bluuebunny/crossref_metadata_2025 huggingface dataset:
Homemade “woodwind” and “brass” instruments.
Authors: Luzader Stephen
Published: March 2010

PVC pipe is an ideal material for the construction of wind instruments, both “woodwind” (using a reed) or “brass” (using the lips). Instruments can be made using a combination of PVC construction along with parts of actual musical instruments, such as a clarinet mouthpiece and reed or a trumpet mouthpiece, or they can be manufactured entirely from PVC and other materials. For panpipes, the lengths of the tubes are easily determined by choosing a standard pitch frequency and the basic interval between tones (e.g., 440 Hz and equal temperament) and then using basic physics to calculate the required tube lengths. For instruments using side holes, the locations of the holes can be determined by choosing a standard pitch frequency and interval and then calculating the required distances of the holes from the driven end of the pipe. The basic theory will be reviewed, and several different instruments will be demonstrated.
Pedagogical possibilities: Some ideas for instrument making in the classroom.
Authors: Hopkin Bart
Published: March 2010

As a brief introduction, historical etchings of a few intriguing 19th century contraptions for classroom demonstrations of acoustic principles will be shown. Following that, several classroom-buildable musical instruments will be described. The emphasis will be on instruments that effectively illustrate acoustic or mathematical principles. They will also be fun to make and play, and practical in a classroom context, requiring a minimum of special tools, skills, or materials. Topics to be illustrated through hands-on instrument making may include relationships between frequency, wavelength and pitch, harmonic and inharmonic overtones, relationships between drivers, radiating surfaces and atmosphere, linear and inverse-squared functions, and more.
Modeling with the use of the commercial software package CADNAA (Computer-Aided Noise Abatement) to estimate the probability of awakening associated with train horns.
Authors: Szulecki Stephen , Zwerling Eric , Anderson Craig , Turpin Barbara
Published: March 2010

The Rutgers University Noise Technical Assistance Center conducted a long-term acoustical study to assess the noise exposure of residents in Teaneck, NJ to noise associated with idling freight trains. One of the noise sources evaluated was idle-related horn usage, at locations other than grade crossings. Trains on an adjacent track overtaking an idling locomotive regularly blow their horn as they approach and pass an idling train. The primary impact on the community due to this type of horn use is sleep disturbance. In order to evaluate this impact, an analysis was performed using CADNAA acoustical modeling software, in an innovative manner, to evaluate the probability of awakening (POA) as a result of idle-related horn usage based on ANSI/ASAS-12.9-2008/Part 6, a standard for estimating awakenings. The standard presents a series of formulas that calculate the POA as a function of a sound exposure level of a single or series of noise events. Other factors influencing the POA are time since retiring and whether the sound is new or existing. The model output is a graphic of equal-probability contours showing the POA at least once throughout the night.
Transit noise and community choices.
Authors: El-Aassar Ahmed , Dubbink David
Published: March 2010

Transit innovations and expansions are a central part of initiatives to construct more livable communities. As part of the National Environmental Policy Act process, public involvement is required and public feedback and support are essential for projects to move forward. Generally, accessibility improvements are welcomed by the public, but the potential for increased noise is often met with opposition—and concerns about transit noise can stifle initiatives. One way to build community acceptance is to accurately compare transit options. The authors explain how community groups and decision makers in Florida responded to a presentation system providing direct acoustic experience of over a dozen transit modes, from light rail guideway transit to commuter railways. The goal of the acoustic presentation was to compare existing freight train sound levels to those of an array of transit technologies. The audio-visual presentation included interactive videos and computer animations, allowing proposed transit modes to be heard at different distances and in outdoor or indoor settings.
Evaluation of crowd noise in Beaver Stadium during Penn State football games.
Authors: Barnard Andrew , Hambric Stephen , Porter Steve
Published: March 2010

Sound pressure level measurements were made at Penn State (PSU) football games at Beaver Stadium, on the PSU campus, in Fall 2009. Twelve sound level meters were positioned around the field, on the press box, on the luxury suites, and outside the stadium to capture the characteristics of the crowd noise. The loudest portion of the sideline area was determined along with the maximum equivalent A-weighted sound pressure level. Additionally a HEAD VISOR acoustic array was utilized in conjunction with a portable white noise generator in order to determine which portions of the student section were generating the majority of the sound pressure on the field level. The results indicate which sections of students are able to most effectively project their voices onto the field.
A three-stage approach to understanding listener perception of weapon signature for small arms.
Authors: Gaston Jeremy , Letowski Tomasz
Published: March 2010

