The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Linda P. Franzoni - One of the best experts on this subject based on the ideXlab platform.
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Absorption‐based scaling method to predict steady‐state broadband sound Fields in enclosures
The Journal of the Acoustical Society of America, 2006Co-Authors: Donald B. Bliss, Jerry W. Rouse, Linda P. FranzoniAbstract:An absorption‐based analysis method is developed for steady‐state broadband sound Fields in enclosures having diffuse or specular reflection boundaries. The wall absorption is expressed as an overall spatially averaged value, with spatial variations around this mean. Interior pressures and intensities are expressed in a power series of the overall absorption, treated as a small parameter, thereby giving a separate problem at each order. The first problem has a uniform mean‐square pressure level proportional to the reciprocal of the absorption parameter, as expected. The second problem gives a mean‐square pressure and intensity distribution that is independent of the absorption parameter and is primarily responsible for the spatial variation of the Reverberant Field. This problem depends on the location of sources and the spatial distribution of absorption, but not absorption level. Higher‐order problems proceed at powers of the absorption parameter, but are essentially small corrections to the primary spa...
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Analysis of temporal decay of diffuse broadband sound Fields in enclosures by decomposition in powers of an absorption parameter
The Journal of the Acoustical Society of America, 2005Co-Authors: Donald B. Bliss, Linda P. Franzoni, Jerry W. Rouse, Ben ManningAbstract:An analysis method for time‐dependent broadband diffuse sound Fields in enclosures is described. Beginning with a formulation utilizing time‐dependent broadband intensity boundary sources, the strength of these wall sources is expanded in a series in powers of an absorption parameter, thereby giving a separate boundary integral problem for each power. The temporal behavior is characterized by a Taylor expansion in the delay time for a source to influence an evaluation point. The lowest‐order problem has a uniform interior Field proportional to the reciprocal of the absorption parameter, as expected, and exhibits relatively slow exponential decay. The next‐order problem gives a mean‐square pressure distribution that is independent of the absorption parameter and is primarily responsible for the spatial variation of the Reverberant Field. This problem, which is driven by input sources and the lowest‐order Reverberant Field, depends on source location and the spatial distribution of absorption. Additional pr...
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Prediction of broadband nonuniform time‐dependent acoustic Fields in enclosures with diffuse reflection boundaries using energy‐intensity modes
The Journal of the Acoustical Society of America, 2004Co-Authors: Donald B. Bliss, Linda P. FranzoniAbstract:A new analysis of high‐frequency broadband Reverberant sound Fields in rooms with diffuse reflection boundaries is described. Depending on shape, source location, and distribution of wall absorption, rooms exhibit spatial variation in steady‐state mean‐square pressure and also spatial dependence of decay time characteristics. The room boundaries can be replaced by a distribution of uncorrelated broadband directional energy‐intensity sources. In steady state with diffuse reflection boundaries, the interior pressure Field produced by these sources satisfies Laplace’s equation. The mean‐square pressure Field is expressed as a sum of constituent modes. The intensity Field, which is related to the pressure Field in a complex way, can be calculated for each mode. Boundary conditions relate averaged intensity and pressure. The mean‐square pressure is expressed in terms of the modal sum. Lower order modes are responsible for the overall smooth spatial variation in the Reverberant Field; higher modes account for m...
