bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the Precedence Effect -- how we arrived where we are today
Authors: Braasch Jonas
Published: May 2008

Throughout his career, Jens Blauert was interested in further exploring the precedence effect, an auditory phenomenon that enables us to localize sounds in rooms and other enclosures. A series of models that were developed at Bochum's Institute of Communication Acoustics under his leadership have changed the way we think about the precedence effect. While this effect as a psychoacoustic phenomenon is known for its complexity -- for which Jens Blauert's talent to define precise terminology and listen critically came in handy -- the modeling aspects are equally challenging due to the non-linear nature of the underlying auditory processes. Blauert and Cobben's binaural model from 1978 was already able to simulate observations related to the precedence effect. A few years later, Blauert's doctoral student Werner Lindemann introduced a binaural model with specific stages to model the precedence effect. Since then, almost all approaches to simulate the precedence effect are based on inhibitory elements. In this talk, the evolution of this class of models over several student generations at Bochum will be described, and the fruitful scientific exchange with other institutions such as Steven Colburn's laboratory at Boston University will be highlighted as well.
Noise generation in an unstable boundary-layer flow over a flexible wall
Authors: Gobert Marie-Laure , Ehrenstein Uwe , Astolfi Jacques Andre , Bot Patrick , Audet Jean , Oudot Guillaume
Published: May 2008

The boundary-layer flow, for instance along a sonar dome, gives rise to hydrodynamic noise due to the pressure fluctuations. The prediction of the resulting self-noise received by the sonar antenna is based on models, which in general take only partially into account the flexibility of the dome wall. The present work readdresses the problem of hydrodynamic noise, considering the geometrically simplified model of a two-dimensional unstable boundary-layer flow along an elastic plate with clamped ends. The incompressible Navier-Stokes equations are fully coupled to the elastic plate model and the system is numerically solved for various plate materials. The unstable flow dynamics is analyzed with respect to the wall properties. The Fourier-transformed stress tensor is then used in the framework of Lighthill's analogy to determine the generated radiative sound, emphasizing the effect of wall-flexibility. This work is supported by Thales Underwater System and DCNS.
Determination of noise sensitivity within an internet survey using a reduced version of the Noise Sensitivity Questionnaire
Authors: Griefahn Barbara
Published: May 2008

The Noise Sensitivity Questionnaire (NoiSeQ), that determines noise sensitivity as a moderator of annoyance globally and separately for different everyday activities is with 35 items too long for extended social surveys. This study aimed at the development of a shorter version. Using 429 questionnaires (266 women, 163 men, 16-74 yrs) three factor analyses were performed leading to the NoiSeQ-R that consists of the three subscales 'Sleep', 'Habitation', and 'Work' with 4 items each. The scores are normally distributed, internal consistency is α= 0.87 and test-retest reliability varies between rtt = 0.66 and 0.74 depending on the time gaps that varied between 1 to 37 months. To test the validity the NoiSeQ-R was applied to a field study where 190 residents (102 males, 88 females, 17-80 years, median: 51 years) in the vicinity of a large airport rated their chronic annoyance (for the previous 12 months) and their actual annoyance hourly during four consecutive days. As expected, noise sensitivity did not correlate with the individual noise load but significantly with annoyance and with age. Thus the NoiSeQ-R, which is available in ten languages, is regarded as a reliable and valid instrument which can be easily applied in even extended surveys.
Uncertainty evaluation in field measurements of airborne sound insulation
Authors: Michalski Ranny L.X. , Ferreira Daiana , Nabuco Marco , Massarani Paulo
Published: May 2008

The Brazilian Committee of Civil Engineering presented a set of standards concerning the evaluation of the performance of several topics for buildings up to five floors. The acoustic performance is one of them. The standards are in approval process and measurements in real buildings will be necessary. Different professionals using different equipment will emit certificates establishing which levels of insulation a certain flat provides and its uncertainties. The expanded measurement uncertainty can provide the basis to compare different measurement results for a same building. The international Guide to the Expression of Uncertainty in Measurement, the ISO GUM, is the document that specifies how to determine and evaluate the uncertainty of a measurement result. The standards concerning sound insulation measurements are ISO 140 and ISO 18233. Uncertainty estimates are available only for the classical technique described in ISO 140, based in repeatability and reproducibility tests performed in laboratories. Field measurements present some characteristics that can contaminate the results, as time variance. Several independent measurements were carried out in a one flat building using ISO 18233 specifications and the ISO GUM was applied to obtain the uncertainty for measurement results of airborne sound insulation between rooms in situ.
Uncertainty of Receiving Space Volume in Field Measurements of Transmission Loss Under ASTM E336-05
Authors: Sacks Jonah
Published: May 2008