The ability to identify and interpret impulse sounds from small arms weapon fire is a very important element of soldier’s situational awareness that is critically needed to avoid potential danger. For example, differentiation of hostile from friendly weapon fire can indicate the need for increased vigilance and can reveal the approximate location of an enemy element. In addition, estimation of weapon size can be used to infer the resources of an enemy element. Despite the potential operational importance of these sounds, little is known about listener perception of impulse weapon sounds. The present work investigates listener ability to differentiate signatures of various small arms based on high-quality recordings of single-shot impulse sounds. Following the three-stage approach developed by Pastore et al. (2008) for studying natural sound perception, the interrelationships between weapon source properties, the physical attributes of the sounds produced and listener perception are evaluated for a number of small arms weapons. The mappings of these relationships provide the basis for developing training techniques for improving listener weapon signature identification ability.
Creation of combined noise maps for noise prediction in petrochemical plants.
Authors: Ghosh Arindam
Published: March 2010

Design of petrochemical plants involves producing detailed noise models with predicted noise contours at fine grids such as 1 m. However, background noise data collected during pre-construction environmental impact assessments (EIAs) are typically gathered at a few selected points. Since it is impractical for all the measurements to match the prediction grid, the measured data must be interpolated. This paper discusses how the survey grid is selected and interpolation optimized to meet the overall project noise control design basis and the post-start-up noise survey needs. The strategy varies based on the existing operational situation (brown-field or green-field), the type of land-use (rural or urban), the nature of terrain (flat or hilly), and the planned plant use (process area, loading and storage area, or administrative buildings). Finally, the unique needs for petrochemical process plants (as opposed to general city planning) for long term and area-wide background noise measurements are outlined.
Anatomy of a quiet power plant: A case study.
Authors: Szymanski Jeff
Published: March 2010

Details of noise control design are presented for a recent power plant expansion project that involved the addition of heat recovery steam generation to a gas-fired power plant in the US. The project, including its expansion, was subject to a 45 dBA nighttime property boundary sound level limit. The development and coordination of noise control design for large and small equipment packages, some of which would be located within several meters of the property boundary, are discussed in detail. Sound level measurements are presented and discussed, particularly with regard to the challenges involved with conducting sound level measurements in the presence of ambient sound levels that often approached the allowable noise limit.
Model for the design of a hydraulic silencer with dispersive liner.
Authors: Marek Ken , Earnhart Nick , Cunefare Ken
Published: March 2010

An in-line hydraulic silencer with a dispersive lining material shows promise for effective fluid noise suppression. For this design, a rigid outer shell encases an annular dispersive medium, where fluid flow is straight through the annulus. A model is developed to predict input port impedance and acoustic transmission loss of the hydraulic silencer. These predictions are used to develop a set of design parameters for the liner, including material properties and geometric dimensions. Design parameters can then be optimized for a given set of working conditions and frequency ranges of interest. Model development is discussed along with comparisons to experimental data.
Mine ventillation silencer.
Authors: Weinstein Jonathan
Published: March 2010

Mine exhaust ventilation fans provide essential fresh air. The extracted air from the mine is often moist and laden with dust, so that conventional silencers would very quickly clog as the wet dust forms on silencer baffles and blocks the perforations in the baffle skins. This paper presents a case history of the solution to this problem where tuned cavity silencer baffles were installed in an existing exhaust evase of a mine ventilation fan. Sound attenuation is achieved using tuned cavities which are resistant to blockage caused by the wet dust. This performance was successfully demonstrated with a half scale model tested in a laboratory wind tunnel.
A true to life application for flow driven resonators: Industrial chiller cooling fan noise reduction.
Authors: Gorny Lee J. , Koopmann Gary H.
Published: March 2010

A project has been conducted to verify the efficacy of tunable resonators in reducing the tonal noise output from an industrial chiller’s cooling fan. The primary goals of this work were to demonstrate resonator source robustness for attenuating blade tone noise generated by fixed speed fans, radiating primarily in a single direction, that have non-ideal, un-ducted flow conditions. BPF tones radiated by the fan are reduced by as much as 14 dB in the flow stream and 10 dB outside, demonstrating the effectiveness of resonators for realistic applications. A manually tunable fixed mouth location resonator configuration was designed and developed as a first step in testing resonator effectiveness for quieting production chillers operating at a fixed speed and steady loading. The test enclosure was developed to simulate the fan’s environment for a production device, mimicking the convoluted inlet flow, exit through a radiator. Changes in loading were accomplished through adjustment of a flow control door. Additional flow obstructions inside of the enclosure added and removed to demonstrate their effect on overall tonal noise radiation and to test resonator effectiveness in reducing various interaction noise sources.
Dissipative diesel engine exhaust muffler featuring sintered metal fiber as acoustical fill liner.
Authors: Storm Mark
Published: March 2010

