bluuebunny/crossref_metadata_2025 huggingface dataset:
Interference patterns in range dependent environments
Authors: Cox Henry , Heaney Kevin D.
Published: October 2013

Interference patterns in space and frequency occur in ocean acoustics due to coherent multipath propagation. The wave guide invariant beta is commonly used to describe the behavior of these patterns [Brikhosvsky and Lysanov, Fundamentals of Ocean Acoustics, 2nd ed. (Springer-Verlag, New York, 1991)]. The standard derivation of this invariant uses a normal mode expansion and is limited to range independent and weakly range dependent environments. A different approach is introduced that describes the interfering components in terms of their travel times. This leads to a very simple derivation of basic results that apply equally well to range dependent environments and to situations, such as Lloyd’s Mirror, in which the normal mode representation is inconvenient. Beta can be expressed in terms of the local phase velocities and the difference in travel times for the interfering components. The travel time differences involve integration over the entire path trajectories from the source to the point where the interference pattern is observed. Numerical examples using ray theory will be presented.
Evidence of three-dimensional waveguide propagation in SWARM 95 data
Authors: Frank Scott , Siegmann William L. , Badiey Mohsen
Published: October 2013

During a period of the SWARM95 experiment, strong nonlinear internal waves passed across two tracks that had airgun pulses propagating along them. Environmental data for this period indicate that the angles between the tracks and the internal wave-fronts, which were roughly planar, were very different—one angle being close to zero, and the other approximately 42 deg. Two-dimensional PE simulations for these waveguides show dramatically different results for depth-averaged, pulse-integrated energy variations. Specifically, the observed levels can be reproduced for the waveguide with the large incidence angle, but not for the one with the small incidence angle. For the latter case, data show significant variations in pulse shapes and in the integrated energy (≊5 dB), while simulations show very small changes in both of these characteristics. Results from several recent computational and theoretical studies suggest that the cause may be three-dimensional effects from horizontal refraction and modal interference due to the nonlinear internal waves. The adiabatic mode parabolic equation [Collins, J. Acoust. Soc. Am. 94 (1993)] is used to quantify the three-dimensional influence of the internal waves on the integrated energy variations. The results demonstrate experimental evidence of three-dimensional effects from strong nonlinear internal waves. [Work supported by ONR.]
A study on simplification of the Biot–Stoll model in water-saturated porous medium
Authors: Lee Keunhwa , Seong Woojae
Published: October 2013

A practical approximate method based on the Biot–Stoll model to represent acoustic waves in the ocean in the presence of porous sediment is presented. The ocean sediment can be described individually by four models; visco-fluid, visco-elastic, equivalent fluid, and water-saturated porous medium. The first two models are approximate forms of the Biot–Stoll model. The equivalent fluid model of Zhang and Tindle [J. Acoust. Soc. Am. 98, 3391–3396 (1995)] derived for the fluid/solid interface is extended to the fluid/porous-medium interface for analytical derivation of the reflection coefficient. Then, the reflection characteristics as functions of frame stiffness (Kb/Kr) and frequency region (f/fc) are discussed for all four models. In weak stiffness and high-frequency region, the equivalent fluid and visco-fluid bottom models describe ocean bottom better than the visco-elastic bottom model. Two-phase property is dominant in strong (high) stiffness or high-frequency region. This demonstrates that the visco-fluid and equivalent fluid models are useful approximate models in weak stiffness porous material such as the marine sediment.
Analysis of very high frequency propagation in sediments: Experimental results and modeling
Authors: Brothers Richard , Page Sarah , Heald Gary , Leighton Tim , Simpson Matt , Dix Justin
Published: October 2013

A current QinetiQ study is investigating the propagation of sound waves into sediment at frequencies higher than 300 kHz. Previous work has found notable discrepancies between model predictions and experimental results and comparisons are inconsistent and unreliable. This new work package investigates the development of new scattering theories for frequencies ranging from 300 kHz to 1 MHz. In particular, the application of a pseudospectral time difference approached is analyzed. The model originally developed for lower frequency applications, is set up in various geometrical scenarios and for varying very high frequencies. Results show the received simulated pulses obtained for hydrophones placed within the sediment and source colocated. Furthermore, simulations are compared in tank experimental data. The controlled tank experiments were conducted by Southampton University and data are analyzed and discussed for various conditions and frequencies.
Reverberation time measurement using integrated impulse response and sweep sine excitation
Authors: Nabuco Marco , Brando Paulo
Published: October 2013

