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Top 20 Most Read Articles
April 2011
The 20 articles with the most full-text downloads during the month, in descending order.
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Cancellation of acoustic scattering from an elastic sphere J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1355-1365 (2011); (11 pages) Online Publication Date: 09 Mar 2011
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Recent research has suggested the possibility of creating acoustic cloaks using metamaterial layers to eliminate the acoustic field scattered from an elastic object. This paper explores the possibility of applying the scattering cancellation cloaking technique to acoustic waves and the use of this method to investigate its effectiveness in cloaking elastic and fluid spheres using only a single isotropic elastic layer. Parametric studies showing the influence of cloak stiffness and geometry on the frequency dependent scattering cross-section of spheres have been developed to explore the design space of the cloaking layer. This analysis shows that an appropriately designed single isotropic elastic cloaking layer can provide up to 30 dB of scattering reduction for ka values up to 1.6. This work also illustrates the importance of accounting for the elasticity of the object and the relevant limitations of simplistic quasi-static analyses proposed in recent papers.
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Sound speed in water-saturated glass beads as a function of frequency and porosity J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL101-EL107 (2011); (7 pages) Online Publication Date: 22 Mar 2011
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Sound propagation in water-saturated granular sediments is known to depend on the sediment porosity, but few data in the literature address both the frequency and porosity dependency. To begin to address this deficiency, a fluidized bed technique was used to control the porosity of an artificial sediment composed of glass spheres of 265 μm diameter. Time-of-flight measurements and the Fourier phase technique were utilized to determine the sound speed for frequencies from 300 to 800 kHz and porosities from 0.37 to 0.43. A Biot-based model qualitatively describes the porosity dependence.
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Factors That Influence the Localization of Sound in the Vertical Plane J. Acoust. Soc. Am. Volume 43, Issue 6, pp. 1255-1259 (1968); (5 pages) Online Publication Date: 21 Jul 2005
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The ability of listeners to locate sound in the vertical plane was investigated. The results showed that for auditory stimuli to be located accurately (1) the stimulus must be complex, (2) it must include frequencies above 7000 cps, and, (3) the pinna must be present. |
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New designs of class V flextensional transducers with ATILA J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S136-S137 (1990); (2 pages) Online Publication Date: 14 Aug 2005
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The improvements sought in range and performance of sonar arrays require the use of higher acoustical powers at lower frequencies from radiators of reduced dimensions. At the present time, flextensional transducers seem to offer a good solution. Two kinds of flextensional transducers are generally employed: classes IV and V. In the first case, the motors consist of parallel stacks of ceramics, the shell providing the prestressing. In the second case, the motors are made from ceramics staves arranged to form a ring, the prestressing being achieved by wrapping the ring with glass fibers under tension. However, because it is not conventional, the application of prestress in these two cases remains delicate and imprecise. The purpose of this paper is to analyze by the finite element code ATILA [Decarpigny et al., J. Acoust. Soc. Am. 78, 1499–1507 (1985)] an original idea for a class V flextensional transducer that does not suffer from this disadvantage. This flextensional transducer is made from a segmented ring on which are mounted classical ceramic stacks arranged in the form of an inscribed polygon. Several shell configurations will be modeled and analyzed with a special emphasis on technical advantages of these new flextensional designs. |
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Guided wave propagation in single and double layer hollow cylinders embedded in infinite media J. Acoust. Soc. Am. Volume 129, Issue 2, pp. 691-700 (2011); (10 pages) Online Publication Date: 24 Feb 2011
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Millions of miles of pipes are being used for the transportation, distribution, and local use of petroleum products, gas, water, and chemicals. Most of the pipes are buried in soil, leading to the significance of the study on the subject of guided wave propagation in pipes with soil influence. Previous investigations of ultrasonic guided wave propagation in an elastic hollow cylinder and in an elastic hollow cylinder coated with a viscoelastic material have led to the development of inspection techniques for bare and coated pipes. However, the lack of investigation on guided wave propagation in hollow cylinders embedded in infinite media like soil has hindered the development of pipe inspection methods. Therefore the influence of infinite media on wave propagation is explored in this paper. Dispersion curves and wave structures of both axisymmetric and nonaxisymmetric wave modes are developed. Due to the importance of the convergence of numerical calculations, the requirements of thickness and element number of the finite soil layer between hollow cylinder and infinite element layer are discussed, and an optimal combination is obtained in this paper. Wave structures are used for the mode identification in the non-monotonic region caused by the viscoelastic properties of coating and infinite media.
