bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow noise reduction techniques for a planar array of hydrophones.
Authors: Ko Sung H. , Schloemer Howard H.
Published: October 2005

This paper presents techniques for reducing turbulent boundary layer pressure fluctuations received by an array of hydrophones embedded within a plane layer of elastomer. Reduction of flow noise can be achieved by spatial filtering through the use of large finite hydrophones or an array of hydrophones, or by filtering high wave-number components through the use of an elastomer layer. The theoretical model used is a plane elastomer layer backed by an infinite elastic plate with finite thickness; the other side of the layer is exposed to turbulent flow. The baseline turbulent wall pressure spectrum that represents the flow excitation function is based on the Corcos model modified to fit a realistic low wave-number estimate. The occurrence of the convective ridge wave number is estimated by using a convective flow speed that is a function of frequency. Results presented are numerically calculated noise reductions, relative to the calculated noise level for a flush-mounted point hydrophone. Noise reductions that can be achieved by various techniques and their sensitivity to the flow noise model chosen, as well as the combined wave-number filtering mechanism, are presented. Some design approaches for achieving specific noise reductions using various combinations of hydrophone size, elastomer layer thickness, and array characteristics for flow over a plane surface will be discussed.
The influence of modal coupling on active sound radiation control of a fluid-loaded plate.
Authors: Gu Yi , Fuller Chris R.
Published: October 2005

It is well known that the vibration modes of a fluid-loaded finite plate are not orthogonal to each other and the nondiagonal elements in the radiation impedance matrix are the cross coupling of one mode to another. The mathematical formulation of the cross-coupling impedance was studied by previous researchers such as H. G. Davies, R. A. Mkhitarov, N. S. Lomas, and S. I. Hayek. Active control of sound radiation from a fluid-loaded plate was investigated by the authors in previous work. Here, the influence of the cross-coupling terms on the control performance is studied. The feedforward controller would be much simpler if the cross coupling were ignored. But the tradeoff is that by disregarding these cross-coupling impedances in the controller design, the control performance is generally deteriorated. The reason is that cross-coupling impedances contain the capability to influence those efficient radiation modes as to reduce the total sound radiation. The numerical calculation results show how the cross-coupling influences the control performance which is illustrated by the far-field pressure and the change of modal composition of the plate response. Unlike in the case of heavy fluid loading, the influence of the cross coupling between the modes in a light acoustic medium, such as air, is insignificant as shown by numerical results. [Work supported by ONR/DARPA.]
A neural tree architecture for recognition of speech features.
Authors: Rahim Mazin , Flanagan James
Published: October 2005

Neural tree networks provide an efficient technique for pattern classification. A typical structure grows the tree to accommodate the varying complexity of different problems. For recognition of speech features in continuous speech (as described by acoustic vectors), this architecture was found to grow unnecessarily when presented with large amounts of training material collected from many speakers. This paper describes a method for forward-pruning the tree through consideration of the degree of ‘‘confusion’’ among the applied patterns. This implementation was tested for recognition of 34 phonemes, extracted from the TIMIT database. Results show that in addition to advantages in computational efficiency and recognition performance, the neural tree architecture provides important correlations among the types of speech features being classified. One observation is that the parent network (first root) performs a separation between two classes of sounds; namely (a) vowels, glides, semivowels, and nasals, and (b) fricatives, affricates, and stop consonants. Subsequent networks are found to classify phonemes according to place of articulation (e.g., alveolar−/s/ and /z/), or manner of articulation (e.g., nasals−/m/, /n/, and /ng/). These phonemic classifications are valuable in improving the networks’ ability to perform feature recognition on data outside the training set.
Prosodic phrase prediction using an embedded hierarchy model of speech.
Authors: Ostendorf Mari , Veilleux Nanette
Published: October 2005

Prosodic phrase structure provides important information for the understanding and naturalness of synthetic speech, and a good model of prosodic phrases has applications in both speech synthesis and understanding. This work describes a statistical model of an embedded hierarchy of prosodic phrase structure, motivated by results in linguistic theory. Each level of the hierarchy is modeled as a sequence of subunits at the next level, with the lowest level of the hierarchy representing factors such as syntactic branching and prosodic constituent length using a binary tree classification. A maximum likelihood solution for parameter estimation is presented, allowing automatic training of different speaking styles. For predicting prosodic phrase breaks from text, a dynamic programming algorithm is given for finding the maximum probability prosodic parse. In experiments on a corpus of radio news, the model has been used to predict minor and major prosodic phrase boundaries from text in the hierarchy: orthographic word ∈ minor phrase ∈ major phrase ∈ sentence. Good results were obtained by using only a simple function word table for part-of-speech assignments and sentence punctuation; use of syntactic information did not improve performance. Out of 23 test sentences, 7 had predicted phrase breaks that matched those used by one of five radio announcers and an additional ten sentences were judged to have acceptable prosodic phrasing. This performance corresponds to correctly predicting a phrase break (major or minor) at 79% of the observed phrase locations and falsely predicting a boundary at only 4% of the boundaries where no break was observed. In comparison, the performance of a tree classifier without the hierarchical formalism yields 62% correct prediction and 3% false prediction.
Acoustic–elastic wave scattering from realistic seafloor models.
Authors: Levander Alan R. , Henrys Stuart A.
Published: October 2005

