bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflection reduction by three-dimensional and two-dimensional phononic crystal slabs
Authors: Ivansson Sven M.
Published: October 2011

A thin rubber coating with scatterer inclusions in a periodic lattice can redistribute sound energy, normally incident on a steel plate in water, in the lateral direction. The scattered energy can be absorbed by the rubber material and the reflection amplitude in the water can be reduced significantly. Coatings with different scatterer material types are here compared: air-filled cavities, high-density inclusions, and high-density inclusions coated by soft silicone rubber (which have attracted much interest in recent phononic crystal research). For each material type, scatterers of spherical (in a doubly periodic lattice) or cylindrical (in a lattice with a single period) shape are considered. Each coating type is optimized by differential evolution, varying a number of material and geometrical parameters to minimize the maximum reflectance within a certain frequency band. The layer multiple-scattering method is used as forward model. Good broad-band reflectance reduction is achieved with cavities (monopole scattering), but even better results are obtained with the coated high-density inclusions (dipole scattering). Combined with mixing scatterers of different sizes, the cylindrical shape, with scatterers in a lattice with a single period, is very powerful. The sensitivity of the performance to different parameters, as well as the incidence angle, is illustrated.
The appearance and use of Bragg scattering effects when sound is perpendicularly incident on a periodic structure
Authors: Liu Jingfei , Declercq Nico
Published: October 2011

In the study of diffraction spectra for sound incident on periodic structures, it has often been thought that different diffraction orders can be observed and studied separately. This assumption was probably a result of geometrical considerations where a bounded beam, incident and diffracted, is considered as a straight line. It has been widely used to study different phenomena such as surface wave generation and its physical relation to Wood anomalies. In this paper, we develop a geometrical study based on the finite beam width of transducer. The study reveals that measurement of the zero order reflected beam is always accompanied by the back-scattered beams of higher (Bragg) diffraction orders. Extensive measurements have been performed that precisely show the appearance of such waves in the diffraction spectra. Furthermore, the study reveals how the presence of such waves can be used for nondestructive characterization of corrugated surfaces, a technique much easier to interpret than earlier techniques based on Wood anomalies physically caused by surface wave generation. The most important feature is that the introduced technique can be applied for normal incidence and not necessarily in situations where surface waves can be physically generated. [Thanks to the French Centre National de Recherche Scientifique (CNRS)and the Conseil Rgional de Lorraine (CRL) for their financial support.]
Influence of periodicity on the reflection properties of finite periodic media
Authors: Cebrecos Alejandro , Romero-García Vicent , Picó Rubén , Snchez-Morcillo Vctor , Garcia-Raffi Luis Miguel , Snchez-Prez Juan Vicente , Staliunas Kestutis
Published: October 2011

The dispersion relation of periodic systems, the well-known bands structure, gives the information about the propagating modes inside the media. These bands reveal both propagating and non-propagating ranges of frequencies. It is well known that the transmission properties, with relation to the propagating modes, can be characterized by both the bands structure and the equifrequency contours. Oppositely, in finite systems, one should consider the reflection properties on the interface defined by the host and the periodic media in order to know the spatial distribution of the reflected field. In this work, we analyze the reflected acoustic field by a periodic system. An experimental set up is proposed in this work to analyze the reflection properties of a periodic media. From the exploitation of the properties of both the interface and the inner periodicity of the crystal, fundamental and applied questions can be discussed using this media.
An advanced version of the vibrating string lab
Authors: Morrison Andrew C.
Published: October 2011

The vibrating string laboratory is a classic of undergraduate physics courses all over. At the introductory level, a common way of setting up a vibrating string lab is with a mechanical shaker and a non-magnetic string. The analysis usually done in the introductory laboratory usually assumes the vibrating string is a linear system. Real vibrating strings are non-linear and are an appropriate choice for exploring non-linear systems in a lab beyond the introductory level. Variations on the introductory lab and pedagogic approaches which make the lab appropriate for advanced undergraduate labs will be presented.
High speed video of commonly studied oscillating systems
Authors: Tucholski Edward J.
Published: October 2011

To allow student visualization of vibrating systems, laboratories and demonstrations have been cleverly designed to include stroboscopes, sand, and cork dust. Sensors in the laboratory are often single point type and must be moved to fully visualize the pattern of a vibrating system. Animations fill in the blanks but are still not real. Standard video recording would be the perfect data gathering and visualization tool except the frame rate is too slow for the most commonly studied oscillating systems. Reasonably priced high speed video cameras provide an alternative. In this paper, simple one and two dimensional vibrating systems (e.g., strings, bars, and membranes) are examined with a camera capable of frame rates up to 16 000 frames per second. Video analysis software is used to strip data from the recordings. More complex oscillating systems are also examined to demonstrate the power of this laboratory tool.
Low cost sound level meters for education and outreach
Authors: Muehleisen Ralph T. , Morrison Andrew C.
Published: October 2011

