and show numerical examples of image degradation due to these effects. [Work supported by the Charles Stark Draper Laboratory, Cambridge, MA.]
A 2AFC adaptive procedure for loudness balances applied to normal-hearing and hearing-impaired listeners
Authors: Zeng Fan-Gang , Turner Christopher W.
Published: October 2005

A two-alternative, two-interval, forced-choice (2AFC) adaptive procedure for subjective judgments is described. This procedure is modified from Jesteadt's widely used procedure [Percept. Psychophys. 28, 85–88 (1980)]. The key modification made in the new procedure is the incorporation of an interchangeable concept that a 250-Hz tone sounds softer than a 1000-Hz tone is equivalent to a 1000-Hz tone sounds louder than a 250-Hz tone. The new procedure is very similar in many respects to a typical adaptive, forced-choice procedure used in measuring the detectability of a signal, and contains the following characteristics: (1) no explicit standard is identified for the subject to match; (2) one simple instruction to the subject and one single type of response from the subject are required (i.e., “which tone sounds louder?”); (3) a decision rule that yields a direct estimate of the 50% point on a psychometric function is incorporated. The new procedure is validated in the successful measurements of the equal loudness contours and loudness growth functions in normal-hearing and hearing-impaired subjects.
The role of beats in the segregation of concurrent sounds based on frequency modulation coherence
Authors: Marin Cécile M. H. , McAdams Stephen
Published: October 2005

Jean-Sylvain Liénard LIMSI, C.N.R.S., B. P. 30, F-91406 Orsay, France Four studies investigated the role that auditory beats might play in perceptual segregation induced by frequency modulation incoherence between two sound sources. Harmonic single-formant sounds were embedded in an unmodulated harmonic background of similar fundamental frequency. The combination of formant and background resulted in a flat spectrum. Subjects were asked to discriminate among different formants (325, 700, 1150, and 1700-Hz center frequencies) in the presence of frequency or amplitude modulation. Two kinds of formants were used: ones with skirts resembling the result of second-order filtering, and “flat” formants consisting of two or three equal-amplitude components, the latter producing much less beating with nearby components of the background than the former. In some conditions, a pink noise floor was introduced to reduce the possible influence of combination tones. The results demonstrate that beats due to within-channel interactions of components be longing to separate sources make only a small contribution to perceptual segregation based on frequency modulation.
Preferred spectro-temporal patterns in signal detection
Authors: Houtgast Tamtoo , Brink Willem A. C. v.d.
Published: October 2005

The masked threshold of a signal presented in continuous broadband noise is measured as a function of the signal's spectro-temporal pattern. All signal patterns considered are confined to a window of 100 ms by three octaves. The independent variable is the shape of the spectro-temporal pattern, i.e., how the signal energy (in terms of E/N0) is distributed within that window. Two types of patterns are found to yield relatively low masked thresholds: (1) narrow-band and long-duration (100 ms), or (2) short-duration and broadband (three octaves). In other words, signal detection appears to be “tuned” to either tones or clicks. It will be shown that this auditory characteristic can be related to the spectro-temporal patterns encountered in, for instance, speech or music.
Relative effects of uncertainty in overall level, component level, and component frequency for multicomponent simultaneous maskers
Authors: Neff Donna L.
Published: October 2005

Large amounts of simultaneous masking can be produced by changing the frequency content of multicomponent maskers with each presentation. This experiment tested whether uncertainty in overall level or component levels would also degrade performance, either alone or in combination with frequency uncertainty. The maskers had 5, 10, or 20 components, drawn at random from a 300- to 3000-Hz range, excluding critical band components around the signal frequency of 1000 Hz. The four types of level uncertainty were (1) overall level fixed at 60 dB SPL and component levels equal; (2) overall level randomized by 10 or 20 dB in 5-dB steps and component levels equal; (3) overall level fixed and component levels randomized by 5 or 10 dB in 1-dB steps; and (4) both overall and component levels randomized. Each was tested in combination with two degrees of frequency uncertainty: (1) random samples within trials and (2) random samples between trials. To test level randomization without frequency uncertainty, masker samples were fixed across blocks of trials for conditions 1 and 4. The results showed large (20- to 25-dB) effects of randomizing overall level, both alone and in combination with frequency uncertainty. In contrast, the effects of randomizing componet levels were much smaller and inconsistent across listeners and conditions. [Work supported by AFOSR.]
Difference limens for synthetic vowel spectra
Authors: Hawks John W.
Published: October 2005