Conventional exhaust muffler design for diesel truck applications often involves a combination of dissipative and reactive elements in order to provide generally broadband sound attenuation for the purpose of suppressing engine exhaust noise during normal operation or engine braking (i.e., venting compressed air through the exhaust system). The reactive portions of the muffler are usually present to provide low-frequency spectrum transmission loss that cannot readily be achieved with classical perforated-n′-packing dissipative design. However, unlike standard perforated metal liners that are used to separate the exhaust gas stream from the muffler’s surrounding volume of acoustically absorbent fill, liner materials such as micro-perforate and sintered metal fiber (SMF) metals offer high porosity and high-flow resistance that should improve low-frequency dissipative sound absorption. This study contrasts the modeled insertion loss, transmission loss, and noise reduction performance of a dissipative-only muffler design featuring an SMF liner with that of a popular conventional dissipative-reactive combination muffler design. Discovered performance advantages and disadvantages should reveal pathways for subsequent muffler design development that utilizes advanced liner materials such as micro-perforates and SMF.
Rapid deterioration of sound level benefits for quieter pavements in Washington state based on the on-board sound intensity method.
Authors: Sexton Tim
Published: March 2010

This paper provides detailed descriptions of the three test sections of “quieter” pavement evaluated by the Washington State Department of Transportation (WSDOT) using the on-board sound intensity (OBSI) method and the unique deterioration of those pavements. Within 6 months of installation, OBSI for the test sections were not audibly lower than the control sections. OBSI is the predominant metric used to evaluate the success of quieter pavements in Washington State. Monthly OBSI measurements describe the seasonal variability in measured sound levels and highlight more rapid general sound level increases in the test pavements relative to the control. Asphalt mix compositions and installation procedures used in Washington were similar, or identical, to those used in southern states where the same pavements have been successful. Challenges to the success of all pavements in Washington State include studded tires, frequent freeze-thaw cycles, and cool summers that encourage lower surface temperatures during installation than in southern states. These challenges are particularly significant for open-graded friction course OGFC pavements as evidenced by spikes in OBSI measurements following seasonal weather events. Parallels between OBSI measurements and structural durability measurements are described in detail.
On-board sound intensity measurements and results in Florida.
Authors: Wayson Roger , MacDonald John , Berrios Mariano
Published: March 2010

This paper describes an investigation of on-board sound intensity (OBSI) and concurrent wayside sound levels along multiple roadway surfaces in the state of Florida. By conducting concurrent sampling of the OBSI and wayside noise not only were insights into the pavement texture noise generation at the tire/pavement interface possible but direct comparisons allowed findings on the propagation characteristics as well. Measurement values, pavement rankings, multiple findings, and preliminary statistical modeling will be shown.
Coupling loss factor estimation for plates joined at a point: Analysis and experiment.
Authors: Ewing Mark , Vatti Kranthi , Vaz Ignatius
Published: March 2010

Coupling loss factors for two lightly damped plates joined at a point, but otherwise free to respond in lateral vibration, have been studied both analytically and experimentally. This study forms the basis for on-going estimations of the transient coupling loss factors of the same system. Statistical energy analysis (using VA ONE) and the finite element method (using NASTRAN) have been used to predict the coupling loss factors. The finite element predictions are based on the averaged responses for a range of boundary conditions on the plates, essentially a “pseudo-statistical” approach. Experimentally, two techniques have been used. First, following the approach by Lai and Soom, a force transducer has been used to measure the force between the plates as it is used to attach them. Simultaneously, the kinetic energies in the two plates are measured by three accelerometers attached to each plate during both transient and persistent excitations of the plates, one at a time. The coupling loss factors are estimated by balancing the transmitted energies with the kinetic energies in the two plates. Then, the coupling loss factors were assessed by a more “traditional” approach, namely, balancing the power input to a plate with the energies of the plates. The estimations from these four approaches compare as well as may be expected for these lightly damped plates.
Coupling loss factor estimation for plates joined along a line: Analysis and experiment.
Authors: Ewing Mark , Vatti Kranthi , Vaz Ignatius
Published: March 2010

Coupling loss factors for two plates joined at a line (a 90-deg bend), but otherwise free to respond in lateral vibration, have been studied both analytically and experimentally. Two cases have been studied: one with no added damping and one in which one of the plates has a small amount of damping provided by a constrained layer treatment. Statistical energy analysis (using VA ONE) and the finite element method (using NASTRAN) have been used to predict the coupling loss factors. The finite element predictions are based on the averaged responses for a range of boundary conditions on the plates, essentially a “pseudo-statistical” approach. Experimentally, one of the plates was excited while the kinetic energy of the two plates was assessed with a scanning laser vibrometer (scanning a dozen or more points) and four accelerometers on each plate. Both impulse and persistent excitations were used. The coupling loss factors were assessed by balancing the power input with the energies of the plates, also using the estimated modal densities. The estimations from the analytical and experimental approaches compare as well as may be expected for the lightly damped plates case, but very well for the case of one plate having a damping treatment.
Development of hybrid one-dimensional finite element/analytical method for analysis of lamb wave propagation characteristics in composit panels.
Authors: Kim Yong-Joe , Han Je-Heon
Published: March 2010

