bluuebunny/crossref_metadata_2025 huggingface dataset:
Reverberation noise modeling using extreme value theory
Authors: La Cour Brian , Luter Robert
Published: October 2013

Normalized matched filter output forms the basis of target detection in active sonar. In a target-free environment, the central theorem, if valid, predicts that the statistics of the envelope follow a Rayleigh distribution, and, to first approximation, this is indeed observed. However, well-known departures from the Rayleigh model are found in the tail end of observed distributions. Traditional approaches to this problem have focused on constructing a simple, parameterized, non-Rayleigh distribution which more closely models observations. This paper suggests a novel alternative which focuses on a robust method of modeling only the tails of the distribution in favor of the less important body. Results from extreme-value theory are used to fit a generalized Pareto distribution (GPD) to the empirical cumulative distribution function, conditioned on a large threshold value. [A random variable X has a GPD if P(X≤x)=1−(1+γx/σ)−1/γ for x≥0, σ>0, and γ real; γ=0 is the exponential distribution.] Estimates of γ and σ are discussed for a broad range of active sonar data, and the results are compared with fits to other popular non-Rayleigh models. The origins of non-Rayleighness are also considered, including finite-size effects, spatial and temporal correlations, and nonuniformity.
Wigner–Ville representations for acoustic source localization
Authors: Michalopoulou Zoi-Heleni , Cohen Leon
Published: October 2013

Signal dispersion in a waveguide can be linked to source and receiver location as well as physical properties of the propagation medium. Traditionally, the main methods used for source localization in the ocean and in geoacoustic inversion problems have been based on the use of the spectrogram for the extraction of the dispersion information. In this work we explore the possibility of using other time-frequency transforms because other transforms, such as the Wigner–Ville representation, reflect the dispersion properties of the waveguide more accurately than conventional spectrograms. We apply the Wigner–Ville distribution, in conjunction with sound propagation models, for inversion with underwater sound. Results with synthetic data calculated for simplified ocean media indicate the potential of the approach for successful parameter estimation. [Work supported by ONR.]
Multichannel active noise control and acoustic equalization using fast affine projection algorithms
Authors: Bouchard Martin
Published: October 2013

In the field of adaptive signal processing, it is well known that affine projection algorithms or their low-computational implementations, fast affine projection algorithms, can produce a good trade-off between convergence speed and computational complexity. Although these algorithms typically do not provide the same convergence speed as recursive-least-squares algorithms, they can provide a much improved convergence speed compared to stochastic gradient descent algorithms, without the high increase of the computational load or the instability often found in recursive-least-squares algorithms. In this presentation, multichannel fast affine projection algorithms are introduced for active noise control or acoustic equalization. Multichannel fast affine projection algorithms have been previously published for acoustic echo cancellation, but the problem of active noise control or acoustic equalization is a very different one, leading to different structures. The computational complexity of the new proposed algorithm is evaluated, and it is shown through simulations that not only can the new algorithm provide the expected trade-off between convergence performance and computational complexity, it can also provide the best convergence performance (even over recursive-least-squares algorithms) when non-ideal noisy acoustic plant models are used in the adaptive systems.
Sex differences in razorbill (Family: Alcidae) parent–offspring vocal recognition
Authors: Insley Stephen J. , Paredes Vela Rosana , Jones Ian L.
Published: October 2013

In this study we examines how a pattern of parental care may result in a sex bias in vocal recognition. In Razorbills (Alca torda), both sexes provide parental care to their chicks while at the nest, after which the male is the sole caregiver for an additional period at sea. Selection pressure acting on recognition behavior is expected to be strongest during the time when males and chicks are together at sea, and as a result, parent–offspring recognition was predicted to be better developed in the male parent, that is, show a paternal bias. In order to test this hypothesis, vocal playback experiments were conducted on breeding Razorbills at the Gannet Islands, Labrador, 2001. The data provide clear evidence of mutual vocal recognition between the male parent and chick but not between the female parent and chick, supporting the hypothesis that parent–offspring recognition is male biased in this species. In addition to acoustic recognition, such a bias could have important social implications for a variety of behavioral and basic life history traits such as cooperation and sex-biased dispersal.
Sound of a cup with and without instant coffee
Authors: Morrison Andrew , Rossing Thomas D.
Published: October 2013

An empty coffee cup, like an ancient Chinese two-tone bell, emits two distinctly different tones, depending upon where it is tapped. When it is filled with hot water, and some instant coffee is added, however, a whole new set of sounds is heard when the cup is tapped. The pitch rises an octave or more as the foam clears due to the dramatic change in the speed of sound in the bubble-filled liquid. A similar, but smaller, effect was noted in beer by Bragg [The World of Sound (1968)] and in hot chocolate by Crawford [Am. J. Phys. (1982)]. We describe the modes of vibration in a coffee cup and the sound emitted by a coffee cup as filled with instant coffee as the bubble density changes.
Computer-animated illustrations of vibrations and waves
Authors: Richards W. Bruce
Published: October 2013