Acoustic–elastic wave propagation was simulated with a 2-D finite-difference method for models of an ocean layer, sediment layer, and rough basalt layer. The roughness profiles along the upper surface of the basalt, specified at 1- or 10-m intervals, are from a self-affine bathymetry model. A low-velocity sediment layer was included in some models as a pond or a blanket on the basalt. A bandlimited point source (maximum frequency 150–300 Hz) was initiated in the water within 150 m of the seafloor. Although the wave field in the water column scattered from the 1-m roughness is more complex than that from the 10-m roughness, the dominant features are similar. The 1-m roughness reduces the coda amplitude but increases its complexity and duration. The scattered field is dominated by diffractions from the larger irregularities along the irregular basalt interface. Sediment layers produce a long coda resulting from P–SV conversion and SV reverberation. SV energy trapped in sediment ponds persists for long travel times, becoming chaotic and contributing to the field observed in the water column.
Investigations in the amplitude of sounded piano tones
Authors: Palmer Caroline , Brown Judith C.
Published: October 2005

The relationship between final hammer velocity and maximum amplitude of radiated piano sound was investigated. Piano tones with varying hammer velocities were produced by a computer-monitored acoustic piano containing optical sensors and solenoids, and the sounded tones were recorded and digitized for analysis. Maximum amplitudes over the duration of the sounded tones were linearly proportional to piano hammer velocities for a range of frequencies and hammer velocities. Changes in room acoustics did not alter the linear relationship. Measurements of maximum amplitudes of individual tones and combined tones (dyads) also indicated a linear relationship between the sum of the maximum amplitudes of the individual tones and the maximum amplitude of the dyads. These findings indicate that the principle of superposition holds for peak amplitudes of sounded piano tones. Findings are discussed with regard to production and perception of musical dynamics.
Global optimum active noise control: Surface and far-field effects
Authors: Cunefare Kenneth A. , Koopmann Gary H.
Published: October 2005

This paper examines the physical characteristics of global optimum active noise control on the surface and in the far field of extended radiators. Global optimum active noise control expresses the total acoustic power radiated by a collection of noise sources and active noise control sources with a quadratic equation in terms of source strengths or, for extended structures and control sources, surface velocities. Quadratic optimization theory is then used to obtain the secondary source strengths or surface velocities that yield the minimum total radiated power. The nature of the quadratic expression guarantees that the solution yields the global minimum, not simply a local minimum. The physical mechanism for optimum active noise control is the increased complexity of the combined sources. That is, with a suitable number of sources, a structure radiating like a monopole to the far field will radiate as a dipole after activation of the active noise control sources. While global optimum control is guaranteed to reduce the net power radiated by the control source/noise source combination, there is no guarantee that the intensity in all directions will also be reduced.
Sound-speed profiles determined from outdoor sound propagation measurements
Authors: Klug Helmut
Published: October 2005

Measurements of sound propagation over distances up to 1000 m were carried out with a plasma impulse sound source generating reproducible, short time signals of high peak level. The measured travel time difference between direct and ground reflected wave allows for determination of the sound-speed profile in the atmospheric surface layer. A simple relationship was found between measured travel time difference and the scaling parameter of a logarithmic sound-speed profile. According to Monin–Obukhov similarity theory a logarithmic-linear profile can be used to describe the refraction profile for stable conditions (i.e., positive temperature gradient). In this case, two travel time measurements at different heights are necessary to determine the profile parameters. The acoustically derived profiles show good agreement with those deduced from wind speed and temperature measurements made at several heights above ground in conjunction with the acoustic measurement. Ray tracing is used for the discussion of meteorological effects on sound propagation in profiles with a positive gradient of refraction (i.e., sound speed increasing with height).
Noise produced by a sawtooth trailing edge
Authors: Howe M. S.
Published: October 2005

An analysis is made of the noise produced by low Mach number turbulent flow over the serrated edge of a flat plate airfoil at zero angle of attack. The serrations are of sawtooth profile of wavelength λ and root-to-tip distance 2h. At frequencies ω satisfying ωh/U≫1 (where U is the velocity of the main stream) it is predicted that the intensity of the radiation is reduced relative to that produced by the same flow over an unserrated edge by at least 10×log[1+(4h/λ)2] dB. Predictions are contrasted with analogous results derived [M. S. Howe, J. Fluids Struct. 5, 33–45 (1991)] for smoothly varying serrations of sinusoidal profile, for which it was concluded that attenuations of order 10×log(6h/λ) dB are possible.
Angular dependence of 12-kHz seafloor acoustic backscatter
Authors: de Moustier C. , Alexandrou D.
Published: October 2005