As acoustical consultants, we are frequently asked by our clients to measure the sound isolating performance of constructions in the field. While it is often preferable to report "system-level" performance ratings such as Noise Isolation Class, there are compelling benefits both to us and to our clients to measuring and reporting "specimen-level" performance ratings such as Apparent Sound Transmission Class, defined by ASTM E336-05 (and E413-04). The accuracy of such ratings depends on accurate assessment of the amount of acoustical absorption present in receiving spaces at the time of testing, arrived at by means of reverberation time measurements and physical measurement of receiving spaces. When a receiving space is irregular in shape, one may feel pressed to use creative judgment to estimate its effective volume, and such judgments can have large impacts on the reported results. We will discuss the challenges of measuring apparent transmission loss in the field, and the compelling reasons to conduct these measurements despite the challenges.
Evoked potential and behavioral hearing thresholds in nine bottlenose dolphins (Tursiops truncatus)
Authors: Schlundt Carolyn E. , Finneran James J. , Branstetter Brian K. , Dear Randall L. , Houser Dorian S. , Hernandez Erica
Published: May 2008

Auditory evoked potentials are popular for assessing hearing in marine mammals because they do not require the same access to and training of animals as behavioral methods; however, within-subject comparisons of behavioral and electrophysiological thresholds are still necessary to benchmark evoked potential results against the more universally accepted behavioral data. In this study, auditory thresholds were measured in nine dolphins using both behavioral and electrophysiological methods. Subjects included eight males and one female, ages 21-43 yrs. Some had a full-range of hearing and others exhibited high-frequency hearing loss. Tests were conducted in-air, in San Diego Bay, and/or in quiet pools. Hearing test stimuli included frequency-modulated, amplitude-modulated, or pure tones projected in the direct field or via a "jawphone" contact transducer. Comparisons reveal good agreement between the evoked potential and behavioral methods, particularly when the testing environments, stimulus delivery methods, and stimulus waveforms are similar. The results show that evoked potential thresholds obtained in a variety of conditions provide reasonable approximations to underwater sensitivity, especially with respect to the shape of the audiogram and the upper limit of hearing.
Inertial and cochlear constraints for high-frequency hearing in phocid and otariid pinnipeds
Authors: Nummela Sirpa , Hemilä Simo , Berta Annalisa , Reuter Tom
Published: May 2008

In air-borne hearing, mammals rely on sound transmission through the tympanic membrane and middle ear ossicles between the surrounding air and the cochlea. The high-frequency hearing limit (HFHL) is determined by the ossicular inertia, and also by the cochlear sensitivity. Due to coevolution, the sensitivity ranges of the middle and inner ear structures generally overlap, and the roles of inertial and cochlear constraints for the HFHL are difficult to discern. For studying this question we considered anatomical and experimental data for two phocid and two otariid pinnipeds. While any detailed mechanism for pinniped underwater hearing remains unclear, an underwater HFHL exceeding that in air is possible. Published in-air and underwater audiograms provide an opportunity for comparing the roles of ossicular mass inertia and cochlear sensitivity in HFHL. Phocid ossicles are very heavy, and their inertia explains the lower HFHLs in air - according to underwater audiograms the phocid cochlea is sensitive to higher frequencies. Otariids have normal-sized mammalian ossicles, and their inertia should allow underwater hearing at higher frequencies than in air. However, the HFHL is approximately equal in air and water for otariids, hence their underwater HFHL is apparently set by the cochlea alone.
Variational assimilation of simulated ocean acoustic tomography data in an ocean model
Authors: Remy Elisabeth , Gaillard Fabienne , Verron Jacques
Published: May 2008

In the concept of large scale observing system for the ocean, ocean acoustic tomography is an original tool to monitor the ocean interior. Analysis of tomographic travel time using inversion gives an estimate of the temporal evolution of the heat content along the observed sections, an important quantity to monitor the ocean climate evolution. At lower scales than the cell size defined by the observational array, it is not possible to estimate the ocean temperature field without using other sources of information. A possible approach is to combine the tomographic observations with a numerical dynamical ocean model to obtain a complete description consistent with the data on a given time interval. We propose to explore a variational method using the adjoint technic to assimilate those integral data. We studied the case of a basin scale observational array, as the one deployed in the Mediterranean sea for the Thetis 2 experiment. Only travel time anomalies due to the sea water properties are considered. The ability of tomographic data to constrain the ocean model circulation is evaluated using simulated observations with a model solution. This approach called twin experiments, allows to compare the result after assimilation with the ''true'' solution.
The fast wave propagation in bovine cancellous bone-experiments and simulation
Authors: Matsukawa Mami , Mizuno Katsunori , Nagatani Yoshiki
Published: May 2008