The objective of this study is to develop a hybrid one-dimensional finite element (1-D FE)/analytical method to analyze the Lamb wave propagation characteristics of composite panels. Here, it is proposed to model a composite panel using a finite element approximation in the thickness direction while analytical solutions are assumed in the plane directions. Thus, it makes possible to use small number of finite elements even for high-frequency analysis in computationally efficient manner. By solving the eigenvalue problem of the resulting 1-D FE/analytical matrix equation, the dispersion relations of the Lamb waves propagating in the composite panel can be calculated in wave number/frequency domain. Note that the dispersion relations can be used to determine the frequency, wavelength, and wave speed of a specific Lamb wave mode that can be used to monitor the specific structural defects of the composite panel. For the purpose of validating the proposed method, the dynamic responses of a composite panel are measured. The measured data are transformed into wave number/frequency domain by applying spatial Fourier transform, which result in measured dispersion relations. It is shown that the dispersion relations obtained by using the proposed hybrid method agree well with the measured dispersion relations.
Modeling the low-, mid-, and high-frequency response of poro-elastic materials in vibro-acoustics applications.
Authors: Cotoni Vincent
Published: March 2010

A method is presented for representing layered poro-elastic materials and acoustic fluids in a finite element (FE) model of a structure. The method is based on the hybrid FE-statistical energy analysis (SEA) formulation that allows the coupling of FE and SEA descriptions of various subsystems in a model. By making use of the dynamic properties of poro-elastic materials and acoustic fluids (in terms of wavelength and uncertainty), the method is made particularly fast and appropriate for the prediction of the vibro-acoustic response at midfrequencies. The method allows to quickly incorporate acoustics and/or noise control treatment in an existing finite element model of a structure. Given the frequency range of applicability, it complements the existing low-frequency methods (structure and poro-elastic material described with FE, acoustic fluid described with FE, infinite elements, or boundary elements) and high-frequency methods (structure, poro-elastic material, and acoustic fluid described with SEA). The formulation is derived and a number of validation examples are presented.
A comparison of visco-thermal models for the vibro-acoustic analysis of hearing aids.
Authors: Cordioli Júlio A. , Martins Gustavo , Jordan Roberto
Published: March 2010

The performance of a hearing aid is directly related to its vibro-acoustics characteristics, which must be taken in account during the design process. Different vibro-acoustic aspects of a hearing aid may be analyzed, including the structural transmission from the loudspeaker to the microphone, which may lead to an unwanted feedback, or the frequency response of the system composed by loudspeaker, tube, earmold and ear channel (considering a behind-the-ear hearing aid). In view of the reduced dimensions of the system it is argued that the vibro-acoustic analysis of such system must take in account visco-thermal effects in the description of the propagation of acoustical waves. In this paper, a simplified system is considered including the loudspeaker membrane, tube, and coupler (element commonly used for testing hearing aids). Results for three different approaches for the vibro-acoustic analysis of the system are compared with experimental data: (i) standard acoustical wave model, (ii) the low reduced frequency model, and (iii) the full linearized Navier–Stokes model. Results show that for the case considered the visco-thermal effects must be taken in account, while the choice between models (ii) and (iii) must be made in view of the system geometry.
An analysis of the Doppler shifted aircraft noise signature as measured by a hydrophone located within an evanescent field and implication for localization.
Authors: Dall’Osto David R. , Dahl Peter H.
Published: March 2010

Simultaneous measurements of the acoustic pressure field across the air-water interface, at site in Puget Sound, WA, are analyzed in terms of the Doppler signature of propeller driven aircraft. Measurements in the 50–300-Hz range are considered for various aircraft over flights. The Doppler shift recorded in air by a microphone placed 3 m above the air-water interface is modeled using standard Doppler theory. The hydrophone, placed at a depth 2.5 m below the air-water interface, reveals two Doppler shifts; one associated with the propagating transmitted acoustic field and the other associated with an evanescent field. A parametrized model for these two observed Doppler shifts is presented, utilizing ray theory and Snell’s law applied to a plane wave decomposition of the source wave fronts with, kH ≫ 1, where H is the source height and k is the wave number. It will be shown that analysis of the underwater acoustic field can be used to determine the altitude and closest point of approach (CPA) of a passing tonal source, with support from experimental data recorded by the hydrophone lying within the detection limits of the evanescent field. [Work supported by Washington Sea Grant and ONR.]
Directivity indices for rocket noise modeling: Measurement considerations.
Authors: Giraud Jarom H. , Gee Kent L.
Published: March 2010

Long-standing rocket noise models use far-field directivity indices to predict acoustic radiation loading on and near a launch vehicle. This approach raises a number of critical questions including where does the geometric far field begin for the frequencies of interest? and how does probable nonlinear propagation of noise away from the source affect these indices? Data collected on a static, horizontally fired GEM-60 solid rocket motor provide some insight into these questions. In the near field, microphones were located along a line approximately eight nozzle diameters from the shear layer. In addition, microphones were placed along two radials near the peak directivity angle at 63, 125, and 250 nozzle diameters. Analysis of these data indicates that nonlinear propagation dramatically affects the high-frequency directivity patterns along the peak radiation angles. In addition, the extended length of the source likely pushes the onset of the geometric far field to beyond 100 nozzle diameters for low frequencies.
A model for the prediction of community noise from launch vehicles.
Authors: Plotkin Kenneth J.
Published: March 2010