The angular dependence of seafloor acoustic backscatter, measured with a 12-kHz multi narrow-beam echo-sounder at two sites in the central North Pacific with water depths of 1500 and 3100 m, respectively, has been determined for incidence angles between 0° and 20°. The acoustic data consist of quadrature samples of the beamformed echoes received on each of the 16 2.66° beams of a Sea Beam echo-sounder. These data are subjected to adaptive noise cancelling for sidelobe interference rejection, and the centroid of each echo is determined. After corrections for the ship’s roll and raybending effects through the water column, the angles of arrival are converted to angles of incidence by taking athwartships apparent bottom slopes into account. For each beam, the mean echo power received is normalized by the corresponding insonified area that depends on the transmit and receive beam patterns, the ship’s roll angle and the local bottom slope. For lack of system calibration, the data are presented as relative mean energy levels in 1° bins. Comparison of these results with theoretical angular dependence functions, based on the Helmholtz–Kirchhoff model for backscatter from a rough surface, indicates that a good fit is obtained in the angular sector from 5° to 20° incidence. In the near-nadir sector (0° to 5°), the data suffer from high variance making the estimate unreliable. The data processing methods presented constitute one of the elements necessary to compile a map of seafloor acoustic backscatter from acoustic measurements made with a multinarrow beam echo-sounder. The angular dependence function obtained will ultimately be used to normalize the backscatter measurements in the athwartships direction.
On the numerical implementation of a Cauchy principal value integral to insure a unique solution for acoustic radiation and scattering
Authors: Wu T. W. , Seybert A. F. , Wan G. C.
Published: October 2005

In this paper, the boundary integral formulation proposed by Burton and Miller [Proc. R. Soc. London Ser. A 323, 201–210 (1971)] to insure a unique solution for all frequencies is implemented in an isoparametric element environment. A regularized normal derivative integral equation, originally derived by Maue [Z. Phys. 126, 601–618 (1949)], is used in the formulation to form a linear combination with the conventional Helmholtz integral equation. This regularized normal derivative integral equation converges in the Cauchy principal value sense rather than only in the finite-part sense. The Cauchy principal value integral can be further transformed into an integral that converges in the normal sense. The C° continuous isoparametric elements are used in the formulation. Collocation points are placed inside each element to insure a unique normal direction and continuity of tangential derivatives of the acoustic pressure. Through a systematic collocation point generation scheme, the number of collocation points is always greater than the number of nodal points. The overdetermined system is then solved by a least-squares procedure. Numerical examples are given for several radiation and scattering problems.
Modeling the interactions between noise exposure and other variables
Authors: Humes Larry E. , Jesteadt Walt
Published: October 2005

The interaction of noise exposure with other variables is reviewed. For the case of the interaction of noise with other variables that produce behavioral threshold shifts, the application of a newly developed model is described and demonstrated. This model, referred to as the modified power-law model, provides an accurate prediction of the combined effects of two threshold-elevating factors. The model accounts for the interaction of post-exposure threshold shift with pre-exposure hearing loss, whether the hearing loss was a pre-existing permanent loss or a pre-existing temporary loss. The model’s application is demonstrated for multiple exposures to steady-state noise in which each exposure lasts as short as 12 min or as long as 6 h. Finally, implications of the model’s application to the interaction of noise with other ototraumatic agents are reviewed.
Insights into hazard from intense impulses from a mathematical model of the ear
Authors: Price G. Richard , Kalb Joel T.
Published: October 2005

In order to provide insight into the mechanisms that operate in the ear when it is exposed to intense sounds, time and frequency domain mathematical models of the ear including significant nonlinearities in the middle ear were developed to trace energy flow from the free field to the inner ear and ultimately allow the calculation of basilar membrane displacement and a consequent hazard function. These models match the ear’s behavior at low intensities and also reproduce many of the features of the data on hearing hazard from intense impulses. They provide critical insights into the loss mechanisms, suggest new strategies for protecting hearing as well as reducing hazard at the source and could also serve as a framework for a new, accurate, theoretically based method for rating hazard from intense sounds.
Maturation of the traveling-wave delay in the human cochlea
Authors: Eggermont Jos. J. , Ponton Curtis W. , Coupland Stuart G. , Winkelaar Richard
Published: October 2005

The maturation of the traveling-wave delay in the human cochlea was investigated in 227 subjects ranging in age from 29 weeks conceptional age to 49 years by using frequency specific auditory brain-stem responses (ABRs). The derived response technique was applied to ABRs obtained with click stimuli (presented at a fixed level equal to 60-dB sensation level in normal hearing adults) in the presence of high-pass noise masking(slope 96 dB/oct) to obtain frequency specific responses from octave-wide bands. The estimate of traveling-wave delay was obtained by taking the difference between wave I latencies from adjacent derived bands. It was found that the traveling-wave delay between the octave band with center frequency (CF) of 11.3 kHz and that with CF of 5.7 kHz decreased (about 0.4 ms on average) in exponential fashion with age to reach adult values at 3–6 months of age. This decrease was in agreement with reported data in kitten auditory-nerve fibers. The traveling-wave delays between adjacent octave bands with successive lower CF did not change with age.
The structural and functional consequences of acoustic injury in the cochlea and peripheral auditory system: A five year update
Authors: Saunders James C. , Cohen Yale E. , Szymko Yvonne M.
Published: October 2005