Undergraduate students in a general-education course on musical acoustics often have difficulty understanding the actual time-domain motions of vibrating systems which textbooks can only depict using static diagrams. In particular, students have difficulty relating the longitudinal average displacements of gas molecules in acoustic waves to (transverse) graphs of these displacements as a function of position. To better convey these ideas, a number of animated graphic diagrams have been programmed on a Macintosh computer. For longitudinal waves, these include one-dimensional standing waves in cylindrical pipes with open or closed ends, various pulse waves reflecting from the open or closed end of a cylindrical pipe, and standing waves in a conical pipe with an open end. In addition, the transverse motions of bowed, plucked, and hammered strings have been programmed. Presented in every case is an exaggerated, slow motion picture of the system’s displacement as it evolves in time. If desired, an adjacent coordinated and animated graph of displacement, pressure, or other dynamical variable may also be displayed. As part of this paper the computer programs will be demonstrated.
Acoustic analysis of an Olmecan whistle
Authors: Beristain Sergio , Menchaca Rolando , Velazquez Roberto
Published: October 2013

Thousands of stone artifacts over 2500 years of age have been found in the Olmecan area in the southeast region of Mexico. These range from the famous big heads with helmets (about 2 m in diameter), to small pieces with precisely drilled holes, which some archaeologists consider to have some simple uses, much simpler than the work needed to produce the stone artifact itself. The one studied here (about 3 cm in size), is considered by the acoustics community as an air-phone, and a detailed anaysis has been done employing FFT techniques in order to find out the frequency spread, the particular tones produced and the sound radiated power through the different holes and cavities. The artifact is made of a very solid stone, so-called ilmenite, believed to have titanium, which is very hard to drill. Nevertheless, many similar pieces have been found in the area, which means they were built on purpose, and the material used gives the idea of a sacred application. Attempts have been made to reproduce the artifacts, which produce sounds similar to those from the original pieces.
Rationale for noise regulation: How we got here and why we may not stay
Authors: Fidell Sanford
Published: October 2013

Today’s framework of environmental noise regulation in the United States is the product of a half century’s evolution in understandings of noise effects, and in societal interest and policy interpretations of them. Although it is tempting to associate the evolution of noise policy with rational adaptations to developments in scientific understanding, this is a myopic and ultimately untenable view. It is hardly surprising that little of practical utility for regulatory purposes has come from decades of research in this area, considering the unsystematic and atheoretical nature of much of what has been learned about individual and community response to noise. Today’s annoyance-based rationale for regulatory policy is only one of several historical perspectives, and not necessarily the most useful of them. Further changes in the rationale for assessing noise impacts may be expected as court rulings increasingly challenge reliance upon long-term exposure metrics as predictors of noise effects; as the magnitude of non-acoustic contributions to annoyance becomes clearer; and as the information that the U.S. Federal Interagency Committee on Noise last reviewed a decade ago becomes more and more stale.
The need to revitalize our national noise policy
Authors: Lang William W. , Beranek Leo L.
Published: October 2013

At the present time, our Nation does not have a national noise policy. The Congress attempted to define one with the passage of the Noise Control Act of 1972 as follows: The Congress declares that it is the policy of the United States to promote an environment for all Americans free from noise that jeopardizes their health and welfare. The Act assigned to the Environmental Protection Agency (EPA) the role of leading Federal agency with the task of coordinating the programs of all Federal agencies relating to noise research and noise control. Ten years later (1982), all funds for noise control were withdrawn from the EPA, and today the Nation is without an effective, overall noise policy. Residual responsibility for the control of environmental and occupational noise currently rests with a dozen agencies of the Federal government, as well as State, municipal, and local authorities. But the activities of these organizations are largely uncoordinated, and the enforcement of existing noise control regulations is at best sporadic, and in some cases nonexistent. To assure our quality of life and to minimize the economic impact of potential trade barriers, a study team is recommending that a national noise policy be developed and then implemented in the immediate future.
Differential surface acoustic wave IDT gyroscope
Authors: K.A Jose , Mehta Anshu , Varadan Vijay K.
Published: October 2013

This paper presents the design and experimental evaluation of a gyroscope based on differential design of a surface acoustic wave (SAW) resonator and a sensor on a piezoelectric substrate. The resonator is divided into two halves, one with metallic dot arrays and other without any metallic dots. Standing waves are formed inside both cavities. The particles at the antinodes of the standing wave pattern experience large amplitude of vibration that serves as the reference vibrating motion for this gyroscope. The metallic dots strategically positioned at the antinode locations experience Coriolis force due to rotation and acoustically amplify the magnitude in the orthogonal direction. However, the other half of the resonator cannot generate any secondary SAW. A wideband SAW sensor arranged orthogonal to the SAW resonator picks up these two secondary SAWs and is fed to a differential amplifier. Any drift in the gyroscope signal can be completely eliminated by this novel design. The performance of this 74.2-MHz gyroscope shows very high sensitivity and dynamic range, which is ideal for many commercial applications. Unlike other MEMS gyroscopes, this gyroscope has a planar configuration with no suspended resonating mechanical structures, thereby being inherently robust and shock resistant.
The times of Ira Hirsh
Authors: Divenyi Pierre L.
Published: October 2013