A model, RNOISE, has been developed for prediction of far-field community noise from the launch and boost phase of launch vehicles. It follows the moving source principles of an early NASA model [Wilhold et al., NASA Report No. TN D-1832 (1963)] but uses a noise source and directivity model developed by Sutherland [AIAA Paper No. 93-4383 (1993)] together with modern propagation algorithms as employed in the time simulation aircraft models NMSIM (NoiseMap Simulation) and AAM (Advanced Acoustic Model). RNOISE, first used for environmental analysis in the mid-1990s, is a spectral time simulation model, generating predictions of one-third octave band spectra on the ground as a function of time. Predictions may be made at a single point or on a grid. Recent improvements to RNOISE are the ability to read flight path data from a PCBoom format trajectory file, and output of time history grids in the TIG format used by NMSIM, AAM, and RNM (Rotorcraft Noise Model). This permits presentation of results as animations as well as traditional static contours.
Assessing the acoustical attributes of preserved historic structures.
Authors: Reuter Eric L.
Published: March 2010

Acoustical attributes of several preserved historic structures have been measured using contemporary techniques and metrics. These include outdoor-to-indoor and indoor-to-indoor impulse response and noise reduction measurements. Combined, these measurements allow for simulation, both quantitative and qualitative, of the indoor soundscapes of the past. These data will be presented, along with audio examples of historical noise sources, as experienced from indoors.
Measurement of whole hike soundscapes in a national park setting.
Authors: Stanley G. (Randy)
Published: March 2010

Measurements of whole hike soundscapes were made in Mount Rushmore National Park. The goal was to capture the time and space varying aural stimulus that a hiker experiences while walking through an environment. Two elements were employed: A portable binaural headset recording system and an array of audio recorders arranged at intervals along the trail. Various elements of the recorded soundscapes will be summarized and reproduced in part for the audience. In addition, expected analyses and anticipated challenges will be discussed.
Exploring the soundscape of nature.
Authors: Siebein Gary W. , Siebein Keely M. , Tsaih Lucky , Park Sang Bum , Jones Chris P. , Skelton Reece , Fisher Joshua
Published: March 2010

A study of a state park situated along a spring fed river was conducted to try to understand the nature of the soundscape of a park intended to be used by people for recreational purposes as well as to preserve the qualities of the natural ecosystems in the area. The study explores the qualitative and quantitative aspects of the ambient sound as composed of a series of specific acoustic events related to natural sounds of wildlife, water flows and weather, human use of the park, maintenance operations by park staff, and off-site noise intrusions from adjoining land uses. The acoustic “rooms” of the site are identified by the characteristics of their impulse responses. The rooms are linked by acoustic itineraries related to each of the user groups. Modeling of animal, weather, and human sounds is used to construct the acoustic rhythms of the site from limited, practical data acquisition of existing sounds. Recordings of real and simulated sound fields from the park were evaluated by listeners to determine qualitative and quantitative relationships of real and modeled sounds.
Ocean dreams.
Authors: Brooks Bennett M.
Published: March 2010

We arise by the sea, the genesis of life. We move inland via various forms of transportation, observing daily activities, ending our visit full circle with the solice at water’s edge.
Urban acoustic and seismic noise measurements in Baltimore.
Authors: Albert Donald G. , Decato Stephen N.
Published: March 2010

Acoustic and seismic sensors have good potential for passive, non-line-of-sight, detection, localization, and monitoring of natural and human activities. However, to fulfill this potential, sensor algorithms must be designed to not only robustly identify signals of interest but also to cope with environmental effects including high levels of background noise often found in urban areas. This paper presents experimental measurements conducted in Baltimore and at other locations to investigate noise levels in rural, urban, and industrial environments for audio frequencies between 6 Hz and 20 kHz and seismic frequencies from 6 to 1000 Hz. Because of the interest in large-scale Earth studies, there are hardly any previous seismic measurements in this high-frequency band and also most were done in remote areas specifically to avoid cultural noise. The measured urban seismic spectra tend to have more structure and variation in shape from one location to another compared to the acoustic spectra, and a more rapid decay with increasing frequency, usually about 30 dB from 30 to 600 Hz. The urban acoustic peak frequency is usually around 60 Hz, while the peak seismic frequencies are usually less than 25 Hz. [Work funded by U.S. Army.]
Investigation of noise barriers with resonators by the indirect boundary element method.
Authors: Auerbach Markus , Bockstedte Andreas , Zaleski Olgierd , Markiewicz Marian , von Estorff Otto , Bartolomaeus Wolfram
Published: March 2010