Cancellous bone is comprised of a complicated network of trabeculae and has strong anisotropy and inhomogeneity. In the cancellous bone, two types of longitudinal waves, fast and slow waves, are observed when the waves propagate parallel to the trabeculae direction. Paying attention to the wave front of observed waves, we have experimentally made clear the effect of anisotropy on the fast wave speeds and shown interesting relation between the mean trabeculae length and wave speeds (Mizuno et. al., IEEE Trans., UFFC, accepted), making use of the microstructural indices of the measured bone. We then compared the experimental results of fast waves with the simulation studies, using the three dimensional X-ray CT data and the Finite-Difference Time-Domain (FDTD) method. In spite of the lack of attenuation effects in the simulation, we can find interesting correlation between the fast wave speeds obtained by experiments and simulation. In addition, the characteristic attenuation behaviors of fast wave were found in both experiments and simulations. Attenuation of fast wave is always higher in the initial state of propagation, regardless of propagation direction and samples.
Modelling sound propagation in a waveguide containing multiple obstacles
Authors: Kirby Raymond
Published: May 2008

Acoustic waveguides often include relatively short area changes and/or complex non-uniform obstacles. Understanding the propagation of sound within such waveguides requires a detailed knowledge of the scattering of sound at each obstacle and how these obstacles interact with one another. Mathematically modelling sound propagation in waveguides containing multiple non-uniform obstacles is challenging, especially if one assumes that the waveguide is relatively large. Accordingly, a computationally efficient hybrid numerical method is presented here that uses the standard finite element method to model non-uniform obstacles, and maps this onto a wave-based modal solution that is used for uniform duct sections only. The hybrid method has the advantage, moreover, of removing the need to numerically enforce a non-reflecting boundary condition downstream of the obstacles, which is often encountered in studies that rely solely on the standard finite element method. In this way, transmission loss predictions for relatively large ducts and multiple obstacles may be generated efficiently, and predictions are presented here for two cylinders placed in a two-dimensional waveguide.
Extension of Optimal Source Distribution principle
Authors: Takeuchi Takashi
Published: May 2008

Binaural reproduction over loudspeaker requires system inversion which is often referred to as cross-talk cancellation. Such process is the major factor to degrade the quality of 3D sound reproduction but Optimal Source Distribution (OSD) provides simple and effective loudspeaker design principle and signal processing which enables lossless crosstalk cancellation process. OSD takes advantage of its physical property where in-phase and out-of-phase components of the binaural reproduction process are balanced, hence the bulk of the crosstalk cancellation is achieved by its loudspeaker design principle and natural interference in the sound field. It is also shown that the advantage of OSD is further enhanced by separating in-phase and out-of-phase components through its loudspeaker design.
Investigating musical sound as a model for the scientific process
Authors: Piacsek Andrew
Published: May 2008

In recent years, science pedagogy at all levels has embraced active student learning, in which students are engaged in the process of discovery, rather than passively receiving information. One of the benefits of active learning in a science curriculum is that students have an opportunity to emulate scientists in their approach to producing knowledge. It is desirable that students at all levels, including those in primary and secondary schools, develop an understanding of (or at least an appreciation for) the scientific process, in addition to learning science content. Presented here is a description of a musical acoustics curriculum used at Central Washington University for non-science students, with emphasis on how the structure of the curriculum and the active-learning elements contribute to accomplishing the objectives of conceptual learning, problem-solving ability, and scientific thinking. An essential feature of this curriculum is the combination of guided and open scientific investigations by teams of students. Portions of this college curriculum have been successfully adapted to the high school classroom and to audiences of children as young as ten years of age. Because musical acoustics incorporates many fundamental topics in physics and engineering, and it is appealing and relevant to students of all ages, this topic can be a significant asset to any science curriculum.
Inquiring activities on the acoustic phenomena at the classroom using sound card in personal computer
Authors: Kim Young H.
Published: May 2008

Inquiring activities on acoustic phenomena have been carried out in the classroom of a high school for highly gifted children. Instead of expensive instruments such as function generators and oscilloscopes, sound cards, installed in a personal computer, were employed for the generation and detection of sound. The stereo function of the sound card offered two sound sources, so that phenomena of interference and beats can be realized in the classroom. The record function of the sound card offered detection of sound, permitting frequency spectrum analysis of sounds from two tuning forks or the sound from a moving fork. Using sound card, a lot of acoustic phenomena can be demonstrated in the classroom. In addition, sound from Rijke tube, which is a typical theromacoustic phenomena, was analyzed by using a sound card. Popup sound of a wine bottle and breaking of wine glasses, which are related to resonace and standing waves, were also investigated. Curiosity of students was greatly increased through a series of inquiring activities with sound cards, so that they were completely absorbed in research on acoustics.
Interacting with virtual musical instruments at the junction nodes
Authors: Erkut Cumhur , Jylhä Antti , Karjalainen Matti
Published: May 2008

