bluuebunny/crossref_metadata_2025 huggingface dataset:
Utilizing head movements in the binaural assessment of room acoustics and analysis of complex sound source scenarios
Authors: Braasch Jonas , Parks Anthony , Pastore Torben , Clapp Samuel W.
Published: September 2012

The measurement of transfer functions is currently standard practice for the acoustic evaluation of performance venues. The pathway between a measurement loudspeaker and a microphone or binaural manikin in a room can be treated as a linear time-invariant system, and meaningful acoustical parameters can be derived from measured impulse responses. Unfortunately, this method neglects that human listeners typically move their heads when exploring an acoustic venue. This paper addresses these implications when designing systems to take head movement into account. A number of approaches will be discussed based on existing research and technology at Rensselaer, including a binaural manikin with a motorized head, a technique to simulate head movements from impulse responses recorded with a higher-order spherical microphone, and a binaural model that can process head movements. The model distinguishes between a room coordinate system and a head-related coordinate system. Its binaural activity map is rotated with head movements in order to separate front-back images, resolve the reverberation-reduced angle of lateral sound sources, assess different surround loudspeaker configurations for immersive sound systems, and separate acoustic sources. The research presented here has received support from the National Science Foundation under Grant No. 1002851.
Reciprocal binaural room impulse response measurements
Authors: Klein Johannes , Pollow Martin , Fels Janina , Vorlaender Michael
Published: September 2012

Multi-channel spherical loudspeakers have been introduced in shapes of cubes, dodecahedra, or higher-order discrete representations of spheres. In this contribution a spherical source with a partial Gaussian distribution of 28 channels is presented. With sequential measurements and rotation of the sphere a radiation of effectively 23rd order of spherical harmonics can be obtained. Accordingly directional patterns of not only sound sources but also of receivers such as HRTF can be modeled in detail up to quite high frequencies. The high order of spherical harmonics allows investigation of individual differences of pinna cues. When applied in a reciprocal measurement of room impulse responses in performance venues, an almost perfect omnidirectional microphone on the stage and an HRTF source in the audience can be used to study spatial room acoustic parameters such as early lateral energy fractions, late lateral strength and IACC of dummy heads and individuals. This is obtained by post processing of just one set of multi-channel impulse responses in the venue. Opportunities and challenges of this approach will be discussed.
Measuring and inferring the directional properties of the early room response
Authors: Botts Jonathan , Clapp Samuel , Xiang Ning , Braasch Jonas
Published: September 2012

In an effort to understand the response of a room more completely, spherical microphone arrays have been used to produce a three-dimensional map of a room impulse response. To locate reflections from various room surfaces, the most common approach is to search for peaks in the beamformed response. Particularly when using this approach with a low-order array there is no way to distinguish a side-lobe from an additional arrival. Furthermore, overlapping arrivals skew the maxima of beampatterns, resulting in incorrect inferences. This talk seeks to demonstrate that a Bayesian, model-based analysis of the data addresses the complete problem of image source estimation, with mechanisms to determine the number and locations of simultaneous arrivals. Particularly with low-order arrays, substantially more accurate estimates can be made, which both increases the overall quality of the analysis and extends the portion of the impulse response that may be reliably analyzed.
Source locations, listener locations, and measurement devices when making acoustical measurements in performance spaces
Authors: Lamour Elizabeth
Published: September 2012

Does the location of the source affect the results of an acoustical measurement? This is the question that sparked the author’s Master’s Project which explores the differences between measurements taken with a source located on the stage of a performance space and a source located higher above the stage using the space’s existing sound system. Impulse responses were gathered from four different performance halls with respect to source location, microphone location, and measurement devices used. Comparisons were made between trends in reverberation time, early decay time, and interaural cross-correlation coefficient. The results are not only interesting, but they also question the typical measurement practices of acousticians and confirm assumptions made regarding important acoustical characteristics of performance spaces.
Autonomous detection of neotropical sciaenid fishes
Authors: Ruiz-Blais Sebastian , Rivera-Chavarria Mario R. , Camacho Arturo
Published: September 2012

Sciaenid passive acoustics are a demonstrated valuable tool for fisheries management. In spite of this, an efficient software tool to detect and identify fish sounds is not currently available. Such tool would be useful for autonomous recognition and array methodologies. For Neotropical environments this lack is even more conspicuous since the availability of corroborated sciaenid sounds is limited. We are developing such tools using corroborated Cynoscion squamipinnis (Pisces: Sciaenidae) sounds. Our approach is based on timbre statistics, short and long-term partial loudness, and the 30 Hz typical pattern found on the signal's stridulations. Relevant fish drums are detected through empirically found fix thresholds for the timbre statistics and the 30 Hz pattern, and a dynamic threshold established by an unsupervised algorithm based on the long-term loudness. Current results show a recognition rate of 80%. Despite these promising numbers, there are still challenges ahead. In the future, we plan to incorporate other variables that affect underwater sound characteristics such as depth, source level distance, and physical chemical properties, which may be crucial to make a user friendly, accurate, and practical tool, for neotropical marine environmental managers. We also plan to extend this method to other soniferous coastal fish.
Fish recordings from NEPTUNE Canada
Authors: Sirovic Ana , Brandstatter Sophie , Hildebrand John A.
Published: September 2012