Noise barriers are the most common solutions to protect against noise pollution. They are very effective in the mitigation of road noise, but their high effectiveness often involves undesirably huge constructions. Following the demand for improving the efficiency without increasing the heights, a new procedure has been developed, which allows for extending a typical noise barrier by a line of resonators in a quite efficient way. It is based on numerical investigations including the indirect boundary element method. Several representative calculations are shown which demonstrate how the new approach can be used. The procedure turns out to be computationally very powerful and it seems to be a very promising step toward a more efficient design of sound barriers featuring high effectiveness at moderate overall heights. Measurements at a 20 m wide and 4 m high noise barrier with and without the device will be presented.
Modeling of sound fields in urban streets using a one-dimensional transport equation model.
Authors: Jing Yun , Xiang Ning
Published: March 2010

This paper presents a one-dimensional transport equation model for acoustic field predictions in urban streets. Considering urban streets as elongated enclosures, acoustic properties of the surfaces are typically quite different. For example, the top and two ends are often open and the streets are usually reflective. A recently developed one-dimensional transport equation [Jing et al., J. Acoust. Soc. Am. 125, 2735 (2009)] is extended to model non-uniform absorption and scattering coefficients and is applied to urban streets acoustic predictions. This paper discusses preliminary experimental results obtained from a tenth scale-model to validate the model.
Parametric study of the sound insulation performance of a ventilation window.
Authors: Tang S. K. , Suen D , Chan S. K.
Published: March 2010

The sound insulation performance of a specifically designed facade device, which allows natural ventilation but can provide relatively high-sound insulation, is studied experimentally in the present study. The experiment was carried out in two coupled rooms with one of them very reverberant and the other made semi-anechoic. The former acted as the receiver room and the latter contained a linear loudspeaker array (25 loudspeakers) as the noise source. The full scale facade device was installed on the concrete brick wall between the coupled rooms. Nine microphones were used to measure the average sound intensity inside the reverberant room. The effect of the size of the device opening (for ventilation) on the sound insertion loss was then determined by the difference between the average intensities with and without the device (an opened window). The present results show that the present facade device can offer additional acoustical protection of ∼12–13 dB(A) compared to that resulted from the conventional openable window design when exposed to traffic noise. The introduction of sound absorption materials at the top internal surface of the window cavity in general can result in a maximum of 2 dB extra benefit.
Three-dimensional pseudospectral time-domain calculations of sound propagation to closed urban courtyards.
Authors: Hornikx Maarten , Forssén Jens
Published: March 2010

Because contemporary urban environments suffer from excessive levels of road traffic noise, access to courtyards with low-noise levels is essential in order to offer urban sound environments of high quality with regard to health and perceived sound. Due to limitations in computational resources, accurate prediction of road traffic noise to urban courtyards has mainly been restricted to modeling the courtyards in two dimensions. To calculate sound propagation from road traffic to three-dimensional courtyards, the extended Fourier pseudospectral time-domain method is used here. This numerical domain discretization method solves the linearized Euler equations, where spatial derivatives are evaluated based on an eigenfunction expansion and thereby requires only two spatial points per wavelength. The time iteration is done using a low-storage optimized six-stage Runge–Kutta method. Calculation results, in time and frequency domains, display the difference of treating courtyards in two and three dimensions. As one of the results, it is concluded that the effect of noise abatement in the form of facade absorption treatments is larger for a setting in three dimensions than in two dimensions.
Influence of impedance distribution and optimal impedance design in the context of noise barriers.
Authors: Jolibois Alexandre , Sparrow Victor W. , Duhamel Denis , Defrance Jérôme
Published: March 2010

Noise barriers are commonly used to protect people from railways or roads traffic noise. However, the optimal design of those barriers is still an open problem since lots of different results have been obtained, depending on the method utilized. In this paper, instead of focusing on the shape of the barrier itself, a new method involving optimization of the impedance distribution on a control surface of simple geometry and containing the barrier has been used. First, numerical simulations have been carried out with the two dimensional boundary element method in order to predict the sound pressure level around any impedance scatterer. Analytical solution for the scattering of a line source by an infinite constant impedance circular cylinder has been derived and used for validation. Second the influence of the impedance distribution in the case of a circular cylindrical control surface has also been studied to determine an optimal impedance distribution to control the noise level in a zone close to the barrier. Specific attention has been paid to the scattering of multiple line sources in order to model high-speed train noise sources more accurately.
Potential noise reduction from mast trailing vanes as downwind-design wind turbine retrofits.
Authors: Storm Mark
Published: March 2010

