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Numerical evidence of mixing in rooms using the free path temporal distribution Billon, Alexis ; Embrechts, Jean-Jacques in Journal of the Acoustical Society of America (2011), 130(3), 13811389 The ergodic propriety of a room has strong effects on its reverberation. If the room is ergodic, the reverberation can be broken up in two steps: a deterministic process followed by a stochastic one. The ... [more ▼] The ergodic propriety of a room has strong effects on its reverberation. If the room is ergodic, the reverberation can be broken up in two steps: a deterministic process followed by a stochastic one. The late reverberation can be then modeled by a reverberation algorithm instead of more computationally consuming methods. In this study, the free path temporal distribution obtained by ray-tracing is used as an indicator of the room’s mixing: the energetic average of the path lengths is computed at each time step. Ergodic rooms are thus characterized by rapidly convergent distributions. The free path value becomes independent of time. On the other hand, path selection mechanism and orbits are observed in non-ergodic rooms. The transition time from the deterministic process to the stochastic one is also studied through the evaluation of the room’s time constant. It is shown that its value depends only on the mean free path and the boundaries scattering value. An empirical expression is obtained which agrees well with simulations carried out in a concert hall. This transition time from a deterministic model to a stochastic one can be used to speed up the acoustical predictions and auralizations in ergodic rooms. [less ▲] Detailed reference viewed: 56 (7 ULg)Masked and unmasked auditory thresholds in three species of birds, as measured by auditory brainstem responde Noirot, Isabelle ; ; in Journal of the Acoustical Society of America (2011) Detailed reference viewed: 22 (0 ULg)Finding good acoustic features for parrot vocalizations: The feature generation approach ; ; Albert, Aurélie et al in Journal of the Acoustical Society of America (2011), 129 A crucial step in the understanding of vocal behavior of birds is to be able to classify calls in the repertoire into meaningful types. Methods developed to this aim are limited either because of human ... [more ▼] A crucial step in the understanding of vocal behavior of birds is to be able to classify calls in the repertoire into meaningful types. Methods developed to this aim are limited either because of human subjectivity or because of methodological issues. The present study investigated whether a feature generation system could categorize vocalizations of a bird species automatically and effectively. This procedure was applied to vocalizations of African gray parrots, known for their capacity to reproduce almost any sound of their environment. Outcomes of the feature generation approach agreed well with a much more labor-intensive process of a human expert classifying based on spectrographic representation, while clearly out-performing other automated methods. The method brings significant improvements in precision over commonly used bioacoustical analyses. As such, the method enlarges the scope of automated, acoustics-based sound classification. [less ▲] Detailed reference viewed: 29 (1 ULg)Biocompatible solid particles for controlled instigation of cavitation during therapeutic ultrasound. ; ; Manhas, Varun et al in Journal of the Acoustical Society of America (2010, October), 128(4), 2440 Detailed reference viewed: 17 (0 ULg)Modeling the sound transmission coupled through partition walls using a diffusion model Billon, Alexis ; ; et al in Journal of the Acoustical Society of America (2008), 123(6), 4261-4271 In this paper, a modification of the diffusion model for room acoustics is proposed to account for sound transmission between two rooms, a source room and an adjacent room, which are coupled through a ... [more ▼] In this paper, a modification of the diffusion model for room acoustics is proposed to account for sound transmission between two rooms, a source room and an adjacent room, which are coupled through a partition wall. A system of two diffusion equations, one for each room, together with a set of two boundary conditions, one for the partition wall and one for the other walls of a room, is obtained and numerically solved. The modified diffusion model is validated by numerical comparisons with the statistical theory for several coupled-room configurations by varying the coupling area surface, the absorption coefficient of each room, and the volume of the adjacent room. An experimental comparison is also carried out for two coupled classrooms. The modified diffusion model results agree very well with both the statistical theory and the experimental