As the capacity and speed of digital processing systems becomes much higher, the integrated impulsive response for reverberation time measurements by the indirect method also becomes more feasible and faster. The MLS technique to obtain the impulse response for LTI has been developed during the last several years and it is very well reported by the bibliography. Some frequency analyzers available in the market are capable to generate and process MLS to get the impulse responses very easily. Sometimes, when the room to be tested is very reverberant, sequences of higher order and a certain number of average are necessary to assure acceptable signal-to-noise ratio. The sweep sine technique or the deconvolution method to obtain impulsive responses presents many new advantages, most of them still reported in various technical documents. This paper presents the results of application of this technique to measure the reverberation time in two different reverberation rooms. Comparisons with MLS, ensemble, and reverberation time averages are presented. The sweep sine technique repeatability was verified in a reverberation chamber for a polyurethane foam sample and showed smaller standard deviations when compared with other techniques. (To be presented in Portuguese.)
Sound absorption in a scale model reverberation chamber
Authors: Nascimento Ranny , Zindeluk Moyses , Feiteira Jose Flavio
Published: October 2013

Scale models of rooms are widely used to investigate architectural acoustics. However, when building a room model, the choice of materials to simulate the surfaces of the original room should follow carefully the similarity conditions. In practice, it is very difficult to model the acoustic parameters of the materials used in room scale models. This work consists in the construction and validation of a small-scale reverberation chamber, according to the international standards, developed in order to improve similarity conditions in scale modeling. Such a chamber is relatively low cost and its configuration can be easily modified. The volume of the model reverberation chamber is 0.389 cubic meters, equivalent at 1:8 scale to a real volume of 200 cubic meters, a standard size for reverberation chambers. Made in wood with one transparent acrylic side, the one-eighth scale reverberation chamber can be used to test theories about room acoustics as well as to test absorbing materials. Experimental results for the chamber qualification are presented and the search for octave band similar materials is reported.
Comparison of the uncertainty budget between the one- and the two-microphone method for reflection and absorption coefficient
Authors: Esquivel D. Adolfo , Muñiz Lorenzo M.
Published: October 2013

The impedance tube is mostly used to measure the reflection and absorption coefficient at normal incidence based on ISO 10534-2. It is possible to use the one-microphone or the two-microphone method, where either a pseudorandom or random signal is used to produce a standing wave pattern inside the impedance tube in order to measure the transfer function and obtain the reflection and absorption coefficient. The transfer function in both methods of measurement can be expressed in three different mathematical ways: (a) by the transfer function given by the signal analyzer itself, (b) by the auto-spectrum and the cross spectrum between the two-microphone positions, and (c) by the coherence between the two-microphone positions. The reflection and absorption coefficient as a function of those variables, and its measurement uncertainty is discussed considering those three cases of the transfer function for the two methods of measurement in the frequency range from 50 Hz to 1.6 kHz. Likewise the analysis of the uncertainties sources and its sensitivity coefficients are studied using a linear approach model for both techniques, and for each of the proposed cases. (To be presented in Spanish.)
A comparison of visual and acoustic marine mammal monitoring methods
Authors: Frankel Adam
Published: October 2013

Concern about the potential effect of increased oceanic noise on marine mammals has led to the consideration of a variety of at-sea marine mammal monitoring methods. A recent marine mammal survey utilized both visual observation and passive acoustic monitoring. Visual observations were conducted using 7×50 binoculars during the day and generation III night vision devices (NVDs) at night. Acoustic data were collected with a towed hydrophone array and analyzed with a customized, PC-based acoustic workstation. Seventy-seven visual sightings were made. Forty sightings were made at night and 37 were made in daylight. The effective range of the NVDs was estimated through observations of a target at known distances; 50% detection rating was achieved at 130 meters. There were 98 acoustic detections. Of the 77 visual sightings, 42 were also detected acoustically. Six sightings were made without comparable acoustic detection, and 19 sightings were made when there was no acoustic monitoring. Conversely, 56 acoustic detections were made without visual sightings. These data suggest that, for species that commonly vocalize, a combined acoustic/visual survey will increase detection probabilities. Furthermore, night vision devices have the potential to be an effective observation tool for marine mammals.
Passive three-dimensional tracking of sperm whales using two towed arrays during the 2001 SWAMP cruise
Authors: Thode Aaron , Mellinger David K , Martinez Anthony
Published: October 2013

The capability to passively track multiple sperm whales simultaneously in three dimensions can provide useful information about the animals’ acoustic interactions, sound production mechanisms, and potential responses to anthropogenic noise. In 2000 this capability was demonstrated using a single towed array in the Gulf of Mexico, by exploiting the multipath information from surface and bottom returns. The relative paucity of bottom returns, and the difficulties involved in automatically detecting these returns, limited the utility of that method. In this presentation data collected during the 2001 SWAMP cruise in the Gulf of Mexico are used to explore how two arrays deployed serially behind a survey vessel can provide a means for automatically extracting all the relevent information required for 3-D tracking. Using the signal-processing program Ishmael, and segments of time where two whales are vocalizing simultaneously, it is shown that enough information can be extracted to track the animals. However, the problem complexity is increased by sound-speed refraction effects and the lack of information about the array depths. [Work supported by SE Fisheries, National Marine Fisheries Service, Minerals Management Service, and the ONR.]
Recording spider monkeys with a microphone array
Authors: Wahlberg M. , Ramos-Fernandez G. , Ugarte F.
Published: October 2013