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Effects of natural sounds on the perception of road traffic noise J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL148-EL153 (2011); (6 pages) Online Publication Date: 28 Mar 2011
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Recent studies show that introducing sound from water features in urban open spaces may reduce the loudness of road traffic noise, but it is not clear in which situations this measure also improves overall soundscape quality. This work describes a listening experiment on loudness, pleasantness, and eventfulness of stimuli that combine road traffic noise with fountain or bird sound at different sound levels. Adding fountain sound reduced the loudness of road traffic noise only if the latter had low temporal variability. Conversely, adding bird sound significantly enhanced soundscape pleasantness and eventfulness, more than what was achieved by adding fountain sound.
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Improving beampatterns of two-dimensional random arrays using convex optimization J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL135-EL140 (2011); (6 pages) Online Publication Date: 28 Mar 2011
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Sensors are becoming ubiquitous and can be combined in arrays for source localization purposes. If classical conventional beamforming is used, then random arrays have poor beampatterns. By pre-computing sensor weights, these beampatterns can be improved significantly. The problem is formulated in the frequency domain as a desired look direction, a frequency-independent transition region, and the power minimized in a rejection-region. Using this formulation, the frequency-dependent sensor weights can be obtained using convex optimization. Since the weights are data independent they can be pre-computed, the beamforming has similar computational complexity as conventional beamforming. The approach is demonstrated for real 2D arrays.
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J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1685-1695 (2011); (11 pages)
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In a previous paper, Linton and Martin [J. Acoust. Soc. Am. 117, 3413–3423 (2005)] obtained two formulas for the effective wavenumber in a dilute random array of circular scatterers. They emerged from a study of the problem of the reflection of a plane wave at oblique incidence to a half-space containing the scatterers. Here, their study is extended to obtain formulas for the reflection and transmission coefficients and to investigate the average fields near the boundary of the half-space. Comparisons with previous work are made.
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Narrow‐band sound localization related to external ear acoustics J. Acoust. Soc. Am. Volume 92, Issue 5, pp. 2607-2624 (1992); (18 pages)
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Human subjects localized brief 1/6‐oct bandpassed noise bursts that were centered at 6, 8, 10, and 12 kHz. All testing was done under binaural conditions. The horizontal component of subjects’ responses was accurate, comparable to that for broadband localization, but the vertical and front/back components exhibited systematic errors. Specifically, responses tended to cluster within restricted ranges that were specific for each center frequency. The directional transfer functions of the subjects’ external ears were measured for 360 horizontal and vertical locations. The spectra of the sounds that were present in the subjects’ ear canals, the ‘‘proximal stimulus’’ spectra, were computed by combining the spectra of the narrow‐band sound sources with the directional transfer functions for particular stimulus locations. Subjects consistently localized sounds to regions within which the associated directional transfer function correlated most closely with the proximal stimulus spectrum. A quantitative model was constructed that successfully predicted subjects’ responses based on interaural level difference and spectral cues. A test of the model, using techniques adapted from signal detection theory, indicated that subjects tend to use interaural level difference and spectral shape cues independently, limited only by a slight spatial correlation of the two cues. A testing procedure is described that provides a quantitative comparison of various predictive models of sound localization. |
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Prediction of sound reflection by corrugated porous surfaces J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1696-1706 (2011); (11 pages)
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The coupled mode (CM) and finite-element methods (FEMs) are developed and used to predict the acoustic reflection coefficient of a semi-infinite porous medium with closely spaced two-dimensional (2D) periodical corrugations. These methods are also applied to predict the reflection coefficient of a periodic array of porous corrugations installed on an acoustically rigid surface. It is shown that the predictions by the both methods agree closely. The reflection coefficient and Brewster angle of total refraction for the corrugated semi-infinite medium predicted with these methods are compared against that predicted by the Biot/Tolstoy/Howe/Twersky and extended Twersky models. A similar analysis is carried out for porous corrugations set on a rigid backing. The behavior of the reflection coefficient and the pole in the expression for the reflection coefficient located close to grazing incidence is studied.