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A study of damping effects on spatial distribution and level of Reverberant sound in a rectangular acoustic cavity
The Journal of the Acoustical Society of America, 1999Co-Authors: Linda P. Franzoni, Danielle S. LabrozziAbstract:Based on computer simulations of sound Fields in rectangular enclosures, important observations are made regarding sound pressure levels and the spatial variation of the broadband Reverberant Field. From these observations an empirical formula is deduced that describes the slow spatial variation of the broadband Reverberant mean-square pressure in one lengthwise direction. Two room shapes were studied: an elongated rectangular enclosure and an almost cubic enclosure, both with broadband sound source(s) on an endwall. Source position, relative phasing of multiple sources, level, and placement of absorptive material were variables in the study. The numerical results for the spatially averaged mean-square pressure in the Reverberant Field were often not in very close agreement with values predicted from a traditional Sabine approach. The prediction was improved by accounting for the power absorbed on the first reflection and an approximate formula is given for this correction factor. The Reverberant sound Field is characterized by a gradual spatial variation in the direction away from the source. This spatial variation scales exponentially with the sidewall absorptivity, as demonstrated by the numerical simulations. An approximate emperical formula is shown to predict this spatial variation fairly well. The computer simulations showed elevated sound pressure levels at the enclosure boundaries, for all cases, and also in the interior, for sound Fields excited by a single broadband source on an endwall. These intensification zones occur along a plane in front of the source and along a plane which corresponds to the reflection of the source, whether or not the source is on a line of symmetry.
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A study of the Reverberant Field in rooms with various absorptions, including prediction of spatial variation
The Journal of the Acoustical Society of America, 1998Co-Authors: Linda P. FranzoniAbstract:The sound Fields of two rectangular rooms of different size and proportion have been studied using a computer simulation. Point sound sources and absorbing walls are mathematically modeled and the wave equation is solved, the direct‐Field is removed, and the result is an exact calculation of the Reverberant Field in the room at any spatial location. Both the overall volume‐averaged sound‐pressure level and the spatially varying cross‐sectional averaged levels are computed and compared to theoretical results. A new theoretical result for the spatial variation is developed using an energy balance applied to cross‐sectional slices of the room. Good agreement is shown between this result and the calculated values. The same theory gives overall levels by integrating cross‐sectional averages, this is compared to classical results (Sabine, etc.) and to the computer generated data. An improvement can be made to the classical theory by reducing the source power to account for first reflections. Some experimental r...
Richard G Barr - One of the best experts on this subject based on the ideXlab platform.
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2 d shear wave dispersion images using the Reverberant shear wave Field approach application in tissues exhibiting power law response
Internaltional Ultrasonics Symposium, 2019Co-Authors: Juvenal Ormachea, Richard G Barr, Kevin J ParkerAbstract:Within the Field of elastography, a relatively new approach analyzes the limiting case of shear waves established as a Reverberant Field. In this framework, it is assumed that a distribution of shear waves exists, oriented across all directions in 3D and continuous in time. The simultaneous multi-frequency application of Reverberant shear wave Fields can be accomplished by applying an array of external sources that can be excited by multiple frequencies, for example 50, 100, 150,…500 Hz, all contributing to the shear wave Field produced in the target organ. We report a Monte Carlo analysis simulation for the validation of the main theoretical principles, and a preliminary study on breast and liver tissues using the multi-frequency Reverberant shear wave technique, employing frequencies up to 700 Hz in breast tissue, and robust Reverberant patterns of shear waves across the entire liver and kidney in obese patients. Dispersion images are shown to have contrast between tissue types and with quantitative values that align with previous studies.
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an initial study of complete 2d shear wave dispersion images using a Reverberant shear wave Field
Physics in Medicine and Biology, 2019Co-Authors: Juvenal Ormachea, Kevin J Parker, Richard G BarrAbstract:Within the Field of elastography, a relatively new approach analyzes the limiting case of shear waves established as a Reverberant Field. In this framework, it is assumed that a distribution of shear waves exists, oriented across all directions in 3D and continuous in time. The simultaneous multi-frequency application of Reverberant shear wave Fields can be accomplished by applying an array of external sources that can be excited by multiple frequencies within a bandwidth, for example 50, 100, 150, …, 500 Hz, all contributing to the shear wave Field produced in the liver or other target organ. This enables the analysis of the dispersion of shear wave speed as it increases with frequency, indicating the viscoelastic and lossy nature of the tissue under study. Furthermore, dispersion images can be created and displayed alongside the shear wave speed images. We report preliminary studies on breast and liver tissues using the multi-frequency Reverberant shear wave technique, employing frequencies up to 700 Hz in breast tissue, and robust Reverberant patterns of shear waves across the entire liver and kidney in obese patients. Dispersion images are shown to have contrast between tissue types and with quantitative values that align with previous studies.
