Panagiotis Charalampous | Cyprus University of Technology (original) (raw)

Papers by Panagiotis Charalampous

Acta Acustica united with Acustica, 2013

The seat dip effect is considered to be one of the intractable acoustical phenomena in room acous... more The seat dip effect is considered to be one of the intractable acoustical phenomena in room acous-tical simulations. This phenomenon is mainly due to edge sound diffraction and scattering. Wave Based Geometrical Acoustics (WBGA), which originates from the image source method, spherical wave propagation, impedance discontinuities and sound pressure summation, accounts for wave phenomena such as reflection from planes, diffraction from edges, refraction due to strati-fication of mediums to mention a few. By applying WBGA, we demonstrate that the seat dip effect can be accurately calculated and predicted. This paper compares results of the seat dip effect calculated using WBGA with published and measured data.

Geometrical acoustics, using plane wave propagation and sound absorption coefficients, fail to ca... more Geometrical acoustics, using plane wave propagation and sound absorption coefficients, fail to calculate room resonances. Usually such wave phenomena are being calculated with numerical methods such as Finite Element Method or similar which are computationally heavy. The WBGA, which is based on the image source method, spherical wave propagation, impedance discontinu-ities and sound pressure summation, can accurately simulate room resonances both in the frequency and spatial domain. In this paper we present calculation results of room resonances using the WBGA compared to published data.

Until recently geometrical acoustics has been considered an approximate method of calculating the... more Until recently geometrical acoustics has been considered an approximate method of calculating the sound field within a 3D environment because of certain limitations in existing methods. Geometrical acoustics mostly refers to the use of ray tracing and image sources. Ray tracing is a pure energetic method, while the image source method, despite calculating complex sound pressures and theoretically representing a solution to the wave equation, has certain limitations. One of the limitations found in most of the image source implementations is the use of plane wave reflection coefficient and absorption coefficients, a fact that prohibited image sources to be an exact solution of the wave equation. In this paper we extend the image source method, using spherical wave reflection and diffraction coefficients as well as complex surface impedance. We compare the results of the calculations with published data and we conclude that the use of spherical wave coefficients and complex impedance can improve room acoustics predictions.

We present a novel algorithm for room acoustic parameters calculation which addresses one of the ... more We present a novel algorithm for room acoustic parameters calculation which addresses one of the major uncertainties in room acoustics prediction, that of user defined termination criteria. One of the uncertainties in room acoustics predictions that take place using geometrical acoustics methods is the user defined termination criteria. Ray tracing algorithms require maximum length and number of rays to be send. Image source algorithms require maximum reflection orders and/or maximum sound attenuation. Our algorithm adjusts progressively its termination criteria until a correct result is approximated, based on an intelligent guessing, therefore removing this burden and risk from the user. We explain the algorithm's termination procedure and we compare with typical implementations. We show that the results approximate measurements equally well or better, having the benefit that the user does not need to worry anymore about these settings.

Ray-tracing software, which normally uses ISO 9613-2 to calculate outdoor sound propagation, is t... more Ray-tracing software, which normally uses ISO 9613-2 to calculate outdoor sound propagation, is typically used to model community noise from large facilities. It is computationally practical for large-scale models. While ray-tracing has been used successfully for designing industrial facilities, the accuracy of some empirical algorithms in 9613 is questionable. It is presumed that ground effects calculated using 9613 are generally accurate for grazing incidence of a ray to the ground, but their use at large angles of incidence and taller sources is of lesser but unknown accuracy. For example, at 100 m, a 100-m high stack has an angle of incidence of 45°, which is much far higher than grazing incidence. Full-wave software, such as Greens Function-Parabolic Equation calculates wave length-effects, and is nominally exact, but too computationally intensive for modeling large-scale industrial facilities. On the other hand, Olive Tree Lab OTL Suite software provides the wavelength effects needed to accurately calculate and model ground reflections, and is computationally practical to model large industrial facilities. The accuracy of excess attenuations of ground effects calculated using 9613 are assessed. Conclusions on the accuracy of 9613 for use in design are made.