It used to be that when you wanted a low cost sound level meter for teaching and outreach, you could purchase a Radio Shack 33-2050 analog sound level meter. These meters were fairly accurate as well as rugged and could be used as a microphone with preamp in a pinch. Now that the Radio Shack meter is no longer for sale what other options are available? In recent years a plethora of meters and software apps have become readily available at a low cost. In this presentation, the authors will discuss some of the qualities one should look for in a low cost meter to be used for outreach and education and suggest some equipment that meets these needs.
Structural vibration studies using finite element analysis
Authors: Hansen Uwe J.
Published: October 2011

Bending wave propagation on a two dimensional structure is usually governed by a partial differential equation the solutions of which represent traveling waves. Imposing boundary conditions generally limits the solutions to standing waves representing the normal modes of vibration of the structure. These deflection shapes can be studied experimentally using holographic interferometry or computer aided modal analysis. Finite element analysis (FEA) provides a tool for calculating such normal modes. Input parameters include geometric variables of the structure along with elastic constants, boundary conditions, and a mesh grid which serves as a calculation basis for the iterative computer calculations. Full functioned FEA programs are generally beyond the means of most University educational laboratories. Among more accessible programs with somewhat limited capabilities is ANSYSED. The bulk of the time allotted for this paper will be spent to demonstrate the operation of this program by doing a detailed calculation of normal modes of a square plate clamped on one edge and also illustrating calculated results for a hand-bell.
Computer modeling in graduate level underwater acoustics
Authors: Isakson Marcia J.
Published: October 2011

The more a student can become part of the teaching process, the more engaged he is. In a laboratory setting, this involves physically implementing the learned theories. However, for upper level graduate courses, laboratory experiments are often unrealistic. For example, in an underwater acoustics class, it is impossible for a student to physically realize ray bending in the ocean without a large-scale experiment. However, computer modeling can bridge the gap. In this example, students write their own simulation of underwater propagation based on concepts learned in the lecture. Through the computer simulation, students manipulate the environment to determine the effects on acoustic propagation. As the course progresses, interface and target scattering and array and signal processing are added to the propagation code, leaving the student with a comprehensive ocean acoustics modeling toolkit.
Modeling of a violin input admittance by direct positioning of second-order resonators
Authors: Maestre Esteban , Scavone Gary P. , Smith Julius O.
Published: October 2011

When approaching violin sound synthesis, the theoretical advantage of body modeling by finite difference or finite element paradigms comes from parameterizing the model by geometry and material properties. However, difficulties in representing the complexity of physical phenomena taking place have kept such approaches from raising more success, due especially to limited modeling accuracy and high computational cost. Conversely, the design of digital filters from admittance measurements, although generally offering a less meaningful parameterization, represents a more affordable technique as it provides significant fidelity at lower computational cost. Within digital filter formulation applied to the violin, modal representations can be considered as among the most physically pertinent, since vibration modes defining the timbre signature are in general observable from admittance measurements. This work introduces a technique for designing violin passive admittances by direct, non-uniform positioning of second-order resonators. Starting from admittance measurements, second-order resonator parameters are designed so that desired modes are modeled from frequency-domain data. Positve real models providing significant accuracy at low order are obtained from second-order resonator parameter fits. As an example, a two-dimensional input admittance is designed from measurements, so that it can be used for a digital waveguide model to include a control for bowing angle.
An overview of the afterglow phenomena compensation
Authors: Spa Carlos , Escolano Jose , Mateos Toni , Garriga Adan
Published: October 2011

In many fields such musical and room acoustics, wave propagation is usually simulated by using discrete-time numerical methods. Since 3-D simulations often show an excessive computational cost, proposals exist for extrapolating results from 3-D simulations conducted in equivalent 2-D scenarios. Among the most significant limitations of such extrapolation techniques, recently it has been pointed out the propagation of a point-like impulse in 2-D exhibits the so-called afterglow effect, which leads to obtaining non-null field values after the arrival of the wavefront. In order to compensate for this effect, a filtering process is proposed to overcome this limitation, not only in free space but also on closed spaces. Therefore, three dimensions-like impulse responses can be efficiently computed from 2-D simulations in the context of complex geometries. Recent results using pseudo-spectral time-domain, finite-difference time-domain, and digital waveguide mesh methods demonstrate the potential of this method to extrapolate impulse response from 2-D simulations with similar properties to those coming from 3-D.
Modalys, a physical modeling synthesizer: More than twenty years of researches, developments, and musical uses
Authors: Causse Rene Emile , Bensoam Joel , Ellis Nicholas
Published: October 2011

