bluuebunny/crossref_metadata_2025 huggingface dataset:
Discrimination of the fundamental frequency of unresolved harmonics
Authors: Hall Joseph W. , Buss Emily , Grose John H.
Published: July 2002

Listeners were presented with five consecutive harmonics centered on the twentieth harmonic of either 50, 100, 150, 200, or 250 Hz. The phase relation among harmonics was either cosine, Schröeder, or random. For each standard fundamental frequency, the smallest discriminable change in fundamental frequency was determined. In general, discrimination performance was better for cosine phase than for the other phase relations, particularly for large standard fundamental frequencies. Results will be considered in terms of the hypothesis that the pitch of unresolved harmonics is based upon both envelope and fine structure cues, with fine structure cues becoming less of a factor in frequency regions where phase locking to fine structure diminishes.
Discrimination of degraded conspecific song in zebra finches (Taeniopygia guttata)
Authors: Lohr Bernard , Dooling Robert J. , Theunissen Frederic , Doupe Alison
Published: July 2002

Thresholds for detecting degraded conspecific songs in zebra finches were measured using operant conditioning. A parametric representation of song obtained by decomposing natural songs using a bank of frequency filters served as a model for synthetic songs. Degraded songs were produced by progressively changing the instantaneous relative phase across adjoining frequency bands. Control songs preserving original phase relationships have generated neural responses in the avian forebrain nucleus HVC that are indistinguishable from responses to natural versions of the bird’s own song (BOS). Our thresholds showed that birds were very sensitive to modifications in BOS, giving results very similar to those obtained from neural recordings in HVC. Moreover, our bird thresholds were similar to those obtained for humans tested with the same task. Unlike electrophysiological results, however, behavioral thresholds for discriminating changes in song were not selective for an individual’s own song, nor for the song played forwards or backwards. These results suggest that precise temporal information present in the relative phase of any complex sound is preserved in both high level general auditory areas as well as in areas specialized for detecting particular songs. [Work supported by NIH.]
Estimation of flow-induced vibration parameters of marine risers
Authors: Stamoulis Catherine , Vandiver J. Kim
Published: July 2002

Flow-induced vibration of marine risers may be characterized by modal frequencies, mode shapes, and participation factors. These parameters cannot always be estimated accurately using methods that require a priori knowledge of the mode shape matrix. Therefore a combined system and subspace identification method was developed to estimate the risers’ modal parameters in the presence of unknown input, i.e., fluid forces. Data were analyzed, from an experiment involving a model riser under uniform and shear flow. ARMA models were used to describe the data dependence in state space. Subspace identification was used to reduce computational time. Modal parameters including structural damping were estimated from the state matrix of the system. Contrary to previous studies, it was found that mode shapes are complex, i.e., the system’s damping is nonproportional. The estimated damping ratios were in the range 0.03–0.07. The deviation of the results from those obtained using conventional methods, which assume that mode shapes are real and may be described approximately by sine functions, was significant when the structure was subjected to shear flow. Thus such a priori assumptions are inaccurate in these cases. In contrast, system identification methods which use only the available data are appropriate.
A sparse ultrasound data set for reconstructing tongue surfaces
Authors: Lundberg Andrew J. , Stone Maureen
Published: July 2002

This work presents a method for reconstructing time-motion sequences of 3-D tongue surfaces during speech from ultrasound data. Earlier work [Stone and Lundberg, J. Acoust. Soc. Am. 99, 3728–3737 (1996)] produced 3-D reconstructions of steady-state tongue surfaces from 60 coronal slices. For motion sequences, collecting 60 coronal slices would be impractical, and possibly unnecessary. Therefore, this study used the steady-state reconstructions as a model for planning data collection and reconstruction from a sparse data set. Six coronal tongue contours were used to reconstruct 3-D surfaces. Selection of contours was globally optimized using simulated annealing. Sparse and dense reconstructions were compared using worst error, average error, and percentage of surface coverage. For all speech sounds, worst error was 2 mm, average error was 0.4 mm, and average reconstruction coverage was 83%. To generalize the method across subjects’ optimal slice locations were estimated in a simpler way. Six midsagittal points were optimized to reconstruct the midsagittal contour. Corresponding coronal slices were then used to reconstruct 3-D surfaces. Errors and reconstruction coverage were comparable to the 3-D optimized sparse set. This method is adequate for calculating a sparse data set, and for collecting time motion data and reconstructing 3-D surface motion. [Work supported by NIH Grant No. DC01758.]
Long range seismic characteristics of Asian elephant (Elephus maximus) vocalizations and locomotion
Authors: Arnason Byron T. , O’Connell Caitlin E. , Hart Lynette A.
Published: July 2002