The potential of using a GPS-linked microphone array [J. Acoust. Soc. Am. 109, 434–437 (2001)] to monitor spider monkeys (Ateles geoffroyi) In the rainforest of the Yucatan peninsula, Mexico, was assessed. This species is of concern for conservation because of their requirement of large areas of relatively undisturbed tropical forest. The array was composed of six independent nodes. Each node consisted of a DAT recorder, a microphone, a GPS receiver and a small computer. The GPS data, containing both timing and location information, was converted into an audio signal and recorded on the tape parallel to the microphone signal. In this manner the recordings were synchronized and the receiver locations logged. The recordings were used to locate vocalizing monkeys. We measured the apparent source level and directionality of monkey vocalizations, and the transmission loss through the rain forest canopy. The system has a potential for studying the behavior of spider monkeys, as well as other sound-producing animals. This could have useful applications for the monitoring of important species for conservation. [Work supported by the Danish National Research Council and Pronatura, Mexico.]
St. Lawrence blue whale (Balaenoptera musculus) vocalizations
Authors: Berchok Catherine , Bradley David , Gabrielson Thomas , Sears Richard
Published: October 2013

The Mingan Island Cetacean Study has been conducting biological field research on St. Lawrence blue whales since 1979. Currently, they have photo-identified 384 individuals and determined the gender of 37% through skin biopsy sampling. In a typical field season, approximately 85% of the 60–90 blue whales identified have been seen before, so a larger percentage (65%) have known gender. During four field seasons (1998–2001), 134 h of acoustic recordings were made in the presence of this well-studied population of blue whales. A calibrated omni-directional hydrophone, suspended from a surface isolation buoy, was deployed from an inflatable boat positioned close to the whales. Simultaneous visual observations were made during the recording sessions, with individual identities confirmed through photo-identification work between sessions. The primary field site for this project was the lower estuary region of the St. Lawrence River, with most recordings made between mid-August and late October. Both infrasonic tonal call sequences as well as aubible downsweep calls were recorded. Temporal and spatial distribution of the two call types will be presented, and possible correlations with behavior and/or social grouping will be discussed. [Work supported by ARL/PSU, NSF, and the American Museum of Natural History.]
Vocal repertoire of the freshwater dolphins Inia geoffrensis and Sotalia fluviatilis in Colombia, South America
Authors: Diazgranados Maria Claudia , Trujillo Fernando
Published: October 2013

The Omacha Foundation conducted a project to identify and compare vocal repertoires of the freshwater dolphins Inia geoffrensis and Sotalia fluviatilis in the Amazon and Orinoco Rivers in Colombia. Field recordings of 2457 min. were made using an omnidirectional hydrophone connected to a cassette recorder. Six different types of sounds were identified for Inia geoffrensis humboldtiana in the Orinoco River. Low-frequency whistles were recorded (fundamental signal around 3 kHz, maximum frequencies of 13 kHz), when foraging/socializing dolphin groups consisted of more than five animals. Screams, squeaks, pulsed sounds, low-frequency sounds, and echolocation clicks were identified as additional sound types for the species. In the Amazon region, where both species of river dolphins are found, recordings were only analyzed when the species occurred separately. Four different types of vocalizations including echolocation clicks, screams, squeaks, and pulsed sounds were identified for Inia geoffrensis geoffrensis. No clear whistles were heard for this species. Sotalia fluviatilis whistled constantly, even when only two dolphins were sighted. Whistles varied in frequency contour and duration. Generally high frequencies were observed with maximum values of 21.7 kHz and a fundamental signal of 15.8 kHz. Squeaking sounds, echolocation clicks, and burst pulses were also recorded. (To be presented in Spanish.)
Remote sensing of sandy sediment ripples using high-frequency backscatter
Authors: Williams Kevin , Tang Dajun
Published: October 2013

The presence of bottom ripples changes the acoustic interaction with sediments. Two important ripple parameters are the height and spatial wavelength. In previous work, in situ measurements of ripple were made using stereophotography and electrical conductivity. Although these methods are accurate and dependable, they can only be carried out over limited areas (the order of 15 meters on the side). Using acoustic backscattering to remotely measure the ripple field, on the other hand, is fast and can cover much larger areas (the order of 50 m by 50 m). Data from a 300 kHz system with two closely spaced receivers was used to estimate ripple wavelength and height. Data analysis and numerical simulation show that, as long as the wavelength of the sound wave is much shorter than the ripple wavelength, it is straightforward to resolve the wavelength of the ripple field. To measure the ripple height, however, is more difficult. The best results were obtained when the horizontal projection of the sound beam was neither parallel nor perpendicular to the ripples. In simulations a composite model was used, where the large scale ripples and small scale roughness are treated as Kirchhoff and Lambertian scatterers, respectively. [Work supported by ONR-USA.]
Geoacoustic inversion of tow-ship noise via near-field matched-field processing
Authors: Battle David J. , Gerstoft Peter , Kuperman William A. , Hodgkiss William S. , Siderius Martin
Published: October 2013