Older wind turbine generators (WTGs) featuring rotors that are “downwind” of the nacelle mast structure have the reputation of being noisier than their “upwind” design counterparts on the argument that the aerodynamic wake from the mast introduces noise-producing turbulence at the interaction area of the passing rotor blades. Possible methods of improving the wake, for the purpose of reducing this blade-interaction turbulence and hence noise production, could include the addition of a flat plate or similar structure or device to the trailing side of a mast structural element. Realization of such a conceptual device would likely be a retrofit to a pre-existing downwind-design WTG—if mast-to-rotor clearance and other practical parameters allow. This study attempts to quantify the noise reduction potential of a sample retrofit concept, using an estimation technique similar to what one might find in the realm of commercial HVAC technology, where axial fan blade interaction with wakes from stators, vanes, pipes, grilles, or guards is a common noise-producing concern.
Effects of atmospheric scattering and refraction on the performance of acoustic direction-finding arrays.
Authors: Wilson D. Keith , Collier Sandra L. , Ostashev Vladimir E.
Published: March 2010

Refraction, turbulent scattering, and other atmospheric propagation effects complicate the performance of outdoor microphone arrays used to infer source bearings. In principle, with good knowledge of the atmospheric profiles, one can compensate for the refraction effects. However, the random angle-of-arrival variations induced by atmospheric turbulence limit array performance even when the signal-to-noise ratio is high. The turbulent scattering effect can be viewed as a coherence loss between elements of the beamforming array. Most research to date on acoustic signal coherence in the atmosphere has dealt with line-of-sight (LOS) propagation paths. A number of complications characteristic of real turbulence have been introduced; these include statistical inhomogeneity, anisotropy, and intermittency of the turbulent eddies. The LOS theory has also been extended to include sensor displacements longitudinal to the propagating wavefronts as well as transverse displacements. Formulations for the Cramer–Rao lower bound (CRLB) on the angle-of-arrival accuracy have been developed from the LOS theory. Based on limited experimental data and modeling, actual performance appears to be substantially worse than the CRLB. Recently, numerical methods have been introduced for solving second-moment parabolic equations, which offer the possibility of incorporating non-LOS effects into coherence calculations.
Comparison of noise levels measured on elevated acoustic sensor arrays mounted on various aerostats.
Authors: Reiff Christian G.
Published: March 2010

The army has fielded acoustic systems for the detection of mortar, rocket, and small arms and it has been demonstrated that elevating the acoustic array by mounting the array on an aerostat can improve signal-to-noise levels. The elevated array receives a cleaner, higher amplitude signal while the noise level also increases. The performance of aerostat mounted acoustic sensor arrays for source detection and localization is limited by these increased noise levels caused by higher wind speeds and airship components. These shortcomings can be mitigated somewhat by using microphone windscreens, array location, and signal processing. Data from experiments on a large tethered rigid airship, a smaller tethered non-rigid aerostat, and a medium rigid motorized airship are compared for noise environment and effects on acoustic detection and source localization.
Estimation of pointing vector using acoustic planar array.
Authors: Damarla Thyagaraju
Published: March 2010

Traditional use of acoustic array of sensors for estimation of azimuth and elevation of a target suffer from inaccuracies, especially in estimation of elevation angle, due to poor resolution in trigonometric functions. For example, a variation of angle 70 × 90 deg result in variation of sine of angle in 0.94–1. In the proposed approach, each pair of elements (sensors) in the array is used to estimate the direction of arrival (DoA) of the signal. This DoA forms a cone along the axis of the line joining the pair of sensors. Several such cones from different pairs of sensors would intersect giving the direction of the target. Since the phase angles between two sensors can be estimated accurately, the DoAs will be accurate and hence the intersection of the cones would result in accurate estimation of the pointing vector to the target overcoming the deficiencies of the traditional methods. In the case of transient events, the time difference of arrival at the pair of sensors gives the DoA. Mathematical formulation for estimating the pointing vector will be given. The technique will be used on some field data and the results obtained will be compared with the ground truth.
Near-ultrasound, broadband noise generated by low-speed airflow over wires.
Authors: Alberts W.C. Kirkpatrick , Sanchez Kevin J. , Coleman Mark A. , Gabrielse Josh , Ligon David A.
Published: March 2010

Vortex shedding due to flow past a cylindrical object and its accompanying sound are well-described phenomena, though research has often focused on the sound broadcast in directions transverse to the wire and downstream in high-speed flows. Here, we investigate the sound broadcast in angles nearly opposite the direction of low-speed flows from nozzles of diameter similar to those of various wires. Also investigated are the effects that several parameters (tension, wire diameter, nozzle-wire separation, etc.) have on the level and frequency content of the recorded sound. It is found that a microphone approximately 3 cm above the outlet of a nozzle records broadband, near-ultrasound noise due to the flow over the wire. Signal levels as high as 20 dB above the nozzle background are observed. Recorded broadband noise spectra associated with vortex shedding from various wires and schlieren images of the interaction between the flow and the wire will be presented.
Oceanic noise: Mechanisms, radiation characteristics, and array results.
Authors: Carey William M.
Published: March 2010