NEPTUNE Canada is a regional-scale ocean observing system deployed off the west coast of Vancouver Island, Canada. Among the data streams broadcast live over the internet are video collected using black and white low-light camera and audio collected with Naxys hydrophone (5 - 3,000 Hz). These data allow for description of sound production by fishes in the vicinity of the system. Concurrent video and hydrophone data are available from the Barkley Canyon node (~900 m depth). While the hydrophone recordings were continuous, strobes for video are only turned on during short, irregular (~10 min) intervals. Approximately 30 h of concurrent video and audio recordings were analyzed. The most commonly seen fish was sablefish (Anoplopoma fimbria), and the most common fish-like sound was a broadband, short pulse that occurred on nearly half of the recordings. On approximately one-fifth of concurrent video and audio recordings both sablefish and fish-like pulsed sounds were detected. It may be possible to use these sounds to monitor sablefish abundance across the northeastern Pacific Ocean. NEPTUNE Canada Data Archive, http://www.neptunecanada.ca, hydrophone and video data from May, June, August, and December 2010 and January and February 2011, Oceans Networks Canada, University of Victoria, Canada. Downloaded 2012.
Rationale behind the Iterative Nonlinear Contrast Source method
Authors: Verweij Martin D. , Demi Libertario , van Dongen Koen
Published: September 2012

Modern medical echoscopy increasingly relies on imaging modalities that exploit the features of nonlinear ultrasound. The development of these modalities and corresponding dedicated transducers requires accurate simulations of pulsed nonlinear acoustic wave fields in realistic biomedical situations. This involves nonlinear media with frequency power law attenuation and spatially dependent acoustic properties. Simulations frequently concern strongly steered beams, hundreds of wavelengths long, and their grating lobes. The Iterative Nonlinear Contrast Source (INCS) method is a full-wave method that has been developed for this purpose. It treats the nonlinear term in the Westervelt equation as a contrast source that operates, alongside other source terms, in a homogeneous linear ‘background’ medium. The background Green’s function is known analytically, and convolution with the source terms yields an integral equation. This is solved iteratively to obtain the nonlinear pressure field. The convolution over the four-dimensional computational domain is performed with FFT’s, and a grid with only two points per wavelength suffices due to prior filtering of the involved quantities. The present talk elaborates on the characteristic steps of the INCS method, i.e. the contrast source formulation and the filtered convolution. Comparisons with other methods will be made, and recent developments will be presented.
Validation of time-domain and frequency-domain calculations of acoustic propagation from breast models derived from magnetic resonance images
Authors: Hesford Andrew J. , Tillett Jason C. , Astheimer Jeffrey P. , Waag Robert C.
Published: September 2012

Magnetic resonance images with an isotropic resolution of 200 microns were collected for two human breast specimens. The images were interpolated to achieve a resolution of 50 microns and segmented to produce images of skin, fat, muscle, ductal structures, and connective tissues in consultation with a breast pathologist. The images were then mapped to acoustic parameters of sound speed, absorption and density. Calculations of acoustic propagation of fields radiated by point sources outside of the specimens were performed using the k-space finite-difference time-domain method and the frequency-domain fast multipole method. Time-domain k-space results were Fourier transformed and the 3-MHz component was compared to 3-MHz frequency-domain calculations. For the first model, measuring 1180 × 1190 × 290 voxels, the two methods were found to agree in a representative coronal slice to within 5.0% (RMS). The second specimen, comprising 1350 × 1170 × 790 voxels, yielded temporal and frequency-domain results that agreed to within 5.8% (RMS) in a representative coronal slice. Comparable results were obtained in other planes orthogonal to the representative slices. The close agreement establishes confidence in the accuracy of the methods when simulating propagation through large, complicated, realistic models of human tissue.
High-order numerical methods for nonlinear acoustics: A Fourier Continuation approach
Authors: Albin Nathan
Published: September 2012

Dispersion errors, which result from the use of low-order numerical methods in wave-propagation and transport problems, can have a devastating impact on the accuracy of acoustic simulations. These errors are especially problematic in settings containing nonlinear acoustic waves that propagate many times their fundamental wavelength. In these cases, the use of high-order numerical schemes is vital for the accurate and efficient evaluation of the acoustic field. We present a class of high-order time-domain solvers for the treatment of nonlinear acoustic propagation problems. These solvers are based on the Fourier Continuation method, which produces rapidly-converging Fourier series expansions of non-periodic functions (thereby avoiding the Gibbs phenomenon), and are capable of accurately and efficiently simulating nonlinear acoustic fields in large, complex domains.
Nonlinear modeling as a metrology tool to characterize high intensity focused ultrasound fields
Authors: Khokhlova Vera , Yuldashev Petr , Kreider Wayne , Sapozhnikov Oleg , Bailey Michael , Crum Lawrence
Published: September 2012