The estimation of geoacoustic parameters of marine sediments and sub-sediment layers involves the measurement of acoustic fields in the ocean waveguide for comparison with accurate forward propagation models. This paper discusses self-noise geoacoustic inversion of tow-ship noise data acquired via a horizontal towed array from the standpoint of near-field matched-field processing (MFP). In particular, the sensitivity of the reconstructed source power to perturbations in the parameters of a short-range propagation model are quantified. Through simulations and experimental results, it is shown that even very quiet ships radiate sufficient noise power to enable self-noise inversion of basic geoacoustic parameters such as effective bottom velocity. The experimental results presented are particularly encouraging in view of the high level of interference shown to be tolerated from nearby shipping.
A self-navigating, unmanned sailboat for studies in acoustical oceanography
Authors: Palmer David R. , Schlieben Ernest W. , Hendee James C.
Published: October 2013

Based on a patent by one of us (E.W.S., Patent No. 3,556,035) RCA developed during the 1970’s the concept of a self-navigating, unmanned, sailboat. It was designed to be deployed from a ship or from shore, to sail for thousands of miles on a predetermined course, to collect upper ocean and meteorological data while station keeping, to telemeter those data back to shore by satellite, and then return to the point of departure, or some other point, up to a year later. It could carry any equipment ordinarily placed on buoys and could function in hostile weather and climatic conditions. This vessel seems ideally suited for the measurement of a number of ocean parameters using acoustical methods. We discuss the characteristics of the prototype that was built and tested with U.S. Navy support and compare its properties with Unmanned Air Vehicles (UAVs) and Autonomous Underwater Vehicles (UAVs) that are presently being used or are under development. We describe our plans for resurrecting the RCA effort and, in particular, a sea trial designed to test the automatic enroute sailing and station-keeping of the vessel in an ocean environment using GPS and modern data transfer capabilities.
Propagation through a stratified ocean waveguide with random volume and surface inhomogeneities, Part II. Application: Internal waves, bubbles, sub-bottom and seafloor anomalies
Authors: Chen Tianrun , Ratilal Purnima , Zanolin Michele , Makris Nicholas C.
Published: October 2013

Analytic expressions for the mean acoustic field propagated through a stratified ocean with a distribution of random volume and surface heterogeneities that may be large compared to the acoustic wavelength, presented in this session by Ratilal and Makris, are used to study the effect of internal waves, bubbles, and sub-bottom anomalies as well as seafloor and seasurface roughness on acoustic propagation in both shallow and deep water. Oceanographic and geologic data are used to probabilistically characterize the acoustic properties of the anomalies in terms of their size, shape, sound speed and densities. The expected scattering function for the anomalies are then computed as a function of depth. These are used to determine attenuation and dispersion coefficients as well as the forward propagated field as a function of range and depth.
Local tissue displacements induced by a focused ultrasound beam
Authors: Deng Cheri
Published: October 2013

The acoustic radiation force generated by an ultrasound beam in a medium where energy density gradient exists as the result of absorption or reflection can induce local tissue movement. Through energy absorption, an ultrasound beam can also cause local temperature rise in tissue, which can induce thermoelastic displacement because of thermal expansion. The radiation-force deformation is related to tissue elasticity and has been investigated for tumor detection in ultrasonic imaging and for monitoring therapeutic lesion size and location in high intensity focused ultrasound (HIFU) applications. In our study, theoretical and numerical models are developed to simulate the displacements induced by a focused ultrasound beam such as a HIFU beam and an imaging pulse, including both the radiation force deformation and thermoelastic displacement. Temperature rise resulted from the beam is computed using a 3D finite-difference algorithm that evaluates the bioheat equation. Thermoelastic displacements are obtained from the temperature rise. Radiation-force displacements are computed using finite-difference algorithm that solves the equations of motion subjected to such internal body force. The mechanical and thermal effects are compared and studied to elucidate how tissue displacements are related to factors including exposure characteristics and tissue properties such as absorption coefficients and Young’s modulus.
Ultrafast imaging of transient shear waves for breast elastography: First clinical results
Authors: Bercoff Jeremy , Catheline Stefan , Chaffai Sana , Tanter Mickael , Sandrin Laurent , Fink Mathias , Meunier Martine
Published: October 2013