Sound synthesis by block-based physical modeling of musical instruments separates the tasks of component modeling and managing their interactions. The components are the exciters or the resonators, and their interactions are managed by explicit interaction blocks, which are obtained from the physical continuity and energy conservation rules. Well-known examples of the interactors include the wave- digital adaptors and the digital waveguide scattering junctions. When the virtual instruments need to be interfaced to the outside environment with sensors and actuators for bidirectional interaction, it is advantageous to reformulate the interactors to accept and provide signal inputs and outputs, respectively. In this contribution, we refer to these elements as nodes, introduce different types of nodes, and discuss their interconnection.
Sound synthesis of circular plates by finite differences
Authors: Arcas Kevin , Chaigne Antoine , Bilbao Stefan
Published: May 2008

This paper shows a method for simulating linear flexural vibrations of circular plates by finite differences (FD) for the purpose of sound synthesis. The vibrations are assumed to follow the Kirchhoff-Love model. In order to solve the continuous problem numerically, the equations are approximated in space and time by FD methods. Two schemes are presented and compared; depending on the coordinate system used for the grid, rectangular and polar, respectively. Cartesian FD are not easily adaptable to circular boundary conditions and generic conservative boundary conditions cannot be found. On the contrary, polar FD allow to find well-adapted conservative boundary conditions. With a polar grid, the distance between consecutive gridpoints decreases from the edge to the center. As a consequence the stability of the algorithm depends on the minimum radius of the grid, where this distance is the smallest. Because of this highly restrictive stability condition, numerical dispersion is high and the high-frequency content of the spectrum is badly reproduced. To avoid this problem an implicit polar FD scheme has been developed which yields simulations with acceptable numerical dispersion. The accuracy of the algorithm is estimated by computing the ratio between numerical and analytic eigenfrequencies in a simple case.
TIMPAN - Technologies to IMProve Aiframe Noise
Authors: Perrin Decroux Stephane
Published: May 2008

TIMPAN is a 3-year Strategic Targeted Research Project of the 6th European Framework Programme, Priority "Aeronautics and Space", launched in 2006. It addresses the community noise reduction objective for commercial aircraft by focusing on main airframe noise sources: landing gear and high-lift devices - responsible, on recent aircraft, for about half of the total noise in approach situation. TIMPAN addresses both sources, within 3 main tasks: 1) Landing gear activity: investigation of both innovative low noise technologies on bluff body structures and the improvement of advanced low noise main gear design, as outcome from previous EC Technology Platform SILENCE(R). 2) High lift device activity: study of both innovative concepts based on flow control technologies and mid-term noise reduction solutions as absorptive wing leading edge treatments and high-lift settings optimization through computational aero-acoustic methods. 3) Technology evaluation: aims to prepare the exploitation phase by evaluating the noise reduction technologies under consideration in terms of noise benefit, integration, cost and performance. TIMPAN brings together 14 actors from the European aeronautics industry including aircraft manufacturers (Airbus and Dassault Aviation), landing gear manufacturers (Messier-Dowty and Messier Bugatti), key research institutes (DLR, ONERA, NLR, EADS-IW), universities (University of Southampton, Technical University of Braunschweig) and SMEs (ATECA, Free Field Technologies).
Simple evaluation of occupational noise exposure without measurements
Authors: Hohmann Beat W.
Published: May 2008

In almost any country, employers must assess the noise exposure of the employees. But for small and medium-sized enterprises (SMEs), individual noise measurements are hardly feasible. Therefore, since almost 30 years, Suva publishes noise level tables, which list typical noise levels of many tools and machines. These 66 noise level tables cover almost any branch of the industry. Moreover, they include shooting noise, music, and so on. However, most SMEs were not able to calculate their workers' long-term noise exposure. Therefore, based on Suva's extensive database, typical noise exposure levels for occupations and activities were calculated. The new type of noise level tables includes now the typical noise exposures for the different occupations. Moreover, since 2007, the noise level tables also indicate the measures to be taken. Therefore, SMEs do not have to put their efforts into the determination of noise exposure but can start immediately to protect the workers against noise-induced hearing loss. The list of the noise level tables available (in French, German and Italian language) and the noise level tables themselves may be found at: www.suva.ch/waswo/86005
Recovery of distortion product otoacoustic emissions (DPOAE) after impulse vs. continuous equal-energy exposures
Authors: Aranda De Toro Miguel Angel , Ordoñez Rodrigo , Reuter Karen , Hammersho/i Dorte
Published: May 2008

The correct assessment of impulse noise from occupational environments for hearing-conservation purposes is still a controversial issue. Currently, no universally accepted standard defines impulse noise accurately nor does a standard method exist to measure impulses. Moreover, current impulse-damage risk-criteria suffer from lack of empirical data needed to quantify impulse noise exposures and assess potential damage. In this experiment human subjects are exposed to binaural recordings of noises from industrial environments. Stimuli consist of impulse noise, continuous noise, and combinations of impulse and continuous noise. Noise exposures are normalized to have the same energy (LAeq,8h= 80dB). The effects in the hearing of the subjects are monitored by measuring the recovery of the distortion product otoacoustic emissions (DPOAE) with high-time resolution. The results can be used to investigate the validity of current assessment methods and descriptors of the temporal characteristics of sound exposures and their relation to the temporal effects produced on the human hearing as well as investigating selected issues that may lead to possible improvements or alternative measuring methods. [Work supported by the Danish Research Council for Technology and Production.]
"Real world" noise exposure beneath hearing protectors : a scattered international practise
Authors: Canetto Pierre , Trompette Nicolas
Published: May 2008