High intensity focused ultrasound (HIFU) is a rapidly growing medical technology with many clinical applications. The safety and efficacy of these applications require accurate characterization of ultrasound fields produced by HIFU systems. Current nonlinear numerical models based on the KZK and Westervelt wave equations have been shown to serve as quantitatively accurate tools for HIFU metrology. One of the critical parts of the modeling is to set a boundary condition at the source. In previous studies we proposed using measurements of low-amplitude fields to determine the source parameters. In this paper, two approaches of setting the boundary condition are reviewed: The acoustic holography method utilizes two-dimensional scanning of pressure amplitude and phase and numerical back-propagation to the transducer surface. An equivalent source method utilizes one-dimensional pressure measurements on the beam axis and in the focal plane. The dimensions and surface velocity of a uniformly vibrating transducer then are determined to match the one-dimensional measurements in the focal region. Nonlinear simulations are performed for increasing pressure levels at the source for both approaches. Several examples showing the accuracy and capabilities of the proposed methods are presented for typical HIFU transducers with different geometries. [Work supported by NIH EB007643.]
Dual-time-scale method for modeling of the nonlinear amplitude-modulated ultrasound fields
Authors: Dontsov Egor , Guzina Bojan
Published: September 2012

This study focuses on modeling of the nonlinear acoustic wave propagation in situations when the amplitude of the focused ultrasound field is modulated by a low-frequency signal. This problem is relevant to both ultrasound imaging applications entailing the use of the acoustic radiation force, and treatment applications such as histotripsy. The difficulty of predicting the pressure wavefield lies in a fact that the excessive length of the low-frequency modulated signal may significantly increase the computational effort. To tackle the problem, this study utilizes the dual-time-scale approach, where two temporal variables are introduced to distinguish between ultrasound-scale and modulation-scale variations. In this case, the Westervelt-type equation can be effectively solved using hybrid time-frequency algorithm for any transient (sufficiently smooth) modulation envelope. To validate the proposed approach, the Khokhlov-Zabolotskaya-Kuznetsov equation was solved in the time domain for an example pressure profile on the boundary. A comparison between the time-domain and hybrid calculations demonstrates that the latter are notably faster, require significantly less memory, and have satisfactory accuracy for the ratios between the modulation and carrier ultrasound frequencies below 0.1.
Evaluating transducer bandwidth and effectiveness on overall acoustic system performance
Authors: Bachand Corey L. , Brown David A. , Aronov Boris
Published: September 2012

Piezoelectric ceramic cylindrical transducers are used extensively for underwater acoustic communication applications on mobile platforms (UUVs). Employing piezoelectric single crystals, used in either fully-active or active-passive segmented cylinders, in the transducer design has the potential to increase the usable bandwidth while reducing the overall size and weight of the device. In some instances, one single crystal transducer may replace several ceramic transducers and reduce the number of hardware channels. The impact on acoustic system design (power amplifier, matching transformer, and tuning network) for several piezoelectric ceramic and single crystal cylindrical transducer technologies is modeled and supported with measured transducer data.
High intensity air ultrasound source for determining ultrasound microphone sensitivity up to 400 kHz
Authors: Campanella Angelo J.
Published: September 2012

A broadband air jet ultrasound source, RSS101U-H, for animal bioacoustics research produces broadband ultrasound to at least 400 kHz. Free field reciprocity calibration of ½” condenser microphones on-axis, grid caps removed, using sine wave excitation by the method of Rudnick and Stein [JASA 20, pp 818-825, (1948)] was made (previously used to 280 kHz [JASA 67, p 7, (1980)]). Measurement from 5 kHz to 100 kHz was made in 1 kHz bins via an FFT analyzer. A communications receiver was used from 40 kHz to 400 kHz. The sensitivity of a ¼” microphone was determined from the free field of the reciprocity ½” microphone source. Air jet ultrasound level at 80 mm distance was then determined with the ¼“ microphone. Communications receiver 2.5 kHz bandwidth data was reduced to 1 kHz bin values. Air humidity sound absorption was determined via ANSI 1.26. The ¼” microphone sensitivity and broadband source sound level results in 1 kHz bands to 400 kHz are presented. Air jet spectral level was 97 dB re 20 uPa @ 75 kHz to 57 dB @ 400 kHz. This can be used to rapidly determine the sensitivity of any air ultrasound microphone over this frequency range.
25 years of distance education in acoustics
Authors: Russell Daniel A. , Sparrow Victor W.
Published: September 2012