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Normal waves in elastic bars of rectangular cross section J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1324-1335 (2011); (12 pages) Online Publication Date: 09 Mar 2011
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This paper addresses a theoretical study of guided normal waves in elastic isotropic bars of rectangular cross-section by an analytical superposition method. Dispersion properties of propagating and evanescent modes for four families are analyzed in detail at various geometric and physical parameters of the bar. A comparison of the obtained results with the well-known properties for waves in infinite plates and circular cylinders is provided. The complicated structure of dispersion spectra is explained. High-frequency limiting values for phase and group velocities of normal waves are established for the first time. Calculated data agree well with the available experimental results.
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On the aeroacoustic tonal noise generation mechanism of a sharp-edged plate J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL154-EL160 (2011); (7 pages) Online Publication Date: 28 Mar 2011
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This letter presents an experimental study on the tonal noise generated by a sharp-edged flat plate at low-to-moderate Reynolds number. Flow and far-field noise data reveal that, in this particular case, the tonal noise appears to be governed by vortex shedding processes. Also related to the existence of the tonal noise is a region of separated flow slightly upstream of the trailing edge. Hydrodynamic fluctuations at selected vortex shedding frequencies are strongly amplified by the inflectional mean velocity profile in the separated shear layer. The amplified hydrodynamic fluctuations are diffracted by the trailing edge, producing strong tonal noise.
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Transmission loss measurement of acoustic material using time-domain pulse-separation method (L) J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1681-1684 (2011); (4 pages)
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An alternative method for measuring the normal incidence sound transmission loss (nSTL) is presented in this paper based on the time-domain separation of so-called Butterworth pulse with a short-duration time about 1 ms in a standing wave tube. During the generation process of the pulse, inverse filter principle was adopted to compensate the loudspeaker response, besides this, the effect of the characteristics of tube termination can be eliminated through the generation process of the pulse so as to obtain a single plane pulse wave in the standing wave tube which makes the nSTL measurement very simple. A polyurethane foam material with low transmission loss and a kind of rubber material with relatively high transmission loss are used to verify the proposed method. When compared with the traditional two-load method, a relatively good agreement between these two methods can be observed. The main error of this method results from the measuring accuracy of the amplitude of transmission coefficient.
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J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL108-EL113 (2011); (6 pages) Online Publication Date: 22 Mar 2011
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The greatest difference in distortion product otoacoustic emission (DPOAE) suppression tuning curves (STCs) in infant and adult ears occurs at a stimulus frequency of 6 kHz. These infant and adult STCs are much more similar when constructed using the absorbed power level of the stimulus and suppressor tones rather than using sound pressure level. This procedure incorporates age-related differences in forward and reverse transmission of sound power through the ear canal and middle ear. These results support the theory that the cochlear mechanics underlying DPOAE suppression are substantially mature in full-term infants.
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Predictions and measurements of sound transmission through a periodic array of elastic shells in air J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3496-3506 (2010); (11 pages)
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Analytical and numerical approaches have been made to the problems of (a) propagation through a doubly periodic array of elastic shells in air, (b) scattering by a single elastic shell in air, and (c) scattering by a finite periodic array of elastic shells in air. Using the Rayleigh identity and the Kirchhoff–Love approximations, a relationship is found between the elastic material parameters and the size of the bandgap below the first Bragg frequency, which results from the axisymmetric resonance of the shells in an array. Predictions and laboratory data confirm that use of a suitably “soft” non-vulcanized rubber results in substantial insertion loss peaks related to the resonances of the shells. Inclusion of viscoelasticity is found to improve the correspondence between predictions and data. In addition the possible influences of inhomogeneity due to the manufacturing of the elastic shells (i.e., the effects of gluing sheet edges together) and of departures from circular cylindrical cross-sections are considered by means of numerical methods.
