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May 2013

Volume 133, Issue 5, pp. EL339-3618

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Towards online maximum-likelihood-based speech clustering and separation

Mehrez Souden, Keisuke Kinoshita, and Tomohiro Nakatani

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL339-EL345 (2013); (7 pages)

Online Publication Date: 08 Apr 2013

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This paper introduces an approach for online speech source clustering and separation, which is based on the utilization of the multichannel location information in a recursive expectation maximization (EM) algorithm. Specifically, the normalized multichannel speech-recording vector is employed as a feature vector and is modeled using Watson mixture model. The model parameters are determined by maximizing the data likelihood at every time-frequency slot in an online processing manner. Consequently, the proposed approach can continuously adjust the speech clusters. Promising results showing the advantage of the proposed approach over the batch EM algorithm in the case of two speakers with speaker movement are obtained.
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43.72.Kb Speech communication systems and dialogue systems
43.72.Dv Speech-noise interaction
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Evidence for a spatial bias in the perception of sequences of brief tones

Davide Rocchesso, Guillaume Lemaitre, and Massimo Grassi

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL346-EL350 (2013); (5 pages)

Online Publication Date: 08 Apr 2013

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Listeners are unable to report the physical order of particular sequences of brief tones. This phenomenon of temporal dislocation depends on tone durations and frequencies. The current study empirically shows that it also depends on the spatial location of the tones. Dichotically testing a three-tone sequence showed that the central tone tends to be reported as the first or the last element when it is perceived as part of a left-to-right motion. Since the central-tone dislocation does not occur for right-to-left sequences of the same tones, this indicates that there is a spatial bias in the perception of sequences.
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43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Rq Dichotic listening
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Optimization of the array mirror for time reversal techniques used in a half-space environment

Blaine M. Harker and Brian E. Anderson

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL351-EL357 (2013); (7 pages)

Online Publication Date: 08 Apr 2013

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Time reversal (TR) utilizes an array of transducers, a time reversal mirror (TRM), to locate sources. Here TR is applied to simple sources using steady-state waveforms in a numerical, point source model in a half-space environment. It is found that TR can effectively localize a simple source broadcasting a continuous wave, depending on the angular spacing. Furthermore, the angular spacing and the aperture of the TRM are the most important parameters when creating a setup of receivers for imaging a source. This work optimizes a TRM when the source's location is known within a region of certainty.
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43.60.Tj Wave front reconstruction, acoustic time-reversal, and phase conjugation
43.60.Fg Acoustic array systems and processing, beam-forming
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Experimental evaluation of inverse filtering using physical systems with known glottal flow and tract characteristics

Derek Tze Wei Chu, Kaiwen Li, Julien Epps, John Smith, and Joe Wolfe

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL358-EL362 (2013); (5 pages)

Online Publication Date: 08 Apr 2013

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The technique presented here uses an impedance head to measure the input impedance spectrum of a physical model of a vocal tract, and then to inject a known glottal flow waveform into the tract. The sound measured outside the mouth is used to evaluate inverse filtering techniques by comparison with the known glottal flow and measured acoustical properties of the tract. The normalized least square errors in the glottal flow were typically a percent or less in the time domain and several percent in the frequency domain. Accurate determination of resonance frequencies and bandwidths required a suitable order of inverse filter.
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43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
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The vowel inherent spectral change of English vowels spoken by native and non-native speakers

Su-Hyun Jin and Chang Liu

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL363-EL369 (2013); (7 pages)

Online Publication Date: 08 Apr 2013

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The current study examined Vowel Inherent Spectral Change (VISC) of English vowels spoken by English-, Chinese-, and Korean-native speakers. Two metrics, spectral distance (amount of spectral shift) and spectral angle (direction of spectral shift) of formant movement from the onset to the offset, were measured for 12 English monophthongs produced in a /hvd/ context. While Chinese speakers showed significantly greater spectral distances of vowels than English and Korean speakers, there was no significant speakers' native language effect on spectral angles. Comparisons to their native vowels for Chinese and Korean speakers suggest that VISC might be affected by language-specific phonological structure.
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43.70.Kv Cross-linguistic speech production and acoustics
43.70.Mn Relations between speech production and perception
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The effect of diffuse reflections on spatial discrimination in a simulated concert hall

