bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite-element modeling of sound transmission blocking materials realized using pancake voids in a soft elastomer
Authors: Calvo David C. , Thangawng Abel L. , Layman Christopher N.
Published: October 2011

The fact that gas-filled voids in a soft elastomer acoustically resemble gas bubbles in a liquid (both having strong low-frequency monopole resonances) was pointed out by analysis and experiment by V. Leroy et al. [Appl. Phys. Lett. 95 (2009)]. The present work reports on the modeling, design, fabrication, and testing of specially designed voids in the soft elastomer polydimethylsiloxane (PDMS) with the aim of creating high performance sound transmission blocking materials. The techniques of soft lithography allow the microfabrication of custom cavity shapes in PDMS to obtain desired microstructural resonances. Results of a finite-element modeling analysis are reported that determine the monopole resonance frequencies of what we term pancake voids embedded in layers of PDMS. Because of the high aspect ratio of these voids, the low-frequency monopole (Minnaert) frequencies are between 3 and 6 times lower than that for a spherical cavity of equivalent volume inside PDMS. In terms of the potential for thin sound blocking slabs, this allows a lowering of the frequency at which blocking begins to take place. We also present modeled transmission loss results for normal incidence on an infinite array of pancake voids (a sonic crystal). [Work sponsored by the Office of Naval Research.]
Modeling of offshore wind turbine noise radiation and propagation
Authors: Kim Huikwan , Potty Gopu R. , Miller James H. , Baxter Christopher
Published: October 2011

Noise generated by offshore wind turbine and support structure can radiate and propagate through the air, water, and sediment. Predicting noise levels around wind turbine structures at sea is required for the estimation of effects of the noise on marine life. To predict radiated noise, we used a finite element analysis (FEA) of a cylindrical shell model of a monopile structure. In the finite element modeling, transient modal dynamic analysis and steady state dynamic analysis (direct and modal) were implemented to simulate both construction and operational noise. The effect of various sediment types and foundation designs are investigated. The FEA package used was ABAQUS version 6.10. The output of the FEA analysis is used as starting field for acoustic propagation models such as PE to produce long range predictions. We present predictions of particle velocity at the structure-acoustic medium interface and sound pressure level as function of frequency at various distances from the structure. Laboratory experiments using scale models of the cylindrical shell have been carried out to verify the noise predictions. Comparison of the FEA model results and experimental data will be presented.
Characterization of scattered acoustic intensity fields of finite cylinders in the resonance region
Authors: Barton Robert J. , Moss Geoffrey R. , Smith Kevin B.
Published: October 2011

The properties of the scattered acoustic vector fields generated by infinite-length and finite rigid and elastic cylinders are investigated. Analytical solutions are derived from general acoustic pressure scattering models and analyzed for wave numbers in the resonance region. The separable active and reactive components of the acoustic intensity are used to investigate the structural features of the scattered field components. Numerical results are presented for the near and transition regions. A finite element model is developed for a rigid cylinder and compared to measured results in-air using an anechoic chamber and acoustic vector sensor probes to measure the scattered acoustic vector field. The finite cylinder model and analysis is then extended to include an evacuated thin-walled elastic shell. The vector properties of the time-independent complex intensity components and their relations to field energy density quantities are summarized.
Bollywood sound stages
Authors: Hoover K. Anthony
Published: October 2011

Sound for bollywood films is rarely recorded live on location, but is looped or added later, in large part because of poor ambient acoustics. Several new sound stages in Film City, Mumbai, India, were intended for “Hollywood” quality acoustics, but construction ceased shortly after starting. Then, after several years' hiatus, the project was renewed with the directive that the existing fragmentary construction be used in the new design and as the foundation for subsequent construction. This paper will discuss the background, site conditions, encroaching hutments, design issues, concerns for local materials and methods, and the results of post-construction acoustical testing.
Subwoofer optimization in rooms for consistancy and efficiency
Authors: Welti Todd S.
Published: October 2011

Early work on optimizing subwoofer placement in rooms focused on trying to minimize variations in sound power response by optimizing room dimensions. Some consideration has also been given to maximizing overall sound power output, typically by putting subwoofers in room corners. Recent research using a sophisticated computer model has instead focused on trying to minimize variation of magnitude response from seat to seat. Using the same computer model, optimal subwoofer configurations are identified, which give consistent seat to seat responses and maximize low frequency efficiency. Consideration is given to different room dimensions and different seating configurations. The resulting plots may be very useful in designing small rooms with full range audio playback systems and multiple seats.
Glass as an aid and as a challenge in acoustics treatment
Authors: Beristain Sergio
Published: October 2011

