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1
Content available remote

Reliability of Sound Field Simulations

100%
Wierzbicki J.
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issue 1
183-185
EN
One of the most important questions in sound field modelling is connected with the reliability of results. The absolute accuracy of values predicted by the software is very difficult to quantify because of an uncertainty in the measurements. But it is possible to determine an influence of the input data accuracy and calculation parameters on the obtained results. Problems and differences in the sound field simulation results are presented in the hereby paper. Test procedures of the sound filed simulation software and also well-documented exemplary objects in an open space will be the main aim of investigations.
2
Content available remote

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.
3
Content available remote

Comparison of Pressure and Intensity Methods in Evaluating the Directional Diffusion Coefficient

80%
Pilch A., Kamisiński T., Zastawnik M.
Acta Physica Polonica A
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2013
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vol. 123
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issue 6
1054-1058
EN
The directional diffusion coefficient characterizes directional uniformity of acoustic energy reflected from a structure. The goal of the paper is to check whether different measurement methods of that coefficient give comparable results and can be used for different diffusing structures. ISO 17497-2:2012 recommends two basic measurement methods for this parameter, both based on sound pressure analysis. In the first method, one microphone and a measurement manipulator is used (the space method), while in the second one, 19 microphones placed on the sound-reflecting plane are required (the boundary method). In the standard it is assumed (as usually in the room acoustics), that the acoustic energy is proportional to the square of sound pressure, what is true only for the plane wave. Correctness of this assumption was checked by the modified space method where the sound intensity probe was installed instead of microphone. The test revealed that pressure methods gave comparable results for both low- and high-diffusion structures, with the boundary method giving moderately higher values for low-diffusion structures and slightly higher for high-diffusion structures. The results obtained in the intensity method were comparable with the pressure method except for the 2000 Hz frequency range.
4
Content available remote

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

Detection and Classification of Selected Noise Sources in Long-Term Acoustic Climate Monitoring

80%
Kłaczyński M., Wszołek T.
Acta Physica Polonica A
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2012
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vol. 121
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issue 1A
A-179-A-182
EN
Continuous acoustical climate monitoring of the environment raises several problems related to large quantities of the recorded data, which often represents information unrelated to the studied noise source. Manual verification of such data is time-consuming and costly. Therefore, developing effective methods for automatic identification of transport noise sources becomes an important task for the proper determination of noise levels. This paper presents a concept of such method of automatic detection and classification of the noise sources from the air and railway transportation in the acoustic environmental monitoring.
6
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.
7
Content available remote

Multi-Channel Sound Synthesis System in Open Area. A Case Study with the Use of FEM

80%
Ciesielka W., Filipek R.
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vol. 125
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issue 4A
A-88-A-92
EN
This paper presents a new model of the multi-channel sound synthesis system. The research objective was to design and construct a sixteen-channel sound control system located in an open area with dimensions of 23.48 m×17.48 m. The main goal of the system operation is to provide, for the controlled acoustic field, the uniformity of the parameters distribution while minimizing the sound pressure level in the protected area. The modeling and simulation researches have been performed using the Finite Element Method (FEM). The results of the analysis include distributions of the sound pressure levels and phase angle for the selected frequencies. The paper presents results of sensitivity studies and optimization for different variants of the sound synthesis system.
8
Content available remote

Variability Influence of Input Parameters οn Result of Room Acoustic Calculation

80%
Mleczko D., Wszołek T.
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issue 1
128-130
EN
For a long time there is a need in industry of acoustical modeling of rooms. Modeling is necessary for new production room design, the exchange of existing machinery, modernization or expansion of production rooms, changes in production profile or acoustical room adaptation for acoustical work conditions improvement. in such cases modeling quality is essential and thanks to uncertainty analysis it is possible to quantitatively estimate the effect that input parameters value variation has on model behavior. The article presents general rules for sound pressure level prediction uncertainty calculation in a room. By partial uncertainty calculation analysis of input parameters influence on uncertainty prediction an effort was taken to find parameters with biggest influence on the prediction process. As an example an industrial production room is presented which was modeled to predict noise level on a work stands after it was expanded.
9
Content available remote

The Role of Acoustic Features in Marking Accent and Delimiting Sentence Boundaries in Spoken Polish

80%
Igras M., Ziółko B.
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vol. 126
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issue 6
1246-1257
EN
In this article the authors investigated and presented statistical models of acoustic phenomena observed within realizations of phonemes and the correlations of the acoustic properties with functional features, such as accents and sentence boundaries. The authors used two databases: the first one contained separately produced sentences and the second one - phrases extracted from larger, continuous stretches of natural speech. The authors also statistically analyzed the selected features of Polish phonemes' realizations (the duration, energy and power of the phonemes, the fundamental frequency of voiced phones) in order to detect their relations with the phone location in a sentence. Additionally, the authors built the probabilistic models and suggested the evaluation methods to assess quantitatively the phenomena known from phonetic literature. Finally, the authors have identified the pre-boundary lengthening of the phones and a decrease of energy and pitch as the markers of sentence endings. In the place of accented syllables, we have observed a significant increase of total energy and power, accompanied by a local increase of F0. Finally, we have indicated possible application of the results for speech technology.
10
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.
11
Content available remote