Seismic components of Asian elephant (Elephus maximus) vocalizations and locomotion were recorded at a range of distances. To study the properties of sound attenuation in the ground, a string of four geophones was placed at approximately 30 m intervals from the elephants, up to 120 m from the signal source. Precise distances between sensors was measured with a differential GPS. Some trials were also conducted using microphone/geophone pairs at 30- and 120-m distances to compare attenuation in the air in relation to attenuation in the ground. Recordings were made with a four channel data acquisition system, processing signals simultaneously from the geophone string and the microphone/geophone pairs at the near and remote locations. Previous studies indicated that elephant vocalizations and locomotion produce Rayleigh waves, a type of ground surface wave. In this study, the long-range seismic characteristics of the signal sources is described. The propagation of elephant vocalizations in the air and ground is quantified at a range of distances up to 120 m and the rates of signal attenuation within each of the two media are compared.
Vocal tract dynamics during calling in nonhuman mammals
Authors: Fitch W. Tecumseh
Published: July 2002

Nonhuman vocal tract anatomy has traditionally been described in static terms, typically based on postmortem dissections. However, cineradiographic studies of chewing and swallowing have revealed that animals are capable of a considerable range of articulatory movements, and video analyses have indicated correlations between lip articulation and call acoustics in nonhuman primates. These observations suggest that our understanding of animal production acoustics could be enhanced by considering dynamic movements of vocal tract articulators: the lips, jaw, tongue, velum and larynx. We present results of a cineradiographic analysis of vocal tract dynamics during calling by several terrestrial mammal species. A substantial decensus of the larynx was observed during calling, which enables animals which normally breathe through the nose to vocalize orally. Further data demonstrate considerably greater attenuation of sound passing through the nasal passages than of orally emitted sound, suggesting that facultative lowering of the larynx into the oral cavity would allow the animal to produce louder calls. These data suggest that vocal track dynamics may play a more significant role in animal vocalization than has been previously recognized.
Response to “Comments on ‘Effects of aircraft overflights on wilderness recreationists’ ” [J. Acoust. Soc. Am. 104, 1726 (1998)]
Authors: Fidell Sanford , Gramann James , Knopf Richard , Pearsons Karl
Published: July 2002

Dr. Staples’ lengthy comments [J. Acoust. Soc. Am. 104, 1726–1728 (1998)] deal less with the matters of research design or data analysis described by Fidell et al. [J. Acoust. Soc. Am. 100, 2909–2918 (1996)] than with her beliefs about the proper study and interpretation of aircraft noise effects in outdoor recreational settings. Her comments nonetheless raise several interesting issues related to the role of technical expertise in noise-related policy analyses. This response therefore concentrates on those of Staples’ comments and arguments that are of general interest, while only secondarily addressing certain inaccuracies and oversimplifications in them.
The behavior of different object functions in a matched-field processing scheme for bottom recognition: A case study
Authors: Taroudakis Michael , Markaki Maria
Published: July 2002

Various object functions for broadband inversions of noisy data using matched-field processing for bottom recognition are studied. The study is based on the inversion results obtained by processing synthetic ‘‘noisy’’ data that have been available at a follow-up stage of a benchmark exercise for bottom geoacoustic inversions that was carried out in 1997 (Vancouver, Canada). A genetic algorithm has been used for the implementation of the matched-field processing. The different behavior of the various processors that has already been observed by the authors at the benchmark exercise based on noise-free data is now considered with data that include noise, and their applicability for bottom recognition is analyzed.
Large two-dimensional sonic band gaps
Authors: Meseguer Francisco , Rubio Constanza , Sanchez-Perez Juan Vte. , Martinez-Sala Rosa , Caballero David , Sanchez-Dehesa Jose , Llinares Jaime
Published: July 2002

In this paper it is shown that a two-dimensional honeycomb structure is a good candidate to produce large full band gaps in sonic band gap (SBG) materials. The full gap of the honeycomb lattice can be increased by reducing the symmetry of the cell as it occurs in photonic band gap (PBG) materials. The evolution of the band gap in the honeycomb-triangular transition has been studied. Starting from a honeycomb lattice (with 4 cm diameter cylinders), one can study the transition to a triangular symmetry by placing rods with different diameter (from 0.6 to 4 cm) at the center of the honeycomb lattice. When the diameter cylinder of the center of the unit cell has the same diameter as cylinders of the unit cell (4 cm), the lattice achieves a triangular symmetry. The obtained results are compared with theoretical calculations performed with a variational method.
Surface waves attenuation by a two-dimensional elastic band gap crystal
Authors: Meseguer Francisco , Llinares Jaime , Benaches Natalia , Holgado Miguel , Lopez Ceferino , Sanchez-Dehesa Jose , Caballero David
Published: July 2002

Experiments on the attenuation of Rayleigh waves in a marble quarry by a periodic array of cylindrical holes, in a honeycomb and in a triangular distribution, are reported. The results are explained in terms of elastic wave crystals, and compared to theoretical calculations performed with scalar waves. The possibility of application to the attenuation of surface waves in seismic movements is also discussed.
Acoustic spectral gaps and discrete transmission in slender tubes
Authors: Kushwaha M. S. , Akjouj A. , Dobrzynski L. , Djafari-Rouhani B. , Vasseur J. O.
Published: July 2002