In the early 1990s, the software was initially created as an open environment with the purpose to serve as a virtual instrument maker workshop. Indeed, the modal formalism offers several interesting advantages, among them the uniform description of numerous mechanical or acoustical systems allowing easy hybridizations. Wildest virtual instruments may well be imagined, played, and manipulated. As there are very few acoustics volumes or mechanical structures tractable by an exact analytical solution, numerical methods, such as FEM, have been programmed for complex geometry for both structures and fluids. The usages are now extending from the virtual reproduction of existing instruments to industrial prototyping. This diversification as the necessity to further improve performance made it necessary to rethink many parts of the software, from the core synthesizer to the numerous interfaces: textual, MAX/MSP, OPENMUSIC, and MATLAB. To control physical modeling synthesis, it is necessary to specify the physical, low-level details of how to play an instrument. Consequently, several recent studies have focused on the study of instrumental gesture and its modeling, thereby increasing the realism of the synthesis. This presentation will review the current possibilities of the software which will be illustrated by examples. Work in progress will also be presented.
Challenges in selecting rural project locations under different types of noise regulations
Authors: Hale Marlund E.
Published: October 2011

It is sometimes desirable to locate certain types of projects in very rural areas, not only because of noise issues, but also because some may need to be close to electrical grid transmission lines, natural gas pipelines, transportation corridors, open space or special topographical features. Examples of such projects include mining operations, military training facilities, power plants, firing ranges, experimental proving grounds, and rescue dog training facilities, among many others. Whenever planners of such specialty facilities identify an appropriate location, invariably there are noise standards that must also be met before construction and operations can be permitted by the respective local authorities. While some noise requirements are quite specific, others are purposefully vague. Some noise regulations are just copied from other municipalities, while others are carefully crafted to provide for the desired community ambiance. However, a major problem can occur when typical community noise standards are applied to rural locations. This paper describes very different types of projects in quiet rural settings and their difficulties complying with the various types of typical municipal noise ordinances. Some suggestions are given to avoid the obvious noise regulation difficulties.
The potential for extracting the electromagnetic earth response from uncorrelated noise
Authors: Slob Evert , Wapenaar Kees , Snieder Roel
Published: October 2011

Thermal electromagnetic radiation from an absorbing medium allows for extracting the response of this medium. In the earth, thermal noise is usually very weak and other forms of electromagnetic noise prevail. Noise below radio frequencies is generated in the atmosphere, ionosphere, and magnetosphere, while cosmic noise generates electromagnetic waves above radio frequencies that reach the earth's surface. The noise requirements are discussed for energy and Lagrangian forms of earth response extraction by correlation and multi-dimensional deconvolution. It is shown that if the uncorrelated noise sources are located outside the earth, only the earth response to incident electromagnetic waves can be extracted. Potential applications are found for ground-penetrating radar, and these are illustrated with numerical examples. For coupled seismic waves and electromagnetic fields in fluid-filled porous media, uncorrelated seismic noise is shown to be sufficient to approximately extract the electro-seismic earth response.
Imaging and monitoring with ambient vibrations: A review
Authors: Eric Larose
Published: October 2011

The principle of passive imaging and reconstructing the Green functions by means of correlating ambient vibrations or noise will be reviewed. Some basic processing procedures for optimizing the convergence of the correlations, along with the role of multiple scattering, will also be presented. Monitoring with ambient noise constitutes a different goal that relies on different assumptions on the background noise structure. Similarities and differences between the imaging and the monitoring approaches will be addressed.
What causes the confusion patterns in speech perception?
Authors: Li Feipeng , Allen Jont
Published: October 2011

It is widely believed that speech contains redundant cues which make it robust in noise. We have discovered that natural speech often contains conflicting cues that cause significant confusion patterns in speech perception. To demonstrate the impact of conflicting cues on the identification of consonant sounds, we selected four plosives /ta, ka, da, ga/ and four fricatives /si, Si, zi, Zi/ that show significant confusion with other sounds from a female high-performance talker in the LDC database and derived a set of test stimuli by removing the dominant cue and manipulating the conflicting cue. It was found that the consonants always morph to their competing sounds, once the dominant cue is unavailable. The confusion can be strengthened by enhancing the conflicting cue. These results demonstrate that the identification of consonant is dependent on a careful balancing between the dominant cue and the conflicting cues. Such prior knowledge about perceptual cues can be used to manipulate the perception of consonants, as demonstrated by the selected examples of nonsense syllables, meaningful words, and sentence.
Invariant acoustic cues of consonants in a vowel context
Authors: Singh Riya , Allen Jont B.
Published: October 2011