A new installation for a broadcast center that included recording and transmission studios had to be constructed in an all transparent glass façade building in a major street in Mexico City. Together with all the acoustical specifications requested and needed for proper response of the studios, it was also requested from the very beginning of the project that the building façade could not be modified at all, i.e., all the glassing could not be obstructed in at least a couple of meters from the edge of the building in order to preserve the look of the building as it was originally constructed. This meant that enough sound insulation for the studios and control rooms as well as the short reverberation times, and resonance control needed by the acoustic conditioning treatment had to be attained with plenty of glass area, which could not be moved, plus all the glassing needed for visual communication between rooms to allow for normal operation of the studios. Construction details and results are presented.
The insertion loss of plenum windows with non-parallel line sources
Authors: Tong Y. G. , Tang S. K.
Published: October 2011

Opened window for natural ventilation becomes difficult to implement for the buildings in densely populated cities due to traffic noise problem. An experimental investigation of plenum window which was staggered inlet and outlet openings to allow natural ventilation through itself was studied. A 1:4 scale down model was adopted in the study to estimate the acoustical insertion loss of plenum windows in the presence of stimulated non-parallel line source. The orientations of plenum window relative to the traffic roads are found to be significant in protecting from transportation noise due to the staggered design. About 15 dBA of acoustical benefits can be obtained by studied ventilation window system compared to the opened window. The minimum insertion loss was recorded around 6 dBA when the tested window was placed perpendicularly to the line source. [Y.G. Tong sponsored by Ministry of Higher Education, Malaysia.]
Relationship between volume backscatter from the mesopelagic boundary community and density of organisms in the waters of the Hawaiian Islands
Authors: Au Whitlow W. L. , Lammers Marc O. , Jung Jakob
Published: October 2011

Spinner dolphins in the near-shore waters of the Hawaiian islands forage on a mesopelagic boundary community of organisms consisting of myctophids, mid-water shrimps, and small squids. To better understand the foraging ecology of spinner dolphins, it is important to understand the relationship between volume scattering coefficient (Sv) obtained with an echosounder and the density of the organisms in the mesopelagic boundary community. A suite of Simrad Ek-60 scientific echosounders operating at 38, 72, 120, and 200 kHz directed vertically downward was used to collect volume backscatter data from a vessel anchored 1 km from shore. Sv tended to be highest at 38 kHz and lowest at 200 kHz, although at some depths Sv at 70 kHz was slight higher than at 38 kHz data. Immediately after collecting the echosounding data, a profiler with a broadband high-resolution echo ranger projecting a simulated dolphin biosonar signal horizontally was lowered into the same volume examined by the EK-60. The number of organism in the echoranger beam out to a specified range was estimated by counting the number of highlights in the echoes after performing an envelope detection. The relationship between Sv and number of organisms was found to be linearly related.
Feature extraction for discrimination of fish species by using the cepstral analysis
Authors: Matsuo Ikuo , Ito Masanori , Imaizumi Tomohito , Akamatsu Tomonari , Wang Yong , Nishimori Yasushi
Published: October 2011

Identification and classification of fish species are essential for acoustic surveys of fisheries. The echo from the fish contains components from multiple reflections, including the swimbladder and other organs. The target strength (TS) and temporal structure, which were measured and analyzed by using the broadband signal, were changed dependent on the incident angles and fish species. It has been shown that these features were important for discrimination of fish species. The incident angles were calculated by using positions and velocities of each fish, which were measured by the tracking process of the four channels split-beam system, and the target strength was calculated individually by using Fourier transform. In this paper, the cepstral analysis, which was defined as the inverse Fourier transform, was used to extract features for discrimination of fish species from the broadband spectral pattern. In free ranging condition, echoes of Japanese jack mackerel (Trachurus japonicus), chub mackerel (Scomber japonicus), and red sea bream (Pagrus major) were measured and analyzed. It was examined whether cepstral analysis was appropriate to extract species specific features. [Work supported by the Research and Development Program for New Bio-industry Initiatives.]
Estimating Atlantic Bluefin Tuna number density using the second moment of intensity
Authors: Schroth-Miller Madeline L. , Weber Thomas C. , Lutcavage Molly
Published: October 2011

Fish number density can be estimated from the normalized second moment of acoustic backscatter intensity [Denbigh et al., J. Acoust. Soc. Am. 90, 457–469 (1991)]. This method assumes that the distribution of fish scattering amplitudes is known and that the fish are randomly distributed following a Poisson volume distribution within regions of constant density. It is most useful at low fish densities, relative to the resolution of the acoustic device being used, since the estimators quickly become noisy as the number of fish per resolution cell increases. The method was applied to an acoustic assessment of juvenile Atlantic Bluefin Tuna, Thunnus thynnus. The data were collected using a 400 kHz multibeam echo sounder during the summer month of 2009 in Cape Cod, MA. Due to the high resolution of the multibeam system used, the large size (approx. 1 m) of the tuna, and the spacing of the fish in the school, we expect there to be low fish densities relative to the resolution of the multibeam system. Results based on the normalized second moment of acoustic intensity are compared to fish packing density estimated using aerial imagery that was collected simultaneously.
Mid-frequency backscatter from spatially organized fish schools
Authors: Weber Thomas C. , Schroth-Miller Madeline L. , Lutcavage Molly , Pe'eri Shachak , Rzhanov Yuri
Published: October 2011