This work reports on the band structure and transmission spectrum for the longitudinal (acoustic) wave propagation in a system made up of N′ dangling side branches (DSB) periodically grafted at each of the N equidistant sites on a slender tube. A periodic pattern of large stop bands is obtained for the airy DSB on the slender water tube. The emphasis is laid on the interesting result of huge gaps and discrete transmission spectrum due only to the DSB grafted at a single site (N=1) on the slender tube. Designing the system with open tubes allows achievement of the lowest gap below a threshold frequency and extending up to zero—thereby providing an entirely discrete band structure and transmission spectrum. This should have important consequences for the suppression of low-frequency noise and for designing filters and transducers.
Time-frequency-scale description of signals
Authors: Cohen Leon
Published: July 2002

Time-varying spectrum is one of the most primitive sensations we experience since we are surrounded by light of changing color, by sounds of varying pitch, and by many other phenomena whose periodicities change. Hence the need to describe how the spectral content of a signal is changing in time, and to develop the physical and mathematical ideas needed to understand what a time-varying spectrum is. Why this is an elegant and challenging problem, the immense strides that have recently been made, and why new interesting physical quantities must be introduced will all be described. In addition, the immense practical applications over the last few years will be shown in such areas as acoustics, biomedical signals, geophysical signals, fault detection, sonar, etc.
Applications of time-frequency signature analysis to target identification
Authors: Gaunaurd G. C. , Strifors H. C.
Published: July 2002

The overlapping subjects of target identification, inverse scattering, and active classification have many applications that differ depending on specific sensors. Many useful techniques for these relevant subjects have been developed in the frequency and the time domains. A more recent approach views target signatures in the combined or coupled time-frequency (t-f) domain. For either ultra-wideband (UWB) projectors, or UWB processing these joint t-f domain techniques are particularly advantageous. Such analysis requires the use of some of the scores of nonlinear distributions that have been proposed and studied over the years. Basic ones, such as the Wigner distribution [E. Wigner, Phys. Rev. 40, 749 (1932)] and its many relatives, have been shown to belong to the well-studied ‘‘Cohen Class’’ [L. Cohen, J. Math. Phys. 7, 781–786 (1966)]. Half-a-dozen of these distributions will be selected to review applications that the authors have addressed and solved in several areas such as: (a) sonor [Appl. Mech. Rev. 50, 131–149 (1997)]; (b) mine classification [Ultrasonics J. 33, 147–153 (1995)]; (c) dolphin biosonar and ID [J. Acoust. Soc. Am. 103, 1547–1557 (1998)]; and (d) radar [IEEE Proc. 84, 1231–1248 (1996)]. These examples illustrate how the informative identifying features required for accurate ID are extracted and displayed in this general domain. [Work partially supported by the authors’ institutions and the ONR.]
Probing the unknowns of sonoluminescence
Authors: Putterman Seth
Published: July 2002

The passage of sound through a fluid with a trapped bubble leads to the clocklike emission of picosecond flashes of ultraviolet light. In this phenomenon, sonoluminescence (or SL), acoustic energy spontaneously focuses by over 12 orders of magnitude. SL is just one example of energy focusing in bubbly flows. Researchers studying cavitation from a fluid accelerating through a venturi tube in the 1960s observed subnanosecond flashes of light and had in fact at that time discovered the world’s fastest manmade source of light. As with many avenues of research on cavitation luminescence, not the least of which is described in Exodus 20:18 [‘‘And all the people saw the sounds’’] these wonderful insights were abandoned. SL is extremely sensitive to ambient temperature, strength of the acoustic drive, and doping with noble gases. Despite a plethora of theoretical publications the most basic aspects of SL remain unexplained. Neither the light emitting mechanism nor the size of the bubble nor the range of acoustic drives at which SL can be achieved are understood. It is also a mystery as to why water is the friendliest fluid for SL and it would be most valuable to understand why pure diatomic gas bubbles are very weak, unstable sources of SL. A reasonable picture of the energy concentrating mechanism starts from Rayleigh’s 1917 work on the high pressure developed in a collapsing bubble. Femtosecond light scattering from an SL bubble indicates that the collapse is strongly supersonic and suggests the formation of an imploding shock wave that further focuses the acoustic field. Measurements find that the flash of SL is emitted at the minimum radius where the acceleration exceeds 1011 g. The flash width is independent of wavelength from the ultraviolet to the infrared suggesting that the light is emitted when the gas is so stressed that it is in a new phase, perhaps a cold dense plasma. Methods of astronomy are being used to beat the diffraction limit and measure the size of the sonoluminescing ‘‘hot-spot.’’ The upper limit of energy focusing that can be achieved with this ‘‘star-in-a jar’’ has not yet been determined.
Time reversal mirror as a tool for inversion
Authors: Song Hee Chun , Gerstoft Peter , Kuperman William A. , Hodgkiss William S. , Akal T. , Ferla C.
Published: July 2002