This presentation considers important developments and new trends related to acoustic injury in the peripheral auditory system reported during the past 5 years. The discussion begins with the effect overstimulation has on the ‘‘active’’ cochlear process, and the associated loss in receptive field (tuning curve) selectivity. Exposure to intense sound also changes the structure and function of the tectorial membrane, sensory hair bundles, tip links, and intracellular organelles. All of these injuries may change the way in which energy is delivered to the transduction channels of the hair cell. Important new evidence describing the quantitative relation between hair cell loss and permanent hearing loss is reviewed, and the possibility that specific exposure conditions cause unique lesions to the inner or outer hair cells is explored. Finally, the importance of hair cell regeneration in the chick cochlea, changes in the CNS following acoustic injury, and the cochlear vascular system are considered.
The role of intermittence in PTS
Authors: Ward W. Dixon
Published: October 2005

Exposure of chinchillas to noise that is continuous results in auditory damage that is a function of the total energy of the exposure, provided that a critical exposure is not exceeded. Breaking a continuous exposure into 45 exposure periods given once a day Monday through Friday for 9 weeks (an interrupted exposure) is shown to result in a slight reduction in damage, but breaking each of the 45 daily exposures into short noise bursts presented at regular intervals (interrupted and intermittent exposures) reduces the damage more significantly. The shorter the noise bursts, the greater will be the reduction in damage. Too few data are available to establish a principle that will predict correctly the amount of reduction afforded by a particular temporal pattern; while the ‘‘equal energy’’ principle predicts no reduction at all, the ‘‘mean level’’ principle derived from studies of temporary threshold shifts (e.g., a noise at 80 dB half the time and at 100 dB half the time has a mean level of 90 dB and will have the same effect as a continuous 90-dB noise) predicts too much reduction.
Field studies: Industrial exposures
Authors: Johnson Daniel L.
Published: October 2005

The databases and models for the prediction of noise-induced permanent threshold shift (NIPTS) from industrial noise exposures are reviewed. Models available in 1973, compared with later models and data, are shown still to be reasonable. The effect of hearing conservation procedures on the acquisition of new data is discussed. Because of the impact of hearing conservation, new research focus is recommended in three areas: sex differences, newly hired individuals exposed for the first time in occupational noise, and the contribution of nonoccupational noise through the use of questionnaires and dosimetry.
Comments on ‘‘A new efficient algorithm to compute the exact reflection and transmission factors for plane waves in layered absorbing media (liquids and solids)’’ by Pierre Cervenka and Pascal Challande [J. Acoust. Soc. Am. 8
9, 1579 (1991)]
Authors: George Jacob
Published: October 2005

It is pointed out that the solution of ‘‘layered media with any sequence of liquid and solid layers’’ has previously been reported in this journal, and is not a ‘‘new feature’’ as the authors claim. Relevant publications are cited and some interesting features of the solution are discussed.
Risk factors for hearing loss at different frequencies in a population of 47 388 noise-exposed workers
Authors: Bauer Peter , Körpert Karl , Neuberger Manfred , Raber Alfred , Schwetz Friedrich
Published: October 2005

Weighted regression analysis was applied to determine the dependence of the hearing thresholds of 47 388 noise-exposed workers on age, sex, noise imission level, ear disease, head injury, tinnitus, hearing protector usage, and audiometric frequency in the range from 0.5 to 6 kHz. It could be shown that the hearing thresholds at any frequency are dominated by the age of the worker and that women, after equivalent exposure conditions, hear better than men. The relative effects of sex, noise imission level, ear diseases, tinnitus, and hearing protector usage are related to the audiometric frequency. Users of hearing protectors at the last audiometric investigation hear worse than nonusers. Hearing protector usage is strongly related with the hearing threshold in the low-frequency range. The noise imission level does not noticeably affect the hearing threshold below 3 kHz. The most important frequency of the noise imission level is as expected 4 kHz. For 4 kHz, it was shown that the variables age, noise imission level, tinnitus, head injuries, and ear diseases act in a good approximation additively on the pure-tone hearing threshold.
Nonparametric estimation of phase variance in auditory-nerve fiber’s responses to tonal stimuli
Authors: Deng Li
Published: October 2005

Statistical estimation of the phase variance from the auditory-nerve fiber’s action potential timing data is studied in this paper. A detailed derivation of the sample-based estimation formulas, which deals specifically with the circularity of the phase variable, is given. The development of the estimator is based on nonparametric statistical inference techniques, making no assumptions on the parametric form of the phase distribution (i.e., shape of period histogram). Some desirable properties of the estimator are demonstrated through numerical examples and applications of the estimator in auditory research are discussed.
Responses of ‘‘lower-spontaneous-rate’’ auditory-nerve fibers to speech syllables presented in noise. I: General characteristics
Authors: Silkes Steven M. , Geisler C. Daniel
Published: October 2005