Ira Hirsh was among the first to recognize that the auditory system does not deal with temporal information in a unitary way across the continuum of time intervals involved in speech processing. He identified the ‘‘short’’ range (extending from 1 to 20 ms) as that of phase perception, the ‘‘medium’’ range between 20 and 100 ms as that in which auditory patterns emerge, and the ‘‘long’’ range from 100 ms on as that of separate auditory events. Further, he was also among the first to recognize that auditory time perception heavily depended on the spectral context. A study of the perception of sequences representing different temporal orders of three tones, by Ira and the author [e.g., Divenyi and Hirsh, J. Acoust. Soc. Am. 64, 1369–1385 (1978)] demonstrated the dependence of auditory sequence perception on both time range and spectral context, and provided a bridge between Hirsh’s view of auditory time and Bregman’s view of stream segregation [Auditory Scene Analysis (MIT Press, Cambridge, MA, 1991)]. A subsequent search by the author for psychophysical underpinnings of the cocktail-party phenomenon [e.g., Divenyi et al., Moh. Mtn. Workshop Appl. SPAA (IEEE, Bellingham, WA, 1997)] suggest that the segregation of simultaneous streams of speech may rely on the ability to follow spectral changes in the demisyllabic-to-syllabic (100- to 200-ms) range, i.e., Ira’s ‘‘long’’ range.
Ira as a pioneer in audiology: His contributions to the clinical measurement of hearing and hearing impairment
Authors: Formby C. , Gagne J. P.
Published: October 2013

Ira Hirsh’s contributions to clinical science and research are diverse and significant. In fact, approximately one-third of the 100+ publications that Ira lists in his curriculum vitae (CV) are clinical in nature, dealing with various aspects of audiology, deafness, hearing aids, aural rehabilitation, and speech and language pathology. The majority of these citations, fully one-quarter of his publication list, addresses problems specific to the clinical measurement of hearing and hearing impairment. Undoubtedly, the most influential of these published works appears in his CV under the citation ‘‘The Measurement of Hearing.’’ The forward for this publication, his only textbook, was penned in June, 1952 (now precisely half a century past at the time of this session). The aims of this presentation are to (1) provide perspective on the fundamental importance of his virtually timeless text in shaping the fledgling discipline of audiology, and (2) celebrate Ira’s many contributions to the profession and practice of audiology. [Preparation for this presentation was supported, in part, by a K24 career development award from NIDCD.]
Genetic encoding for sound package configuration optimization
Authors: Lai Heng-Yi
Published: October 2013

The acoustic properties of poroelastic materials can be accurately predicted by the Biot–Allard model if the required acoustic parameters have been successfully characterized. In conjunction with the transfer matrix approach, one can use the model to analytically design an acoustic liner comprising different materials that can provide better performance or cost reduction advantages over their homogeneous counterparts. However, optimizing the layer configuration remains to a challenging task as it is a combinatorial problem and the search for the optimal configuration can be difficult or expensive if simply based on the build-and-test approach. The Generic Algorithm (GA) was identified as a better optimization method over the gradient-based methods for this task due to its nature in finding the combinatorial solutions. This approach is, to the best of our knowledge, novel in applying the GA to this design problem. The performance of the GA method is compared with the exhaustive search in maximizing the sound absorption coefficient of an acoustic liner with constraints set for its cost, thickness, and total weight. The features of the Generic Algorithm and the preliminary proof-of-concept results will be discussed and presented.
Acoustic tracking of towed-array hydrophone positions during tow-vessel maneuvers
Authors: Duncan Alec J. , McMahon Darryl , Ghiotto Alessandro
Published: October 2013

This paper describes an experiment in which a vessel towing an array of hydrophones executed a series of maneuvers designed to bring the array into orientations favorable for imaging noise sources on the tow-vessel. Signals from tracking beacons on the tow-vessel and transient signals from implosive sources deployed from a second vessel were received on the array hydrophones and were used to obtain independent estimates of hydrophone position. Array shape estimation and tracking algorithms are described and the results of applying these algorithms to the experimental data are presented.
Adaptive beamforming of a towed array during a turn
Authors: Gerstoft Peter , Hodgkiss William S. , Kuperman W. A. , Song Heechun , Siderius Martin , Nielsen Peter L.
Published: October 2013