Recent time-reversal mirror (TRM) experiments conducted in the Mediterranean Sea in April 1996 showed that TRM can be used for inverting for the ocean environment [Kuperman et al., J. Acoust. Soc. Am. 103, 25–40 (1998)]. The inversion involves comparing the VRA data resulting from time reversal to the SRA data backpropagated to the VRA in simulation. One natural objective function is the Bartlett power. In this paper, both the Bartlett power objective function and an inversion using an objective function based on the compactness of the backpropagated pulse on the VRA are explored. A global inversion genetic algorithm code will be used along with an efficient broadband normal mode forward propagation model.
Retro-focusing of a time reversing acoustic array in noisy environments
Authors: Khosla Sunny R. , Dowling David R.
Published: July 2002

The presence of a noise field can significantly alter the focusing properties of a time-reversing array (TRA). A linear, vertical TRA in simple environments containing omni-directional noise is considered. The noise is treated as a Gaussian process and a time reversal formulation incorporating a restriction on the maximum array power output is constructed. Ambient noise present in shallow oceanic environments can lead to a reduction in the retrofocus field signal amplitude because rebroadcast noise consumes array output power. Using the received SNR at the array as the independent parameter, the first and second moments of the time-reversed field are predicted theoretically. Monte-Carlo simulations showing the spatial variation in the field amplitude from realization to realization will also be presented. The results show that the spatial distribution of the rebroadcast mean field is independent of the initial received SNR while the field variance is strongly dependent on it. [Work sponsored by the Office of Naval Research, Ocean Acoustics.]
Vascular changes in the inner ear perhaps related to intense sound
Authors: Kohut Robert I.
Published: July 2002

Vascular disorders of the inner ear have been hypothesized as a cause of hearing loss. Vascular changes of the labyrinth in humans have only been confirmed histopathologically in two instances, an isolated anterior inferior cerebellar artery (AICA) thrombosis and a secondary AICA thrombosis due to basilar artery thrombosis. A third human case is under re-evaluation. The oxygen and carbon dioxide levels in perilymph from humans having sudden hearing loss are consistent with, but not conclusive for, vascular compromise. In animals, recent blood flow studies using Doppler techniques suggest that there can be changes with certain noxious agents, including loud sound. Using other techniques, investigators have demonstrated dynamic vessel changes, blood cell aggregation, offset rebound vasodilation, and A–V shunting in animals in response to loud sound. For systematic vascular disorders, histopathologic studies in humans concerning vascular changes in the inner ear have not been feasible previously. One new collection of human temporal bones at the Department of Otolaryngology at Wake Forest University School of Medicine is unique. Obtained from consecutive autopsies, the collection represents a cross section of society. Studies are underway which should further the understanding of pathogenic mechanisms of abnormalities of hearing and balance, including vascular disorders of the inner ear.
Outdoor sound propagation in the U.S. Civil War
Authors: Ross Charles D.
Published: July 2002

In a number of major battles in the U.S. Civil War, unusual atmospheric acoustics played a major role. In this study, the probable causes of the unusual acoustics are given and the resulting effect on military command decisions is described. The causes discussed include sound absorption, wind shear, temperature gradients, and combinations of these. Several cases will also be described in which multiple ground reflections caused sounds of battle to be heard at unusually great distances. The battles studied include Gettysburg, Seven Pines, Perryville, Iuka, Fort Donelson, Gaines Mill, Five Forks, and Chancellorsville.
Efficient calculation of scattering into an acoustic shadow zone using empirical orthogonal functions and the Markov approximation
Authors: Wilson D. Keith
Published: July 2002

In many previous studies, the mean sound level of a signal scattered by turbulence into an atmospheric refractive shadow zone has been calculated using a Monte Carlo procedure. This procedure involves generating many (typically 10 to 100) random realizations of the turbulent field, using a parabolic equation (PE) code to solve for the sound field corresponding to each realization, and then averaging. Unfortunately, this method is computationally intensive because of the large number of PE runs required. In this paper, a different approach, based on combining a distorted-wave Born approximation, a ‘‘quasi’’-Markov approximation, and decomposition of the turbulence into empirical orthogonal functions, is described. Here ‘‘quasi’’ refers to the fact that the Markov approximation is applied only in the nominal (horizontal) direction of propagation, since the exact direction of propagation is variable. Initial results are promising in that the mean scattered field can be calculated in a small fraction of the time required for a single PE run. However, the new approach underpredicts the Monte Carlo result by 5 to 10 dB. Possible sources of the discrepancy include the Markov approximation, multiple scattering, and inexact treatment of boundary effects.
Influence of viscosity on acoustic diffraction by a half plane
Authors: Pierce Allan D. , Zampolli Mario
Published: July 2002