Assessing occupational noise exposure "beneath" Hearing Protection Devices (HPD) is a topical subject. Standardized methods allow to calculate the exposure by using the HPD attenuation. The HPD attenuations declared by manufacturers are much higher from the "real-world" ones. To reduce this difference, some "compensation" methods are proposed. The methods and their rules vary a lot from one country to another. The "derating" rmethod reduces the declared values from a certain amount, according to the HPD kind. "Double-labelling" method uses attenuation values measured in laboratory with untrained subjects. "Statistical range enlargement" widens the statistical confidence of the laboratory-test results. All these methods propose a global solution: the reasons due to human behaviour (mainly bad HPD wearing) , products quality, and the difference between laboratory and industrial situations are mixed. This "blind" approach could be considered as endorsing the lack of workers' training, and could impede the progress in HPD developments. But a "short-term" answer to the problem is needed. It should allow to build a more relevant medium-term answer, which could be worked out possibly on an international scale.
Sound path(s) to the ear protected by double hearing protection
Authors: Buck Karl , Hamery Pascal , McKinley Richard
Published: May 2008

Studies have shown that the attenuation performance of double hearing protection is limited by bone or tissue conduction. We present the first results of a program to determine the different paths of the sound to the ear when a person is protected by double hearing protection. In order to determine the contribution of the noise signal passing by secondary sound paths (bone or tissue conduction) into the volume of the ear canal behind the earplug, identical tests have been performed on humans and artificial heads. Time delay and attenuation through the hearing protection (NR) were measured on the ipsi- and contra-lateral side of the head. The measurements show differences in time delay and attenuation between artificial heads and humans which indicate that the main transmission mechanism is different. They also give a strong indication that the path of the acoustic signal depends on the angle of arrival when using double HP. This may partly explain the poor sound localization performance when using double HP that was reported by Brungart (2002). The single HP, and the double HP were then used in a sound localization experiment. The localization performance of these conditions will be presented along with the related parameters.
A time domain boundary element method for compliant surfaces
Authors: Hargreaves Jonathan A. , Cox Trevor J.
Published: May 2008

The best way of representing compliant surfaces in time domain prediction models, such as the transient Boundary Element Method (BEM), is currently unresolved. This is not true of frequency-domain, time-invariant models, where the common practice is to represent the characteristics of a material by its surface impedance. A BEM may be used to predict the scattering of sound, and reduces the problem of modelling a volume of air to one involving surfaces conformal to the obstacles. Surface impedance is a convenient concept for inclusion in the frequency domain BEM as it abstracts the obstacle's characteristics into a property of the conformal surface. The time domain BEM predicts transient scattering of sound, and is usually solved in an iterative manner by marching on in time from known initial conditions. For surface impedance data to be utilised it must be Fourier transformed from a frequency dependent multiplication into a temporal convolution. This approach typically yields convolution kernels which involve future sound, hence is not compatible with time-marching solvers. In this paper an alternative time domain representation of compliant locally reacting materials is proposed to overcome this problem, and its implementation and limitations discussed.
Spatial and temporal sound field fluctuations due to propagating internal waves in shallow water
Authors: Badiey Mohsen , Katsnelson Boris , Lynch James F.
Published: May 2008

Fluctuating three dimensional acoustic wave propagation in shallow water presents a challenge due to the anisotropic nature of the environment. Temporal and spatial changes in the water column caused by the passage of internal waves are among the the primary causes of the anisotropy. Three main mechanisms for the acoustic field variations have been determined: 1) adiabatic propagation,. 2) horizontal refraction, and 3) mode coupling. All these mechanisms provide different characteristics of the sound fluctuations, and depend on the angle between the internal wave direction and the source receiver propagation path, as well as frequency and mode number. In a recent multi-institutional shallow water experiment (SW06) a series of source-receiver positions were created to examine the effects of 3D environmental fluctuations on the propagation of low to mid frequency (0.05-3 kHz) broadband acoustic signals while extensive environmental observations were made. These recent observational results confirm the above theoretical hypothesis. Work supported by ONR-321OA and RFBR.
Short-range acoustic propagation through non-linear internal waves
Authors: Rouseff Daniel , Tang Dajun , Williams Kevin L. , Moum James , Wang Zhongkang
Published: May 2008