The Influence of Sound Source Directivity on Acoustics Parameters Distribution in Kraków Opera House

80%
Gołaś A., Suder-Dębska K., Filipek R.
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EN
Determining of Kraków Opera House's basic acoustics parameters by using numerical simulations is presented in the paper. Parameters have been obtained by using numerical simulation methods. Sound sources have been created by means of FEA, however acoustic field distributions have been analysed by geometrical methods. Apart from the room parameters definition, it is necessary to determine sound source parameters like acoustic power level and directivity pattern. In the simplest case, the sound source can be assumed as omni-directional point source. However it does not reflect most real-live sources precisely. When the literature and databases do not contain any information about the sound source directivity pattern, it can be obtained numerically using FEA. First, the sound source model is created, and then results from its spherical boundary are used to define the source in a program based on geometrical methods. Here have been analysed several distributions of acoustic parameters like: Direct Energy, Sound Pressure Level (SPL), Clarity index (C80) etc. The results indicate that influence of sound source directivity on acoustics parameters changes is essential.
12
Content available remote

Verification of Inverse Image Source Method Applied for Acoustic Field Creation in Open Area

70%
Gołaś A., Suder-Dębska K., Ciesielka W., Filipek R.
Acta Physica Polonica A
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2011
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vol. 119
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issue 6A
966-971
EN
The paper presents an original method for sound reinforcement in open areas. The method enabled both a regular sound reinforcement and the required spatial impressions of sound to be achieved in the area used for the study. The inverse image source method was used for the disposition of sound sources in order to find the inverse problem solution for determining the configuration of additional sound sources. Simulations demonstrated the improvement of sound impressions in the area in question and the simulations results were verified experimentally. The intended result of the proposed method was the increase of the lateral energy fraction and lateral energy fraction coefficient parameter values by 6 and 8 points, respectively, for the simulation by 5 and 7 points for the experiment. It should be stated that, in both the simulation and the experiment, eligible values for the acoustic parameters were obtained after using the sound system with additional sound sources, the speech intelligibility value parameters remain at an excellent level. In conclusion, it may be claimed that the proposed sound reinforcement system makes the creation of the intended spatial sound impressions in an open area possible.
13
Content available remote

Synthesis of the Impulse Response of the Transmission Path in a Selected Area of the Sound Field

61%
Czajka I., Suder-Dębska K., Gołaś A.
Acta Physica Polonica A
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2013
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vol. 123
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issue 6
1072-1077
EN
Providing appropriate sound field parameters in the listening area is very important. It often determines the possibilities of being able to use a facility. Assuming that the sound system is a linear object, it can be described by the impulse response. Unfortunately, it is not possible to designate a single impulse response for such a facility because it is a continuous system. Thus each path between the transmitter and the receiver has its own impulse response. Therefore, the authors have made an attempt to synthesize the impulse response for transmitter-receiver paths with suitable parameters of the sound field in the neighbourhood of the receivers. A technical implementation of the presented synthesis will take place through introduction of additional sources. An experimental determination of the impulse response is relatively simple. The transient response can be numerically determined by using, for example, the finite element method or the boundary element method. Unfortunately, determining the impulse response through simulation of, e.g., planned objects, is much more difficult due to the high computational cost and the lack of precise data on the properties of the materials. For this reason, the authors used an energetic analogue of the impulse response, the echogram.
14
Content available remote

The Effect of Changes in Position of Sound Source and Microphone on Acoustic Measurements in Small Rooms. A Case Study

61%
Mleczko D., Wszołek T.
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vol. 125
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issue 4A
A-131-A-134
EN
Results of computer simulations and measurements in real interior for varying location of sound source and microphone are shown in the paper. A small room with a volume of 47 m^3 was used for this purpose. The objective of measurements and calculations was to determine the sound pressure level and other parameters derived from the room impulse response (T_{30}, EDT, C_{80}, STI) followed by the sensitivity analysis of those parameters to changing the location and orientation of the sound source and the receiver. In order to determine these parameters, the room impulse response was measured using MLS method. Experimental studies have been used to verify the acoustic room model built with use of enhanced radial method algorithms and its sensitivity. That allowed complementary and extended simulation studies on the room acoustic characteristics and finally determination of sensitivity of output parameters to changes of location and orientation of the measurement channel elements.
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