An approximate solution for the diffraction of sound by a half plane in a viscous fluid is given. The solution is derived from the linear equations of fluid dynamics, where the Euler equation is replaced by the Navier-Stokes equation. The resulting equations can be represented as the sum of acoustic and vorticity mode components. The acoustic mode is governed by the acoustic wave equation, while the vorticity mode is governed by a diffusion equation. The two modes each have nonzero velocity at the half plane, but the superposition of the two velocity fields is such that the sum of the tangential components and the sum of the normal components both are zero, in accord with the no-slip condition. Each mode can be approximately represented in terms of Fresnel integrals of complex argument. The solution implies that there is a boundary hemisphere in the vicinity of the edge in which there is no singularity and in which the vorticity mode is of equal importance to the acoustic mode. Outside the boundary hemisphere the acoustic mode dominates and the solution in that region is very nearly the same as originally predicted by Sommerfeld in 1896.
Symmetric-wave coincidence-frequency and Rayleigh-wave tunneling backscattering enhancements for plastic shells and solid spheres in water
Authors: Hefner Brian T. , Marston Philip L.
Published: July 2002

Unlike the case of metallic objects, most solid-polymer ‘‘plastic’’ objects have shear and Rayleigh wave phase velocities less than the speed of sound in water. Furthermore, the density contrast with water is relatively small. These differences combine to significantly alter the dominant scattering processes for plastic objects. For example, since the high-frequency limit for the lowest symmetric (or s0) Lamb wave velocity approaches the Rayleigh velocity, reducing the frequency raises the velocity and brings it closer to the speed of sound in water. It is calculated that for shells there is a corresponding rise in radiation damping and that the order of the ray-theoretic coincidence frequency backscattering features is predicted to be reversed in comparison to the order for metallic shells [P. L. Marston and N. H. Sun, J. Acoust. Soc. Am. 92, 3315–3319 (1992)]. The low-frequency supersonic s0 branch is also greatly affected near the coincidence condition. In addition, backscattering by some solid plastic spheres is predicted to be enhanced in the ka=2–10 region due to tunneling coupling with Rayleigh wave resonances which have been modeled with ray theory. [Work supported by the Office of Naval Research.]
Narrow-band and broadband active control in an enclosure using energy density sensors
Authors: Parkins John W. , Tichy Jiri , Sommerfeldt Scott D.
Published: July 2002

An active control system has been constructed based on the minimization of the energy density at discrete points within an enclosure. Though most control systems for use in enclosures are based on squared pressure as a cost function, a system based on energy density is more capable of sensing modes contributing to the acoustic field. The enclosure used is lightly damped and measures 1.5×2.4×1.9 m. A measurement system within the enclosure is capable of spatially sampling the pressure field and decomposing the field into complex modal amplitudes, which yield insight into the control phenomena. The control system can use squared pressure as well as energy density as a cost function for comparisons of the two methods. The squared pressure and energy density control are consistent with predictions of active control performance in the case of single-frequency multiple sensor/source configurations. Global control of up to 18 dB is achieved. Broadband control results using a single sensor and control source are also presented.
Connecting phonetics and phonology: Evidence from Western Arrernte
Authors: Anderson Victoria
Published: July 2002

This study investigates two aspects of the relationship between phonetics and phonology. The first section looks for evidence of the influence of phonological patterns on phonetic implementation: specifically, do the number of phonological contrasts along a given phonetic continuum affect the articulatory detail of those contrasts? The second section looks for evidence of the influence of phonetic properties of segments on phonological patterns: in particular, do perceptual characteristics of segments determine distributions of contrasts? To address the two questions in focus here, instrumental articulatory, acoustic, and perceptual evidence was collected from Western Arrernte, a language of Central Australia which provides good test cases for these issues. Results do not indicate evidence for effects of phonological patterns on phonetic implementation, but show evidence for effects of phonetic characteristics on phonological structure. [This investigation was supported by grants from the National Science Foundation and the Aboriginal and Torres Strait Islander Language Initiatives Program (Australia).]
On the effect of spatial dispersion on the degeneracies of acoustic-wave branches in crystals
Authors: Shuvalov A. L.
Published: July 2002

The effect of spatial dispersion on the phase-speed degeneracies of acoustic waves in noncentrosymmetric crystals is explored in the framework of continuum elasticity. It is shown that the degeneracies, which in the nondispersive limit occur in directions neither lying in a symmetry plane nor parallel to a rotation inversion axis, are lifted on account of spatial dispersion. The degeneracies lying in symmetry planes change their in-plane orientation depending on the frequency, unless remaining fixed to a symmetry axis. Given that the degeneracy with regard for linear spatial dispersion occurs in some direction m, the value of degenerate phase speed coincides with the value of one of the speeds assigned to m in the nondispersive limit. Relations for the acoustic-wave parameters with dispersive corrections are derived and discussed for various particular cases.
Acoustic performance of flexible bellows
Authors: Munjal M. L. , Vinay J.
Published: July 2002