Difference limens (DLs) along synthetic vowel continua were measured as distances in the auditory-perceptual space proposed by J. D. Miller [J. Acoust. Soc. Am. 85, 2114–2134 (1989)]. The continua represent straight lines that lie parallel with one of the axes of the space (x′, y′, and z′). Groups of six continua share a common center value, or reference point. Movement along these continua result in distinct patterns of frequency change for F1, F2, and F3 relative to the reference point formant values. These patterns vary with the direction and axis of movement. Reference points were selected from the interiors of ten vowel zones and seven boundary areas between vowel zones. An adaptive up—down procedure employing a cued, two-alternative, forced-choice (2AFC) task was utilized to estimate the 79.5% correct point along each continuum. Vowel tokens representing the reference points served as the cue stimuli. DLs were estimated twice for each continuum from each of four subjects. In general, the results of this experiment reflect smaller DLs for vowel formant frequencies than have been found in the past and suggest that while an overall average DL for distance in the auditory-perceptual space may be estimated, DLs vary significantly with the axis of movement. Additionally, no significant difference was found between continua associated with vowel centers and vowel boundaries. These results will be compared with similar results estimating DLs for single-formant variation in vowels. [Work supported by NIDCD.]
Spectral envelope distortion and vowel perception: Evidence for a central, auditory form of perceptual compensation
Authors: Watkins Anthony J.
Published: October 2005

The response of an /I/-/E/ spectral difference filter (SDF) is the spectral envelope of /I/ minus the spectral envelope of /E/. An “itch” to “etch” continuum was constructed by interpolating between the spectral envelopes of the vowels of appropriate VCs. These test sounds were preceded by a carrier sound filtered by an SDF and presented for identification. Perceptual compensation produces a phoneme boundary difference between the /I/-/E/ SDF and its inverse. Carriers were the phrase “the next word is” spoken by the same (male) speaker as the test sounds, signal correlated noise derived from this phrase, the same phrase spoken by a female speaker, male and female versions played backward, and a repeated end-point vowel. The carrier and test were presented to the same ear, to different ears, and from different directions (by varying interaural time delay). The gap between carrier and test was either 160 ms or zero. The pattern of results indicates that the compensation observed is unlike peripheral phenomena, such as adaptation, and unlike speech-specific effects, such as vowel normalization.
New directions in speech and audio coding
Authors: Atal Bishnu S.
Published: October 2005

Rapid progress has been made in recent years in synthesizing high-quality natural sounding speech at low bit rates. The progress in speech coding together with advances in VLSI circuits has sparked great interest in using low-bit-rate speech coding technology for practical applications. and new standards are being developed for transmitting digital speech at 4.8, 8, and 16 kbits/s. New algorithms have brought the bit rate for coding of CD-quality audio signals down to 128 kbits/s. The rapidly increasing demand for communication over digital channels (cellular radio and ISDN) is providing a strong impetus for decreasing the bit rates even further—to 4 kbits/s or lower for speech and to 64 kbits/s or lower for CD-quality audio. Present coding algorithms make use of concepts such as linear prediction, transform coding, vector quantization, and subjective error criteria for lowering the bit rate. As important as these concepts are, just incremental improvements of the present coders cannot bring the bit rate down further without degrading the signal quality. A critical review of the present state of the art in speech coding will be provided and new results from recent work will be presented.
Smart materials and structure
Authors: Measures Raymond M.
Published: October 2005

Fiber-optic sensors that are imbedded within composite materials could provide structural information during the life of the component, thereby avoiding many of the mechanical failures that today result in death, injury, or environmental accidents. Eventually this fiber-optic smart structure technology could lead to radical new thinking in terms of engineering and structural integrity monitoring. An overview of this progress will be given, which will include the development and characterization of a number of fiber-optic strain sensors including a fiber-optic strain rosette for mapping two-dimensional strain fields within composite materials, the detection of stress-induced acoustic emission, and the development and testing of a multilayered fiber-optic damage detection system fabricated within a full-scale composite aircraft leading edge.
Experimental and theoretical results of acoustic agglomeration at high pressures and high temperatures
Authors: Reethof Gerhard , Song Limin , Koopmann Gary
Published: October 2005