The classic JASA papers by French and Steinberg (1947), Fletcher and Galt (1950), Miller and Nicely (1955), and Furui (1986) provided us with detailed CV+VC confusions due to masking noise and bandwidth and temporal truncations. FS47 and FG50 led to the succinctly summarizing articulation index (AI), while MN55 first introduced information-theory. Allen and his students have repeated these classic experiments and analyzed the error patterns for large numbers of individual utterances [http://hear.beckman.illinois.edu/wiki/Main/Publications], and showed that the averaging of scores removes critical details. Without such averaging, consonant scores are binary, suggesting invariant features used by the auditory system to decode consonants in isolated CV. Masking a binary feature causes the consonant error to jump from zero to chance (within some small subgroup of sounds), with an entropy determined by conflicting cues, typically present in naturally spoken sounds. These same invariant features are also used when decoding sentences having varying degrees of context. A precise knowledge of acoustic features has allowed us to reverse engineer Fletcher's error-product rule (FG50), providing deep insight into the workings of the AI. Applications of this knowledge is being applied to a better understanding of the huge individual differences in hearing impaired ears and machine recognition of consonants.
Dynamic spectral structure really does support vowel recognition
Authors: Lowenstein Joanna H. , Nittrouer Susan
Published: October 2011

Traditional approaches to the study of speech perception manipulate cues that are spectrally and temporally discrete, assuming these cues define phonetic segments. Alternatively, dynamic structure across longer signal stretches may support recognition of linguistic units. Strange and colleagues [Strange et al. J. Acoust. Soc. Am. 74, 695–705 (1983)] seemed to support this view by showing that adults can identify vowels in CVCs even when large portions of the syllable centers are missing, but dynamic structure at the margins is preserved. However, adults may just be “filling in the missing parts,” having learned how structure at the margins covaries with structure in the middle. To test these alternatives, adults and 7-yr-olds labeled sine-wave, and vocoded versions of silent-center stimuli. The former preserves dynamic structure; the latter obliterates it. If listeners simply fill in missing parts, adults should perform equally well with sine-wave and vocoded stimuli, and children should perform equally poorly with both. Instead, all listeners performed better with sine-wave stimuli. These outcomes provide further support for the perspective that speech perception is facilitated by broader and longer acoustic structure than that represented by notions of the acoustic cue. [Work supported by NIDCD Grant DC-00633.]
Invariants for phones or phonemes?: Only literacy leads us to expect them
Authors: Port Robert
Published: October 2011

This special session asks about “invariants,” but invariants in what domain under what transformations? If it is acoustic invariants for phones or phonemes, i.e., letter-sized units for spelling words, which implies the same acoustic cues for all contexts where a phone or phoneme is used in transcription. This clear impossibility is why Liberman turned to “motor invariants.” Yet acoustic invariants for phones are what is required for perceptual categorization. Phones (and phonemes) must be rejected as a linguistic memory code due to, at least, (a) evidence of indexical information in speech memory, (b) lack of evidence of discrete jumps for feature changes, and (c) evidence of real-time patterns in language (see Port and Leary, 2005, Lang; Port, 2011, Eco Psych). Our strong intuitions of abstract and letter-like linguistic memory result from our lifelong training with an alphabet, not from data. Memory for speech must incorporate rich detail and continuous (not serial) time and also supports some degree of abstraction for generalization to new contexts. Linguistic units like distinctive features, phones, and phonemes are merely categories, not symbol tokens. Categories are cultural conventions regarding events “considered the same” by some community (like tree and game) and do not necessarily have any invariant properties.
Acoustic tracking using compressive sensing
Authors: Edelmann Geoffrey F. , Gaumond Charles F.
Published: October 2011

This paper presents the application of compressive sensing to several problems of acoustic detection and localization on numerical and at-sea data. Compressive sensing results are shown for the detection of ship tones, bearing estimation from horizontal towed array, and target detection using a vertical array. Compressive sensing is established to be robust to low signal-to-noise ratio, to require few snap shots, and to need few sensors to achieve high probability of detection and low probability of false alarm. As a technique, compressive sensing appears insensitive to noise anisotropy, noise spectral coloration, and mild signal deviations from the sparseness paradigm. This technique potentially applies to a broad spectrum of acoustic applications. [Work supported by the Office of Naval Research.]
Sediment acoustic models and Biot's theory
Authors: Chotiros Nicholas P. , Isakson Marcia J.
Published: October 2011