Bellows are generally used for vibration isolation in ducts. However, conical expansions and contractions lead to acoustic transmission loss as well. In this paper plane wave propagation through a bellow has been investigated. The wave equation for a stationary medium has been solved exactly with the help of a practical assumption. But, for the case of mean flow, with its convective as well as dissipative effects, an equivalent simple expansion-contraction chamber model has been developed based on some parametric studies. Effects of different parameters like thickness of the bellow wall, radius, length, and Mach number of mean flow have been studied. A reasonable agreement has been found between the theoretical and experimental results.
Measurement of viscous sound absorption at 50–150 kHz in a model turbid environment
Authors: Brown Niven R. , Leighton Timothy G. , Richards Simon D. , Heathershaw Anthony D.
Published: July 2002

The visco-thermal absorption of sound by suspended particulate matter can be reliably measured using a reverberation technique. This absorption may have an adverse effect on the performance of sonars operating at 50–300 kHz in coastal waters where suspensions are often present in significant concentrations. A series of experiments has been performed to study the viscous absorption by suspensions in the frequency range of 50–150 kHz. In the test volumes employed, the effect is small. It is therefore measured by taking the difference in reverberation times of a volume of water with and without particles. This greatly reduces the effect on the measurement of the other sources of absorption. Even so, it is necessary to design the experiment to characterize and minimize acoustic losses which occur at the surfaces of the container, the hydrophones, and their cables, and losses associated with bubbles and turbulence. These effects are discussed and results for particulate absorption for suspensions of spherical glass beads are presented and compared to theoretical predictions. Measured absorption agrees well with that predicted by theory for concentrations above 0.5 kg/m3 and up to 2.0 kg/m3.
Interaction between a Timoshenko–Mindlin plate and an attached rib
Authors: Rumerman M. L.
Published: July 2002

In contrast to a thin plate having no shear component of deformation, a Timoshenko–Mindlin plate cannot support a concentrated line dipole moment exerted by a pair of equal and opposite line forces acting normal to its lateral surface. In this paper, it is argued that, in order to account for all the connectivity between a rib and the plate, it is necessary to assume a nonzero width footprint for the rib upon the plate. This footprint is idealized by a connection between the rib and plate along two lines parallel to the rib. The problem posed is one dimensional, with plate responses invariant in the direction of the rib; therefore, along each line of contact, the rib exerts upon the plate only a normal force and a tangential (shear) force perpendicular to the rib. These four initially independent forces combine to produce resultant opposing forces acting on the end of the rib which generate velocities of the rib that can be related to those of the plate. The response quantity of interest is the structural power reflected from the rib due to a wave propagating freely in a direction normal to the rib and incident upon it. It is shown that the rib footprint cannot be set equal to zero if the rib’s rotational properties are to have a meaningful influence on the calculated reflected power.
Numerical studies of acoustic boundary control for interior sound suppression
Authors: Hirsch S. M. , Sun J. Q.
Published: July 2002

There are two mainstream methods for the active control of noise in enclosures: active noise cancellation (ANC) and active structural acoustic control (ASAC). ASAC systems are most effective when the primary noise source is the radiation from a vibrating structure, but cannot efficiently control sound from other sources. ANC systems are effective when other noise sources are present, but will sometimes require a much higher dimensionality than ASAC systems to control structural radiation. This paper proposes a practically motivated implementation strategy for ANC actuator placement. Specifically, it proposes to implement an array of acoustic control sources in front of vibrating boundaries to form an acoustic boundary control layer. This provides low-power performance comparable to ASAC systems for controlling sound radiation from the boundary, but also an efficient system for controlling noise from other disturbances. Numerical simulations are presented to demonstrate the ability of the acoustic boundary control to suppress interior noise due to acoustic and structural sources. Because of the expense of implementing large active control systems, there is great interest in developing an actuator grouping strategy to reduce the control system dimensionality. A preliminary feasibility study, to establish under which conditions actuator grouping may be successful, is presented. A strategy in which actuators are grouped through an off-line analysis of the control problem is studied.
Temporal factors associated with cochlear nerve tuning to dual and single tones: A qualitative study
Authors: Henry Kenneth R.
Published: July 2002

The simultaneous presentation of a 10- and 10.86-kHz tone produces an 860-Hz cochlear nerve difference tone (DT) response in the gerbil which persists for the duration of the stimulus. Forward masking shows this response is generated by neurons sharply tuned to the stimulus frequencies. When compared with the DT response, the cochlear nerve compound action potential (CAP) to a single tone is smaller in amplitude, has a higher nonmasked threshold, and produces a less sensitive tuning curve (TC). Forward maskers can also produce amplitude enhancement of the CAP, but this was not observed for the onset portion of the DT response. The CAP TC is as sharply tuned as the TC of either the DT onset response or the entire DT response. A comparison was made of tuning of the DT response to the onset, the first half and second half of the 23-ms duration probe stimulus, using either a 5- or 15-ms masker-probe interval. An increase of the tip threshold of the TC to all three portions of the stimulus occurred as the interval was increased between the end of the masker and the midpoint of the portion of the stimulus under question. The 15-ms masker-probe interval produced sharper TCs.
Binaural and monaural auditory filter bandwidths and time constants in probe tone detection experiments
Authors: Holube Inga , Kinkel Martin , Kollmeier Birger
Published: July 2002