Patrick A Naylor - One of the best experts on this subject based on the ideXlab platform.
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EUSIPCO - An acoustic image-source characterisation of surface profiles
2018 26th European Signal Processing Conference (EUSIPCO), 2018Co-Authors: P. J. Dawson, E. De Sena, Patrick A NaylorAbstract:The image-source method models the specular reflection from a plane by means of a secondary source positioned at the source's reflected image. The method has been widely used in acoustics to model the Reverberant Field of rectangular rooms, but can also be used for general-shaped rooms and non-flat reflectors. This paper explores the relationship between the physical properties of a non-flat reflector and the statistical properties of the associated cloud of image-sources. It is shown here that the standard deviation of the image-sources is strongly correlated with the ratio between depth and width of the reflector's spatial features.
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source localization and signal reconstruction in a Reverberant Field using the fdtd method
European Signal Processing Conference, 2014Co-Authors: Niccolo Antonello, Toon Van Waterschoot, Marc Moonen, Patrick A NaylorAbstract:Numerical methods applied to room acoustics are usually employed to predict the sound pressure at certain positions generated by a known source. In this paper the inverse problem is studied: given a number of microphones placed in a room, the sound pressure is known at these positions and this information may be used to perform a localization and signal reconstruction of the sound source. The source is assumed to be spatially sparse meaning it can be modeled as a point source. The finite difference time domain method is used to model the acoustics of a simple two dimensional square room and its matrix formulation is presented. A two step method is proposed. First a convex optimization problem is solved to localize the source while exploiting its spatial sparsity. Once its position is known the source signal can be reconstructed by solving an overdetermined system of linear equations.
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EUSIPCO - Source localization and signal reconstruction in a Reverberant Field using the FDTD method
2014Co-Authors: Niccolo Antonello, Toon Van Waterschoot, Marc Moonen, Patrick A NaylorAbstract:Numerical methods applied to room acoustics are usually employed to predict the sound pressure at certain positions generated by a known source. In this paper the inverse problem is studied: given a number of microphones placed in a room, the sound pressure is known at these positions and this information may be used to perform a localization and signal reconstruction of the sound source. The source is assumed to be spatially sparse meaning it can be modeled as a point source. The finite difference time domain method is used to model the acoustics of a simple two dimensional square room and its matrix formulation is presented. A two step method is proposed. First a convex optimization problem is solved to localize the source while exploiting its spatial sparsity. Once its position is known the source signal can be reconstructed by solving an overdetermined system of linear equations.
Donald B. Bliss - One of the best experts on this subject based on the ideXlab platform.
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Absorption‐based scaling method to predict steady‐state broadband sound Fields in enclosures
The Journal of the Acoustical Society of America, 2006Co-Authors: Donald B. Bliss, Jerry W. Rouse, Linda P. FranzoniAbstract:An absorption‐based analysis method is developed for steady‐state broadband sound Fields in enclosures having diffuse or specular reflection boundaries. The wall absorption is expressed as an overall spatially averaged value, with spatial variations around this mean. Interior pressures and intensities are expressed in a power series of the overall absorption, treated as a small parameter, thereby giving a separate problem at each order. The first problem has a uniform mean‐square pressure level proportional to the reciprocal of the absorption parameter, as expected. The second problem gives a mean‐square pressure and intensity distribution that is independent of the absorption parameter and is primarily responsible for the spatial variation of the Reverberant Field. This problem depends on the location of sources and the spatial distribution of absorption, but not absorption level. Higher‐order problems proceed at powers of the absorption parameter, but are essentially small corrections to the primary spa...