Philip Robinson, Jukka Pätynen, and Tapio Lokki

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL370-EL376 (2013); (7 pages)

Online Publication Date: 08 Apr 2013

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This letter presents results from a study on diffusive architectural surfaces and auditory perception. Spatial discrimination of multiple sources is investigated in a simulated performance venue with various diffusive surface treatments. Simulations were generated with closely spaced sound sources on the stage of a concert hall and a listener in the audience area. Subjects were asked to distinguish signals in which pairs of simultaneous talkers were presented at various lateral separations, in halls with flat or diffusive surfaces. The experiments reveal that discriminating differences in the lateral arrangement of sources is possible at narrower separation angles when reflections come from flat rather than diffusive surfaces.
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43.66.Lj Perceptual effects of sound
43.66.Qp Localization of sound sources
43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Fw Auditorium and enclosure design
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Infants' name recognition in on- and off-channel noise

Rochelle S. Newman, Giovanna Morini, and Monita Chatterjee

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL377-EL383 (2013); (7 pages)

Online Publication Date: 08 Apr 2013

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Previous work by Polka, Rvachew, and Molnar [Infancy 13(5), 421-439 (2008)] has reported that infants are poor at focusing their attention on a particular frequency range, and, as a result, are distracted by maskers that are outside of the target frequency range. The current study explores this effect of irrelevant distractors further and finds that 8-month-old infants are significantly less affected by maskers outside the frequency range (off-channel maskers) than by on-channel maskers. Thus while infants may display difficulty ignoring irrelevant distractors, they are able to do so to at least some degree, suggesting some ability to perceive speech from spectrally remote maskers, despite the demonstrated presence of greater informational masking at this age.
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43.71.Ft Development of speech perception
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Preboundary lengthening and preaccentual shortening across syllables in a trisyllabic word in English

Taehong Cho, Jiseung Kim, and Sahyang Kim

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL384-EL390 (2013); (7 pages)

Online Publication Date: 09 Apr 2013

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This study demonstrates some new aspects of preboundary lengthening and preaccentual shortening on a test word banana in American English. Preboundary lengthening was found to be extended to the initial unstressed syllable beyond the main-stressed syllable, presenting more complexity than has previously been assumed. Preaccentual shortening was observed regardless of boundary strength or the stress pattern (trochaic vs iambic) of the following context word, suggesting that it operates globally at an utterance level. The locus of preaccentual shortening, however, was modulated by prosodic boundary: It is realized on the final vowel IP-finally but on the non-final stressed vowel IP-medially.
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43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation
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English vowel identification in long-term speech-shaped noise and multi-talker babble for English and Chinese listeners

Lin Mi, Sha Tao, Wenjing Wang, Qi Dong, Su-Hyun Jin, and Chang Liu

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL391-EL397 (2013); (7 pages)

Online Publication Date: 10 Apr 2013

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The identification of 12 English vowels was measured in quiet and in long-term speech-shaped noise (LTSSN) and multi-talker babble for English-native (EN) listeners and Chinese-native listeners in the U.S. (CNU) and China (CNC). The signal-to-noise ratio was manipulated from −15 to 0 dB. As expected, EN listeners performed significantly better in quiet and noisy conditions than CNU and CNC listeners. Vowel identification in LTSSN was similar between CNU and CNC listeners; however, performance in babble was significantly better for CNU listeners than for CNC listeners, indicating that exposing non-native listeners to native English may reduce informational masking of multi-talker babble.
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43.71.Hw Cross-language perception of speech
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
43.71.An Models and theories of speech perception
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Distributional training of speech sounds can be done with continuous distributions

Karin Wanrooij and Paul Boersma

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL398-EL404 (2013); (7 pages)

Online Publication Date: 10 Apr 2013

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In previous research on distributional training of non-native speech sounds, distributions were always discontinuous: typically, each of only eight different stimuli was repeated multiple times. The current study examines distributional training with continuous distributions, in which all presented tokens are acoustically different. Adult Spanish learners of Dutch were trained on either a discontinuous or a continuous bimodal distribution of the Dutch vowel contrast /ɑ/–/aː/. Both groups improved their perception of the contrast; this shows that continuous training works equally well as discontinuous training. Using the more natural continuous distributions is therefore recommended for future distributional learning experiments.
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43.71.Ft Development of speech perception
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
43.71.An Models and theories of speech perception
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Modifying the normalized covariance metric measure to account for nonlinear distortions introduced by noise-reduction algorithms