Responses of auditory-nerve fibers in anesthetized cats to nine different spoken stop- and nasal-consonant/vowel syllables presented at 70 dB SPL in various levels of speech-shaped noise [signal-to-noise (S/N) ratios of 30, 20, 10, and 0 dB] are reported. The temporal aspects of speech encoding were analyzed using spectrograms. The responses of the ‘‘lower-spontaneous-rate’’ fibers (<20/s) were found to be more limited than those of the high-spontaneous-rate fibers. The lower-spontaneous-rate fibers did not encode noise-only portions of the stimulus at the lowest noise level (S/N=30 dB) and only responded to the consonant if there was a formant or major spectral peak near its characteristic frequency. The fibers’ responses at the higher noise levels were compared to those obtained at the lowest noise level using the covariance as a quantitative measure of signal degradation. The lower-spontaneous-rate fibers were found to preserve more of their initial temporal encoding than high-spontaneous-rate fibers of the same characteristic frequency. The auditory-nerve fibers’ responses were also analyzed for rate-place encoding of the stimuli. The results are similar to those found for temporal encoding.
High-resolution wave-number-frequency methods for towed arrays
Authors: LeBlanc Lester R. , Salisbury John I.
Published: October 2005

In passive narrow-band or broadband target detection sonars, line arrays are used to enhance performance. In large towed arrays, wave-number-frequency (k-ω) data analysis methods have been used on an experimental basis to detect and identify the presence of noise generators. The noise sources are composed of acoustically radiating sources located in the ocean, vibrational energy within the array, and pressure disturbances along the array. In this paper, a hybrid autoregressive (AR) technique is presented that will generate k-ω solutions having better spatial resolution than is currently possible with methods that make use of a two-dimensional fast Fourier transform (FFT). The hybrid AR method is implemented by applying a one-dimensional FFT on the sampled time series data and using this result to obtain an averaged array cross-spectral density matrix. The AR method is now applied to the spatial cross spectral density matrix to obtain a wave-number-frequency spectrum. For the hybrid AR method, equations are presented for calculating the spatial wave-number resolution as a function of signal-to-noise ratio (SNR), array size, and time-bandwidth product (T-BW). The equations for resolution and array gain are useful for determining when to apply the hybrid AR method. In addition to the hybrid AR development, a modification of the FFT–FFT method is introduced that provides efficient and rapid computation of a standard wave-number-frequency spectrum. Comparisons for various SNR, AR order, and T-BW conditions using computer simulated, and actual at-sea data are made between the k-ω solutions obtained using this modified FFT method and our proposed hybrid AR technique.
Limitations on towed-array gain imposed by a nonisotropic ocean
Authors: Stergiopoulos Stergios
Published: October 2005

This study is concerned with the limitations imposed by the characteristics of the ocean on the gain of hydrophone arrays and on the process of creating a synthetic aperture by using towed-array measurements. The multielement synthetic or physical aperture of a passive array operates in a nonisotropic noise field and in a medium of limited spatial coherence length. In particular, it is assumed that, due to distant shipping, the noise field is partially directive and imposed upon an isotropic noise background, and in the rough-bounded, transmitted medium, many multipaths exist which are closely spaced in arrival time and arrival angle. In the theoretical development of this study, a processing scheme is suggested for the determination of the array gain from the received signal and the directivity pattern of the noise field, which is assumed to be known. Results from simulations of this processing scheme have indicated that a comparison of the experimental estimates of towed-array gains with the above array gain predictions for different values of the spatial coherence length can provide an approximate estimate of the coherence length of the medium. Results from real-data applications of the theoretical development indicate that the coherence properties of the ocean can be sufficient for effective long (80λ) towed-array applications and that the formation of a very long (250λ) synthetic aperture in an anisotropic medium can be successful. The algorithm that is used to create a synthetic aperture is the extended towed-array measurements (ETAM) technique.
Sound wave propagation through emulsions, colloids, and suspensions using a generalized Fick’s law
Authors: Schwarz W. H. , Margulies T. S.
Published: October 2005

A multiphase, continuum theory, that uses volume-averaged balance equations for mass, linear momentum, and energy, is developed to predict the speed and attenuation of small-amplitude sound waves propagating through a suspension of rigid spherical particles. Both a total and a diffusive momentum equation are used rather than the linear momentum equations for each individual phase. Furthermore, this approach admits constitutive equations that satisfy the second law of thermodynamics and enables phoretic effects, such as thermophoresis and barophoresis, to be expressed explicitly as flux terms for the production of linear momentum in Fick’s law. Including the phoretic terms in the viscothermal acoustics problem results in a bicubic algebraic equation for the complex propagation coefficient whose roots can be determined numerically. A low-frequency expansion provides the interpretation that attenuation is due to viscous, thermal conduction, phoretic and Dufour effects. Furthermore, it has been found that by using only the definition of the diffusion coefficient in the constitutive equation for the linear momentum supply, and the hydrodynamic formula for the drag on a particle given by Stokes, one obtains the Einstein formula for the diffusion coefficient.
Surface-wave characterization of the interface between two anisotropic media
Authors: Chevalier Y. , Louzar M. , Maugin G. A.
Published: October 2005