During maneuvering, towed-array beamforming will degrade if a straight array is assumed. This is especially true for high-resolution adaptive beamforming. This problem can be reduced if a proper curved array is assumed. The tow vessel’s Global Positioning System (GPS) can be used to estimate this curvature, and this reduces the need for instrumentation in the array. Based on estimated array shape from GPS, both the conventional beamformer and the white-noise-constrained (WNC) adaptive beamformer are shown to track the source well. For calculating the steering vector in the WNC approach, a matrix inversion of the cross-spectral density matrix is involved. This matrix inversion can be stabilized by averaging the cross-spectral density matrix over neighboring frequencies.
Subarray partitions of large aperture planar towed arrays
Authors: Watson Jennifer A. , Baggeroer Arthur B. , Zurk Lisa M. , Tracey Brian H.
Published: October 2013

The current focus of passive detection and localization is in littoral regions where acoustic propagation becomes complicated by severe bottom interaction. The resultant high-transmission loss motivates the need for high-array gain for effective performance over long ranges. Large planar seismic arrays, with aperture dimensions upwards of 3 km×0.5 km, have potential to achieve high gain and good resolution when using matched field processing. In realistic environments, however, large arrays are suceptible to signal gain degradation mechanisms, particularly due to spatial decorrelation of the signal and non-stationary environments. One approach to overcoming this is partitioning the array. Subarray processing reduces stationarity requirements and extracts optimum coherent gain, thus achieving higher gain than that of smaller arrays. This work examines criteria for partitioning planar arrays to perform localization using MFP. Trade-offs between spatial resolution, array gain, and resilience to motion will be quantified and discussed. Performance of different subarray geometries will be presented using adaptive and conventional MFP. [Work sponsored by DARPA under Air Force Contract No. F1962800-00-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed by the Department of Defense. AB’s work was supported by ONR through the SECNAV CNO Chair.]
Estimating the velocity of a moving object submerged in an ocean waveguide with active sonar
Authors: Lai Yi-san , Makris Nicholas
Published: October 2013

Standard active sonar and radar systems are often used to estimate the velocity of a moving target in free space by resolving the Doppler shift of the scattered waveform. In an ocean waveguide, multimodal propagation and dispersion make the Doppler effects far more complicated than in free space. In a waveguide, multiple frequency components are typically present in the field scattered from a moving object even if the active source of radiation is harmonic. Applying a free space Doppler correction to the field scattered from a moving object in a waveguide is insufficient to account for the Doppler distortion of the signal in typical ocean waveguides and active sonar scenarios. Spectral and modal formulations for the Doppler-shifted field scattered from a horizontally moving target in a horizontally stratified medium have been developed by Lai and Makris [J. Acoust. Soc. Am. 110, 2724 (2001)]. These formulations are used with the maximum likelihood method to estimate the velocity of the moving target by modeling the multiply Doppler distorted scattered signal measured with noise in a shallow water waveguide. The performance of the maximum likelihood estimate is evaluated by asymptotic analysis of its bias and mean-square error as a function of signal-to-noise ratio.
Time-frequency analysis and conditional moments of shallow-water sound propagation
Authors: Loughlin Patrick J.
Published: October 2013

Shallow-water sound propagation is inherently nonstationary owing to such effects as geometric dispersion. The spectrogram has been a principal means to study the nonstationarities and dispersion characteristics of shallow-water sound propagation. In this talk, we give the low-order conditional spectral and wave number moments of sound propagation in dispersive environments, and show how they characterize the nonstationarities induced by channel dispersion on the propagating wave. [Work supported by ONR (N00014-02-1-0084).]
The importance of early reflections for speech intelligibility in rooms
Authors: Bradley John , Sato Hiroshi
Published: October 2013

New results demonstrate that in rooms for unamplified speech communication early reflections are important for achieving adequate speech intelligibility and that early reflection energy is typically much greater in magnitude than the direct sound energy. Speech intelligibility was measured using a rhyme test in simulated sound fields that included a direct sound with varied early reflections and reverberant sound along with a constant level of ambient noise. The results confirmed that added early reflection energy is equivalent to increased direct sound energy. The combination of direct sound and early reflections increases the effective signal-to-noise ratio and the related speech intelligibility scores for both impaired and nonimpaired listeners. The new results also show, that for common conditions where the direct sound is reduced, it is only possible to understand speech because of the presence of early reflections. Analyses of measured impulse responses in rooms for speech, in terms of a measure of the benefit from early reflections, show that early reflections can increase the effective signal-to-noise ratio by up to 9 dB. The primary goal of room acoustics design should be to maximize early reflection energy to make possible increased effective signal-to-noise ratios.
Distinct US modes in trabecular bones: Properties and modeling
Authors: Kaczmarek Mariusz , Pakula Michal
Published: October 2013