During the Shallow Water 2006 Experiment (SW06), mid-frequency acoustic transmission data were collected on a vertical array over a continuous 7-hour period at range 550 m. The relatively short range was deemed desirable for studying the effects of internal waves; individual waves in a packet of nonlinear internal waves might be isolated between the acoustic source and receiver. Of present interest are data immediately before, during and after the passage of a non-linear internal wave on 18 August 2006. Among other features, the data show a new acoustic path being generated as the internal wave passes the acoustic source. A ray-based model is developed for the observed effect that uses as input nearby oceanographic measurements. [Work supported by ONR.]
Intensity fluctuations of mid-frequency sound signals passing through moving nonlinear internal wave in experiment sw06
Authors: Katsnelson Boris , Grigorev Valery , Lynch James F. , Tang Dajun
Published: May 2008

Fluctuations of an intensity of the broadband pulses are studied in mid-frequency area (2 - 4.5 kHz) propagating in the shallow water in the presence of intensive internal waves (IW) moving approximately along an acoustic track. Theory elaborated earlier predicts that in this case specific features of fluctuations are provided by modes coupling (for low frequency sound) or ray scattering (high frequency area) and depend on direction of propagation of signals relative wave front of IW. The corresponding research was carried out during multi-institutional experiment sw06 in New Jersey shelf. We analyze temporal dependence of intensity for the sequence of the sound pulses radiated from the R/V Knorr during approximately one hour - 15:31 -16:20 GMT (August 13, 2006) and received by two separate single hydrophone units (SHRUs) placed at different distance from the source (̃4 km and ̃12 km). The corresponding acoustic tracks had a little different directions relative wave front of IW. Properties of IW were established using temperature records of sensors in different locations. It is shown that frequency spectra of fluctuations for these SHRUs have different predominating frequencies in accordance with mentioned directions of acoustic tracks. Results of measurements are compared with theoretical estimations and demonstrate good consistency.
An in situ sediment sound speed measurement platform: Design, operation and experimental results
Authors: Yang Jie , Tang Dajun , Williams Kevin L.
Published: May 2008

A unique Sediment Acoustic-speed Measurement System (SAMS) was developed to directly measure sediment sound speed. The system consists of ten fixed sources and one receiver. In a typical deployment, the SAMS is deployed from a ship that is dynamically positioned. The sources are arranged just above the sea bottom and the receiver is drilled into the sediment with controlled steps by a vibro-core. The maximal sediment penetration depth is 3 meters. At each receiver depth, the 10 sources transmit to the receiver at different angles in the frequency range of 2-35 kHz, providing 10 estimates of sound speed through time-of-flight measurements from the known source-to-receiver geometry. SAMS was deployed three times during the recent Shallow Water Experiment 2006 (SW06) on the New Jersey shelf at 80 m water depth. Preliminary results of sediment sound speed are 1618 ± 11, 1598 ± 10, and 1600 ± 20 m/s at three separate deployment locations. Little dispersion in sediment sound speed was observed. (Work supported by ONR)
Environmental effects on frequency behavior of modal attenuation coefficients for sandy bottoms
Authors: Saintval Wendy , Carey William M. , Pierce Allan D. , Lynch James F. , Siegmann William L.
Published: May 2008

The modal attenuation coefficients (MACs) can be determined using a recent simplification of Biot theory [A.D. Pierce et al., J. Acoust. Soc. Am. 114, 2345 (2003)]. Numerical calculations use sandy bottom sediments and isospeed, linear, and piecewise linear water profiles, which are simplifications that preserve key features of those obtained in experiments off the New Jersey Shelf. The calculations indicate the importance of downward refracting profiles and the strength of near-interface gradients for increasing energy loss. Principal characteristics of the MACs that are observed from the calculations include: increases with interface gradient, reordering of least attenuated modes, and variations of the frequency power-law exponents of the MACs from f-1 to f1 at frequencies up to 2 kHz. Evidence of the behavior observed in the calculations is in good agreement with previous analysis of results in Gulf of Mexico experiments [F. Ingenito, J. Acoust. Soc. Am. 53, 858--863 (1973)], for profiles that were classified as weakly downward refracting or nearly isospeed. [Work partially supported by ONR.]
Laboratory sound speed measurements on high water content sediment samples
Authors: Martin Vanessa A. , Alexis Alain , Martin Vincent
Published: May 2008

Laboratory measurements of sound speed in fluid viscous materials are known to be difficult, especially for frequencies of a few kHz. An experimental set up which allows such measurements is developed. Tests are run on sediment samples of various lengths (5cm - 20cm), all water-saturated but with different water contents (or densities). When sound speed only depends on the water content over a narrow frequency bandwidth, its estimation originates from time-of-flight measurements on samples of different lengths. It will appear that the water content does play a significant role on the speed of sound. When sound speed depends on frequency (dispersive waves) due to the sediment viscoelastic behaviour, the dependency can be taken into account. An analysis according to the sample length will be given to characterize the sound dispersion for different water contents. It will be shown that both the above studies on the experimental campaign yield sound speed estimations against sample lengths under various hypotheses. In these conditions, the estimation leads to information about saturated sediment behaviour.
Active sonar discrimination of water-column objects from bottom clutter using waveguide invariant modeling of distributed backscatter
Authors: Krolik Jeffrey , Goldhahn Ryan , Hickman Granger
Published: May 2008