The propagation of interface waves between two anisotropic (orthotropic) media is examined for various interface mechanical conditions. While perfect bonding yields Stoneley waves with the ad hoc combination of materials, slip conditions, either general or of the elastic type, or with Coulomb friction, allow one to show the existence of both sagittally and horizontally polarized interface waves. The latter, in particular, are dispersive and exhibit a cutoff that could be used as an indicator of the quality or deterioration of the bonding between materials at the interface.
The acoustical background for a submerged elastic shell
Authors: Werby M. F.
Published: October 2005

The resonance process can be viewed as a superposition of an acoustical background (a rigid scatterer for elastic solids) and the resonance response. [H. Überall, ‘‘Modal and surface-wave resonances in acoustic-wave scattering from elastic objects and in elastic-wave scattering from cavities’’ in Proceedings of the IUTAM Symposium: Modern Problems in Elastic Wave Propagation, Northwestern Univ., Evanston, IL, 12–15 Sept. 1977, edited by J. Miklowitz and J. D. Achenbach (Wiley, New York, 1978), pp. 239–263; L. Flax, L. R. Dragonette, and H. Überall, ‘‘Theory of elastic resonance excitation by sound scattering,’’ J. Acoust. Soc. Am. 63, 723–731 (1978)]. The subtraction of an appropriate acoustical background proved valuable for isolating the lower-frequency resonances as well as understanding the nature of resonances excited by acoustical signals impinging on elastic solids.

In particular, the rigid background could be subtracted mode by mode in partial wave space to isolate the resonances. An analogous background for elastic shells has been elusive to find over the years, although for very thin shells a soft background has proven adequate for the lower-frequency region; for thicker shells and at appropriately higher frequencies, a rigid background has in some cases proven useful. In this work a new model is proposed that describes the background of an elastic shell for a suitable thickness region over the entire frequency range. Further, in the limit of thin shells at the lower frequency end, it is shown to equal a soft background, while for thicker shells and at higher frequencies it goes into a rigid background. The appropriate mass dependence for the new background is also observed. The usefulness of the new background is demonstrated for several examples, where it is shown that by subtracting the new background, resonances can be better isolated than for the elastic soft/rigid analogs.
Sound propagation in capillary-tube-type porous media with small pores in the capillary walls
Authors: Arnott W. Patrick , Sabatier James M. , Raspet Richard
Published: October 2005

Sound propagation in gas-filled capillary-tube-type porous media was investigated. The capillary tubes were taken to be nominally straight with very small pores in the walls of the capillary tubes. The complex wave number and the characteristic impedance of such media were evaluated. Application to ceramic samples having capillary pores with square cross sections and porous walls is developed as an explanation for the anomalous tortuosity factor previously inferred for this material. Specific acoustic impedance (SAI) measurements were performed for rigid-backed square pore ceramic media having finite wall porosity. It is shown that phase velocity is decreased, attenuation is increased, and characteristic impedance is decreased by finite wall porosity. SAI measurements were also performed after the wall pores were filled with water. These measurements agree favorably with the porous wall and nonporous wall theories, respectively. This work provides a model for the acoustical properties of gas-filled monolithic catalyst supports of which the square pore ceramic media is an example.
Nature of the sound sources in low-speed jet impingement
Authors: Powell Alan
Published: October 2005

The impingement of a turbulent jet on a large flat inclined plate results in the formation of a turbulent wall-jet, which adds considerably to the aerodynamic noise. The ‘‘image argument,’’ the ‘‘three sound-pressures theorem,’’ and the principles of compactness and of symmetry can be applied to elucidate the nature of the source mechanisms involved. Applying all these and neglecting the effect of dissipation on the source mechanism, the result is that the aerodynamic sound sources must be reducible to lateral quadrupole form, axially symmetric with maxima normal to the plane and parallel to it with half the amplitude, the minimum being at about 55° to the axis (35° to the plate); this is consistent with observations of a free jet. The inclusion of viscosity results in additional shear dipoles associated with the viscous traction forces that lie in the plane of the plate, which reduce to shear quadrupoles in the case of symmetry, while the effect of the viscous dissipation in the noise generating mechanism results in the addition of monopole sources (or, three equal quadrupoles orthogonally arranged), a simple physical argument being used in the latter case. These shear and dissipative sources also yield the usual U8 relationship for aerodynamically generated noise, but can be expected to be relatively weak in engineering applications of high Reynolds number. If the condition of axial symmetry is relaxed, the lateral quadrupoles are still likely to be dominant, but the minima occur at 45° to the plate; this is also consistent with experiment (though for not small Mach number).
Wave processes in media with strong acoustic nonlinearity
Authors: Ostrovsky L. A.
Published: October 2005