Transient elastography of soft human tissues has been developed in our lab for several years. This technique consists in following the shear wave propagation induced by a low frequency pulsed vibrator located at the surface of the body with an ultrasonic imaging system. As the shear wave speed can reach up to 10 m/s, an ultrafast imaging system made of 128 fully programmable and independent channels has been developed able to produce 5000 images/s. Such frame rates are attainable by limiting the emission to a plane wave illumination and achieving the beamforming only in the receive mode. The comparison of successive images by classical cross-correlation techniques allows us to produce a 2-D movie of the displacements induced by the shear wave deep inside the body. An inversion algorithm is then used to recover the shear modulus map from the spatiotemporal data. We present here the first clinical results obtained on 20 female patients. These preliminary results of quantitative imaging of breast elasticity are very promising. The limits of the system due to shear wave diffraction are discussed and the improvements planned for the next clinical experiments are discussed.
Optoacoustic probe for prostate cancer diagnostics
Authors: Andreev Valeriy G. , Karabutov Alexander A. , Oraevsky Alexander
Published: October 2013

The optoacoustic probe for prostate cancer detection was developed and tested. The 10-ns pulses of the YAG:Nd laser were delivered by an optical fiber with a turning mirror at its tip. A fiber tip was placed above an ultrasonic array which was employed for the detection of acoustic transients excited inside prostate tissue. The increased infrared light absorption inside prostate tumors resulted in acoustic pulses with enhanced peak pressure providing 200%–300% optoacoustic contrast. The transducer array and the optical fiber were wrapped inside a 20-mm diameter thin cylindrical shell filled with ultrasonic gel transparent for infrared radiation. Each acoustic transducer was made of 0.05-mm thick PVDF film with dimensions of 1 mm×12 mm. The frequency bandwidth of transducer array provided 0.3-mm axial in-depth resolution. The lateral resolution is defined by the array length and was estimated as 0.8-mm for 32-element array with 1-mm gap between transducers. Transducer sensitivity of 0.05 mV/Pa allowed the detection of 2-mm tumor located at 50 mm depth. The optoacoustic probe performance was evaluated via the acquisition of two-dimensional optoacoustic images of small absorbing spheres in prostate-tissue phantoms. [Work supported by NIH and FIRCA grants.]
Design of a coreless electromagnetic projector for an A-size sonobuoy
Authors: Clark Joseph A. , Young Jane A.
Published: October 2013

An electromagnetic projector has been designed that uses a pair of closely spaced pancake coils to produce low-frequency, high-power, steady-state and transient underwater pressure waves. The design requires no magnetic core materials with their associated weight and saturation limits. The projector is inexpensive to build, robust in construction, and small enough to fit with a power source in an A-size sonobuoy. An electromechanical circuit analysis of the design shows that high efficiencies can be achieved at low frequencies because the large surface motions, required to generate useful acoustic flows, do not cause significant stressing of the projector. [Research supported by ONR.]
Testing of a coreless electromagnetic projector for an A-size sonobuoy
Authors: Young Jane A. , Clark Joseph A.
Published: October 2013

The feasibility of using coreless electromagnetic coil projectors as underwater sources of coherent sound was explored by building and testing a projector in an acoustic test facility. Electrical measurements of the projector determined the resistance and inductance of the unit as a function of frequency and also the change in inductance as a function of spacing between two coils. Voltage and current measurements of the projector while driven by a power amplifier determined electrical power input, while acoustic pressure measurements near the face of the projector and at a range of 1 yard characterized the acoustic power output. Both long and short duration tonebursts were used to study the operation of the projector and to obtain data for comparison with a theoretical analysis of the projector design. [Research supported by ONR.]
The design, fabrication, and acoustic calibration of a 1-3 piezoelectric polymer composite-based two-dimensional array for UUV applications
Authors: Benjamin Kim C. , Szelag Jeffrey A.
Published: October 2013

A two-dimensional planar transducer array containing 52 1-3 piezocomposite elements was acoustically calibrated in the frequency range 10–100 kHz. The active substrate thickness was 25.3 mm giving the elements a single low-Q half-wave resonance frequency around 60 kHz. This was the only in-band resonance for this array. The construction approach described is scaleable with respect to the size and number of elements and could accommodate singly and doubly curved apertures. The injection-molded ceramic preform used in this study would allow one to realize an element center-to-center spacing of approximately 9.5 mm. Also, this construction approach would enable element apertures of arbitrary geometry (i.e., nonrectangular). This paper will present the fabrication approach, associated tooling, and measured acoustic results. It will also discuss the use of Navy Type VI piezoceramic material under high drive and high duty cycle conditions. [Work sponsored by the U.S. Navy.]
Piezocomposites 1–3 with two periodicities to avoid the lateral modes
Authors: Perez Nicolas , Negreira Carlos A.
Published: October 2013