The development of geo-physical descriptions of the sediment and models to predict the acoustic properties are critical to the application of sediment acoustics. The former follow standard geo-physical methods of sediment classification, based on grain size, density, and other physical descriptors. The latter started as a fluid approximation, followed by a visco-elastic approximation with five frequency-independent parameters, consistent with sediment acoustic data up to the 1980s. Recent experimental data have revealed deficiencies in this approach, particularly in the case of sandy sediments, which cover a large fraction of the continental shelves. The measurements are more consistent with a poro-elastic model, consisting of Biot's theory with extensions to account for the particular physics of granular media. There are currently two approaches to the remedy: (a) a visco-elastic model with frequency dependent parameters that mimic the experimental data and (b) a poro-elastic model with the necessary attributes. It is shown that (a) would be a significant improvement over existing models, but (b) is the preferred solution. A recent discovery concerning the viscosity of nano-meter water films has resolved a problem with the dimensions of the grain contact gap. Future plans will center on further rationalization and reduction of input parameters to develop a practical poro-elastic model. [Work supported by the Office of Naval Research, Ocean Acoustics Program.]
Bottom loss from geoacoustic inversions
Authors: Chapman N. Ross
Published: October 2011

The concept of bottom loss has traditionally been used as a measure of acoustic reflectivity and transmission at the ocean bottom. The measure was generally derived experimentally from measurements of transmission loss versus range, using a simple model that assumed perfect reflection at the sea floor to process the transmission loss data of bottom reflected signal paths. More recently, the interaction of sound with the ocean bottom has been described in terms of a geoacoustic model that defines a physical structure of sound speed, density and attenuation in the material beneath the sea floor. The model parameters are inferred from acoustic field data or observables derived from the field using sophisticated inversion techniques. The estimated model can be compared with bottom loss measurements through calculations of the plane wave reflection coefficient. This paper illustrates comparisons of bottom loss measurements for low- and high-frequency bands (50 –20,000 Hz) and calculations from estimated geoacoustic profiles for deep and shallow water environments. Conditions are discussed that limit the performance of present day inversion techniques: rough interfaces on and below the sea floor, consolidated material that supports shear wave propagation and range variation of sub-bottom structure. [Work supported by ONR Ocean Acoustics Team.]
Bottom loss measurements and their use in studying the physics of sound propagation in marine sediments
Authors: Holland Charles W.
Published: October 2011

Bottom reflection loss measurements have been conducted for four decades and have provided key insights into the physics of propagation in marine sediments. The advantage of bottom loss as an analysis quantity is that, in principle, it completely isolates the role of the seabed and permits separation and identification of key physical mechanisms. For example, it was early deep water bottom loss measurements that first made it clear that strong positive sediment sound speed gradients existed and the concomitant surprising realization that the dominant seabed interacting path was the refracted and not reflected path over a wide angular and frequency band. In this talk, various discoveries from bottom loss measurements are discussed including the role of sediment layering, attenuation gradients, and shear waves.
Bottom loss modeling and sand grain size
Authors: Isakson Marcia J. , Chotiros Nicholas P.
Published: October 2011

Bottom loss is a critical parameter in sonar performance assessment and propagation modeling. There exist many empirical models that predict bottom loss based both on measured parameters and on sand grain size. In this study, the empirical model predictions are compared with in situ measurements of bottom loss. The predictions are based on both the measured parameters and the sand grain size. It is found that at mid frequencies, the predictions based on sand grain size are much more consistent with the measurements than the model based on the measured parameters. This is due to unrealistic empirical sediment parameters such as density which mimic other physical processes not included in the model. However, when the empirical sand grain size model is extrapolated to predict bottom loss at higher frequencies, the results are inconsistent with measurements. [Work supported by ONR, Ocean Acoustics.]
Role of rattlers in bottom loss and sound wave propagation
Authors: Berryman James G.
Published: October 2011

It is known from both laboratory and numerical experiments that weakly or poorly consolidated granular media have some fraction of the grains that do not contribute to the overall mechanical strength of the granular system. Such loose grains are sometimes called rattlers, and their presence affects both acoustic wave speeds and attenuation. Sound wave speeds tend to be reduced while the wave attenuation tends to be increased. An analytical model of such systems will be presented and comparisons to available data will be shown.
High frequency dispersion model for the water-saturated granular medium
Authors: Yang Haesang , Lee Keunhwa , Seong Woojae
Published: October 2011

Dispersion relation for the p-wave sound speed and attenuation has been described by several models based on continuum or scattering theory. As an alternative approach, this study proposes a model describing the dispersion relation for the p-wave in case of grain scatterers existing in background porous medium. Dispersion relations are shown as a function of different grain size distribution and Rayleigh parameter ka. For quantitative analysis of the proposed model, experiments are performed using water-saturated glass beads. Two sets of experiments employing unimodal and bimodal grain size distributions are performed and are used for comparison with the current proposed model.
Adaptive ocean sampling for acoustic ocean uncertainty reduction
Authors: Heaney Kevin D. , Campbell Richard L.
Published: October 2011