A class of elastic media is considered in which, due to structural inhomogeneities, the parameter of acoustic nonlinearity Γ proves to be much larger than in ‘‘ordinary,’’ homogeneous solids. As an example, porous ‘‘rubberlike’’ media where the transversal wave velocity ct is much less than the longitudinal one cl are shown to have a value of Γ of the order of (cl/ct)2 at the porosity as small as (ct/cl)2 for spherical and cylindrical pores. Experimental data confirm these predictions. Another model discussed here is a ‘‘bimodular’’ medium having different elastic moduli on compression and on stretch. Equations of longitudinal elastic waves and some of their solutions are obtained provided all ‘‘kinematic’’ nonlinear effects can be neglected in comparison with the structural nonlinearity. It is supposed that the class of strongly nonlinear solids can be wide enough and include rocks, metals and other microinhomogeneous materials.
Solid elastic sphere radiometer and transient thermoelectric methods for ultrasound intensity determination.
Authors: Dunn F.
Published: October 2005

The radiation force on a solid sphere suspended freely in an inviscid fluid, described by King [Proc. R. Soc. London Ser. A 123, 212 (1935)] and by Hasegawa and Yosioka [J. Acoust. Soc. Am. 46, 1139 (1969)], provides a simple method for determining the absolute intensity of an ultrasonic field in the frequency range 0.1 to 10 MHz, to, respectively, ±5% to ±10%. The transient thermoelectric method, in which a small thermocouple junction is imbedded in an absorbing medium and which yields a temperature increase in proportion to acoustic intensity, can also provide absolute determination (±3% at 0.2 MHz to ±10% at 10 MHz), though details of the absorbing material are required. Alternatively, this method provides a secondary standard convenient for singular field measurements. It has been used to 2 GHz. [Work partially supported by NIH.]
Development of measurement techniques to determine the temperature rise caused by diagnostic ultrasound equipment in a tissue-mimicking test object.
Authors: Bacon David R. , Esward Trevor J.
Published: October 2005

An experimental test facility has been developed for determining the heating caused by diagnostic ultrasound. This incorporates fine-wire thermocouples embedded in a tissue-mimicking gel, along with a mechanical positioning system to align the transducer with the test object. To study experimental errors, information on the beam profile and the temperature rise as a function of time has been obtained for a variety of thermocouples. The viscous heating artifact is caused by the relative motion of the gel and the thermocouple, and this effect can be greater than the true temperature rise, particularly in highly focused fields, where the beam radius may be on the order of 0.5 mm. Conduction of heat away from the thermocouple junction is also important, and has been studied experimentally and theoretically for a range of thermocouple types. Improved methods of correcting for these sources of error have been developed and the corrected results are shown to agree with theory, for the best thermocouples used (50-μm-diam. manganin and constantan wires). When both sources of error are large (greater than about 50%), the correction methods are inadequate and errors on the order of 100% can occur. The system has been used to measure temperature rises on the order of 1 °C in the field of a diagnostic scanner.
Potency of interaural differences of intensity on the lateralization of interaurally delayed bands of noise.
Authors: Buell Thomas N. , Trahiotis Constantine
Published: October 2005

Listeners indicated the intracranial position of noises (bands of from 50 to 400 Hz) for several combinations of interaural differences of intensity (IDI), time (IDT), and/or phase (IDP). All IDT and IDP combinations produced an interaural delay of 1500 μs at the centerfrequency of the noise. The interaural phase spectra were constructed to produce several patterns of putative cross-correlation functions. Potency of IDIs depended greatly on particular combinations of bandwidth, IDT, and IDP. For some combinations, changing the IDI by only 3 dB resulted in large shifts in laterality (sometimes moving the image from near one ear to near the other). Generally, potency of the IDIs was found to be greatest for narrow bands of noise having pure IDTs. The complex interactions observed make the results incompatible with the traditional notion that IDIs simply act as weights or scalars. Instead, the data are aptly described by cross-correlation models that incorporate ‘‘pattern analysis.’’ [Research supported by NIH and AFOSR.]
Azimuthal localization and the asymmetry of the plausibility hypothesis.
Authors: Hartmann William Morris , Fontana Paul
Published: October 2005