Fei Chen and Yi Hu

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL405-EL411 (2013); (7 pages)

Online Publication Date: 15 Apr 2013

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In this study, two methods are proposed to modify the normalized covariance metric (NCM) measure to reduce the effects of gain-induced nonlinear distortions introduced by most noise-suppression algorithms. Considering that the gain-induced distortions behave differently dependent on the signal-to-noise ratio between the noise-reduced speech and the noise, the first approach introduces a penalty factor involving this ratio in the modified NCM measure. The second approach deemphasizes segments marked with amplification distortions that contribute less to intelligibility via adaptive thresholding. Significantly higher correlations with intelligibility scores were obtained from the modified NCM measures compared with the original NCM measures.
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43.71.Gv Measures of speech perception (intelligibility and quality)
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
43.71.An Models and theories of speech perception
43.66.Ts Auditory prostheses, hearing aids
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On a reference-free speech quality estimator for hearing aids

David Suelzle, Vijay Parsa, and Tiago H. Falk

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL412-EL418 (2013); (7 pages)

Online Publication Date: 16 Apr 2013

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A reference-free speech quality measure is proposed and assessed for hearing aid applications. The proposed speech quality metric is validated with subjective ratings obtained from hearing impaired listeners under a number of noisy and reverberant conditions. In addition, a comparison is drawn between the proposed measure and a state-of-the-art electroacoustic measure that relies on a clean reference signal. The results showed that the reference-free measure had a lower correlation with the subjective ratings of hearing aid speech quality in comparison to the correlations achieved by the measure utilizing a reference signal. Nevertheless, advantages of the reference-free approach are discussed.
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43.66.Ts Auditory prostheses, hearing aids
43.71.Ft Development of speech perception
43.71.Ky Speech perception by the hearing impaired
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Wide-area assessment of topographical and meteorological effects on sound propagation by time-domain modeling

Dietrich Heimann

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL419-EL425 (2013); (7 pages)

Online Publication Date: 16 Apr 2013

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Noise mapping with a three-dimensional finite-difference time-domain (FDTD) model over larger areas suffers from its high computational demand. This study shows that an FDTD model in combination with a meteorological model can be used for at least qualitative assessments of topographical and meteorological effects on sound propagation in domains of even some kilometers extension. This is achieved by restricting the acoustical simulations to low frequencies which allow the use of a rather large numerical grid spacing.
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43.50.Vt Topographical and meteorological factors in noise propagation
43.28.Js Numerical models for outdoor propagation
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Vibroacoustic response sensitivity due to relative alignment of two anisotropic poro-elastic layers

Eleonora Lind Nordgren, Peter Göransson, Jean-François Deü, and Olivier Dazel

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL426-EL430 (2013); (5 pages)

Online Publication Date: 16 Apr 2013

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The effects of relative alignment of two different types of anisotropic open cell porous materials are investigated in terms of the acoustic response of a multi-layered configuration. Numerical experiments, where gradient based optimization techniques were used, are conducted to find possible extremal values. It is shown that, depending on the degree of anisotropy of the porous material properties, their angular orientations have a significant and frequency dependent influence on the measured response. The results highlight the importance of further advancing the knowledge of anisotropic porous material behavior.
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43.50.Gf Noise control at source: redesign, application of absorptive materials and reactive elements, mufflers, noise silencers, noise barriers, and attenuators, etc.
43.35.Mr Acoustics of viscoelastic materials
43.20.Jr Velocity and attenuation of elastic and poroelastic waves
43.55.Ev Sound absorption properties of materials: theory and measurement of sound absorption coefficients; acoustic impedance and admittance
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Adding thermal and granularity effects to the effective density fluid model

Kevin L. Williams

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. EL431-EL437 (2013); (7 pages)