Schools of Atlantic bluefin tuna, Thunnus thynnus, can exhibit highly organized spatial structure. A stochastic simulation has been used to investigate the impact of this spatial structure on the backscattered acoustic field at frequencies below 10 kHz. The simulations are seeded with realizations of schools of juveniles based on field observations from 2009 in Cape Cod Bay. The field observations, which consist of both aerial imagery and 400 kHz multibeam echo sounder backscatter, have been used to characterize the school morphology, number of fish, and spatial structure within the school. The simulation examines various degrees of structure within the school, starting with fish locations that are constrained by the school boundaries but are otherwise the result of a Poisson process, and gradually incorporating components of school structure such as nearest neighbor distance and quasi-crystalline school sub-structures containing different numbers of fish. Results of the simulation suggest that multiple scattering is negligible except at low frequencies near the swimbladder resonance. Above resonance, even a modest degree of structure within the school (e.g., spatial constraints on pairs of fish) results in appreciable changes to the scattered field. [Work supported by ONR.]
Steve Schock and the Narragansett Bay Project
Authors: Walsh Kenneth M.
Published: October 2011

One of the first tasks for Steve Schock's sub bottom measurement system was with the Naval Undersea Warfare Center at Newport, RI. A research CRADA was established between NUWC and Precision Signals (Dr. LeBlanc and Dr. Schock) to measure the bottom sediment beneath the torpedo test range. The measurements were successful. The bay at the test range was measured down to bed rock at 64 m. The results indicated that the bay had been a glacial lake from the time the ice receded; until the sand bar that blocked the mouth of the bay eroded and the lake became a salt water bay, open to the ocean. Dr. Schock and Dr. LeBlanc authored a number of technical papers detailing the technology and its application. They founded the Chirp Lab at Florida Atlantic University in Boca Raton, Florida, where the technology has been advancing. Some of the latest techniques were presented in a special session at the May 2011 ASA meeting in Seattle.
Delay, scale, and sum migration for planar layer imaging
Authors: Lehman Sean K.
Published: October 2011

Wave-based remote sensing and imaging provide methods for investigating structures or objects with minimal or no contact. Delay, scale, and sum migration is one such method (in some circles this is known as ``beam forming'' or ``migration'' but must not be confused with beam forming for target location or geophysical migration). Migration assumes coherently scattered fields will sum constructively at a scattering target and destructively elsewhere. There is an additional assumption that multiple scattering can be neglected but this can be relaxed as the forward model sophistication is increased. This presentation summarizes the forward scattering model and derived inverse imaging algorithm as applied to a two planar layer medium. The measurement system operates in a broadband reflection mode in the one layer with the goal of imaging the second layer. Examples are presented using real data in (1) an ultrasonic experiment to measure a flaw in an aluminum/copper multilayer and (2) a ground penetrating radar in an air/sand environment. The examples provide a proof-of-principle using real data and may be scaled to other wavelengths and environments. [LLNL-ABS-485305 This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.]
Eastern and Western free reed mouth organs: Acoustics and history
Authors: Cottingham James P.
Published: October 2011

The Asian mouth blown free reed instruments are of ancient origin and typically employ a free reed strongly coupled to a pipe resonator. In these reed-pipes, the same reed often operates on both directions of airflow and behaves as a blown-open or outward striking reed, with playing frequency above both the resonant frequency of the pipe and the natural frequency of the reed. Although the Asian instruments were known in Europe when the Western free reed family originated there about 200 yr ago, the Western free reed instruments use a different mechanism. In these instruments, the reed tongue is offset from the opening in the frame, permitting operation on only one direction of air flow. Pipe resonators are not required and generally not used. These free reeds behave as blown-closed or inward striking reeds, with playing frequency below the natural frequency of the reed. This paper presents some episodes in the history of the Eastern and Western free reed instruments and a summary of the important acoustical properties of each.
Aeroelastic analysis of a closing reed of the mouth organ (harmonica)
Authors: Antaki James F. , Kim Jeongho , Singhal Abhinav , Burgreen Greg , Shu Fangjun
Published: October 2011