Azimuthal localization of sound is determined by interaural time differences (ITD) and interaural intensity differences (IID). The relative importance of these cues in a localization decision is the subject of time-intensity trading. The plausibility hypothesis [B. Rakerd and W. M. Hartmann, J. Acoust. Soc. Am. 78, 524–533 (1985)] says that ITD cues are subconsciously discounted if they do not agree with ITDs that are possible in free field or with free-field cues that would become visually observable sources. Experiments of the present work looked for a comparable effect with IID cues. Recordings made with an artificial head in an anechoic environment were played back to listeners in the same environment, but through headphones so that implausible IIDs could be achieved. It was found that for 500-Hz tone pulses, and for 500-Hz tones without onset transients, IIDs continue to contribute to localization judgments even when they are highly implausible. Although an IID of only 5 dB is completely implausible at 500 Hz, significant differential sensitivity to IID remains for IIDs up to 20 dB. The results indicate an asymmetrical plausibility hypothesis, one that operates dramatically on ITD but not on IID. [Work supported by the NIDCD, DC00181.]
Effects of hearing aids on directional hearing.
Authors: Sullivan Jean A. , Wong Lena , Soli Sigfrid D.
Published: October 2005

Plomp’s model of hearing handicap [R. Plomp, J. Acoust. Soc. Am. 63, 533–549 (1978)] incorporates the effects of hearing aids, G, and distortion, S, on the prediction of speech reception thresholds (SRTs) in noise; however, S does not include the effects of the hearing aid(s) on binaural cues, particularly cues present when the signal and noise originate from different azimuths. Here, S has been estimated for binaural listening conditions by measuring differences between aided and unaided monaural and binaural SRTs with speech and noise at the same azimuth and with speech and noise at different azimuths. Normal hearing subjects were tested to dissociate the effects of hearing loss from the estimates of S. Signals were presented from the desired azimuths to KEMAR and ear canal microphones. The ear canal resonances were equalized, the amplitude of unaided and aided signals were matched, and the resulting binaural signals were presented to listeners through headphones. Comparisons will be presented of the unaided and aided measures, and the importance of hearing aid S for binaural cues will be discussed.
The effects of frequency range, duration, context, practice, and feedback on the discrimination of tonal order in auditory sequences.
Authors: Barsz Kathy
Published: October 2005

Previous studies have shown that factors associated with perceptual grouping [e.g., K. Barsz, Percept. Psychophys. 43, 293–303 (1988)] affect sequence discrimination. The present study manipulated factors associated with attention [M. R. Leek, in AuditoryProcessingofComplexSounds, edited by W. A. Yost and C. S. Watson (Erlbaum, Hillsdale), pp. 278–288] to examine whether ‘‘attention’’ can diminish the effects of ‘‘grouping.’’ The four-tone sequences differed in the order of their tones so that the two low frequencies were shifted relative to the two high frequencies. For example, if the standard sequence was H1 L1 H2 L2, then the different sequence was L1 H1 L2 H2. Each sequence was started at a random point and repeated without pause. d’ was highest when the frequency range was narrow (e.g., 2500, 2250, 2375, 2137.5 Hz). When the sequence had a wide range (e.g., 2500, 625, 2375, 593.75 Hz), d’ was 0 for 200-ms tone durations but improved for 100-ms tone durations. Performance on middle range sequences (e.g., 2500, 2125, 2375, 2018.75) depended to some extent on the types of sequences included in a block of trials. d’ was somewhat lower when middle range sequences were presented with narrow range sequences than when they were presented with wide range sequences. Except in isolated instances, listeners’ performance did not appear to be affected by the presence of feedback or by extended practice (all listeners improved during the first few sessions). The data confirm previous reports that a wide frequency range impairs discriminations based on the order of the tones, and further suggest that discrimination is best for the sequences in the block that have the narrowest range. Decreasing the tone duration should have increased perceptual segregation; thus its facilitating effect on discrimination suggests that factors other than perceptual grouping have an impact on sequence discrimination. On the whole, factors associated with perceptual grouping had more impact on discrimination performance than factors associated with attention.
Modeling the nonlinear cochlear mechanical basis of psychophysical tuning.
Authors: Goldstein Julius L.
Published: October 2005

The multiple-bandpass-nonlinearity (MBPNL) model of nonlinear cochlear mechanical response [J. Goldstein, Hear. Res. 49, 39–60 (1990)] was used to study the basis for sound-level dependence of human psychophysical tuning [R. Wegel and C. Lane, Phys. Rev. 23, 226–285 (1924)]. Comprehensive psychophysical tuning curve (PTC) data reported by P. Stelmachowicz and W. Jesteadt [J. Speech and Hear. Res. 27, 396–402 (1984)] and supplemented by Nelson and Fortune [J. Speech Hear. Res. 34, 360–373 (1991)] were simulated with a single MBPNL filter channel tuned to the 2-kHz probe tone and detected by a classical Weber–Fraction energy detector. Accurate simulation of most of the PTC data was obtained with MBPNL parameters similar to values estimated earlier from physical cochlear measurements. Nelson and Fortune showed that masking of aural combination tones significantly broadens the PTCs at high probe levels. The model simulations confirm their finding by providing better agreement with their broader high-level PTCs. This research establishes that human auditory frequency analysis is mediated by similar nonlinear cochlear mechanical responses as measured invasively in animal experiments, and that the MBPNL model provides a useful quantitative representation of human nonlinear auditory frequency analysis. [Work supported by NIDCD.]