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The influence of pinnae‐based spectral cues on sound localization J. Acoust. Soc. Am. Volume 75, Issue 4, pp. 1195-1200 (1984); (6 pages)
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The role of pinnae‐based spectral cues was investigated by requiring listeners to locate sound, binaurally, in the horizontal plane with and without partial occlusion of their external ears. The main finding was that the high frequencies were necessary for optimal performance. When the stimulus contained the higher audio frequencies, e.g., broadband and 4.0‐kHz high‐pass noise, localization accuracy was significantly superior to that recorded for stimuli consisting only of the lower frequencies (4.0‐ and 1.0‐kHz low‐pass noise). This finding was attributed to the influence of the spectral cues furnished by the pinnae, for when the stimulus composition included high frequencies, pinnae occlusion resulted in a marked decline in localization accuracy. Numerous front–rear reversals occurred. Moreover, the ability to distinguish among sounds originating within the same quadrant also suffered. Performance proficiency for the low‐pass stimuli was not further degraded under conditions of pinnae occlusion. In locating the 4.0‐kHz high‐pass noise when both, neither, or only one ear was occluded, the data demonstrated unequivocally that the pinna‐based cues of the ‘‘near’’ ear contributed powerfully toward localization accuracy. |
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Contribution of spectral cues to human sound localization J. Acoust. Soc. Am. Volume 112, Issue 4, pp. 1583-1596 (2002); (14 pages) Online Publication Date: 27 Sep 2002
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The contribution of spectral cues to human sound localization was investigated by removing cues in ½-, 1- or 2-octave bands in the frequency range above 4 kHz. Localization responses were given by placing an acoustic pointer at the same apparent position as a virtual target. The pointer was generated by filtering a 100-ms harmonic complex with equalized head-related transfer functions (HRTFs). Listeners controlled the pointer via a hand-held stick that rotated about a fixed point. In the baseline condition, the target, a 200-ms noise burst, was filtered with the same HRTFs as the pointer. In other conditions, the spectral information within a certain frequency band was removed by replacing the directional transfer function within this band with the average transfer of this band. Analysis of the data showed that removing cues in ½-octave bands did not affect localization, whereas for the 2-octave band correct localization was virtually impossible. The results obtained for the 1-octave bands indicate that up–down cues are located mainly in the 6–12-kHz band, and front–back cues in the 8–16-kHz band. The interindividual spread in response patterns suggests that different listeners use different localization cues. The response patterns in the median plane can be predicted using a model based on spectral comparison of directional transfer functions for target and response directions. © 2002 Acoustical Society of America. |
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Ocean bottom profiling with ambient noise: A model for the passive fathometer J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1825-1836 (2011); (12 pages)
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A model is presented for the complete passive fathometer response to ocean surface noise, interfering discrete noise sources, and locally uncorrelated noise in an ideal waveguide. The leading order term of the ocean surface noise contribution produces the cross-correlation of vertical multipaths and yields the depth of sub-bottom reflectors. Discrete noise incident on the array via multipaths give multiple peaks in the fathometer response. These peaks may obscure the sub-bottom reflections but can be attenuated with use of minimum variance distortionless response (MVDR) steering vectors. The seabed critical angle introduces discontinuities in the spatial distribution of distant surface noise and may introduce spurious peaks in the passive fathometer response. These peaks can be attenuated by beamforming within a bandwidth limited by the array geometry and critical angle.
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Acoustic multipath arrivals in the horizontal plane due to approaching nonlinear internal waves J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL141-EL147 (2011); (7 pages) Online Publication Date: 28 Mar 2011
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Simultaneous measurements of acoustic wave transmissions and a nonlinear internal wave packet approaching an along-shelf acoustic path during the Shallow Water 2006 experiment are reported. The incoming internal wave packet acts as a moving frontal layer reflecting (or refracting) sound in the horizontal plane. Received acoustic signals are filtered into acoustic normal mode arrivals. It is shown that a horizontal multipath interference is produced. This has previously been called a horizontal Lloyd’s mirror. The interference between the direct path and the refracted path depends on the mode number and frequency of the acoustic signal. A mechanism for the multipath interference is shown. Preliminary modeling results of this dynamic interaction using vertical modes and horizontal parabolic equation models are in good agreement with the observed data.
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Acoustic radiation torque and the conservation of angular momentum (L) J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1679-1680 (2011); (2 pages)
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This note concerns the evaluation of the static acoustic radiation torque exerted by an acoustic field on a scatterer immersed in a nonviscous fluid based on far-field scattering. The radiation torque is expressed as the integral of the time-averaged flux of angular momentum over a spherical surface far removed from the scattering object with its center at the centroid of the object. That result was given previously [G. Maidanik, J. Acoust. Soc. Am. 30, 620–623 (1956)]. Another expression given recently [Z. W. Fan et al., J. Acoust. Soc. Am. 124, 2727–2732 (2008)] is simplified to this formula. Comments are made on obtaining it directly from the general theorem of angular momentum conservation in the integral form.
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