A 3-D numerical simulation of the fluid-structure-interaction of a vibrating free reed was conducted representing an isolated closing reed of the mouth organ. Air flow was considered Newtonian and compressible. The reed was considered mildly viscoelastic. Both large eddy and SST turbulent models were evaluated. Independent variables included upstream resonant chamber dimensions (length and cross section), lateral reed clearance, and offset gap. Particular attention was given to the influence of the initial pressure impulse upon initiation of self sustained oscillations. Numerical results were corroborated by flow visualization within a transparent replica of an isolated harmonica cell using high speed videography (3 000 frames/s) with smoke tracer. These results provide guidelines for improving the responsiveness of the initial transient attack and avoidance of the phenomenon known as “reed choking."
Chromatic playing on a diatonic harmonica
Authors: Levy Howard
Published: October 2011

The purpose of my demonstration is to show how a diatonic harmonica player can get all the chromatic pitches on an instrument not intentionally designed for this purpose. I will recount my participation in the research done by Henry Bahnson and James Antaki in the 1990s that led to a more complete understanding of this phenomenon, and will describe my discovery of overblows and overdraws which enable a diatonic harmonica player to get the so-called missing notes, not obtainable by conventional draw and blow bending techniques. I will demonstrate conventional note-bending techniques as well, and play samples of my playing in different styles making use of these techniques—Blues, Jazz, Ethnic music, Classical, etc., on the ten hole diatonic harmonica.
Wall vibrations in air-driven free reed bamboo pipes
Authors: Faaborg Miles , Cottingham James P.
Published: October 2011

In previous investigations of wall vibrations in bamboo pipes from Asian free reed mouth organs, modal frequencies and mode shapes of a number of pipes were measured. Measurements of pipe input impedance were made, some of which suggested possible changes occurring as a result of damping the pipe vibrations. [Cottingham, J. Acoust. Soc. Am. 114, 2348 (2010)]. The goal of this current work is to study the vibration of the pipe walls for the mechanically blown reed-pipe combination. This was done for undamped pipes and pipes heavily damped with sand or other damping material. Measurements of the internal sound field for both damped and undamped pipes were made as well as measurements of pipe impedance. Effects of the damping of wall vibrations on the radiated sound and the sounding frequency were also explored. [Work partially supported by National Science Foundation REU Grant PHY-1004860.]
Modeling of vibration, sound, and stresses using the virtual source approach
Authors: Pavic Goran
Published: October 2011

Analytical solutions of acoustical, vibration, or stress problems are available only for some simple structural systems, e.g., a rectangular simply supported plate or a parallelepipedic cavity. An usual way of finding a solution where complex systems are concerned is to apply field discretization in conjunction with some numerical methods such as FE or BE. Yet the use of analytical models is desirable for its simplicity and better physical understanding of phenomena concerned. On top of this, analytical models give the possibility of assessing quantities like energy flow which are linked to higher spatial derivatives, the latter being difficult to model numerically. The method of virtual sources enables one to obtain analytical solutions of systems of rather simple but non-trivial geometry. A key advantage of the method is the full control over the computation error. The method consists in applying a layer of virtual sources to a simple mother system of known analytical solution. These sources are adjusted in such a way as to produce particular boundary conditions on a target part of the mother system. The target part can be given a complex geometry which cannot be directly treated analytically. The paper will be accompanied by a number of examples which illustrate the approach.
The effect of ribbing and pressurization on the vibro-acoustic response of a turbulent boundary layer excited panel
Authors: Shepherd Micah R. , Hambric Stephen A.
Published: October 2011

One of the largest contributors to interior aircraft noise is the direct radiation from the wall panels excited by turbulent boundary layer (TBL) flows. The wall panels are designed with ribbing to increase their stiffness and strength while maintaining a relatively low weight. The effect of the ribbing on the vibro-acoustic response is examined for TBL flow excitation. Normal modes of a typical aluminum aircraft panel are computed and compared with and without the ribs. Wavenumber transforms of the mode shapes reveal increased sensitivity of the ribbed panel to high wavenumber excitation. TBL forcing functions are then converted into modal space and used to compute the radiated sound power of each panel. The increase in radiated sound power will be discussed in terms of wavenumber sensitivity. A preload due to pressurization is then applied to the ribbed panel and the modes, wavenumber spectrum and radiated sound power are recomputed. The pressurization causes a significant change in the modal content and subsequently the wavenumber spectrum and radiated power. The general effect of preload will be discussed in the context of interior aircraft noise predictions.
Effective control of machinery noise on offshore platforms
Authors: Ghosh Arindam
Published: October 2011