Online education is quickly becoming a popular means of delivering course content to the masses. Twenty-five years ago this Fall, the Graduate Program in Acoustics at Penn State began offering graduate level instruction in acoustics to students at a distance. In 1987 courses were offered via satellite links to Navy and industry labs, with PictureTel video conferencing to two centralized locations added in 1992. By 1994 videotapes allowed for broader content distribution to students at more varied locations. In 2002 videostreaming lectures over the internet expanded the delivery even further. Currently courses are taught to a blended audience of both resident and distance students, with lectures being live streamed over the internet and archived digitally for offline access. This talk will briefly summarize the history and development of online graduate education in acoustics at Penn State. We will discuss the use of technology both as a tool for delivering course content as well as the impact that technology has on the quality and means of instruction and the interaction between teacher and students. The necessary adaptation of teaching styles and the adjustments required to meet the varied needs of a blended student audience will also discussed.
Teaching graduate level acoustics courses to a blended enrollment of resident and distance education students
Authors: Russell Daniel A.
Published: September 2012

The Graduate Program in Acoustics offers courses leading to the M.Eng. in Acoustics online through Penn State’s World Campus. The current method of course content delivery is to live-stream (with digital video archive) lectures to a blended student audience consisting of about 10-15 resident students physically present in the classroom and another 15-20 students at a distance who may be watching the class live, or who may be viewing the archived recording afterward. This paper will explore several issues involving the engagement of this blended audience of students. How does one encourage and enable students with a broad range of backgrounds, interests, and physical locations to engage with the topic material? How does one foster collaboration and interaction between distance students and the teacher and between resident and distance students? How does one manage office hours, help sessions, group projects, experiments, and student presentations for a blended student audience? Current practice and personal experiences from our faculty will be shared, and ideas from the audience will be welcomed.
Relevance and applicability of the soundscape concept to physiological or behavioral effects caused by noise at very low frequencies which may not be audible
Authors: Bray Wade
Published: September 2012

A central tenet of the Soundscape concept is that humans immersed in sonic environments are objective measuring instruments (New Experts), whose reports and descriptions must be taken seriously and quantified by technical measurements. A topic category in acoustics meetings of recent years is “Perception and Effects of Noise.” There is growing evidence from the field, and from medical research, that the ear’s two-part transducer activity involving inner hair cells (IHC, hearing, velocity-sensitive) and outer hair cells (OHC, displacement-sensitive) may, through demonstrated OHC activation and neural signals at up to 40 dB below the audibility threshold, produce behavioral and physiological effects as reported by a growing number of people. The Soundscape concept centering on human responses, New Experts, is as important and applicable to responses to effects from sound as it is to responses to directly audible sound. In a wider sense, this is a new sound quality and psychoacoustic issue.
Sound preference prediction in a design stage—A case study in the Shenzhen Dongmen Open Space
Authors: Yu Lei
Published: September 2012

Attention on visual effects is insufficient in urban open spaces, while soundscape is complementation and sound design is crucial. In this paper, sound effects in the Shenzhen Dongmen Open Space have been studied. It shows that exist sounds are not delightful to satisfy acoustic comfort but to cause annoy perceptions. Therefore, this study is focused on examining various sound effects in the Shenzhen Dongmen Open Space concerning on sound preference evaluations. Based on various sounds influencing the subjective preference evaluations, Artificial Neural Network (ANN) models have been developed to predict how delightful of the sonic environment in terms of different sound design schemes to the space. Furthermore, the sound preference predictions of ANN models' output will be compared with the preference evaluations from lab experiments, and then validated by the lab results.
Psychoacoustic assessment of a new aircraft engine fan noise synthesis method
Authors: Okcu Selen , Allen Matthew P. , Rizzi Stephen A.
Published: September 2012

Simulation of aircraft flyover events can facilitate psychoacoustic studies exploring the effects of noise generated by future aircraft designs. The perceived realism of a simulated flyover event may be impacted by the perceived realism of the synthesized fan noise of the aircraft engine. Short-term fluctuations in tonal amplitude and frequency are important cues contributing to that perception of realism, but are not accounted for by predictions based on long-term averages. A new synthesis method has been developed at NASA Langley Research Center to generate realistic aircraft engine fan noise using predicted source noise directivities in combination with short-term fluctuations. In the new method, fluctuations in amplitude and frequency are included based upon analysis of static engine test data. Through psychoacoustic testing, this study assessed perceived effectiveness of the new synthesis method in generating realistic fan noise source. Realism was indirectly assessed by judging the similarity of synthesized sounds (with and without fluctuations) with recordings of fan noise. Results of ANOVA analyses indicated that subjects judged synthesized fan noise with fluctuations as being more similar to recordings than synthesized fan noise without fluctuations.
A geospatial model of ambient sound pressure levels in the continental United States
Authors: Mennitt Dan , Fristrup Kurt M. , Sherrill Kirk
Published: September 2012