Marrow saturated trabecular bones are two-phase composites in which the propagation of ultrasonic waves is influenced by relative motion of phases. In particular, in studies in vitro two longitudinal wave modes are observed with specific behavior of attenuation and dispersion. Although the existence of the modes is predicted by the macroscopic model proposed by Biot some of their basic properties cannot be derived from the model [see Hosokawa and Otani (1997)]. Thus numerous modifications of the macroscopic model have been developed including layered structure [see Hughes et al. (1999)] or incorporating scattering [see Strelitzki et al. (1998)] in order to obtain better agreement with experimental results. Still, however, some important features such as high attenuation of the fast wave, insignificant dispersion and moderate attenuation of the slow wave, for relatively short waves as compared with the characteristic size of pores or trabeculae are not well described. This paper discusses predictions of the proposed microscopic (or exact) two-phase model developed for chosen cellular geometries [see Kaczmarek et al. (2002)]. The comparison of theoretical results with our own and other experimental data is performed. Additionally, references to results obtained for model material (phantoms) with structure corresponding to the models adopted are made.
QUS devices for assessment of osteoporosis
Authors: Langton Christian
Published: October 2013

The acronym QUS (Quantitative Ultrasound) is now widely used to describe ultrasound assessment of osteoporosis, a disease primarily manifested by fragility fractures of the wrist and hip along with shortening of the spine. There is currently available a plethora of commercial QUS devices, measuring various anatomic sites including the heel, finger, and tibia. Largely through commercial rather than scientific drivers, the parameters reported often differ significantly from the two fundamental parameters of velocity and attenuation. Attenuation at the heel is generally reported as BUA (broadband ultrasound attenuation, the linearly regressed increase in attenuation between 200 and 600 kHz). Velocity derivatives include bone, heel, TOF, and AdV. Further, velocity and BUA parameters may be mathematically combined to provide proprietary parameters including ‘‘stiffness’’ and ‘‘QUI.’’ In terms of clinical utility, the situation is further complicated by ultrasound being inherently dependent upon ‘‘bone quality’’ (e.g., structure) in addition to ‘‘bone quantity’’ (generally expressed as BMD, bone mineral density). Hence the BMD derived WHO criteria for osteoporosis and osteopenia may not be directly applied to QUS. There is therefore an urgent need to understand the fundamental dependence of QUS parameters, to perform calibration and cross-correlation studies of QUS devices, and to define its clinical utility.
On the relationship of ultrasonic properties to density and architecture in trabecular bone
Authors: Nicholson Patrick , Bouxsein Mary
Published: October 2013

As previously reported elsewhere, we have made ultrasonic measurements in human trabecular bone and have explored relationships with microstructural properties, the latter derived from microcomputed tomography. However, multicollinearity in these data means that conventional regression analysis cannot reliably identify the underlying causal relationships. In an effort to move beyond such limitations, we used our experimental data to test some models of possible interactions between ultrasound and bone. In particular, we compared several models for predicting acoustic velocity in two-phase media as a function of the bone volume fraction. We found good agreement only with the theory of Kuster and Toksoz [Geophysics 39, 587 (1974)] based on scattering by an effective medium. Turning our attention to attenuation, we examined relationships with trabecular thickness (Tb.Th) and the number of trabeculae per unit volume (Tb.N). The exponent relating attenuation to Tb.Th was 3.2, lower than the value of 4 predicted for long wavelength inelastic scattering by cylinders. This may be due to multiple scattering, since restricting the analysis to specimens with relatively low Tb.N yielded an exponent of 3.9. The exponent relating attenuation to Tb.N was 1.3, higher than the expected value of unity, which may again reflect the influence of multiple scattering.
Obstacle avoidance sonar for submarines
Authors: Dugas Albert C. , Webman Kenneth M.
Published: October 2013

The Advanced Mine Detection Sonar (AMDS) system was designed to operate in poor environments with high biological and/or shallow-water boundary conditions. It provides increased capability for active detection of volume, close-tethered, and bottom mines, as well as submarine and surface target active/passive detection for ASW and collision avoidance. It also provides bottom topography mapping capability for precise submarine navigation in uncharted littoral waters. It accomplishes this by using advanced processing techniques with extremely narrow beamwidths. The receive array consists of 36 modules arranged in a 15-ft-diameter semicircle at the bottom of the submarine sonar dome to form a chin-mounted array. Each module consists of 40 piezoelectric rubber elements. The modules provide the necessary signal conditioning to the element data prior to signal transmission (uplink) through the hull. The elements are amplified, filtered, converted to digital signals by an A/D converter, and multiplexed prior to uplink to the inboard receiver. Each module also has a downlink over which it receives synchronization and mode/gain control. Uplink and downlink transmission is done using fiberoptic telemetry. AMDS was installed on the USS Asheville. The high-frequency chin array for Virginia class submarines is based on the Asheville design.
Robust identification/fingerprinting of audio signals using spectral flatness features
Authors: Herre Juergen , Allamanche Eric , Hellmuth Oliver , Kastner Thorsten
Published: October 2013