Offshore noise control must consider operational noise levels in the Topsides work areas from the perspective of hearing conservation. At the same time, for human comfort, it must consider both direct and structure-borne noise transmission from the Topsides sources to the occupied spaces. This paper will summarize design stage case studies for controlling centrifugal compressor and water injection pump noise integrating commercially available outdoor and indoor noise modeling packages and statistical energy analysis software. Practicality and economics of achieving the specified noise limits will be demonstrated based on cost effectiveness and noise reduction capacity of mitigation measures such as acoustic insulation, acoustic blankets, in-line silencers, enclosures, anti vibration mounts, and damping cassettes. For centrifugal compressor noise control, controlling the piping radiated noise by acoustical insulation provides the greatest benefit. For water injection pump noise control, controlling the base plate radiated noise through viscoelastic damping proves most effective. Economic and technical barriers to effective employment of the advanced analysis tools to the field of offshore noise control will be discussed.
Energy scattering in weakly non-linear systems
Authors: Spelman Graham , Woodhouse Jim , Langley Robin
Published: October 2011

The Chinese Tam-Tam exhibits non-linear behavior in its vibro-acoustic response. The frequency content of the response during free, unforced vibration smoothly changes, with energy being progressively smeared out over a greater bandwidth with time. This is used as a motivating case for the general study of the phenomenon of energy cascading through weak nonlinearity. Numerical models based upon the Fermi-Pasta-Ulam system of non-linearly coupled oscillators, modified with the addition of damping, have been developed. These were used to study the response of ensembles of systems with randomized natural frequencies. Results from simulations will be presented here. For un-damped systems, individual ensemble members exhibit cyclical energy exchange between linear modes, but the ensemble average displays a steady state. For the ensemble response of damped systems, lightly damped modes can exhibit an effective damping which is higher than predicated by linear theory. The presence of a non-linearity provides a path for energy flow to other modes, increasing the apparent damping spectrum at some frequencies and reducing it at others. The target of this work is a model revealing the governing parameters of a generic system of this type and leading to predictions of the ensemble response.
The plane wave expansion method applied to thin plates
Authors: Oviedo-de-Julián Ismael , Méndez-Sánchez Rafael A. , Manzanares-Martínez Betsabé , Ramos-Mendieta Felipe , Báez-Juárez Elsa
Published: October 2011

The plane wave expansion method refers to a computational technique in electromagnetics to solve Maxwell's equations. This method is popular in the photonic crystal community, because it is possible to obtain the band structure (dispersion-relation) of photonic crystals with specific forms. Since photonic crystals are periodic systems, the method expands all parameters crystal in Fourier series (plane waves). These expansions transform the wave equation in an eigenvalue equation. In this work, we will follow the line of previous investigations where the plane wave method was applied to the classical theory of thin plates. In particular the plane wave expansion method will be applied to the Mindlin equation. This equation describes the out-of-plane vibrations of thin plates in a better way—the classical theory of thin plates.
Time reversal communications in a time-varying sparse channel
Authors: Song Hee-Chun
Published: October 2011

Recently, time reversal (TR) communications has been extended to time-varying channels. The basic idea is to implement it on a block-by-block basis such that within each block the channel remains time-invariant and subsequently is updated using detected symbols (decision-directed mode). Using experimental data (12–20 kHz) collected in shallow water, this letter investigates three different block-based TR approaches: (1) without explicit phase tracking, (2) with phase tracking, and (3) exploiting channel sparsity. The TR approaches then are compared to a conventional adaptive multichannel equalizer. It is found that approach (3) generally provides the best performance and robustness.
High frequency multiple-input/multiple-output time reversal acoustic communication
Authors: Song Aijun , Badiey Mohsen
Published: October 2011

Current acoustic communication technologies using a single transmitter can only provide limited data rates due to the narrow bandwidth available in the underwater acoustic channel. Significant data rate increases can be achieved through the use of multiple-input/multiple-output (MIMO) systems in the underwater environment. However, in addition to the time-varying inter-symbol interference (ISI), co-channel interference (CoI) occurs as a result of multiple data streams sharing the channel at the same time and at the same bandwidth. Removal of both the CoI and ISI is a challenging problem in the underwater channel. This is especially true for high frequency acoustic communication (greater than 10 kHz). In order to achieve high data rate, reliable communication, time reversal MIMO processors have been developed. In the receiver, both the time-varying ISI and the CoI are addressed. Field data from recent high frequency acoustic experiments in the Pacific Ocean are used to demonstrate the receiver performance. Environmental impacts on acoustic MIMO communication will also be shown. [Work supported by ONR Code 322OA.]
Underwater acoustic communication channel simulation using parabolic equation
Authors: Song Aijun , Senne Joseph , Badiey Mohsen , Smith Kevin B.
Published: October 2011