Auditory filter bandwidths and time constants were obtained with five normal-hearing subjects for different masker configurations both in the frequency and time domain for monaural and binaural listening conditions. Specifically, the masking level in the monaural condition and the interaural correlation in the binaural conditions, respectively, was changed in a sinusoidal, stepwise, and rectangular way in the frequency domain. In the corresponding experiments in the time domain, a sinusoidal and stepwise change of the masker was performed. From these results, a comparison was made across conditions to evaluate the influence of the factors “shape of transition,” “monaural versus binaural,” “frequency domain versus time domain,” and “subject.” Also, the respective data from the literature were considered using the same model assumptions and fitting strategy as used for the current data. The results indicate that the monaural auditory filter bandwidths and time constants fitted to the data are consistent across conditions both for the data included in this study and the data from the literature. No consistent relation between individual auditory filter bandwidths and time constants were found across subjects. For the binaural conditions, however, considerable differences were found in estimates of the bandwidths and time constants, respectively, across conditions. The reason for this mismatch seems to be the different detection strategies employed for the various tasks that are affected by the consistency of binaural information across frequency and time. While monaural detection performance appears to be modeled quite well with a linear filter or temporal integration window, this does not hold for the binaural conditions where both larger bandwidth and time constant estimates are found.
Inverse Neumann obstacle problem
Authors: Couchman L. S. , Ghosh Roy D. N. , Warner J.
Published: July 2002

Results are reported for direct and inverse scattering of plane acoustic waves from sound-hard scatterers of arbitrary shapes in an infinite, homogeneous ambience. The direct problem is solved via a shape deformation technique which is valid for finite deformations. The resulting solution requires solving only a set of algebraic recursion relations, but neither integral equations nor Green’s function. The methodology has three essential features: all calculations refer exclusively to a known simple boundary Γs instead of the iteratively updated scatterer shapes; the Jacobian of the scattered field is evaluated by solving a series of Helmholtz’s equations (with different boundary data) in the region exterior to the simple shape Γs; and no ambiguity in the solution arises due to the interior eigenvalues. The inverse problem of recovering the scatterer boundary shape is solved by least square minimization using the Levenberg–Marquardt algorithm. Inversions of several two-dimensional shapes with varying degrees of complexity are reported. The procedures described generalize straightforwardly to transmission and three-dimensional problems.
A technique for measuring the ellipticity and rotation of the polarization plane of ultrasound
Authors: Gudkov V. V. , Tarasov B. V.
Published: July 2002

A technique for investigating magnetoacoustic phenomena such as the ultrasonic analogs of the Faraday, Cotton–Mouton, and Kerr effects is reported. This technique makes it possible to measure the ellipticity and the angle of rotation of the polarization plane of ultrasound. Measurements were made using data on amplitude and phase variations of the voltage on a receiving piezoelectric transducer as a function of the magnetic induction.
The role of level, spectral, and temporal cues in children’s detection of masked signals
Authors: Allen Prudence , Jones Rhiannon , Slaney Pamela
Published: July 2002

Preschool-aged children and adults were asked to detect masked signals in four conditions that evaluated the role of level, spectral, and temporal cues on performance. Psychometric functions fitted to percent correct data at several signal-to-noise ratios showed higher thresholds and shallower slopes for the children in all conditions. Performance was similar in fixed and roving level conditions for both age groups suggesting use of level-invariant cues. When the signal was moved to the spectral edge of the masker the performance of the adults improved but that of the children did not. This suggested that children did not benefit from the additional cues provided by the off-center signal. Children’s performance worsened when the signal was a narrow-band noise rather than a pure tone but the adults’ did not, suggesting children’s reliance on temporal changes in the masker with the introduction of the signal. Analyses of the stimuli suggested that the children’s thresholds corresponded to signal-to-noise ratios at which multiple cues were present at magnitudes that were great enough to be discriminable.
Sensitivity to changes in level and envelope patterns across frequency
Authors: Richards Virginia M. , Lentz Jennifer J.
Published: July 2002

In the first experiment, two measurements were compared—sensitivity to across-frequency changes in level and sensitivity to across-frequency changes in the modulation phase of SAM tones. For the level task, multi-tone stimuli composed of 2–80 tones ranging in frequency from 200 to 5000 Hz were used. For the phase task, the same frequency range was used, and 2–80 SAM tones were tested. For the level task, observers discriminated between a multi-tone, equal-amplitude standard and one of two signals—a one-step or an up–down signal. The one-step signal had higher levels at low frequencies and lower levels at high frequencies. The up–down signal had components with levels that varied high-low–high-low. For the phase task, the standard was the sum of SAM tones with identical modulator phases across frequency. The one-step signal had a common modulator phase at low frequencies and a different common modulator phase at high frequencies. The up–down signal had modulator phases that varied lag-lead–lag-lead. The results suggest that sensitivity to across-frequency changes in level and modulation phase reflect similar initial processing stages. In a second experiment, SAM tones were used, and psychometric functions were measured for the level task, the phase task, and a condition in which changes in level and modulator phase were both present. The standard was “flat,” and an up–down signal was to be detected. For one observer, the data suggest that level and phase information are independently represented. For the other two observers, interactions between the two features of the stimuli are apparent. A multiple-looks model was moderately successful in accounting for the data.
Effects of ear of entry and perceived location of synchronous and asynchronous components on mistuning detection
Authors: Gockel Hedwig , Carlyon Robert P.
Published: July 2002