Online Publication Date: 17 Apr 2013

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Previously, an effective density fluid model (EDFM) was developed by the author [J. Acoust. Soc. Am. 110, 2276–2281 (2001)] for unconsolidated granular sediments and applied to sand. The model is a simplification of the full Biot porous media model. Here two additional effects are added to the EDFM model: heat transfer between the liquid and solid at low frequencies and the granularity of the medium at high frequencies. The frequency range studied is 100 Hz–1 MHz. The analytical sound speed and attenuation expressions obtained have no free parameters. The resulting model is compared to ocean data.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.20.Jr Velocity and attenuation of elastic and poroelastic waves
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Characterization of acoustic emissions resulting from particle collision with a stationary bubble

Wen Zhang, Steven J. Spencer, and Peter Coghill

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. 2523-2527 (2013); (5 pages)

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The present work characterizes the acoustic emissions resulting from the collision of a particle driven under gravity with a captive bubble. Conventional methods to investigate the bubble particle collision interaction model measure a descriptive parameter known as the collision time. During such a collision, particle impact may cause a strong deformation and a following oscillation of the bubble–particle interface generates detectable passive acoustic emissions (AE). Experiments and models presented show that the AE frequency monotonically decreases with the particle radius and is independent of the impact velocity, whereas the AE amplitude has a more complicated relationship with impact parameters.
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43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance
43.20.Ye Measurement methods and instrumentation
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Coarse-grid computation of the one-way propagation of coupled modes in a varying cross-section waveguide

Jean-Baptiste Doc, Simon Félix, and Bertrand Lihoreau

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. 2528-2532 (2013); (5 pages)

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A one-way approximation is investigated for the computation of wave propagation in varying cross-section waveguides. The proposed method derives as a basic approximation of the extensively studied multimodal admittance method. When integrated with a Magnus scheme, this matrix one-way equation exhibits an unexpected behavior, as the deviation from the exact solution is minimum when only two discretization points per wavelength are taken. This peculiar property makes this method efficient to compute the wave propagation for a large variety of geometries, beyond the initially stated framework of weakly non-uniform waveguides.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Fn Scattering of acoustic waves
43.28.En Interaction of sound with ground surfaces, ground cover and topography, acoustic impedance of outdoor surfaces
43.30.Bp Normal mode propagation of sound in water
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Experimental verification of transient nonlinear acoustical holography

Yun Jing, Jonathan Cannata, and Tianren Wang

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. 2533-2540 (2013); (8 pages)

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This paper presents an experimental study on nonlinear transient acoustical holography. The validity and effectiveness of a recently proposed nonlinear transient acoustical holography algorithm is evaluated in the presence of noise. The acoustic field measured on a post-focal plane of a high-intensity focused transducer is backward projected to reconstruct the pressure distributions on the focal and a pre-focal plane, which are shown to be in good agreement with the measurement. In contrast, the conventional linear holography produces erroneous results in this case where the nonlinearity involved is strong. Forward acoustic field projection was also carried out to further verify the algorithm.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography

Interaction of torsional and longitudinal guided waves in weakly nonlinear circular cylinders

Yang Liu, Ehsan Khajeh, Cliff J. Lissenden, and Joseph L. Rose

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. 2541-2553 (2013); (13 pages)

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The nonlinear forcing terms for the wave equation in general curvilinear coordinates are derived based on an isotropic homogeneous weakly nonlinear elastic material. The expressions for the nonlinear part of the first Piola-Kirchhoff stress are specialized for axisymmetric torsional and longitudinal fundamental waves in a circular cylinder. The matrix characteristics of the nonlinear forcing terms and secondary mode wave structures are manipulated to analyze the higher harmonic generation due to the guided wave mode self-interactions and mutual interactions. It is proved that both torsional and longitudinal secondary wave fields can be cumulative by a specific type of guided wave mode interactions. A method for the selection of preferred fundamental excitations that generate strong cumulative higher harmonics is formulated, and described in detail for second harmonic generation. Nonlinear finite element simulations demonstrate second harmonic generation by T(0,3) and L(0,4) modes at the internal resonance points. A linear increase of the normalized modal amplitude ratio A2/A12 over the propagation distance is observed for both cases, which indicates that mode L(0,5) is effectively generated as a cumulative second harmonic. Counter numerical examples demonstrate that synchronism and sufficient power flux from the fundamental mode to the secondary mode must occur for the secondary wave field to be strongly cumulative.
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43.25.Dc Nonlinear acoustics of solids
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Yb Ultrasonic instrumentation and measurement techniques
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Acoustic properties of low growing plants