The ability to differentiate water-column returns from clutter discretes due to backscatter from bottom features is critical to improving the detection performance in active sonar. Previous approaches include the use of statistical feature-based classifiers and physics-based depth estimation. Such methods are typically challenged by the convolutive effect of both uncertain multipath propagation and complex scattering characteristics in sonar returns. In previous work, we used waveguide invariant theory to model frequency-selective fading observed in distributed backscatter from the ocean bottom. In particular, the short-time energy spectrum of backscatter from the sea bottom at a given range can be well estimated along striations in time-frequency energy predicted by waveguide invariant theory. In this paper, we present a statistic which tests the observed frequency-selective fading of the short-time energy spectrum for a range cell under test against the spectrum predicted by waveguide invariant theory for a bottom feature using neighboring ranges and frequency bins. Results are presented for discrimination of a water column target versus bottom clutter using data simulated via a normal mode propagation model with environmental parameters from the Malta Plateau. Receiver operating characteristic analysis is performed showing good discrimination of equal energy targets from clutter. [Work supported by ONR].
Using a dispersive source signal to generate a dispersive field in a nondispersive medium
Authors: Walker Shane C. , Kuperman William A.
Published: May 2008

In typical treatments, dispersion is considered to be a property of the medium. For example, a free space, static, homogeneous medium is dispersionless while gravity waves, particularly in the case of surface waves in a deep body of water, exhibit dispersion. Here it is shown that dispersion in the field can also result from dispersion in the source signal. As a demonstration, a dispersive source signal is shown to introduce dispersion in a dispersionless medium. Consequently, through proper design of the source signal, it is possible to tailor the resulting field dispersion to suit a variety of applications. Here potential applications to imaging in complex media are discussed. Simulation and experimental results are presented.
Conservative initial-boundary value problems for the Wide-Angle PE in waveguides with variable bottoms
Authors: Antonopoulou Dimitra , Dougalis Vassilios , Sturm Frederic , Zouraris George
Published: May 2008

We consider the third-order, Claerbout-type Wide-Angle Parabolic Equation (PE) in the context of Underwater Acoustics in a cylindrically symmetric medium consisting of water over a soft bottom B of range-dependent topography. There are strong indications, that the initial-boundary value problem for this equation with just a homogeneous Dirichlet boundary condition on B, may not be well-posed, for example when B is downsloping. In previous work we proposed an additional bottom boundary condition that, together with the zero field condition on B, yields a well-posed problem. In the present paper we continue our investigation of additional bottom boundary conditions that yield well-posed, physically correct problems. Motivated by the fact that the solution of the wide-angle PE in a domain with horizontal layers conserves its L2 norm in the absence of attenuation, we seek additional boundary conditions on a variable-topography bottom, that yield L2- conservative solutions of the problem. We identify a family of such boundary conditions after a range-dependent change of the depth variable that makes B horizontal. We discretize the continuous problems by second-order accurate Crank-Nicolson type finite difference schemes, and show, by means of numerical experiments, that the new models yield accurate simulations of the acoustic field in standard, wedge-type domains with upsloping and downsloping bottoms.
On the use of ancient theatres for modern performances: a scale model approach
Authors: Farnetani Andrea , Prodi Nicola , Pompoli Roberto
Published: May 2008

Ancient theatres are widely used today for modern performances including drama, music and ballets. Despite the state of conservation of the stage, the scenery is seldom designed with little care about its acoustical efficiency. Moreover, depending on the specific venue, a sound system can be employed in the performance. To clarify the acoustical impact of all these elements in ancient theatres, different stage settings and a sound sytem were investigated by means of scale model measurements. The scale model is a 1:20 scale reproduction of the ancient theatre of Siracusa (Italy). It is conceived as modular structure so that different configurations of the cavea and of the stage can be reproduced. To investigate the stage-set effects different groups of reflecting panels were arranged on the platform and an orchestra shell was tested too. Then, to simulate the sound system, two directional high frequency sources were assembled and optimized. The interplay of stage, sound system and theatre architecture was outlined by a comprehensive set of acoustical measurements.
The Parpalló Cave: A singular archaeological acoustic site
Authors: Jiménez González Noé , Picó Rubén , Redondo Javier
Published: May 2008