Noise produced by the oscillation of microbubble distributions and impacts (raindrops and splash) in the air-sea boundary zone results in doublet radiation patterns and noise fields with definitive temporal and spatial characteristics. Turbulence generated noise is quadrupole, and nonlinear wave-wave interactions are infrasonic. Plausible mechanisms provide a framework for a review of directional noise measurements in range dependent oceanic and bathymetric environments. Slope interaction converts higher angles to lower angles and results in a frequency dependent vertical directionality. Low-frequency (0.02–1 kHz) measurements reveal a temporally dynamic noise field with persistent directional characteristics. Higher frequency (1-kHz or greater) measurements exhibit a local stationary characteristic influenced by the boundary zone mixed layer. Beam noise cumulative distribution functions are shown to depend on the distribution of ships, basin size, and boundaries. Directional noise computations are presented along with the issues of shipping distributions, the air-sea boundary zone, and assimilated satellite observations of wind speed, white caps, and sea surface temperature. The computation of basin scale directionality basically estimates the persistent characteristic. Improved calculation with the directional radiation from modern ships and the inclusion of the dynamic ship distribution ships are presented to estimate the beam noise statistics.
Trends in low-frequency deep ocean ambient noise levels: New results from old data.
Authors: Chapman Ross , Price Andrea
Published: March 2010

Concern about effects of anthropogenic sound generated by ships, seismic exploration, naval operations, and ocean acoustic research on marine life has stimulated new studies of marine animal bioacoustics. An underlying issue in assessing the noise impact establishes the present-day background noise level and compares it to noise levels from previous times. The most generally accepted prediction of noise level trend at low frequencies (below 500 Hz) is due to Ross, who used noise levels from the 1950s and the mid-1960s to predict an increase of about 3 dB/decade. This paper addresses the issue of the trend in low-frequency ambient noise levels in the ocean and presents measurements taken in the intermediate years between the mid-1960s and the present time. The measurements were made using a calibrated multi-element volume array (MEVA) at deep ocean sites in the Northeast Pacific from 1978 to 1986. The array provided spectral noise levels and horizontal and vertical directionalities. Compared to the 1965 values, the MEVA values are 6–8 dB greater between 10–50 Hz and 1–3 dB greater from 50–400 Hz, respectively. The data presented here provide evidence that the trend predicted by Ross extended at least into the mid-1980s.
Depth-profiling ambient noise in the deep ocean.
Authors: Barclay David R. , Simonet Fernando , Buckingham Michael J.
Published: March 2010

Deep Sound is an untethered instrument platform designed to free-fall from the sea surface to a preassigned depth, at which point a burn wire releases a weight, allowing the system to return to the surface under buoyancy. The descent and ascent rate is 0.6 m/s. A Vitrovex glass sphere houses lithium-ion batteries and a suite of microprocessor-controlled electronics for data acquisition, data storage, power management, and system control. Outside the sphere, several hydrophones are arranged in vertical and horizontal configurations, a CTD returns environmental data, and motion sensors monitor pitch, roll, and yaw. Data may be downloaded, and the batteries may be recharged, via throughputs in the sphere. The hydrophones, with a bandwidth of 30 kHz, are rated to a depth exceeding 11 km, and the sphere itself has a depth-rating of 9 km. The system made three descents in the Philippine Sea in May 2009, to depths of 5100, 5500 and 6000 m; and in November 2009, two descents were made in the Mariana Trench to a depth of 9000 m. On all these deployments, ambient-noise time-series were recorded continuously, yielding the power spectrum and vertical coherence of the noise as functions of depth. [Research supported by ONR.]
Deep water ambient noise on the seafloor.
Authors: Stephen Ralph A.
Published: March 2010

Long, continuous time series of ocean bottom seismometer (OBS) and co-located hydrophone data from the seafloor offer an unprecedented opportunity to study the physical mechanisms of seafloor ambient noise in the frequency band from 1 to 100 Hz. The Ocean Seismic Network Pilot Experiment (OSNPE) in 1998 compared noise and signal levels for a hydrophone at the seafloor with three-component observations from OBSs on the seafloor, buried 1 m into the soft sediment, and clamped in a borehole 10 m into basaltic basement. The Hawaii-2 Observatory (H2O) acquired over 3 years of nearly continuous, real-time data from a shallow-buried seismic and seafloor hydrophone system. On the North Pacific Acoustic Laboratory experiment in 2004 (NPAL04) three vertical-component geophone/hydrophones were deployed beneath vertical line arrays in the water column. In addition to ambient noise data, controlled source transmissions were received from ranges out to 3200 km. In the absence of shipping noise, whale calls, and local sea state, what controls the noise floor on the deep seafloor? Interesting observations include banded coherence structure between the vertical geophones and hydrophones, peaks in ambient noise levels due to resonances in the sediment layer, and Stoneley/Scholte wave particle motions. [Work supported by the NSF, ONR and WHOI.]