Kirill V. Horoshenkov, Amir Khan, and Hadj Benkreira

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. 2554-2565 (2013); (12 pages)

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The plane wave normal incidence acoustic absorption coefficient of five types of low growing plants is measured in the presence and absence of soil. These plants are generally used in green living walls and flower beds. Two types of soil are considered in this work: a light-density, man-made soil and a heavy-density natural clay base soil. The absorption coefficient data are obtained in the frequency range of 50–1600 Hz using a standard impedance tube of diameter 100 mm. The equivalent fluid model for sound propagation in rigid frame porous media proposed by Miki [J. Acoust. Soc. Jpn. (E) 11, 25–28 (1990)] is used to predict the experimentally observed behavior of the absorption coefficient spectra of soils, plants, and their combinations. Optimization analysis is employed to deduce the effective flow resistivity and tortuosity of plants which are assumed to behave acoustically as an equivalent fluid in a rigid frame porous medium. It is shown that the leaf area density and dominant angle of leaf orientation are two key morphological characteristics which can be used to predict accurately the effective flow resistivity and tortuosity of plants.
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43.28.En Interaction of sound with ground surfaces, ground cover and topography, acoustic impedance of outdoor surfaces
43.20.El Reflection, refraction, diffraction of acoustic waves
43.50.Gf Noise control at source: redesign, application of absorptive materials and reactive elements, mufflers, noise silencers, noise barriers, and attenuators, etc.
43.20.Bi Mathematical theory of wave propagation

Influence of a forest edge on acoustical propagation: Experimental results

Michelle E. Swearingen, Michael J. White, Patrick J. Guertin, Donald G. Albert, and Arnold Tunick

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. 2566-2575 (2013); (10 pages)

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Acoustic propagation through a forest edge can produce complicated pressure time histories because of scattering from the trees and changes in the microclimate and ground parameters of the two regions. To better understand these effects, a field experiment was conducted to measure low-frequency acoustic pulses propagating in an open field, a forest, and passing through a forest edge in both directions. Waveforms measured in the open field were simple impulses with very low scattering, whereas waveforms at the edge and within the forest had stronger reverberations after the direct arrival. The direct wave pulse shapes increased in duration in accordance with the path length in the forest, which had an effective flow resistivity math to math that of the grassy open field. The measurements exhibit different rates of attenuation in the two regions, with relatively lower attenuation in the open field than higher rates in the forest. Decay of SEL transmitted into the forest was 4 dB more per tenfold distance than for outbound transmission. Stronger attenuation in the 1–2 kHz range occurs when propagating into the forest. While the measured meteorological profiles revealed three distinct microclimates, meteorological effects are not sufficient to explain the apparent non-reciprocal propagation.
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43.28.En Interaction of sound with ground surfaces, ground cover and topography, acoustic impedance of outdoor surfaces
43.28.Lv Statistical characteristics of sound fields and propagation parameters
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The depth-dependence of rain noise in the Philippine Sea

David R. Barclay and Michael J. Buckingham

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. 2576-2585 (2013); (10 pages)

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During the Philippine Sea experiment in May 2009, Deep Sound, a free-falling instrument platform, descended to a depth of 5.1 km and then returned to the surface. Two vertically aligned hydrophones monitored the ambient noise continuously throughout the descent and ascent. A heavy rainstorm passed over the area during the deployment, the noise from which was recorded over a frequency band from 5 Hz to 40 kHz. Eight kilometers from the deployment site, a rain gauge on board the R/V Kilo Moana provided estimates of the rainfall rate. The power spectral density of the rain noise shows two peaks around 5 and 30 kHz, elevated by as much as 20 dB above the background level, even at depths as great as 5 km. Periods of high noise intensity in the acoustic data correlate well with the rainfall rates recovered from the rain gauge. The vertical coherence function of the rain noise has well-defined zeros between 1 and 20 kHz, which are characteristic of a localized source on the sea surface. A curve-fitting procedure yields the vertical directional density function of the noise, which is sharply peaked, accurately tracking the storm as it passed over the sensor station.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field

