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Uncertainty Evaluation in Modelling of Acoustic Phenomena with Uncertain Parameters Using Interval Arithmetic

100%
Batko W., Pawlik P.
Acta Physica Polonica A
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2012
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vol. 121
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issue 1A
A-152-A-155
EN
Uncertainty assessment in modelling of acoustic phenomena with uncertain parameters using interval arithmetic on the example of the reverberation time estimation, are presented in the paper. The application of the classical interval analysis formalism as well as its expansions are shown. Statistical methods of estimation of the reverberation time are based on parameters, which are related, among others, to the geometry of the analysed room, characteristics of sound absorption, and interior transmission. Values of these parameters are usually difficult to determine, which has a significant influence on the modelling result. The interval analysis allows to determine the variability interval of the parameter being estimated. The authors determined the influence of the input parameters uncertainty on the estimated reverberation time, calculated according to the Sabine, Eyring-Norris and Millington-Sette formulae. The uncertainty analysis was performed for the literature data, related to the reverberation time calculations of the room of a certified acoustics.
2
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Sound Field Diffusivity Assessment in Non-Stationary State by Measuring Nonuniformity of Sound Decay Curve

100%
Leo K.
Acta Physica Polonica A
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2012
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vol. 121
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issue 1A
A-197-A-200
EN
Methods of sound diffusion assessment presented in literature require information on directional properties of the sound field in stationary state. These methods are complicated and not often applicable in measurement practice. Measurement of the sound field diffusivity during its formation can be assessed from sound level decay curve deviation from a linear shape. With this method, the degree of diffusivity has been determined in three rooms. Measurements were performed in rooms differing in volumes and sound absorption. Changes in sound decay uniformity were noted, which can be translated into diffusion coefficient changes. Results indicate that diffusion increases as room absorption decreases. Diffusion does not depend on room volume. Changes of sound decay uniformity follow trends that are well described by power function.
3
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Numerical Modelling of Coupled Rooms: Evaluation of Decay Times via Method Employing Hilbert Transform

80%
Meissner M.
Acta Physica Polonica A
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2011
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vol. 119
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issue 6A
1031-1034
EN
In the paper, a usefulness of the Hilbert transform in a computer modelling of reverberant behaviour of rooms is demonstrated for the enclosure consisting of two coupled subrooms. In numerical simulations a decay of the sound pressure is computed and the Hilbert transform methodology is used to determine an envelope of this decay. Calculation results have shown that, because of the mode localization, a distribution of absorbing material has a great influence on decay times evaluated from changes in the pressure envelope. For example, when a difference between the sound damping in subrooms is large, the localization effect is responsible for a creation of a nonlinear decay of the sound pressure level characterized by rapid early and slow late sound decays.
4
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Simulation of Acoustical Properties of Coupled Rooms Using Numerical Technique Based on Modal Expansion

80%
Meissner M.
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issue 1
123-127
EN
In the present study, the acoustic characteristics of coupled rooms were investigated using the computer modelling application based on the modal expansion method. A numerical procedure enables the computation of shape and frequency of eigenmodes, and allows one to predict sound decay times at any point of a room space. Results of numerical simulation have shown that along with a change in a coupling area the effect of a mode degeneration appeared and there are two main reasons for this. First, a mode degeneration is associated with a convergence of frequencies of neighbouring modes with a decrease of coupling area. Another reason for the mode degeneration are variations in a sequence of modes with a change in the coupling area. It was demonstrated that in the coupled rooms several modes exhibit a considerable localization. A degree of mode localization was described theoretically by the "existence surface" of mode and it was found that the localization phenomenon has a great effect on the reverberation process because for some absorbing material distributions it caused the double-slope decay characterized by steep initial and slow late sound decays.
5
Content available remote

Sound Energy Field in a System of Coupled Rooms

80%
Meissner M.
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vol. 125
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issue 4A
A-103-A-107
EN
The paper presents a theoretical basis of calculations of the sound intensity in enclosed spaces and shows results of numerical visualization of the active intensity in a room with absorptive walls formed by two coupled rectangular subrooms. The study was focused on the low-frequency range, therefore to describe the active and reactive intensities, the modal theory of room acoustics was applied. Space distribution of eigenfunctions, modal frequencies and modal damping coefficients were calculated numerically using the forced oscillator method (FOM) and the finite difference time-domain (FDTD) method. Based on theoretical and numerical results, the computer program has been developed to simulate the active intensity vector field when the room is excited by a harmonic point source. Calculation data have shown that the active intensity was extremely sensitive to position of the source since at a fixed source frequency, different source locations always generate different distributions of characteristic objects of the active sound field such as energy vortices and stagnation points. Because of complex room shape, the vortex centers are in most cases positioned irregularly inside the room. Almost regular arrangement of vortices was found only in the case when the source frequency was tuned to the frequencies of modes which were strongly localized in one of the subrooms.
6
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Evaluation of Acoustical Properties of an Auditorium after a Modernisation Program

80%
Czerwiński A., Dziechciowski Z.
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vol. 125
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issue 4A
A-71-A-76
EN
This study summarises and compares the measurement results of acoustical properties of an auditorium located on the campus of the Faculty of Mechanical Engineering at the Cracow University of Technology. The auditorium was thoroughly modernised and its acoustic features adapted. Measurements of the room acoustics were first taken prior to the modernisation program and were repeated after completion of the modernisation works. Evaluation of auditorium acoustics was based on the following parameters: reverberation time, early/late energy ratio (clarity) C_{50}, early decay time, speech intelligibility indices, and uniformity of sound distribution. The effect of the modernisation program on levels of those parameters are explored and conformity to the design objectives is analysed.
7
Content available remote

Acoustic Field Distortions Caused by Helium-Filled Balloons

80%
Majkut L., Olszewski R., Pluta M.
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vol. 125
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issue 4A
A-84-A-87
EN
In this paper, an automated measurement system was proposed that uses a probe hung below a remotely controlled balloon to measure parameters of the acoustic field in the whole volume of a room. The study was conducted to estimate distortions that such system may cause in the acoustic field at the measurement point. The most significant source of the distortions will be the buoyancy element - one large balloon or a number of smaller ones. This paper considers different spatial configurations of spherical balloons with regards to alterations they cause in the acoustic pressure levels measured below them. Interior of a room without and with a group of spherical balloons was modeled using the boundary element method. Using a larger number of smaller spheres instead of a single large one did not significantly reduce the related distortions. However, using two spheres slightly decreased distortions when the distance between the balloons and the recording point was relatively small.
8
Content available remote

The Study of Sound Scattering Structures for the Purposes οf Room Acoustic Enhancement

80%
Kamisiński T., Rubacha J., Pilch A.
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EN
Acoustic structures are currently classified mainly in terms of their acoustic absorption and insulation properties. Knowing the sound scattering parameter can significantly improve the useful value of materials and identify their best applications. Currently no studies are performed in Poland on the sound scattering coefficients of materials. This is due to a complex measurement procedure and a lack of legal requirements. The authors have attempted to make such measurements on the basis of the standard ISO 17497-1:2004: Acoustics - Sound-scattering properties of surfaces - Part 1: Measurement of the random-incidence scattering coefficient in a reverberation room. Measurement and calculation methods are presented, and problems encountered during this study have been described. This issue is of particular importance, especially in the acoustic design of interiors.
9
Content available remote

Acoustic Simulation and Experimental Studies of Theatres and Concert Halls

80%
Kamisiński T.
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EN
Paper presents a numerical simulation of the acoustics of selected concert halls performed using CATT-acoustic software, and the results of acoustic measurements performed in these spaces.
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