High frequency acoustic communication (8–50 kHz) has attracted much attention recently. At these high frequencies, vaHigh frequency acoustic communication (8–50 kHz) has attracted much attention recently. At these high frequencies, various physical processes, including surface waves, subsurface bubbles, and ocean volume fluctuations, can significantly affect the communication channel. While there is an on-going work, however, the research community is still lacking adequate numerical models that can provide realistic representations of both deterministic and stochastic channel properties in the dynamic ocean. Advancements in underwater acoustic communication technologies mainly rely on at-sea experiments, which are very costly. Our studies show that it is possible to simulate realistic communication channels through parabolic equation (PE) modeling. The Monterey-Miami PE model with an evolving sea surface has been used to generate time-varying impulse responses. Data from our recent experiments are used to evaluate the model in predicting acoustic communication performance. [Work supported by ONR Code 322OA.]
Resource allocation for orthogonal frequency division multiplexing (OFDM) underwater acoustic cooperative transmission with limited feedback
Authors: Huang Xiaopeng , Lawrence Victor
Published: October 2011

In this paper, we first compare the difference between the wave cooperative (WC) protocol (designed for acoustic propagation) and amplify-forward (AF) protocol. In WC protocol, the relay nodes will transmit the received signal from the transmitter to the destination immediately (one time slot), in order to overcome the low transmission data rate problem in acoustic communication systems. Then we will propose the closed-form expression of the WC protocol with single relay. We will adopt the underwater acoustic (UWA) Rayleigh fading channel model and ambient noise in this cooperative transmission system. We propose capacity criterion based power allocation for UWA cooperative transmission (WC model) with the total transmitted power constraint, achieved under different levels of quantized CSI feedback using Lloyd algorithm. Meanwhile, limited feedback general procedure and Lloyd algorithm based codebook design will be presented. Simulation results will compare the system capacity with different bits of feedback, perfect feedback and non-feedback. In addition, the effect of relay locations on the system performance and the convergence speed of the Lloyd algorithm will be explored in the results.
Reflection and refraction of sound on on smoothed boundaries
Authors: Maltsev Nick
Published: October 2011

Classic problems of reflection and refraction of sound waves on the boundary of two liquid half spaces are reformulated for more complicated and more realistic case, when acoustical properties of media change smoothly. Refraction and reflection of plane, cylindrical and spherical waves on smoothed boundaries is discussed. The propagation of waves in Pekeris waveguide with smoothed boundaries is also formulated and solutions for the point source are discussed. New formulas for rays and modes are derived for both cases.
Fast direct integral equation-based analysis for acoustic scattering using non-uniform grid accelerated matrix compression
Authors: Brick Yaniv , Boag Amir
Published: October 2011

An approach for the fast direct solution of scattering problems via compression of boundary element method (BEM) matrices is presented. Such an approach is advantageous for large resonant problems where iterative solvers converge poorly, or if the solutions are sought for multiple directions of incidence, so that the computational cost becomes proportional to the number of desired solutions. The compression is achieved by revealing the ranks of interactions between source and observation subdomains via algebraic analysis of the source subdomains' interactions with coarse non-uniform grids (NGs) surrounding the observation subdomains and vice versa. The NG field representation, originally developed for acceleration of iterative solvers [Y. Brick and A. Boag, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 57, 262–273 (2010)], is used to facilitate the computation of interacting and non-interacting mode sets that serve as a basis for a subsequent transformation of the BEM matrix. Only a highly compressed system linking the interacting modes is solved prior to the solution's extraction for the non-interacting ones. Further compression and acceleration of a multilevel scheme is suggested based on a “layered-localized” field representation via modes sorted according to their radiation, directivity, evanescence, and focusing properties, which are also computed using the NG approach.
Effects of random bottom bathymetry on temporal and spatial coherence in shallow water propagation
Authors: Wylie Jennifer , Lourenco Felipe , DeFerrari Harry
Published: October 2011

Fixed system measurements for three experimental shallow water sites reveal systematic dependence of temporal and spatial coherence of individual mode arrivals on frequency and mode number that cannot be fully explained with internal wave variability. Here random fluctuations in bottom bathymetry are introduced to propagation models. Mode structures are randomized and coherence times and lengths decrease with increasing amplitude of bathymetry fluctuations for the same internal wave variations. Distinct mode features blur as frequency of pulse signals increased. Mode coupling and eventually a smearing of continuous modes are observed with increasing frequency and magnitude of bathymetry variations. For low frequencies and bathymetry variations constrained a small fraction of a wavelength, the bottom appears flat and nearly perfect discrete modes are formed. Modes are reinforced by specular reflections all along the path of propagation. Coherence depends entirely on internal wave fluctuations. All mode arrivals have nearly the same coherence times. But modes break up as height of bathymetry fluctuations become comparable to acoustic wavelength. Then sensitivity to sound speed fluctuation increases and coherence is reduced. Two dimensional bathymetry fluctuations account for observation out to 10–20 km and three-dimensional effects become important at longer ranges.
Characterization and scattering measurements from rock seafloors using high-resolution synthetic aperture sonar
Authors: Olson Derek R. , Lyons Anthony P.
Published: October 2011