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Boundary element prediction of steady‐state broadband interior sound Fields using absorption‐based scaling
The Journal of the Acoustical Society of America, 2006Co-Authors: Donald B. Bliss, Jerry W. RouseAbstract:Energy‐intensity boundary elements are used in combination with the method of absorption‐based scaling to predict steady‐state broadband sound Fields in enclosures with diffuse reflection boundaries. The wall absorption is expressed in terms of an overall absorption parameter—the spatially averaged value—and spatial variations around this mean. Boundary element strengths are expressed in a power series of the overall absorption, treated as a small parameter, thereby giving a separate problem at each order. The first problem has a uniform mean‐square pressure proportional to the reciprocal of the absorption parameter. The second problem gives mean‐square pressure and intensity distributions that are independent of the absorption parameter and are primarily responsible for the spatial variation of the Reverberant Field. This problem depends on the location of sources and the spatial distribution of absorption, but not overall absorption. Higher order problems proceed in powers of the absorption parameter, a...
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Analysis of temporal decay of diffuse broadband sound Fields in enclosures by decomposition in powers of an absorption parameter
The Journal of the Acoustical Society of America, 2005Co-Authors: Donald B. Bliss, Linda P. Franzoni, Jerry W. Rouse, Ben ManningAbstract:An analysis method for time‐dependent broadband diffuse sound Fields in enclosures is described. Beginning with a formulation utilizing time‐dependent broadband intensity boundary sources, the strength of these wall sources is expanded in a series in powers of an absorption parameter, thereby giving a separate boundary integral problem for each power. The temporal behavior is characterized by a Taylor expansion in the delay time for a source to influence an evaluation point. The lowest‐order problem has a uniform interior Field proportional to the reciprocal of the absorption parameter, as expected, and exhibits relatively slow exponential decay. The next‐order problem gives a mean‐square pressure distribution that is independent of the absorption parameter and is primarily responsible for the spatial variation of the Reverberant Field. This problem, which is driven by input sources and the lowest‐order Reverberant Field, depends on source location and the spatial distribution of absorption. Additional pr...
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Prediction of broadband nonuniform time‐dependent acoustic Fields in enclosures with diffuse reflection boundaries using energy‐intensity modes
The Journal of the Acoustical Society of America, 2004Co-Authors: Donald B. Bliss, Linda P. FranzoniAbstract:A new analysis of high‐frequency broadband Reverberant sound Fields in rooms with diffuse reflection boundaries is described. Depending on shape, source location, and distribution of wall absorption, rooms exhibit spatial variation in steady‐state mean‐square pressure and also spatial dependence of decay time characteristics. The room boundaries can be replaced by a distribution of uncorrelated broadband directional energy‐intensity sources. In steady state with diffuse reflection boundaries, the interior pressure Field produced by these sources satisfies Laplace’s equation. The mean‐square pressure Field is expressed as a sum of constituent modes. The intensity Field, which is related to the pressure Field in a complex way, can be calculated for each mode. Boundary conditions relate averaged intensity and pressure. The mean‐square pressure is expressed in terms of the modal sum. Lower order modes are responsible for the overall smooth spatial variation in the Reverberant Field; higher modes account for m...
Andrea Sassaroli - One of the best experts on this subject based on the ideXlab platform.
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Acoustic source localization in a Reverberant environment by average beamforming
Mechanical Systems and Signal Processing, 2010Co-Authors: Paolo Castellini, Andrea SassaroliAbstract:Abstract This paper presents a strategy for the application of acoustic beamforming to locate noise sources in a Reverberant Field. In the hypothesis of stationary phenomena, the average amplitude and standard deviation of the output of beamforming, obtained from different array locations, are calculated. The standard deviation, normalized by the maximum value, can be used for beamforming output weighting, so as to enhance the source contribution, which is space invariant, and to attenuate the mirrors and sidelobe peaks, whose spatial position changes with changes in array position. The availability of microphone signals acquired when moving the array to a different position also allows a super-array to be obtained, i.e. an array obtained considering all the data as coming from a unique array. In this way, the capability of the averaging procedure to reject mirrors effects and disturbances is combined with high resolution beamforming for application in Reverberant Fields. These improvements are extended to the entire frequency range, since the procedure is not greatly affected by signal wavelength.