Listeners were required to detect mistuning imposed on the center (“target”) component of a 200-ms complex consisting of the first seven harmonics of a 500-Hz fundamental. In the standard interval of each 2IFC trial, all components were frequency modulated in-phase by a 5-Hz sinusoid. In the signal interval the frequency modulation of the target component was inverted in-phase, thereby introducing a mistuning proportional to the depth of FM. In a similar experiment, using monaural presentation, Carlyon [J. Acoust. Soc. Am. 95, 2622–2630 (1994)] reported a substantial elevation of thresholds in the presence of an unmodulated asynchronous interferer with frequency identical to the mean frequency of the target. This was attributed to the interferer, causing the target component to be perceptually segregated from the remainder of the complex, thereby impairing across-frequency comparisons. Experiment 1 of the present study showed that an interferer presented contralaterally for 200 ms before and 100 ms after the signal complex (no simultaneous presentation) also impaired performance, but to a lesser extent than an ipsilaterally presented one. Experiment 2 showed that an interferer which was presented dichotically with an interaural level difference (ILD) of 10 dB, so that it was perceived contralaterally, had the same (large) effect as if it were presented ipsilaterally. Experiment 3 showed that, in the absence of any interferer, performance was impaired when the nontarget components were presented contralaterally to the target component. However, performance was not impaired when the nontarget components were presented dichotically with an ILD of 20 dB, so that they were perceived contralaterally to the target component. It is concluded that the level of performance in the mistuning task is determined by whether the target is presented to the same ear as the rest of the complex, rather than by its perceived location.
The Helmholtz–Kirchhoff approach to modeling penetration of acoustic waves into rough seabeds
Authors: Pouliquen Eric , Lyons Anthony P. , Pace Nicholas G.
Published: July 2002

The Helmholtz–Kirchhoff integral is applied to model the penetration of sound waves into sandy seafloors at grazing angles above and below the critical angle. Although the conditions for the validity of the Kirchhoff approximation can be limiting, this approximation should be valid at high frequency for gently undulating seafloor surfaces even at moderate to low grazing angles, providing that the self-shadowing effect is carefully removed. The analytical development of the method is first presented, followed by numerical examples and comparisons with the experimental data of Maguer et al. [SACLANTCEN report, SR-287, April 1998]. The model predicts, in agreement with the 2- to 15-kHz acoustic data, the frequency where the contributions due to roughness effects begin to dominate those due to the evanescent wave. Secondary effects such as Bragg interference patterns and the loss of signal coherence with grazing angle or depth are correctly predicted. The model simulations strongly suggest that roughness of the sediment interface is most likely the cause of anomalous sound penetration into the seabed.
Using iterative regression for estimating reverberation times in two coupled spaces
Authors: Xiang Ning , Vorlaender Mecheal
Published: July 2002

Sound energy decay in two coupled spaces is, under certain conditions, of a double-slope nature. The present paper deals with identifying two reverberation quantities in these spaces from room impulse responses using Schroeder’s backward integration method. Using this method, different decay portions of double-slope decay functions can not always be distinctly recognized since the last part of the decay functions can be strongly deformed by the background noise effect. To overcome this difficulty, a nonlinear, iterative regression approach is proposed to evaluate reverberation quantities in coupled spaces. A multislope decay model is exploited to meet the need of evaluating double-slope decay functions. The present paper reports on the investigation of the approach in terms of simulating decay functions using the decay model. The convergence study on the nonlinear iterative regression conducted in this investigation reveals both the potential feasibility and limitations of the proposed approach.
A comparison of active and adaptive passive noise control systems for the DC-9
Authors: Swanson Douglas , Altieri Russell , Fowler Leslie
Published: July 2002

The aft interior of the DC-9 aircraft is generally considered to be uncomfortably loud (100–110 dBC). This noise is primarily periodic and is caused by imbalances in the fan and turbine of the Pratt Whitney JT8D engine. Lord Corporation has recently developed active and adaptive passive systems to combat this problem. The active system uses four force-generating actuators located on the left and right engine pylons to minimize the response at eight control microphones which are located in the rear of the cabin. The adaptive passive system consists of eight tuned vibration absorbers whose natural frequency is adapted to the engine speed. An overview of each system with theory will be presented as well as experimental results where the tonal noise reduction and engine speed tracking capabilities of each system were evaluated using an identical engine vibration input on a DC-9 fuselage. These experimental results showed that the active system achieved larger tonal noise reductions and had faster tracking ability than the adaptive passive system.