In the frequency range 1–5 MHz the lateral modes of the periodic piezocomposites 1–3 disturbs the optimal performance of the transducer in the thickness mode and produces a defocalization of the ultrasonic field. In previous works nonperiodic piezocomposites 1–3 were built to suppress the Lamb lateral modes. In this paper an analysis is proposed for the vibration modes in piezocomposites 1–3–1 samples three-phase PZT–polymer-holes constituting a network with two periodicities. This kind of configuration has a system of double stop-band and greatly improves the electromechanical coupling factor. This fact reduces drastically the lateral Lamb modes and broadens the bandwidth of the principal mode. This was obtained in a different way to the usual one, that is increasing the backing, which leads to a reduction of the sensitivity. To avoid the distortion in the vibration produced by the holes, the samples were covered with a flexible thin film electrode. In order to obtain the vibration modes, the electrical admittance was measured and ultrasonic spectroscopy was done to the samples surface. These results were compared with the numerical simulations performed by finite elements. The diffracted field by this kind of structure was also experimentally analyzed.
A frequency-domain technique for noninvasive, ultrasonic fluid detection in submerged sealed canisters
Authors: MacIntosh Scott , Sinha Dipen N. , Kaduchak Gregory , Kwiatkowski Christopher S.
Published: October 2013

There are situations where canisters containing specialized parts and/or materials are submerged underwater for storage or safety purposes. In some cases, leaks in the canisters can be detrimental and must be detected as early as possible. The present research describes an ultrasonic method for determining the presence of fluid in sealed, submerged canisters. In this research, the canisters are metallic and are filled with a random array of loose objects. The technique is based on two phenomena: the radiation damping effect of the internal fluid on the container wall and spectral signatures that result from internal reflections within the canister. The experiment utilizes a pair of piezoelectric transducers with a lateral separation of 27 mm. The transducers are placed at a standoff distance of 5 mm from the container wall and traverse the vertical dimension of the canister on a stepper-slide assembly. The transmitter is swept between 0.8–4.0 MHz and a frequency spectrum is collected. By analyzing the contributions to the spectrum from internal radiation damping and internal reflections separately, it can be determined whether the container wall is fluid or air backed. Current results demonstrate that fluid levels as low as 1 cm can be detected.
Modal analysis of guitars
Authors: Rossing Thomas D.
Published: October 2013

The complex vibrations of a guitar body are conveniently described in terms of normal modes of vibration, which involve the coupled motion of the component parts, mainly the top plate, back plate, ribs, and air cavity. These normal modes are generally determined from observing operating deflection shapes at frequencies near the principal resonances. We compare the normal modes, generally obtained by holographic interferometry, of several different types of guitars by various makers. The effects of bracing pattern and other design features on acoustical behavior are discussed.
Acoustics of the guitar at the National Autonomous University of Mexico
Authors: Boullosa Ricardo R.
Published: October 2013

Ongoing work in the field of Musical Acoustics (among other areas of interest) has been carried out at the Acoustics Laboratory at the Centro de Investigaciones Aplicadas y Desarrollo Tecnológico in the Universidad Nacional Autónoma de México (UNAM). This research began almost 15 years ago and although there have been times when no work was made, due to the effort involved in the characterization of the chambers at this laboratory and the development of other areas, some results are worth mentioning. In this paper the main work done in the laboratory in the field of musical acoustics, in particular, that related to the guitar is summarized. The topics studied so far deal with the objective and subjective evaluation of the sound of the guitar, the role of high frequency radiation, the string–body interaction and tuning problems, and the fretboard’s influence on the sound radiation, among other things. Most of this work has been published elsewhere, but the aim in this presentation is to give a general view of the work done by the Acoustics Laboratory, to the author’s acknowledge, the only group in México working in this area.
A guitar in vacuum: How does it sound?
Authors: David Bertrand , Boutillon Xavier
Published: October 2013

The loudness of the radiated sound is one prominent quality feature of guitars. However, few studies have been devoted to the ratio between the radiated energy and that which is lost in the wooden structure. In order to evaluate this ratio experimentally, yielding the acoustical efficiency of the instrument, we have compared the vibrations of a guitar at different ambient pressure levels. The guitar is installed in a large tank where the open bass string is automatically plucked. The pressure is varied between atmospheric level and vacuum, which implies a proportionally vanishing radiated power. The decay time of the most energetic component of each partial is estimated. It turns out that decay times are sometimes shorter in vacuum. This can be explained through a model of the coupling between the string and the bridge, the important parameter being the ratio of the real part of the mechanical impedance of the bridge to its imaginary part. The efficiency is measured every 82 Hz between 80 and 2500 Hz. Values are widely scattered between 15% and 60%. A comparison will be presented with acoustical efficiencies of other structures (plates, piano soundboard) and with values obtained on guitars by other methods and authors.
The acoustic effects of guitar components
Authors: Inta Ra , Gilet Gerard , Smith John , Wolfe Joe
Published: October 2013

The guitar is a complex oscillatory system made up of many vibrating components. Because of the variable mechanical properties of wood, it is not easy for makers to reproduce good instruments. Reproducibility can be improved if we know how the mechanical properties of the components interact to produce the sound of the completed instrument. Three steel-string acoustic guitars were constructed, in parallel and as similarly as possible, the only design difference being the timber used for the top-plates. Prior to construction, the Young’s moduli, densities, and moisture contents of a selection of top-plate brace, neck, and bridge materials were measured and the most similar were retained for creating the three instruments. Transfer functions and Chladni modes of the top-plates were measured at seven stages of construction, and the radiation patterns and acoustic efficiencies of the finished instruments measured. The effects of brace scalloping and neck attachment systems are reported. These results, and the behavior of some simple systems, are compared with finite element simulations that include scalloped bracing and glue bonding. [Work supported by the Australian Research Council and Gilet Guitars, Australia.]
Modal analysis of a classical guitar
Authors: Cohen David , Rossing Thomas D.
Published: October 2013