There has been much effort in the US and worldwide to measure, understand and manage natural soundscapes which are often complex due to a multitude of biological, geophysical, and anthropogenic influences. The sound pressure level is a time and space varying quantity that represents the aggregate of present sources. This work presents a predictive model relating seasonal sound pressure levels to geospatial features such as topography, climate, hydrology and anthropogenic activity. The model utilizes random forest, a tree based machine learning algorithm, which does not explicitly incorporate any apriori knowledge of acoustic propagation mechanics. The response data encompasses 271,979 hours of acoustical measurements from 192 unique sites located in National Parks across the contiguous United States. Cross validation procedures were used to evaluate model performance and identify GIS explanatory variables with predictive power. Using the model, the effect of individual explanatory variables on sound pressure level can be isolated and quantified revealing trends across environmental gradients. An example application of projecting predicted sound pressure levels across the Olympic peninsula is discussed. Because many wildlife habitats, geological processes, and anthropogenic impacts occur on a regional scale, the extent of acoustical analyses must be on similar scales.
Modeling of transcranial ultrasound for therapeutic and diagnostic applications
Authors: Clement Gregory T.
Published: September 2012

Ultrasound’s use in the brain has conventionally been limited by its inability to penetrate the skull. To overcome these limits, we have been investigating techniques to maximize energy transfer and minimize distortion through the skull bone. These model-based aberration correction approaches - now in the early stages of clinical testing - rely on both practical and accurate numeric methods. Efforts to improve these methods necessitate an increasingly detailed consideration of skull heterogeneity. To facilitate this numerically-intensive problem, we are utilizing an inhomogeneous pressure simulation code, based on a pseudo-spectral solution of the linearized wave equation. Forward and scattered waves are determined over a pre-specified volume with scattering determined by the impedance mismatch between a given voxel and regional points in the projection plane. The total forward-scattered pressure is recorded over the relevant k-space, while reflected energy is processed in a separate backward projection. This process is repeated iteratively along the forward projection plane until the volume of interest has been traversed. This procedure can be repeated an arbitrary number of times N, representing N-1 order scattering. Abilities and limitations of the method will be demonstrated by comparison with FDTD simulation.
Ultrasound assessment of bone with ultrasound: Present and future
Authors: Laugier Pascal
Published: September 2012

Bone is a composite, porous and anisotropic material whose complex hierarchical structure extends over several levels of organization from the nanoscale to the macroscopic scale. One of the striking features of this tissue is its ability to adapt to variable loading conditions. This results in spatially, temporally and directionally variable elastic properties leading to a perfect adaptation to locally varying functional demands. Elastic properties of bone are nowadays widely used in fundamental studies, in conjunction with numerical models, to investigate the structure-function relationships and in clinical applications to predict fracture risk or to monitor fracture healing. However, the problem of multiscale assessment of bone elastic properties, spanning the full range of applications from in vitro to in vivo applications, remains a challenge. Novel emerging quantitative ultrasound technologies, taking benefit of the scalability of ultrasound, have emerged to noninvasively investigate elastic properties at multiple organization level. These include scanning acoustic microscopy, ultrasonic resonant spectroscopy and guided waves propagation. These techniques will be presented to show how they can help in characterizing the anisotropic stiffness tensor in vitro or determine bone properties in vivo. Relationships of quantitative ultrasound variables with structural and elastic alterations will be illustrated through multiple examples.
Ultrasonic measurements of clays and silts suspended in water
Authors: Carpenter Wayne O. , Wren Daniel G. , Kuhnle Roger A. , Chambers James P. , Goodwiller Bradley T.
Published: September 2012

Ongoing work at the National Center for Physical Acoustics is aimed at using acoustics to provide monitoring for fine sediments suspended in water. The ultimate goal of the work is to field an acoustic instrument that can monitor fine particle concentration in rivers and streams. Such an instrument would have several advantages over currently available technologies. Expanding upon work from Carpenter et. al (2009), two immersion transducers were placed at a fixed distance to measure attenuation and backscatter from acoustic signals at 10 MHz and 20 MHz propagated through clays (bentonite, illite, and kaolinite) and silt. The resulting data set encompasses a wide range of concentrations (0.01 - 14 g/L) and particle sizes (0.1 - 64 micron diameter particles). Backscatter and attenuation curves for each material across the range of concentrations will be shown and compared to the theoretical attenuation curves developed by Urick (1948). This work has produced a data set for model development using a combination of backscatter and attenuation to allow for single-frequency discrimination between clay and silt particles suspended in water.
Acoustic wave propagation in a channel bifurcated by an elastic partition
Authors: Aho Katherine , Thompson Charles
Published: September 2012

Linear wave propagation in a narrow channel that is axially partitioned by a flexible membrane is examined. The enclosed fluid is excited by the time harmonic displacement in the channel cross-section. The axial variation in the acoustic impedance of the partition gives rise to the generation of evanescent modes in the channel. The effect of these evanescent modes on the vibration of the membrane is of particular interest. It is shown that in the limit of high channel aspect ratio one can model these modes by an effective source distribution along the surface of the membrane. The asymptotic analysis of the source distribution is presented. (NSF Grant 0841392)
Multi-frequency modes in dispersive media
Authors: Dolder Craig N. , Wilson Preston S.
Published: September 2012