Observations of shallow water marine ambient sound: The low frequency underwater soundscape of the central Oregon coast

Joseph H. Haxel, Robert P. Dziak, and Haru Matsumoto

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. 2586-2596 (2013); (11 pages)

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A year-long experiment (March 2010 to April 2011) measuring ambient sound at a shallow water site (50 m) on the central OR coast near the Port of Newport provides important baseline information for comparisons with future measurements associated with resource development along the inner continental shelf of the Pacific Northwest. Ambient levels in frequencies affected by surf-generated noise (f < 100 Hz) characterize the site as a high-energy end member within the spectrum of shallow water coastal areas influenced by breaking waves. Dominant sound sources include locally generated ship noise (66% of total hours contain local ship noise), breaking surf, wind induced wave breaking and baleen whale vocalizations. Additionally, an increase in spectral levels for frequencies ranging from 35 to 100 Hz is attributed to noise radiated from distant commercial ship commerce. One-second root mean square (rms) sound pressure level (SPLrms) estimates calculated across the 10–840 Hz frequency band for the entire year long deployment show minimum, mean, and maximum values of 84 dB, 101 dB, and 152 dB re 1 μPa.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field
43.80.Nd Effects of noise on animals and associated behavior, protective mechanisms
43.30.Sf Acoustical detection of marine life; passive and active

Reconstructing surface wave profiles from reflected acoustic pulses

Sean P. Walstead and Grant B. Deane

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. 2597-2611 (2013); (15 pages)

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Surface wave shapes are determined by analyzing underwater reflected acoustic signals. The acoustic signals (of nominal frequency 200 kHz) are forward scattered from the underside of surface waves that are generated in a wave tank and scaled to model smooth ocean swell. An inverse processing algorithm is designed and implemented to reconstruct the surface displacement profiles of the waves over one complete period. The inverse processing uses the surface scattered pulses collected at the receiver, an initial wave profile (two are considered), and a broadband forward scattering model based on Kirchhoff's diffraction formula to iteratively adjust the surface until it is considered optimized or reconstructed. Two physical length scales over which information can be known about the surface are confirmed. An outer length scale, the Fresnel zone surrounding each specular reflection point, is the only region where optimized surfaces resulting from each initial profile converge within a resolution set by the inner length scale, a quarter-wavelength of the acoustic pulse. The statistical confidence of each optimized surface is also highest within a Fresnel zone. Future design considerations are suggested such as an array of receivers that increases the region of surface reconstruction by a factor of 2 to 3.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.30.Hw Rough interface scattering
43.60.Rw Remote sensing methods, acoustic tomography

Probabilistic two-dimensional water-column and seabed inversion with self-adapting parameterizations

Jan Dettmer and Stan E. Dosso

J. Acoust. Soc. Am. Volume 133, Issue 5, pp. 2612-2623 (2013); (12 pages)

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This paper develops a probabilistic two-dimensional (2D) inversion for geoacoustic seabed and water-column parameters in a strongly range-dependent environment. Range-dependent environments in shelf and shelf-break regions are of increasing importance to the acoustical-oceanography community, and recent advances in nonlinear inverse theory and sampling methods are applied here for efficient probabilistic range-dependent inversion. The 2D seabed and water column are parameterized using highly efficient, self-adapting irregular grids which intrinsically match the local resolving power of the data and provide parsimonious solutions requiring few parameters to capture complex environments. The self-adapting parameterization is achieved by implementing the irregular grid as a trans-dimensional hierarchical Bayesian model with an unknown number of nodes which is sampled with the Metropolis-Hastings-Green algorithm. To improve sampling, population Monte Carlo is applied with a large number of interacting parallel Markov chains with adaptive proposal distributions. The inversion is applied to simulated data for a vertical-line array and several source locations to several kilometers range. Complex acoustic-pressure fields are computed using a parabolic equation model and results are considered in terms of 2D ensemble parameter estimates and credibility intervals.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.60.Pt Signal processing techniques for acoustic inverse problems
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.60.Rw Remote sensing methods, acoustic tomography
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