Automated target detection systems are known to perform poorly in shallow water environments having high levels of reverberation and strongly varying scattering, such as rock outcroppings. Prediction of the scattering statistics is difficult because scattering from rock seafloors is not well understood. There is a lack of characterization methods, scattering strength measurements, and accurate approximate models for such interfaces. This research aims to measure the scattering strength of rock seafloors using an uncalibrated synthetic aperture sonar (SAS). An effective calibration has been made using a seafloor with a known scattering response. Scattering strength measurements will be used in conjunction with local slope information provided by interferometric SAS to characterize the rough interface.
Acoustics of green buildings
Authors: Muehleisen Ralph T.
Published: October 2011

As the world realizes the considerable environmental impacts of building construction and operation, a strong movement to create more sustainable buildings, i.e., “green” buildings has developed. While energy and resource use of green buildings is reduced and some indoor environmental conditions are improved, the acoustics of green buildings are often ignored and are frequently worse than in conventional buildings. In this tutorial presentation, the sustainable building movement is reviewed, the major design differences between green and conventional buildings are explained, and the impact of green design on acoustics is explored. There will be animations and auralizations to help attendees better understand acoustic impacts of green building design choices. Finally, lest ye think all is bad, the presentation will discuss solutions to the green building acoustic problem and present some of the positive impacts of green buildings can have on acoustics.
Would a rose sound as sweet
Authors: Ortallono Sam
Published: October 2011

Would a rose sound as sweet? In this presentation, we will explore perception of individual microphones. The same vocalist will be recorded with five different microphones. Volunteers will be presented with two sets of tracks to evaluate. The first set of tracks will be labeled only with letters, microphone A, B, C, D, and E. The second set of tracks will be labeled with the names of the microphones. Then the subjects will be asked to rate subjective qualities of both sets. Each person will be their own control by judging one set blind and one with the knowledge of the name of the microphone. Will preconceived notions of a microphonex's reputation change the outcomes?
Binaural room acoustics
Authors: Hartmann William M. , Rakerd Brad , Cook Ryan A.
Published: October 2011

Room acoustics concerns the geometrical and materials properties of rooms as they determine measurable sound field parameters that are perceptually important to listeners. For example, the volume and absorption in a room determine the reverberation time, which is important to the comprehension of speech and the enjoyment of music. Binaural room acoustics concerns the properties of rooms as they affect measurable interaural parameters, important to the human binaural perceptual system. For example, room properties affect the short-term interaural cross-correlation, which is important to the perception of apparent source width. Our recent work emphasizes room effects on steady-state interaural level and phase differences, important to sound localization in the horizontal plane. Particularly, we have sought to give mathematical meaning to a “binaural critical distance.” If a sound source and a listener are separated by less than the binaural critical distance, there is good probability that the interaural differences correctly indicate whether the source is on the listener's left or right. Experimentally, we have focused on sine tones in the range 200–1200 Hz, but we expect the results to be more generally applicable. [Work supported by the AFOSR (grant 11NL002) and by the NSF REU program.]
Stonehenge-like auditory illusion evoked by interference pattern
Authors: Waller Steven J.
Published: October 2011

Blindfolded participants hearing an interference pattern attributed the dead zones to the presence of acoustic obstructions in an arrangement reminiscent of Stonehenge. Without prior mention of interference or Stonehenge, participants were brought blindfolded to an open field with two English flutes atop thin 1 m tall wooden stands 2 m apart, connected via tubing to an air pump, giving a sustained pitch of C#5 (1 100 Hz). One by one, participants were led blindfolded in a 7.6 m radius circle around the pair of flutes. Afterward, faced away from the setup, they were instructed to remove blindfolds and independently “draw and describe what you thought was between you and the noise.” Although there actually were no physical obstacles, the resulting drawings from all three participants represented arrangements of objects having many characteristics in common with Stonehenge; verbal descriptions included “pillars,” “solid objects,” “openings,” “tall vertical slats.” These pilot results demonstrate regions of low sound intensity due to destructive interference of sound waves from musical instruments can be misperceived as an auditory illusion of acoustic shadows cast by a ring of large obstructions. Measurements of acoustic shadows radiating out from Stonehenge are consistent with the hypothesis that interference patterns served as blueprints for the design.
Measuring absorption: Bad methods and worse assumptions
Authors: Sauro Ronald
Published: October 2011