For many oceanic environments, acoustic propagation is critically dependent upon the local environment through boundary interaction and volume variability and fluctuations. In shallow water, near the continental shelves, ocean dynamics and variability can lead to significantly different propagation regimes on timescales of hours and spatial scales of kilometers. Optimal adaptive sampling, with assimilation of oceanographic variables into a dynamic ocean model, can be used to reduce the model forecast uncertainty and improve the confidence in acoustic predictions. Oceanographic uncertainty and acoustic sensitivity, however, are not always well correlated. In this paper, an acoustic uncertainty cost function will be used to drive the adaptive sampling of an oceanographic AUV in coastal water. Applications to an experiment off the coast of Taiwan (quantifying, predicting, and exploiting uncertainty) will be performed, with model-data comparisons of acoustic propagation for moving sources and drifting receivers. During the test, acoustic adaptive sampling computations were performed in real time, oceanographic measurements were made, assimilated into a dynamic ocean model and acoustic transmissions were recorded. [Work Supported by ONR.]
Interfaces between acoustic prediction, embedded signal processing, and behaviors at NATO Undersea Research Centre
Authors: LePage Kevin D. , Baralli Francesco , Been Robert , Goldhahn Ryan , Hamilton Michael J. , Kemna Stephanie , Micheli Michele , Sildam Juri , Vermeij Arjan
Published: October 2011

The use of acoustic sensing systems for ASW in heterogeneous sensor networks utilizing marine robots has been a subject of research at the NATO Undersea Research Centre for the past several years. In this talk, we discuss the unique challenges of implementing ASW on autonomous, collaborative networks of AUVs, including the challenges of embedding the active sonar signal processing, implementing effective underwater messaging, and designing adaptive behaviors to optimize system performance. Theoretical studies, simulations, and results from the recent GLINT series of sea trials are shown and the way forward for autonomous sensor system studies at NURC is discussed.
Solutions to retain acoustical functionality against the tide of fad, fashion, and finance
Authors: Good Kenneth
Published: October 2011

Too often in recent years, building acoustics have been the casualty of other design considerations. Changes in design styles, flexibility, and building densities have left many building occupants stressed and distracted. The Center for the Built Environment and other data suggest that the recent Green focus has made the situation even worse as the (acoustical) function of buildings is being compromised to fad, fashion, finance, and other considerations. This paper will look at the acoustical properties of products to meet these changes, solutions to maintain the acoustical functionality of interior spaces.
The dB focus tube uses to improve the transmission loss efficacy of walls, ceilings, and pipes
Authors: Schnitta Bonnie
Published: October 2011

Studies indicate that locating and treating even very small acoustic leakage points in wall, floor, and/or ceiling partitions will significantly improve the FSTC performance of these partitions. The dB focus tube, patented on March 22 of this year, is an inexpensive small mechanism that can easily be transported to and from job sites. It is audible even during high levels of construction activity. The resulting patented small tube can be utilized by an acoustic engineer to locate even the smallest of acoustic leakage points in a partition which, when sealed, could increase the FSTC performance of the partition by typically 10 points. Additionally, when an engineer is trying to determine the main paths of flanking, this tube proves to be an ideal mechanism for facilitating this problem solving method. An acoustic installer can use the focus tube to confirm the optimum efficacy of the acoustic treatment of PVC piping or duct work. In addition, another interesting application is using the dB focus tube to locate air leaks in window assemblies which, when sealed, improve the window performance in regards to not only the STC and air infiltration, but also its thermal capacity.
Increasing diffuser efficiency through asymmetrical third dimension modification
Authors: Lenz, Richard L.
Published: October 2011

In 1975, Dr. Manfred Schroeder presented his seminal work on quadratic-residue diffusion, giving us a frequency-based method for creating acoustic diffusers. The QRD equation defines the method for creating the depths (Z plane) of the wells in a diffuser. Subsequent work has given us understanding of the effects of the width of the diffuser wells (X plane) on high frequency performance. One artifact not addressed in the Schroeder equation is the inherent absorption realized in the execution of the design. This absorption becomes more pronounced as the design gets deeper, thereby limiting the practical low-frequency cutoff of QRDs. Experiments by the author, utilizing an asymmetrical cellular acoustic diffuser design, have yielded surprising results in the efficiency of acoustic diffusion. By reducing both the width of the cells and separating the diffuser into asymmetrical zones in the X and Y (vertical) planes, it has been shown that the absorption below the design cutoff frequency of the diffuser design can be dramatically reduced. The presentation will show the evidences of these experiments and the increased efficiency of QRD design through asymmetrical third dimension modification. [Work support was provided by Ron Sauro of NWAA Labs.]
Conference rooms: Criteria, guidelines, acoustical problems solutions (case studies)
Authors: Evans Jack B. , Leasure Joshua D.
Published: October 2011