Using holographic interferometry, we have determined the modes of vibration of a classical guitar (by the first author) having an asymmetrically-braced top plate and a crossed braced back of unique design. The vibrational modes and acoustical properties are compared with other classical guitars.
The Brazilian National Standards in Acoustics
Authors: Hoffmann Walter E. , Massarani Paulo M. , Gerges Samir N. Y.
Published: October 2013

The elaboration of technical standards is a difficult and expensive activity, not always necessary, since there are international standards that can be used. Therefore, the elaboration of technical standards in Brazil is, in general, linked to several programs and regulations developed in this country. Among these are the Brazilian labeling program, which intends to label domestic appliances; the approval of new car models and the annual control of the existent fleet; occupational noise control programs and the growing requirement for the accreditation of calibration and testing laboratories. In particular, in the electroacoustics area, in 1998 a Technical Committee formed of 3 Working Groups was created, which developed 11 technical standard projects relating to specific programs in the process or in the elaboration phase such as the introduction of the conformity tests for equipment used for acoustic measurements, the creation of a conformity label for audio equipment, and an intercomparision program at the national level for the calibration of audiometers. This contribution aims to show a general vision of the state of the art of Brazilian standardization as well as the several programs for which these standards will serve as support.
Prevention, monitoring, and correction law for urban acoustical contamination in the province of Buenos Aires
Authors: Plana Senator , Rizzo La Malfa Ana Mara , Forte Luis , Velis Ariel , Bontti Horacio , Mendez Antonio , Ruffa Francisco , Kantor Pablo , Basso Gustavo
Published: October 2013

In the last decades, many cities of the Buenos Aires Province, in Argentina, have grown significantly. This expansion was a disorderly process, and produced important damage to environmental quality, expressed among other things, as high levels of acoustical contamination. Not many measures have been taken in order to obtain an effective solution to this problem. The cities’ governments could only take limited action using several regulations which only partially answer the people’s complaints. Regarding this situation it becomes necessary to create legal regulations for the jurisdictions mentioned before, in order to include the whole matter from a holistic and systematic point of view. The purpose of this law is to create an easy tool for the cities’ governments to use, thus allowing them to deal with the acoustic contamination problem in a global manner, and not in a fragmented way as it is now. The proposed law is oriented to the prevention, monitoring, and correction of the acoustic contamination for the whole provincial jurisdiction, and brings together as an innovation the fields of environment, planning, and noise. (To be presented in Spanish.)
Physical and perceptual assessment of glass plate boundary conditions
Authors: Marquis-Favre Cathy , Faure Julien
Published: October 2013

Building structures act as input filters to outer noise pollution. Windows constitute one of the weak points of the building envelope despite their increasing acoustic performances. The latter depend on the structural parameters and have been achieved thanks to the understanding of physical phenomena. Our concern is to improve acoustic comfort by integrating sound perception and people’s expectation. Actually, this work aims at studying the influence of the structural parameters on sound perception. The approach consists in investigating relationships between the vibroacoustic behavior of the structure and the perceptual attributes of sounds it transmits. The understanding of these relations will lead to improved sound quality of the structure by optimizing its structural characteristics. This communication will focus on the influence of various boundary conditions of a glass plate on sound perception. Broad-band sounds are synthesized from physical model and submitted by pairs to a panel of subjects for dissimilarity and preference judgments. Coupling of both vibroacoustic analysis and perception tests results will be presented. [Work supported by ADEME, the French Agency for Environment and Energy Management.]
The role of soundscape in children’s learning
Authors: Lubman David , Sutherland Louis C.
Published: October 2013

The soundscapes of classroom and play areas influence children’s behavior and learning. For example, the sustained high noise levels of shouting children frequently reported in day care centers are averse to behavior, learning, and teaching. To some extent this Lombard effect, or reflex to the reverberant buildup of room noise, can be tamed by generous application of sound absorption treatment to room surfaces. Low ambient noise allows children to perceive and enjoy quiet sounds, such as the subtle sounds of pets housed in classrooms. The benefits of improved interior soundscape may justify reducing reverberation time below the maximum value of 0.6 s permitted in the new classroom acoustics standard ANSI S12.60-2002. Exterior play areas are also vital to children’s socialization, informal learning, and environmental awareness. Reducing noise in outdoor play areas will promote the development of soundscapes favorable to learning. This paper suggests uses of natural outdoor soundscapes to promote learning. Also shown are uses of acoustical technology for sound playgrounds, such as those pioneered by Bill and Mary Bucken. Using such devices as sound focusing structures and sound transission channels built into playground equipment, sonic playgrounds stimulate learning, increase sonic awareness, and provide experiential enjoyment of the soundscape.
An investigation on source distribution characteristics obtained with the equivalent sources method
Authors: Gounot Yves , Musafir Ricardo E. , Slama Jules G.
Published: October 2013