Acoustic agglomeration (AA) of the fly-ash particles from coal combustion in pressurized, fluidized bed combustors for power plants is an intermediate treatment of the aerosol to improve the fractional removal efficiency of conventional particle removal devices such as cyclones so that recently proposed clean air requirements can be met. Tests were performed on Penn State's high-pressure (10 atm), high-temperature (891 °C) acoustic agglomerator (6-in. i.d., 14-ft length) at 158 dB and about 850 Hz, with particle loading of 10–18 g/m3 and residence times of about 4 s. The sound source was a high-efficiency siren of Penn State's design providing about 1500 acoustic watts. The mass fraction in the critical 0.5- to 5-μm particle size range was reduced by a factor of 5 and the 10- to 20-μm size range increased by a factor of 3. An acoustic agglomeration simulation model (AASM) computer code that predicts AA quite reliably at both atmospheric and HTHP conditions was developed at Penn State. The simulation results in terms of particle size distribution agree quite well with the test results from both test conditions. The simulation also predicts that better AA could have been obtained at higher frequencies (2000 Hz) and higher acoustic intensities (160 dB). [Work supported by DOE.]
Application of the transfer function method to acoustic measurements in a duct with flow
Authors: Mongeau Luc , Thompson Donald E.
Published: October 2005

The acoustic noise propagating as plane waves in a cylindrical duct with a mean flow was measured following a transfer function method [J. Y. Chung and D. A. Blaser, J. Acoust. Soc. Am. 68, 907 (1980)]. A special facility was used. The cylindrical duct consisted of two Plexiglas sections having different inside diameters connected by a streamlined fiberglass transition. The downstream end of the duct is connected to a fan, while an anechoic termination, screens, flow straighteners, and a bell-mouth are located in that order at the upstream end. The facility ensures a very steady uniform pipe flow and enables the acoustic measurements to be carried out simultaneously in low-velocity and higher velocity mean flows with a velocity ratio of 4. The maximum Mach number achieved in the smaller duct is around 0.08. Excellent agreement between the acoustic power measured in the large section and in the small section is achieved at all Mach numbers. This successful calibration entitles the facility to be used for a study of the importance of flow noise on the flush-mounted microphones and the influence of a turbulent boundary layer, obtained by tripping the flow, on the accuracy of the acoustic intensity calculation. [Work sponsored by ONR.]
Active three-dimensional sound-field cancellation
Authors: Lan Jun , Varadan Vijay K. , Varadan Vasundara V.
Published: October 2005

This paper introduces a new method for three-dimensional active sound-field cancellation. Analytical considerations include the problem of an incident plane wave interacting upon a rigid sphere as the scattering object. An array with elements consisting of a set of rings perpendicular to the sphere's pole axis is arranged on the surface of the sphere. This discussion will present an analytical technique for cancellation of the scattered sound field to arbitrary extent over either the whole space or the partial area of interest, as long as the number of the array elements is sufficient. Further considerations include a fixed and a variable incident plane-wave direction with respect to the pole axis of the sphere.
Longitudinal axial resonances in the form function for backscattering from a fluid spherical shell
Authors: Kargl Steven G. , Marston Philip L.
Published: October 2005

Reverberations of longitudinal waves between the inner and outer surfaces of a hollow shell can strongly affect the backscattering amplitudes at frequencies associated with a thickness resonance. The phenomena are studied for the idealized case of vanishing shear stresses by letting the material of the shell be an inviscid fluid; the surrounding fluid is water. An exact partial-wave series (PWS) gives the form function f (θ,ka) and plots of |f(θ = π,ka)| display a structure from resonances. Here, ka = 2πa/λ is the size parameter, where a is the outer radius of the shell and λ is the wavelength in water of the incident acoustic wave. The resonant structure is also recovered in a geometrical calculation of f (π,ka), which sums the amplitudes associated with rays multiply reflected within the curved shell. The geometric synthesis demonstrates that the effects of curvature are essential to modeling f (π,ka). The analysis gives the geometric divergence factors of successive internal reflections. In addition to numerical comparisons with the PWS, the geometrical synthesis is tested by considering several limiting cases. These limiting cases correctly give results anticipated from elementary considerations. [Worked supported by ONR.]
Localization of scatterers by swept-frequency imaging
Authors: Eschenberg Kent E.
Published: October 2005

A method has been developed that determines the location of a scatterer by exploiting the frequency dependence of the scattered field. Nearly any object will have a range of frequencies over which its scattered field is a simple function of frequency. An estimate of this function has been constructed and tested through simulation for scattering by a fiat plate and a pair of point sources. This algorithm has been incorporated into the swept-frequency imaging method and exercised for a variety of noise-free simulations. Results indicate that this method can offer high resolution when the scatterer and bistatic geometry are suitable, or poor resolution in other cases.