Conference rooms are subject to privacy and sound containment issues, intrusive and distracting noise, excessive continuous background sound, and reflection/reverberation problems, particularly those with microphones and loudspeakers. Good acoustical environments are necessary for intelligible speech communications and remote signal transmissions, while sound isolation is needed for privacy and prevention of distraction. Acoustical criteria are presented with practical guideline parameters. Case studies cover acoustical problem issues that needed correction in existing conference rooms. On-site observations, acoustical measurements and analyses of facility plans were used to diagnose problems and determine correction approaches. Photographs are shown to illustrate difficult conditions. While little is original, the case studies point out classic problems of flutter echoes, ceiling-mounted or suspended microphones, back radiated loudspeaker noise in ceiling plenums, glass walls, multiple sound flanking paths, and similar problems found. Solutions developed or implemented are presented. In some cases, before and after data are provided to show results.
The build up rate of broadband spatial coherence between multi-sensor passive arrays in the ocean waveguide
Authors: Walker Shane
Published: October 2011

Broadband noise correlation methods for the passive extraction of information about the point-to-point propagation of waves between distant sensor locations have received considerable attention in the literature. This talk addresses the rate at which the wave coherence accumulates to overcome stochastic random fluctuations in a spatially correlated random wave field. It is shown that the expected magnitude of the random uncertainty associated with a single realization of the sample cross-correlation function depends on the total power incident on the sensors. This notion is applied to quantify the emergence rate of the coherence between correlated beams in the ocean waveguide. The point-to-point build-up rate is compared to the gain achieved through the application of directional filters over multi-sensor line arrays. Various array geometry scenarios of experimental interest are considered. These results are straight forwardly extendable to other environments such as seismics, helioseismics, and nondestrutive testing.
Low-frequency broadband noise correlation processing in deep-water
Authors: Fried Stephanie , Sabra Karim G. , Kuperman W. A. , Prior Mark K
Published: October 2011

The Comprehensive Nuclear-Test-Ban Treaty Organization operates an International Monitoring System (IMS). The IMS includes hydroacoustic stations composed of hydrophones deployed in the ocean deep-sound-channel in a two-kilometers-side triangular configuration(referred to as triad) in the horizontal plane. Data are continuously recorded on hydrophone triads (with a sampling frequency of 250 Hz) and have been archived during the last decade. Previous experimental studies have demonstrated that coherent waveform can be extracted from broadband coherent processing of ocean ambient noise, typically above f > 100 Hz [e.g., see Roux et al., J. Acoust. Soc. Am. 116(4), 1995–2003 (2004)] . We investigated here the emergence of coherent arrivals from the correlation processing of the low-frequency broadband ambient noise recorded during the years 2006–2007 on IMS hydrophones located in the Southern Hemisphere. This low-frequency acoustic ambient noise includes various components from anthropogenic and biological sources as well as from seismic origin (e.g., earthquakes and microseims) and also significant ice-breaking noise originating from Antarctica especially during the Austral summer period. The feasibility of passive basin scale tomography using long-term monitoring of ocean noise will be discussed.
Passive geoacoustic inversion in a dispersive waveguide
Authors: Bonnel Julien , Gervaise Cedric , Nicolas Barbara , Mars Jerome
Published: October 2011

This study introduces a single-receiver geoacoustic inversion method adapted to shallow water and low frequency sources. Because of the single receiver context, most existing methods are based on the time-frequency (TF) analysis of the received signal, and their practical applications are restricted to impulsive sources. The proposed method is different and allows for geoacoustic inversion using unknown frequency-modulated sources. To perform the inversion, the modes are first filtered from the received signal using advanced TF analysis. Then, the filtered modes are processed in the frequency domain using a new transformation called modal reversal. This transformation, parametrized using environmental information, undoes dispersion for a given mode. When environment is well known, dispersion is perfectly compensated and all the reversed modes are in phase. This is not the case when modal reversal is ill-parametrized. Consequently, modal reversal can be used as the core of an original inversion scheme. Inversion results are obtain through a specific cost function adding up the reversed modes. Source/receiver range and source frequency-law are obtained as a by-product of the geoacoustic inversion. The method can thus be adapted to the study of low-frequency calls of marine mammals in shallow water.
Seismo-acoustic propagation effects at the seafloor with applications to geoacoustic inversion using hybrid parabolic equation solutions
Authors: Metzler Adam M. , Collis Jon M.
Published: October 2011

Accurate and efficient prediction of propagation over realistic models of elastic ocean sediments has been achieved recently using parabolic equations. Historic treatments that ignore effects due to elasticity may not be accurate for certain scenarios, specifically for example shallow-water environments. Neglecting elastic phenomena does not account for second order effects such as energy loss due to frequency dependent attenuation. In this presentation, a three-layer ocean environment is examined consisting of a fluid overlying a transitional solid layer overlying an elastic basement. The transitional solid layer is investigated for various types of media, including fluid, poro-elastic, and elastic. Solutions obtained from hybrid parabolic equations are used to quantify the nature of the transitional solid layer and establish regimes where each approximation would be appropriate. An application in geoacoustic inversion to identify bottom type is shown through comparisons of interface wave structure for different transitional solid layers. [Work supported by the ONR.]
Estimation of shear speed using interface wave dispersion
Authors: Giard Jennifer , Potty Gopu R. , Miller James H. , Greene Jeannette M. , McNeese Andrew R. , Wilson Preston S.
Published: October 2011