A common phenomenon in acoustics is the existence of multiple eigenfunctions (mode shapes) corresponding to the same eigenvalue (frequency), which is known as degeneracy. In highly dispersive media the opposite can occur, whereby a single eigenfunction corresponds to multiple eigenvalues. Several ways to visualize the source of, and interpret the physical meaning of, this phenomenon are presented. Instances of this phenomenon occurring in analytical models and experiments are used as examples.
Estimating the acoustic impedance of the ground using signals recorded by a 3D microphone array
Authors: Alberts W. C. Kirkpatrick
Published: September 2012

In applications where there is a need to accurately classify impulsive acoustic events, the impedance of the ground can significantly alter the reflected wave such that the superimposed direct and reflected waves could lead to erroneous classifications. If the phase and amplitude changes attributable to impedance ground are considered, knowledge of the ground impedance near every array site can mitigate classification errors caused by impedance ground. Under controlled experimental conditions, the ground impedance in the vicinity of an array can be deduced using standard methods. However, when an array is fielded in an uncontrolled environment, alternative ground impedance estimation techniques must be explored. Soh et al. [J. Acoust. Soc. Am, 128(5), 2010] demonstrated that the impedance of the ground could be directly determined using a pair of vertically spaced microphones and an impulsive source 400 m from the microphones. With some increase in complexity, this direct method of determining ground impedance can be applied to recordings from typical three dimensional acoustic arrays. Estimates of the acoustic ground impedance obtained directly from recordings by microphones distributed in a 1 m radius tetrahedral array will be discussed.
Evaluating duplex microstructures in polycrystalline steel with diffuse ultrasonic backscatter
Authors: Du Hualong , Turner Joseph A.
Published: September 2012

The performance of metallic components is governed in large part by the microstructure of the base material from which the component is manufactured. In this presentation, diffuse ultrasonic backscatter techniques are discussed with respect to their use for monitoring the microstructure of polycrystalline steel as a result of the manufacturing process. To improve the mechanical properties, the surface of polycrystalline steel is quenched, a process which transforms the initial phase to a pearlite phase within grains. A diffuse ultrasonic backscatter model is developed that includes the duplex microstructure through the addition of an additional length scale in the two-point spatial correlation function. This function defines the probability that two randomly chosen points will fall into the same grain and/or same crystallite. The model clearly shows the dependence of the diffuse ultrasonic backscatter signal with respect to frequency, average grain size and lamellar spacing of the crystallites. Experimental results are used to show how the two length scales can be extracted from the measurements. The spatial variation of the microstructure with respect to depth from the quench surface is also examined. These diffuse ultrasonic techniques are shown to have the sensitivity to deduce the duplex microstructure throughout the sample.
Macro ocean acoustics
Authors: Cox Henry
Published: September 2012

Today, physical insight based on fundamental principles and invariants frequently gives way to precise computations based on sophisticated models with less than perfect inputs. In the spirit of Preston W. Smith it is appropriate to revisit what can inferred from the sound speed profile and simple power flux reasoning without extensive computations. For example, based on the sound speed profile, the angle at the axis, the turning depths, the grazing angles at the surface and bottom, ray angle diagrams, the cycle length, cycle time, the group velocity, the adiabatic invariant and the so-called shallow water invariant all can be parameterized in terms of the phase velocity of each mode or ray. Applications of Preston’s ideas to ambient noise near the bottom on the deep ocean, coherence and interference patterns will be discussed.
Beam broadening for planar transmit arrays with maximal transmit power constraint
Authors: Berkman Evan F.
Published: September 2012

Broad active sonar transmit beamwidth enables wide sector search. Many active search sonars attain wide transmit beamwidth by virtue of a cylindrical or spherical geometry which provides naturally wide beamwidth when all elements are driven in phase. However, planar array geometry is desired for some applications. Arrays often utilize many elements with resulting aperture large compared to an acoustic wavelength in order to provide high power output. However, planar arrays with aperture large compared to an acoustic wavelength will have naturally narrow beams which cannot be appreciably broadened by conventional amplitude shading without sacrifice of total power output and inefficient use of transducer and power amplifier channels. Maintenance of broad sector coverage over large fractional bandwidth with all element channels fully driven for maximum power output over the entire frequency band is also challenging. Thus, in order to maintain efficiency of element usage a scheme has been developed for obtaining a specified broad transmit array beamwidth invariant over a wide frequency range by frequency dependent phasing of array elements with all elements constrained to uniform amplitude gain. The intuitive physical basis for the phasing scheme is described as well as the mathematical results. A numerical example is provided.
Statistical characterization of multipath sound channels
Authors: Cable Peter
Published: September 2012

Averaged transmission characteristics for underwater sound channels, using energy flux descriptions, were independently introduced and developed by Leonid Brekhovskikh [Sov. Phys.-Acoust. 11, 126-134 (1965)], David Weston [J. Sound Vib. 18, 271-287(1971)], and Preston Smith [J. Acoust. Soc. Am. 50, 332-336 (1971)]. While most attention in these studies was focused on elucidating averaged transmission loss in range dependent environments, Preston, in particular, also examined the application of energy flux techniques to other statistical characterizations of multipath environments, including channel impulse response and spatial coherence. Preston’s incisive physical insight resulted in channel statistical characterizations that were simple to apply, but notably effective for signal processing and sonar studies. My purpose in this talk will be to trace the development of statistical characterizations of multipath channels based on energy flux notions, and to sketch some specific applications of these ideas, such as to source or receiver motion induced acoustic fluctuations.
Preston Smith and NASA Contractor Report CR-160
Authors: Lyon Richard H.
Published: September 2012