Recently, the problem of content-based identification material has received increased attention as an important technique for managing the ever-increasing amount of multimedia assets available to users today. This talk discusses the problem of robust identification of audio signals by comparing them to a known reference (‘‘fingerprint’’) in the feature domain. Desirable properties of the underlying features include robustness with respect to common signal distortions and compactness of representation. A family of suitable features with favorable properties is described and evaluated for their recognition performance. Some applications of signal identification are discussed, including MPEG-7 Audio.
Resonant frequency response and surface particle velocity profiles for buried land mines: Theory and experiment
Authors: Sabatier James M. , Velea Doru , Xiang Ning , Waxler Roger
Published: October 2013

Acoustic-to-seismic coupling is currently used to detect buried landmines by measuring a contrast in the particle velocity of the air–soil interface directly above the mine (on-target) and away from the mine (off-target). Field measurements reveal a resonance phenomenon of the mine–soil system at frequencies around 100 Hz. The resonance frequency and the spatial profile of the on/off-target velocity ratio depend on the type of the mine, depth, and soil characteristics. Experimental results for antitank mines will be presented. These results will be compared with predictions by a recently developed model for the scattering of normally incident sound off of a landmine. The model assumes that the mine has a compliant top and the soil is an effective fluid. [Work supported by the U.S. Army Communications-Electronics Command Night Vision and Electronic Sensors Directorate and the U. S. Army Research Office.]
Acoustic-to-seismic coupling variations in cold regions
Authors: Albert Donald G.
Published: October 2013

Experiments were conducted to investigate the variations that may occur in acoustic-to-seismic coupling arising from changes in local near-surface conditions. The emphasis of the investigations was on cold regions, where many different surface conditions exist and where conditions may change over a short time period from wind, precipitation, freezing, or thawing. The measurements were conducted by recording blank pistol shots with surface geophones and microphones. Results are presented for grassland, thin and thick seasonal snow covers, polar firn, thin grounded ice, thick glacier ice, and floating river ice. The ratio of induced ground motion to acoustic pressure ranged from 0.5 to 20 micro-meters per second per Pascal. Often two arrivals were detected on the geophones, a high-speed seismic compressional wave followed by the air wave. [Work funded by the U.S. Army.]
Prediction of flow induced sound: Past, present, and future
Authors: Blake William , Zawadzki Irek
Published: October 2013

The prediction of flow-induced vibration and sound has developed into a refined analysis technology. At its genesis the capability to provide engineering evaluations of flow-driven surfaces was crude and semi-empirical. The ability to provide acoustic estimations of fidelity depended on empiricism, similitude, and engineering experience. Very little was known of the physics of flow–structure interaction to permit otherwise. Currently, capabilities to make high-fidelity engineering predictions have benefitted from continual advances in three major areas. Our knowledge of the physics of flow sources has matured to understand acoustically-relevant flow structures and the interaction of flows with surfaces. Our ability to computationally model structural response and acoustic Green’s functions has evolved because of parallel advances in structural acoustics. Computational fluid dynamics has developed into a refined tool for simulating flow over complex geometries. It is continuing to evolve as we learn how to model acoustically relevant subsonic flow structures with large eddy simulation and direct numerical simulation. Once principally a technology available only to military application, these tools are becoming more commonplace in industrial applications. This lecture will trace some of these developments, show some examples, and indicate promising areas of advancement.
Trailing edge noise reduction in a backward-curved impeller
Authors: Lauchle Gerald C.
Published: October 2013

Motorized impellers are used in many air-moving applications including room circulation, duct flow, roof and wall exhaust, and cooling of electronic components in cabinets. These fans are backward-curved centrifugal blowers that operate with no volute casing. These fans radiate broadband noise due to turbulence ingestion and trailing edge (TE) noise generating mechanisms. Considered here are trailing edge noise generation and its reduction in a typical motorized impeller. The sound power of the subject fans is measured in an acoustically transparent test plenum according to ANSI Standard S12.11-1987. Two different serrated TE treatments are designed. The designs assume that a turbulent boundary layer exists at the blade TE, but the actual fan Reynolds number based on chord length is transitional. Therefore, to assure that a turbulent boundary layer exists at the TE, two different inlet turbulators are implemented. These trip the blade boundary layer to a turbulent state. Reported are the effects of the TE serrations and turbulators acting individually on the fan noise, along with the synergistic effects of using them in combinations. Up to 6 dBA of noise reduction is observed when the two are used together. [Work supported by Nortel Networks.]
Predicting wall pressure fluctuations beneath a turbulent flow
Authors: Farabee Theodore M.
Published: October 2013