data. The diffusion model can then be used as an alternative to the statistical theory, especially when the statistical theory is not applicable, that is, when the reverberant sound field is not diffuse. Moreover, the diffusion model allows the prediction of the spatial distribution of sound energy within each coupled room, while the statistical theory gives only one sound level for each room. [less ▲] Detailed reference viewed: 25 (1 ULg)On the use of diffusion equations to model the acoustics of coupled rooms Billon, Alexis ; ; et al in Journal of the Acoustical Society of America (2008), 123(5), 3910-3910 he acoustics of coupled rooms are characterized by energy exchanges through apertures and/or partition walls. The use of systems of diffusion equations allows to predict the temporal and spatial energy ... [more ▼] he acoustics of coupled rooms are characterized by energy exchanges through apertures and/or partition walls. The use of systems of diffusion equations allows to predict the temporal and spatial energy distributions in these configurations quite accurately. In this presentation, the diffusion formalism for room acoustics-prediction is summarized. The systems of equations to be solved in the case of coupling through an aperture and through a partition wall are presented. For two rooms coupled through an aperture (two classrooms connected through an open door), the results obtained with the diffusion model are compared to experimental data, in terms of sound pressure levels and sound decays. On the other hand, for the case of two classrooms connected through a partition wall, the diffusion model is compared to experimental data in terms of sound pressure level difference only. Finally, an engineering application is presented in the configuration involving a workroom including multiple sound sources (e.g., machines) connected to offices through open and closed doors. [less ▲] Detailed reference viewed: 31 (1 ULg)Prediction of the sound pressure levels using a diffusion model: numerical validations and experimental comparisons Billon, Alexis ; in Journal of the Acoustical Society of America (2008), 123(5), 3924-3924 redictions of sound propagation in urban areas have attracted a considerable over the years. If the sound energy is assimilated to particles with a constant energy, their movement can be described by a ... [more ▼] redictions of sound propagation in urban areas have attracted a considerable over the years. If the sound energy is assimilated to particles with a constant energy, their movement can be described by a transport equation. In canyon streets, this transport equation can be reduced to a diffusion equation whose expression is more simple. In this presentation, sound absorption at the boundaries (buildings facades and ground), as well as atmospheric sound attenuation are introduced. The problem is then solved numerically using a finite elements method for the configuration of a canyon street. A systematic validation of the obtained model is carried out in terms of sound pressure level by comparison to numerical simulations taken from the literature. Comparisons with experimental data are then conducted. Finally, applications in more complex configurations are presented. [less ▲] Detailed reference viewed: 54 (1 ULg)Introducing atmospheric attenuation within a diffusion model room-acoustic predictions Billon, Alexis ; ; et al in Journal of the Acoustical Society of America (2008), 123(6), 4040-4043 This paper presents an extension of a diffusion model for room acoustics to handle the atmospheric attenuation. This phenomenon is critical at high frequencies and in large rooms to obtain correct ... [more ▼] This paper presents an extension of a diffusion model for room acoustics to handle the atmospheric attenuation. This phenomenon is critical at high frequencies and in large rooms to obtain correct acoustic predictions. An additional term is introduced in the diffusion equation as well as in the diffusion constant, in order to take the atmospheric attenuation into account. The modified diffusion model is then compared with the statistical theory and a cone-tracing software. Three typical room-acoustic configurations are investigated: a proportionate room, a long room and a flat room. The modified diffusion model agrees well with the statistical theory (when applicable, as in proportionate rooms) and with the cone-tracing software, both in terms of sound pressure levels and reverberation times. [less ▲] Detailed reference viewed: 42 (2 ULg)On the use of a diffusion model for acoustically coupled rooms Billon, Alexis ; ; et al in Journal of the Acoustical Society of America (2006), 120(4), 2043-2054 A numerical model is proposed to predict the reverberant sound field in a system of two coupled volumes that are connected through an open