When I came from a post-doc in England to BBN in 1960, Preston had already been at BBN for a few years. One of his interests was the interaction of structural resonances and reverberant sound fields. He had found that if the damping of the structure were to vanish, the response would not diverge, but reach a limit proportional to the sound pressure alone, independent of structural parameters. It turned out that this limit corresponded to modal energy equality between the sound field and the structure and was consistent with work I had done at Manchester on the energy flow between resonators. The combination of the two approaches was the beginning of SEA, presented to the community in "Sound and Structural Vibration, NASA Contractor Report CR-160 by Preston W. Smith Jr. and Richard H. Lyon", March 1965, the first publication on Statistical Energy Analysis (SEA). Interestingly, the words "Statistical Energy Analysis" did not appear in the report, but the ideas and viewpoint were there.
Imaging-based quantitative characterization of fatigue crack for structural integrity monitoring using nonlinear acousto-ultrasonics and active sensor networks
Authors: Su Zhongqing , Zhou Chao , Cheng Li , Hong Ming
Published: September 2012

The majority of today’s damage detection techniques rely substantially on linear macroscopic changes in either global vibration signatures or local wave scattering phenomena. However, damage in real-world structures often initiates from fatigue cracks at microscopic levels, presenting highly nonlinear characteristics which may not be well evidenced in these linear macroscopic changes. It is of great significance but also a great challenge to quantitatively characterize micro-fatigue cracks without terminating the normal operation of an engineering structure. This is a critical step towards automatic and online structural integrity monitoring (SIM). By exploring the nonlinearities of higher-order acousto-ultrasonic (AU) waves upon interaction with fatigue cracks, a damage characterization approach, in conjunction with use of an active piezoelectric sensor network, was established, with the particular capacity of evaluating multiple fatigue cracks at a quantitative level (including the co-presence of multiple cracks, and their individual locations and severities). Identification results were presented in pixelated images using an imaging algorithm, enabling visualization of fatigue cracks and depiction of overall structural integrity in a quantitative, rapid and automatic manner. The effectiveness of the proposed technique was demonstrated by experimentally characterizing multiple fatigue cracks near rivet holes in aluminium plates.
Production of English vowels by speakers of Mandarin Chinese with prolonged exposure to English
Authors: Evanini Keelan , Huang Becky
Published: September 2012

Previous studies of non-native production of English vowels have demonstrated that a native-like attainment of certain distinctions is not guaranteed for all speakers, despite prolonged exposure to the target (e.g., Munro et al. 1996, Flege et al. 1997). The current study examines the applicability of this finding to a group of non-native speakers from the same L1 background (Mandarin Chinese) who are all long-term residents in the USA (7 years minimum) and adult arrivals (> age 18). These non-native speakers (N=36) and a control group of native speakers (N=22) were recorded reading two sets of materials: the Stella paragraph (Weinberg 2012) and five sentences from Flege et al. (1999). Vowel formant measurements were extracted for all tokens from the following three pairs of vowels: [i] ~ [ɪ], [e] ~ [ɛ], and [a] ~ [ʌ]. Euclidean distances between the z-normalized (F1, F2) mean values for the two vowels in each pair for each speaker show that the non-native speakers produce each of the three pairs significantly less distinctly than the native speakers. This finding corroborates previous similar findings and suggests that a speaker's L1 continues to have a strong influence on vowel production, despite long-term exposure to the target.
How tongue posture differences affect reduction in coronals: Differences between Spanish and English
Authors: Parrell Benjamin
Published: September 2012

It has been suggested that both flapping of English coronal stops [e.g. Fukaya & Byrd, JIPA, 2005; De Jong, JPhon, 1998] and spirantization of Spanish voiced stops [e.g. Parrell, LabPhon, 2012] result from reductions in duration. If this is indeed the case, why would reducing duration in one language lead to spirantization (Spanish) and in another to flapping (English)? We suggest that these differences are the result of different ways the tongue is used to attain oral closure in the two languages: in Spanish, coronal stops are made with blade of the tongue at the teeth; in English, with the tongue tip placed at the alveolar ridge. Because of this difference, the tongue tip is oriented differently in the two languages: upward in English and downwards in Spanish, leading to differing articulatory and acoustic outcomes as duration is shortened. We examine these postural differences using tongue movement data, which allows for direct and dynamic examination of tongue posture and shaping of coronals in both languages. Differences between the two languages will be modeled using TaDA [Nam et al., JASA, 2004] to test how they may lead to different articulatory and acoustic outcomes as duration is reduced. [Supported by NIH.]
Perception of American English final consonants by speakers of New York-Dominican Spanish
Authors: Berkowitz Shari S.
Published: September 2012