The source of excitation for a wide range of flow-induced vibration and noise problems is the unsteady surface pressure field imposed by flow of a turbulent boundary layer (TBL). In addition, for flow-over discontinuities, the TBL surface pressures constitute an incident wave field that is scattered at discontinuities resulting in sound production for even a rigid surface. For these reasons alone, interest in predicting TBL wall-pressure fluctuations has existed as long as there has been an interest in understanding and estimating flow-induced noise and vibration. Current approaches for predicting, or estimating, wall-pressure fluctuations fall into one of three general categories: direct numerical computations, in which the governing equations are solved directly; a statistical modeling approach which couples time-averaged flow calculations to theoretically derived modeling functions for wall pressures; and empirical methods which assume that wall pressures follow a known scaling relationship formed using relatively standard flow parameters that are easy to prescribe for the flow of interest. The merits of using each of these methods for the purposes of assessing flow-induced noise and vibration will be reviewed and discussed.
Estimation of broadband power radiated from ribbed plates under turbulent boundary layer excitation
Authors: Rumerman M. L.
Published: October 2013

‘‘Exact’’ calculation of the acoustic power radiated due to the vibration of ribbed underwater panels driven by a turbulent boundary layer (TBL) requires consideration of the interactions among ribs and end supports. This paper shows that the power radiated in broad frequency bands may be directly estimated by considering the discontinuities to act independently. Analysis of a string loaded with identical masses or springs, and subjected to a wave-number-white forcing spectral density, is first used to demonstrate that the mean-squared attachment force within a broad frequency band may be estimated by ignoring coupling among attachments. A water-loaded membrane having parallel line mass attachments is then used to show that each attachment can be considered to radiate independently of the others when the acoustic wavelength is less than the spacing between them. These simple models are generalized and combined to develop an estimate of the vibration-related power radiated by finite ribbed steel plate sections in water driven by TBL-like surface pressures. The approximation is compared to results based on an exact formulation for a doubly periodic plate that represents ribs and end supports, and found to agree within 3 dB. [Work supported by ONR.]
Unit-cell finite element analysis of the response of complex structures to flow excitation
Authors: Martin Nathan C. , Dees Robert N.
Published: October 2013

Analytic estimation of the vibration response of rib-reinforced structures excited by turbulent boundary layer (TBL) wall pressure fluctuations is a subject of ongoing interest for numerous applications in airborne and underwater acoustics. Previous investigators have developed a variety of closed form and approximate analytic methods for estimating the response of structures of interest. Fluid-loading and rib-reinforcement effects make problems involving the response of sea-going vessels particularly challenging. Recent advances in finite element based methods and the enhanced capabilities of modern computer hardware now permit the application of the FEA method to such flow-induced vibration problems. This paper describes the application of the unit-cell capability in BBN’s SARA-2D finite element code to evaluate the response of fluid-loaded, rib-reinforced cylinders to TBL excitation. An overview of the unit-cell modeling method is presented, and example results are provided to illustrate the effects of variations in rib and shell dimensions.
Excitation by flow over an obstructed opening
Authors: Zoccola Paul J.
Published: October 2013

The effect on flow-induced cavity resonance of the presence of an obstruction in the cavity opening is considered. The presence of a single obstruction or of a grid generally alters the flow so that the excitation occurs on the smaller length scale created by the obstructions. However, discussion of resonant excitation on the length scale encompassing the obstructions has not been found in the literature. For this study, measurements of cavity pressure due to flow over a cavity with an obstruction of varying dimensions in the opening were made. Measurements of the flow field around the single obstruction were also made. The cavity pressure measurements show that flow over an obstructed opening does result in the occurrence of classical resonant excitation at the large length scale. The frequency of the excitation and the amplitude of the response at the large length scale are reduced, depending on the dimensions of the obstruction. Flow field results show the effects that an obstruction has on the flow, including effects on the vortex convection velocity and the energy production distribution.
Vibrations of infinite plates and the mean value vibrations of finite plates excited by turbulent boundary layer flows
Authors: Hambric Stephen , Hwang Yun-Fan
Published: October 2013

The vibration response of a turbulent boundary layer (TBL) excited flat plate is analyzed using a finite-element model and infinite plate theory. For the finite-element models, discretization sufficient to resolve the convective fluctuations in the flow excitation field is used for the study. Clamped boundary conditions are assumed for the finite-element models and analyses are conducted at a variety of flow speeds and structural loss factors. Two equivalent TBL wall pressure excitation models are applied to the plates: (1) a modified Corcos cross-spectrum model for the finite-element models, and (2) a wave-vector-frequency spectrum model (the Fourier transform of the modified Corcos cross spectra) for the infinite plate theory. The TBL wall pressure autospectrum is approximated using the model derived by Smolyakov and Tkachenko. The infinite plate predicts the mean value response of the finite plate very well for all speeds and loss factors considered, showing consistency with Skudrzyks mean value theory and its usefulness for generating sound and vibration estimates.
Two structural intensity prediction methods in plates excited by turbulent boundary layers
Authors: Daley Michael J. , Hambric Stephen A.
Published: October 2013