aperture. The model is based on the numerical implementation of a ... [more ▼] A numerical model is proposed to predict the reverberant sound field in a system of two coupled volumes that are connected through an open aperture. The model is based on the numerical implementation of a diffusion model that has already been applied to predict the sound-energy distribution and the sound decay in single rooms. In comparison with the statistical theory, the proposed approach permits the prediction of the sound field by taking into account the sound source location and the receiver locations as well as the transition from one room to the other at the coupling aperture. Moreover, the diffusion model results match satisfactorily the experimental data in terms of sound-pressure level and reverberation times, both in the room containing the source and in the receiving room. Simulations with a ray-based model are also carried out, leading to results similar to those of the diffusion model, but at a cost of larger computation times. [less ▲] Detailed reference viewed: 52 (3 ULg)Experimental investigation of targeted energy transfers in strongly and nonlinearly coupled oscillators ; Kerschen, Gaëtan ; et al in Journal of the Acoustical Society of America (2005), 118(2), 791-799 Our focus in this study is on experimental investigation of the transient dynamics of an impulsively loaded linear oscillator coupled to a lightweight nonlinear energy sink. It is shown that this ... [more ▼] Our focus in this study is on experimental investigation of the transient dynamics of an impulsively loaded linear oscillator coupled to a lightweight nonlinear energy sink. It is shown that this seemingly simple system exhibits complicated dynamics, including nonlinear beating phenomena and resonance captures. It is also demonstrated that, by facilitating targeted energy transfers to the nonlinear energy sink, a significant portion of the total input energy can be absorbed and dissipated in this oscillator. (C) 2005 Acoustical Society of America. [less ▲] Detailed reference viewed: 18 (2 ULg)Experimental validation of a diffusion equation-based modeling of the sound field in coupled rooms Billon, Alexis ; ; et al in Journal of the Acoustical Society of America (2005, April), 117(4), 2581-2581 Sound modeling in coupled rooms (i.e., two acoustically coupled rooms separated by an open area) has attracted considerable attention in the past. However accurate and operational models are still needed ... [more ▼] Sound modeling in coupled rooms (i.e., two acoustically coupled rooms separated by an open area) has attracted considerable attention in the past. However accurate and operational models are still needed, principally when three or more rooms are coupled. In recent papers, a diffusion equation-based model has been applied to unusual room shapes. For the coupled rooms geometry, this diffusion model has been validated successfully by comparison with the classical statistical theory in a parametrical study of the coupling parameters [Billon et al., J. Acoust. Soc. Am. 116, 2553 (2004)]. In the present work, the diffusion model results are validated by means of a comparison with experimental results, both in terms of sound attenuation and reverberation time. A comparison is also provided with results given by the statistical theory and a ray tracing program. For this purpose, experiments have been conducted in two coupled classrooms with two different sound source locations. The results show a very good agreement between the diffusion model and the experiments. Conversely, the statistical model is not valid for modeling accurately the sound field distribution and decay in both coupled rooms. At last, the diffusion model runs much faster than the ray tracing program. [less ▲] Detailed reference viewed: 20 (0 ULg)Reverberated sound field modeling in coupled rooms using a diffusion equation Billon, Alexis ; ; et al in Journal of the Acoustical Society of America (2004, October), 116(4), 2553-2553 Sound modeling in coupled rooms has attracted considerable attention in the past, but accurate and operational models are still needed. In recent papers, a diffusion equation based model has been applied ... [more ▼] Sound modeling in coupled rooms has attracted considerable attention in the past, but accurate and operational models are still needed. In recent papers, a diffusion equation based model has been applied with success to unusual room shapes. This approach allows nonuniform repartition of energy, and is especially relevant in room acoustics for long rooms or complex spaces such as networks of rooms. The present work aims at validating the behavior of the diffusion model in the case of two acoustically coupled rooms separated by an open area. In this purpose, the time-dependent diffusion equation is