Our recent work has highlighted the effect of shear on the dispersion of acoustic normal modes. Specifically, sediment shear speed can significantly impact compressional modal arrival times near the airy phase. In addition to underwater acoustic propagation effects, shear properties of sediments are directly related to the strength of the sediments in geotechnical applications. All of these factors emphasize the importance of estimating shear speeds in semi-consolidated shallow water sediments. One of the most promising approaches to estimate shear speed is to invert the shear speed profile using the dispersion of interface waves (Scholte waves). The propagation speed and attenuation of the Scholte wave are closely related to shear-wave speed and attenuation over a depth of 1–2 wavelengths into the seabed. Results from the tests conducted at Narragansett Bay in water depths ranging from 10 to 25 m using the shear measurement system, developed at the University of Rhode Island based on this concept, will be presented. Combustive sound source (CSS) will be used to generate interface waves. Data collected during these tests will be shown and preliminary estimates of the shear speed will be presented and compared with ground truth data. [Work supported by Office of Naval Research.]
Asymptotic behavior of vertical travel-time sensitivity kernels with increasing propagation range
Authors: Skarsoulis E. K. , Cornuelle B. D. , Dzieciuch M. A.
Published: October 2011

Vertical travel-time sensitivity kernels (VTSKs) describe the effect of horizontally uniform sound-speed changes on travel-times in range-independent environments. Wave-theoretic VTSKs can be obtained either analytically, through perturbation of the normal-mode representation, or numerically, as horizontal marginals of the corresponding 2D and 3D travel-time sensitivity kernels. In previous works it has been observed that, as the propagation range increases, wave-theoretic VTSKs approach the corresponding ray-theoretic sensitivity kernels even for low frequencies. In the present work an asymptotic expression of the wave-theoretic finite-frequency VTSKs is obtained, using a stationary-phase approach. Numerical results show that wave-theoretic VTSKs converge with increasing range toward the asymptotic form, which in turn lies very close to the ray-theoretic VTSK. [Work supported by ONR.]
Scattering reduction of an acoustically hard cylinder covered with layered pentamode metamaterials
Authors: Boisvert Jeffrey E. , Scandrett Clyde L. , Howarth Thomas R.
Published: October 2011

Unlike traditional target strength reduction coatings that rely on energy dissipation or other mechanisms to mitigate reflection, a coating comprised of metamaterials would behave as an acoustic waveguide that diverts sound energy around the object, thus reducing scattered energy. The majority of the literature has featured theoretical ideal metamaterial designs that have unrealizable properties, i.e., infinite mass, vanishing bulk modulus. However, our analysis has suggested that it may be possible to obtain effective scattering reductions with realizable material properties in a layered configuration using metafluids. In this context, realizable implies material properties that are constrained to lie within reasonable ranges relative to the density and bulk modulus of water. The multistatic scattering reduction of an acoustically hard cylinder covered with layered metafluids for plane wave incidence is analyzed. A range of coatings are considered, from those comprised of fluid layers that are isotropic in bulk moduli with anisotropic density (inertia) to those having anisotropic bulk moduli and isotropic density (pentamode). [Work supported by NAVSEA Division Newport ILIR.]
An acoustic directional antenna with isotropic materials
Authors: Layman, Christopher N. , Martin Theodore P. , Orris Gregory J.
Published: October 2011

New acoustic metamaterial devices offer promising applications, ranging from tunable sound blocking with superior efficiency to acoustical diodes. Transformation acoustics (TA), relying on the invariance of field equations under coordinate transformations, in conjunction with metamaterial features, has further expanded the range of functionalized acoustic materials. However, for a large variety of devices based on TA, such as ones relying on Pendry's concept, physical realization remains limited owing to the requirement of anisotropic effective properties. Here we examine the behavior of a directional four-wave acoustic antenna, designed from finite embedded coordinate transformations (FECT), which eliminate the constraint of anisotropy by way of a suitable conformal mapping. The two dimensional antenna consist of a square rod with an inhomogeneous and isotropic distributed mass density and bulk modulus designed from the FECT perspective. The rod is imbedded in an acoustically matched matrix and subsequently subjected to an internal coaxially line source to evaluate its transmitting performance across a large bandwidth. Passive characteristics are also studied by probing the antenna with a point source-receiver setup. Experimental data are compared to both established analytical FECT models and full-wave simulations. [Work is supported by the Office of Naval Research.]