The Parpalló Cave is located in the slopes of Montdúber, in Valencia (Spain). It is one of the most important Palaeolithic sites, not only in Spain, but in the world. It was a privileged location for its inhabitants from the Upper Palaeolithic onwards. It has one of the most spectacular collections of Palaeolithic art mobilier found to date. The Parpalló cave features a considerably large opening which, undoubtedly, influences its acoustic properties. Indeed, the sound pressure field inside the cave is not excessively reverberant and intelligibility is significantly better than in similar enclosures. In this work a study of the acoustic properties of the Parpalló cave is performed by using numerical simulation.
Re-evaluating Noise Criterion in Digital Audio Recording Environments
Authors: Gedemer Linda
Published: May 2008

The absence of audible noise in recording studios is highly desirable. For this reason, the acoustic design of recording facilities usually involves an accurate assessment of the audibility of background noise. However, noise criterion that sets levels for inaudible noise do not take in account the sensitivity of today's digital recording equipment and post production processing. Noise-level criterion and measurement techniques exist in order to created an atmosphere where noise is rated at a level of audibility with respect to the type of space being measured. In this paper these criterion will be analyzed in terms of critical recording spaces. The criterion will be considered in terms of current building practices and digital audio recording equipment used. A set of questions were sent to working sound engineers in order to received first hand opinions regarding noise issues in recording studios. It is not the intention of this report to suggest a new noise criterion but rather to better understand existing problems which could then help in the creation of a more relevant noise criterion to be developed in the future.
New Roadway noise modeling to predict noise propagation in front of urban façade
Authors: Hossam Eldien Hany , Woloszyn Philippe
Published: May 2008

Roadway noise is the most important example of a linear noise source, since it comprises about 80 percent of the environmental noise exposure for humans worldwide. Due to the complexity of the variables, a line source acoustic model is realized by a computer model . In this paper we propose a new approach system based upon Schröder's quadratic residue diffuser modeling for modeling a linear traffic source. 1/10th scale model has been used to simulate the traffic noise propagation in front of the building façade and for a free field. The line source directivity is made quasi-uniform in the aperture angle of interest. The line source directivity measurements were made using a 1/4" microphone Larson Davis type 2530. The sequence of the quadratic residue diffusor is calculated following the Schröder's modulo formula and with 1.60m length, 0.14m height, and 0.11m width. The line source has also been weighted by a full-size equivalent normalised traffic noise spectrum according to the French standard NF EN 1793-3.
Intense sonar pings induce temporary threshold shift in a bottlenose dolphin (Tursiops truncatus)
Authors: Mooney T Aran , Nachtigall Paul E. , Vlachos Stephanie
Published: May 2008

For over a decade it has been suggested that high intensity anthropogenic sounds, such as sonar, could induce a temporary threshold shift (TTS) in odontocetes. Although TTS has been examined in marine mammals, the temporary physiological effects of sonar sounds have yet to be established. This study explored the effects of high-intensity (up to 203 dB re: 1 μPa), mid-frequency sweeps (2-4 kHz) on the hearing of a bottlenose dolphin (Tursiops truncatus). The goal was to determine if these sounds could induce TTS and what sound exposure levels (SEL; dB re: 1 μPa2s) were necessary for TTS to be induced. Fatiguing sounds were presented to mimic that of mid-frequency sonar. Hearing thresholds were measured before and after exposures using auditory evoked potentials to determine amount of shift and rate of recovery. Temporary threshold shifts of 5-6 dB were measured using SELs of 214 dB, in situations when 15 sonar pings were presented in series. Recovery to normal hearing was rapid, typically within 5 to 10 min. Exposure levels required to induce TTS were high, supporting the notion that relatively short sounds must be of relatively high intensity to induce threshold shifts.
Decalcifying Protocol of Odontocete Ear Samples with RDO®
Authors: Morell Maria , Degollada Eduard , Alonso Josep Maria , Jauniaux Thierry , Leopold Mardik , Camphuysen Kees , Andre Michel
Published: May 2008

The study of the organ of Corti is essential to assess the impact of underwater noise on cetaceans. While classical histology techniques (including EDTA decalcification) have been previously considered, the process is time consuming and artifacts, probably directly deriving from the protocol, often appear and difficult the analysis. However, no matter the choice of the analysis technique, one of the challenging step after extraction and fixation of the samples is to decalcify the bone envelope to access the cochlea without damaging the soft tissues. Here, we propose to use a fast commercial decalcifier (RDO®). 103 ears from 12 different odontocetes species stranded in the Mediterranean, Spanish North Atlantic and North Sea have been used to precisely determine the decalcification time. Specifically, the species processed were: Phocoena phocoena (n=45), Stenella coeruleoalba (n=12), Stenella frontalis (n=12), Tursiops truncatus (n=13), Delphinus delphis (n=4), Kogia simus (n=3), Kogia breviceps (n=2), Globicephala macrorhynchus (n=3), Globicephala melas (n=2), Steno bredanensis (n=4), Lagenodelphis hosei (n=2) and Ziphius cavirostris (n=1). Depending on the species, the decalcification time ranged from several hours to a few days, allowing a subsequently faster observation of the cochlear structures through routine microscope techniques.