Although the equivalent sources method is frequently used to solve acoustics radiation and scattering problems, very few investigations focus on the behavior of source distributions obtained as solutions, as well as on the general properties and restrictions these solutions must fulfill. In spite of the fact that the equivalent sources are highly dependent on the direction of the incident wave, for the rigid body scattering problem, the combined use of three different source distributions, satisfying the relevant energy requirements, may provide a satisfactory source system. The advantages of using such a system are investigated using three-dimensional numerical experiments, both for monopole configurations and for an expansion in spherical harmonics. Procedures for choosing between these two types of equivalent sources for a general problem are discussed. Characteristics of the source distributions found, using two particular variants of the equivalent sources method—one using a ‘‘least square minimization’’ technique and the other being Ochmann’s ‘‘full-field equations’’ method—are compared and discussed.
Scatter of ultrasonic waves by rough crack edge
Authors: Borovikov Vladimir , Fradkin Larissa Ju
Published: October 2013

Our aim in this talk is to describe statistical properties of an ultrasonic field scattered from a rough crack edge assuming that the statistics of the rough crack edge are known. The crack is embedded into a homogeneous solid. In order to develop the necessary algorithms we assume that the crack surface is planar and the crack edge is a polygonal line. The problem is approached in three stages: First, we derive approximate expression for the scattered field in the form of an integral over the crack edge. To this end, we use a version of the Geometrical Theory of Diffraction (GTD) which is called the Integral GTD (IGDT). Second, we obtain approximate analytical expressions for the mean and variance of the diffracted field in terms of statistics of the corner points. Finally, we use the Monte Carlo method for simulating different realizations of the crack edge using a prescribed statistical probability distribution and study statistics of the resulting diffracted field. The model is rather unrealistic but it gives us a rule of thumb for assessing the influence of edge roughness on the pulse echo which we hope to extend later to cases of practical interest.
Diffraction by systems of finite strips
Authors: Karlovich Yuri
Published: October 2013

The talk is devoted to wave diffraction problems for the two-dimensional Helmholtz equation. Boundary-transmission problems for a union of intervals (i.e., strips of a negligible thickness) which lie on a system of one or several parallel lines are considered in a Sobolev space setting. These problems include the mixed Dirichlet/Neumann and impedance boundary and transmission problems. Such problems for a union of intervals are reduced to equivalent systems of Wiener–Hopf equations on Lebesgue spaces over the positive real semiaxis. The matrix symbols of corresponding Wiener–Hopf operators are semialmost periodic, that is, they are continuous on the real line and have, in general, different almost periodic behavior at semineighborhoods of infinity. The solvability of obtained systems of Wiener–Hopf equations is studied on the basis of factorization techniques for oscillating and sectorial matrix functions and a corona problem approach developed in M. A. Bastos, Yu. I. Karlovich, and A. F. dos Santos [Integr. Eq. Oper. Th. 42, 22–56 (2002)], A. Bottcher, Yu. I. Karlovich, and I. M. Spitkovsky [Convolution Operators and Factorization of Almost Periodic Matrix Functions (Birkhauser-Verlag, Basel, 2002)], and L. P. Castro and F.-O. Speck [Integr. Equat. Oper. Th. 37, 169–207 (2000)].
Intraoral pressure trajectories during voiced and voiceless stops in women and children
Authors: Rothman Gabrielle , Koenig Laura L. , Lucero Jorge C.
Published: October 2013

Vocal-fold vibration requires that subglottal pressure (Psub) exceed intraoral pressure (Pio) values by a threshold amount. The increasing Pio that accompanies stop consonants can thus halt voicing. Muller and Brown, studying Pio trajectories in men, found that most voiced stops were produced with slowly rising (concave) contours, whereas voiceless stops had fast-rising (convex) contours. Modeling work indicated that concave trajectories resulted only when supraglottal volume was increased, and the authors argued that their subjects must have used active cavity expansion maneuvers to slow Pio increase during voiced stops. Here, we extend the measurement techniques of Muller and Brown to Pio data from women and children (5 and 10 years). Although Psub values are comparable between men and women, supraglottal volumes are systematically smaller in women. Children have both higher Psubs and smaller supraglottal cavity sizes than adults. Fully voiced stops are rare in young children, perhaps because children have limited abilities to manipulate oral volumes. Our discussion focuses specifically on the extent to which Muller and Brown’s original results are valid for women and child populations, and more generally on how consonantal voicing may be affected by anatomical and physiological differences between speakers as functions of age and sex.