solved in three dimensions using a finite-element solver. It allows one to predict both sound attenuation and reverberation time at any point of the coupled rooms. Parameters influencing the coupling, i.e., room relative sizes, aperture size and room absorption areas, are investigated. Results are then compared with the classical statistical theory of coupled rooms. Finally, a comparison with experimental data in two coupled classrooms is also provided. [less ▲] Detailed reference viewed: 36 (0 ULg)Interaction of a slot-tone with a pipe Billon, Alexis ; ; in Journal of the Acoustical Society of America (2002, November), 111(5), 2373-2373 The self-sustained tone generated by a low Mach number free flow impinging on a slotted plate, usually referred to slot-tone, is experimentaly studied. In this work we focus on its coupling with the pipe ... [more ▼] The self-sustained tone generated by a low Mach number free flow impinging on a slotted plate, usually referred to slot-tone, is experimentaly studied. In this work we focus on its coupling with the pipe from which the jet flows out. The jet nozzle and the beveled slot are aligned and have the same large aspect ratio. The tones generated have a single well defined frequency (around 1 kHz), a high amplitude (typically, 105 to 115 dB) and exhibit typical characteristics of self-sustained tones. Their frequencies are about the same order of magnitude than the natural frequency of the shear layer calculated from the linear stability theory. For some Reynolds numbers and some plate distances, a standing wave pattern is observed in the pipe. The outer and inner acoustic fields show high coherence and the slot-tone locks on a pipe eigenmode, which indicates an acoustic feedback. However, especially for lower Reynolds numbers, this coherence vanishes but the self-sustained tones are still present. It suggests that the hydrodynamic feedback becomes preponderant. [less ▲] Detailed reference viewed: 32 (0 ULg)Broad Spectrum Diffusion Model for Room Acoustics Ray-Tracing Algorithms Embrechts, Jean-Jacques in Journal of the Acoustical Society of America (2000), 107(4), 2068-81 Geometrical acoustics methods have already been transformed to account for diffusely reflecting boundaries. In randomized ray-tracing algorithms, the sound rays are either specularly reflected or ... [more ▼] Geometrical acoustics methods have already been transformed to account for diffusely reflecting boundaries. In randomized ray-tracing algorithms, the sound rays are either specularly reflected or scattered, according to the value of a random number which is compared with the diffusion factor. However, this method becomes inefficient if this factor depends on frequency, since the process must then be repeated for each frequency band. A method is proposed in this paper to compute all frequency components simultaneously in a single pass. The diffuse reflection model is based on the definition of a new concept: the "splitting coefficient," which can differ from the diffusion factor. First, the randomized ray-tracing method is described and the diffusion model is applied to a single diffusing surface in free field. It is shown that the results computed by the program are in accordance with theoretical results. Then, the method is shown to work properly when it is applied to more realistic enclosures: This is proved in theory and illustrated by some examples. A particular problem is the increase of the statistical error which has been solved by an appropriate control of the splitting coefficient. [less ▲] Detailed reference viewed: 39 (11 ULg)On-line Cough Recognizer System ; ; et al in Journal of the Acoustical Society of America (1999), 106(4:2), 2191 Until now the intelligent, controlled, and automated use of acoustic bio-responses in cattle houses as indicators of animal condition has been limited to human perception. Although the appearance of ... [more ▼] Until now the intelligent, controlled, and automated use of acoustic bio-responses in cattle houses as indicators of animal condition has been limited to human perception. Although the appearance of coughing, sneezing, etc., may point to an environmental deficiency in the animal habitat or the presence of diseases amoung the cattle, in order to use this kind of acoustic information as a bio-response signal in practice it is necessary to develop a simple on-line algorithm. In this paper an on-line registration technique for pig coughing is presented. The application of a distance function to a spectral sound analysis allows us to distinguish coughing from other animal and environmental sounds like metal clanging, grunting, noise, etc. The sound database was collected on a group of six healthy animals [less ▲] Detailed reference viewed: 74 (4 ULg) |
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