The English language uses many final consonants and final clusters to convey meaning, especially for morphological endings. The Spanish language employs fewer final consonants than the English language, and Caribbean Spanish speakers treat many final consonants as optional. In this experiment, speakers originating from the Dominican Republic (N = 25) participated in a listening task in which they had to identify final consonants in fast and clear sentences in English (stimulus corpus Ito, K, 2011). A small group of native American English speakers was tested, and performed at ceiling. Spanish-speaking participants' performance on the experimental task varied from 40% to native-like accuracy and was statistically different from the native speakers’ performance (Mann Whitney U = 8, p < .003). In addition, Spanish-speaking pariticpants’ performance on the final consonant perception task correlated strongly with performance on a standardized aural/oral language battery known as the Versant Test (Pearson Corp, 2011)(r = .76, p < .001); performance also correlated strongly with age of acquisition. The coarticulation of adjacent speech sounds played a role in which consonants were most difficult to perceive. Future directions, including the current testing of speakers of Puerto Rican Spanish, Kannada and Russian, and implications for intervention, will be discussed.
The effects of first-language sound change on second-language speech production
Authors: Kim Mi-Ryoung
Published: September 2012

Recent studies have shown that the stop system of Korean is undergoing a sound change in which a consonantal opposition between lax and aspirated stops is merging in terms of voice onset time (VOT) whereas the contrast between the two stops is being maximized in terms of fundamental frequency (f0). This study investigates how the ongoing sound change of acoustic parameters in L1 Korean influences L2 English stop production. Results showed that, unlike the VOT merger in L1 Korean, it does not occur in L2 speech production. In contrast, similar to onset-f0 interaction in L1 Korean, there is a strong onset-f0 interaction in L2 English: voiced-low f0 and voiceless-high f0. Korean English learners use not only VOT but also f0 in contrasting an underlying [voice] distinction. The results suggest that f0 differences between lax and aspirated stops in L1 Korean are transferred to those between voiced and voiceless counterparts in L2 English. The findings are discussed with respect to cross-language phonetic effects and synchronic sound change.
Non-native perception and production of Basque sibilant fricatives
Authors: Baese-Berk Melissa M. , Samuel Arthur G.
Published: September 2012

Differences in perception and production of non-native contrasts are thought to be driven by the relationship between sound inventories of the native and target languages (Best, McRoberts, and Goodell, 2001). The current study examines non-native perception and production of sibilant fricatives and affricates in Basque. Basque has a 3-way place contrast for sibilant fricatives and affricates (apico-alveolar /s/ and /ts/, lamino-alveolar /s/ and /ts/, and post-alveolar /∫/ and /t∫/). In contrast, /s/ and /t∫/ are the only voiceless sibilants that Spanish has in this region. The results suggest that in the case of Basque sibilant phonemes, similarity to an existing contrast (i.e., fricative-to-affricate contrasts) results in better perception and production. Native Spanish speakers performed better on discrimination and repetition of the /s/ - /ts/ contrast than the /s/ - /s/ or /s/ - /∫/ contrasts. Spanish speakers are able to leverage their ability to discriminate and produce /s/ and /t∫/ in their native language to perceive and produce a new contrast in Basque, even though the contrast in Spanish differs by two features, rather than just one as in Basque. However, the lack of a contrast between sibilant fricatives prevents them from discriminating or producing the fricative-to-fricative contrasts.
Sibilant production patterns in three generations of Guoyu-Taiwanese bilinguals
Authors: Shih Ya-ting , Kallay Jeffrey , Zhang Jennifer
Published: September 2012

This study investigates the effects of age and language dominance on sibilant production in a bilingual community. Guoyu (Taiwanese Mandarin) has 3 sibilants: alveolar /s/, retroflex /ʂ/ and alveolo-palatal /ɕ/, while Taiwanese (a Southern Min dialect) only has /s/, which is palatalized before /i/ and /io/. Productions of sibilant initial words were elicited using a word repetition task. Subjects were 30 adults in three age bands from 20-80 years, with the oldest being the most Taiwanese-dominant. The spectral centroid was obtained from the middle 40ms of each sibilant, along with the onset F2 of the following vowel. In the low-vowel /a/ context, the youngest speakers clearly separate /s/ in both languages from the Guoyu /ʂ/ and /ɕ/ along the centroid dimension. The /ʂ/ is then separated from /ɕ/ by F2. However, the oldest speakers show no clear separation of these sounds in terms of centroid, although Guoyu /ɕ/ can still be differentiated by F2. Also, the three generations demonstrated differences in the assimilation patterns of palatal sounds. The younger Guoyu-dominant speakers assimilated Taiwanese palatalized one to Guoyu /ɕ/ in both centroid and F2, while older speakers matched the Guoyu /s/~/ɕ/ distinction to that of the Taiwanese pattern.