Structural intensity (S-I) fields may be used to identify energy flow paths through a vibrating structure, as well as energy source and sink regions. Boundary layer excitation of structures occurs in numerous aerospace and underwater applications. This study describes two methods of predicting S-I fields in structures excited by turbulent boundary layers. The first prediction method combines well known multiple-input/multiple-output system theory with finite differencing techniques to obtain S-I predictions. The second method uses an analytic computation technique. This technique combines response matrices between applied pressures and response stresses and velocities to form cross spectra matrices with units of power. These cross spectra matrices are proportional to S-I. The two prediction methods are described in detail and a set of case studies incorporating these methods is presented. The case studies are based on a simply supported plate with an attached point damper. The Corcos model of the boundary layer spatial wall pressure correlation is applied to the plate due to its simplicity. The case studies include intensity fields due to flows above, at, and below aerodynamic coincidence (the frequency at which a structural wavelength equals a convective wavelength). [Work supported by The Applied Research Laboratory, Penn State.]
Speech recognition in continuous and fluctuating maskers by listeners with normal and impaired hearing: Effects of presentation level
Authors: Summers Van , Molis Michelle
Published: October 2013

Listeners with normal hearing show better speech recognition in the presence of fluctuating background sounds, such as a single competing voice, than in unmodulated noise at the same overall level. These performance differences are greatly reduced in listeners with hearing impairment who generally show little benefit from fluctuations in masker envelopes. If this lack of benefit is entirely due to elevated quiet thresholds and the resulting inaudibility of low-amplitude portions of signal+masker, hearing-impaired listeners should show an increasing benefit from masker fluctuations as the presentation levels increase. Normally hearing and hearing-impaired listeners were tested for sentence recognition at moderate and high presentation levels in a competing speech-shaped noise, in competing speech by a single talker, and in competing time-reversed speech by the same talker. Normal-hearing listeners showed more accurate recognition in the fluctuating maskers than in unmodulated noise with some evidence that modulated:unmodulated performance differences may decrease at high presentation levels. Hearing-impaired listeners showed more similar performance across maskers and presentation levels. The results suggest that audibility does not completely account for the group differences in performance with fluctuating maskers: supra-threshold processing differences between groups may also contribute to the disparity in performance. [Work supported by NIH.]
The time course of learning during a vowel discrimination task by hearing-impaired and masked normal-hearing listeners
Authors: Davis Carrie , Kewley-Port Diane , Coughlin Maureen
Published: October 2013

Vowel discrimination was compared between a group of young, well-trained listeners with mild-to-moderate sensorineural hearing impairment (YHI), and a matched group of normal hearing, noise-masked listeners (YNH). Unexpectedly, discrimination of F1 and F2 in the YHI listeners was equal to or better than that observed in YNH listeners in three conditions of similar audibility [Davis et al., J. Acoust. Soc. Am. 109, 2501 (2001)]. However, in the same time interval, the YHI subjects completed an average of 55% more blocks of testing than the YNH group. New analyses were undertaken to examine the time course of learning during the vowel discrimination task, to determine whether performance was affected by number of trials. Learning curves for a set of vowels in the F1 and F2 regions showed no significant differences between the YHI and YNH listeners. Thus while the YHI subjects completed more trials overall, they achieved a level of discrimination similar to that of their normal-hearing peers within the same number of blocks. Implications of discrimination performance in relation to hearing status and listening strategies will be discussed. [Work supported by NIHDCD-02229.]
Perceptual cue weighting of voiceless stop consonants as represented by mismatch negativity and P300
Authors: Franklin Cliff , Harkrider Ashley
Published: October 2013

Changes in high-frequency content form the basis of differentiating between the perception of voiceless stop consonants, /p/ and /t/. Behavioral studies show that two cues, the formant transition onset frequency and the relative amplitude of the burst component of the stop consonant, contribute to the perception of these consonants, and that the weight of these cues differs for normal-hearing versus hearing-impaired individuals. Our goal in the current study was to obtain a measure of cue weighting electrophysiologically in twelve normal-hearing adults and compare the results with those previously reported in behavioral studies. Two physiological indices of perceptual discrimination of acoustical changes, the attention-independent mismatch negativity (MMN) and the attention-dependent P300, were measured by varying each cue independently and in combination. This resulted in three MMN and three P300 responses per subject in response to (a) changing the formant transition cue with a constant, neutral relative amplitude, (b) changing the relative amplitude cue with a constant, neutral formant transition cue, and (c) changing both cues. Measures from individual and group mean waveforms will be used to determine cue weighting based on sum of square values derived from multivariate analysis of variance. Results will be discussed relative to behavioral perception and attention.