Ever since Sabine described the use of absorptive materials to affect reverberation time, the acoustic community has been trying to quantify this effect. Standards like C-423 and ISO-354 have been developed to aid in that process. These standards, describing coefficients ranging from 0.0 to 1.0, have been inadequate to fully describe the actual absorption of the tested materials. It is not uncommon to find actual measurements that result in coefficients exceeding the number 1.0. When this happens, assumptions are made that other properties of the material are not taken into account by the coefficient. The present standards also suffer from inadequacies of methodology. They do not measure the full range of absorptive qualities. This paper describes the incorrect assumptions about absorption and measuring it as well as illustrates the incorrect methodologies that are used in these standards. Because of the flaws in the assumptions and the inherent defects in the methodologies, this author believes the current standards need to be replaced by new standards. Replacement instead of correction is preferable because of the extremely large database of materials already measured and the difficulty explaining how new measurements based upon corrections would be comparable to old measurements.
Uncertainty factors in determining the random-incidence scattering coefficient
Authors: Müller-Trapet Markus , Vorländer Michael
Published: October 2011

When determining the random-incidence scattering coefficient with measurements that have been carried out according to ISO 17497-1, several quantities from four different measurements have to be combined to finally produce the sought-after coefficient. These include the reverberation time and atmospheric conditions to account for air absorption. As in most measurement situations, one has to keep in mind that uncertainties have affected the measurements, so that an absolute statement about the scattering coefficient might not be possible. This work will give an insight as to how each of the mentioned measured parameters and their uncertainty will affect the evaluation of the scattering coefficient. The “Guide to the Expression of Uncertainty in Measurement” will be employed to investigate the effect of both systematic and random errors. Within the limits of applicability, intervals for the necessary accuracy of the measured parameters that lead to an acceptable uncertainty in the final result will be given.
Repeatability and reproducibility concepts in acoustical laboratories
Authors: LoVerde John , Dong Wayland
Published: October 2011

There are many categories of variability in acoustical laboratory testing. The repeatability of acoustical testing is usually defined based on repeated testing of the same assembly over a short time period. Other variability, such as rebuilding an assembly in the same lab or building a nominally identical assembly in a different lab, is generally termed reproducibility. A previously undocumented variability is what may be termed “long term repeatability,” the repeated testing of the identical specimen in the same laboratory with the same equipment and operator, but over an extended time period. The authors recently had the opportunity to measure the long term repeatability of a wood joist floor/ceiling assembly that remained in the same test chamber at an accredited acoustical laboratory over 50 days. The results are compared with previously known variability, and the implications for manufacturers and designers are discussed.
Automated extraction and classification of contours in humpback whale vocalizations
Authors: Ou Helen H. , Au Whitlow W. L. , Lammers Marc O. , Pack Adam A. , Zurk Lisa M.
Published: October 2011

Humpback whales produce songs which consist of a sequence of short, continuous sounds known as units. This paper introduces an automated algorithm to extract the unit contours. An unsupervised classification is developed to provide a set of distinct units of the singing group. The analysis is performed on the vocalization spectrograms, which are normalized and interpolated into a squared time-frequency image. Unit contours are detected using two edge detection filters capturing sharp changes in the image intensities. The algorithm generates a group of rectangular image segments each containing a single contour unit, with the pixels outside the contour edge lines set to zero. The contours are compared with one another to identify distinct units. The comparison is quantified using parameters including the contour pixel intensity correlation, contour area, frequency range, and frequency of the peak pixel. A pairwise comparison provides a coarse division of classes, where each class is then represented by a candidate unit. The candidate units are compared with one another, and the ones with low similarity are advanced to the final set. The algorithm has been tested on humpback whale songs obtained during the winter season in Hawaiian waters in 2002 and 2003.
A chimpanzee responds best to sine-wave speech with formant tones 1 and 2 present
Authors: Heimbauer Lisa A. , Beran Michael J. , Owren Michael J.
Published: October 2011

A seminal study by Remez and colleagues [R. E. Remez, et al., Science, 212, 947–949 (1981)] demonstrated that listeners were more successful in identifying sine-wave speech when the first two (T12) or all three formant tones (T123) were present than when either were absent (forms T13 and T23). To determine whether a language-trained chimpanzee (Panzee) with the ability to recognize English words in sine-wave form [L. A. Heimbauer, et al., Curr. Biol., doi:10.1016/j.cub.2011.06.007 (2011)] would respond similarly, she and 13 humans were tested with words synthesized in the four forms used by Remez et al. Indeed, for each species, perception of speech was significantly better when the first and second tones were both present. Panzee's performance suggests that she is attending to the same spectro-temporal features of sine-wave speech that are critical to humans. The outcomes further indicate that basic capabilities involved in speech perception could have been present in latent form in the common ancestor of humans and chimpanzees. [Work supported by NICHD.]