We present a hybrid algorithm which combines image source method, ray tracing and intelligent pri... more We present a hybrid algorithm which combines image source method, ray tracing and intelligent prioritization for faster calculation of impulse responses to be used in real time sound rendering. We use the image source method to calculate sound reflections from specular surfaces and we use a prioritized ray tracing algorithm for fast detection and evaluation of valid image sources from the tree of candidate image sources. Our algorithm delivers improved acoustical results in most cases when compared to a non prioritized version of it, a ray tracing algorithm and a best first image source algorithms, indicating that prioritization can deliver performance gains in real time sound rendering methods.

20th International Conference on Virtual Systems and Multimedia , Dec 11, 2014

Sound propagation in 3D spaces is governed by similar physical principles as light. As a result,... more Sound propagation in 3D spaces is governed by
similar physical principles as light. As a result, sound rendering
in a 3D virtual environment can benefit from methods developed for graphics rendering and vice versa. In this review, we provide an overview of methods used for sound rendering that share concepts and techniques with graphics rendering. Firstly we describe geometrical propagation techniques where the computations are based on ray theory similar to ray tracing techniques in computer graphics. Secondly, we review numerical techniques. These techniques, similar to the idea of radiosity, are based on the subdivision of the space into elements. Then we describe acceleration techniques that can be used in combination with other methods to speed up calculations. Lastly, for the sake of completeness, a quick overview is given of sound computation techniques that simulate specific sound effects that do not apply on illumination. The aim of this survey is to share knowledge among the two disciplines using familiar and known concepts.

Ray-tracing software, which uses ISO 9613-2 to compute outdoor propagation, is practical, and has... more Ray-tracing software, which uses ISO 9613-2 to compute outdoor propagation, is practical, and has been used successfully for design. However, serious doubts exist regarding the accuracy of some of the various empirical algorithms used, such as algorithms for ground effects and reflections, source height, reflections by objects, and ground cover. Further, 9613-2 has no algorithms for turbulence, phase, and wave length (except barrier diffraction). New wave-based image-source software (Olive Tree Lab-Terrain by PEMARD) uses theoretically accurate 3-dimensional algorithms that agree more closely with measurements than 9613. It takes into account reflections from finite impedance surfaces and finite-sized objects, applying Fresnel zone corrections as well as diffractions of unlimited orders from edges. The new software also calculates constructive and destructive interferences that are not possible with simpler algorithms, including 9613-2. Full-wave solutions (such as Greens Function-Parabolic Equation), which can also calculate wave-length effects, are usually too computation-intensive for design. The new software is computationally practical for the very large number of sources and sub-sources that are typically modeled during design. This paper compares results of calculations using selected advanced calculation algorithms from OTL-Terrain with measurements and those from 9613-2 both as a function of frequency and distance.

A major category of algorithms for simulating sound propagation in three dimensional environments... more A major category of algorithms for simulating sound propagation in three dimensional environments is the category of geometrical acoustics which are based on various tracing techniques. All tracing techniques are essentially tree traversals throughout a tree of candidate sound paths which could potentially affect the sound field at a given receiver location. Even though there is significant literature for speeding up tracing in three dimensional spaces for use in real time applications, the type of these algorithms has barely been discussed. In this work, we implement an image source method variant and we compare three different tree traversal approaches, depth-first, breadth-first and best-first. We examine their performance in respect to time and we highlight the advantages and disadvantages of each one and evaluate the applicability of each in real time sound propagation calculations.

DAGA 2014

The path from a noise source to a receiver involves complicated mechanisms such as diffractions a... more The path from a noise source to a receiver involves complicated mechanisms such as diffractions and reflections from ob-
stacles, ground and material properties, as well as meteorological conditions. In this paper, we present the methodology
applied by P.E. Mediterranean Acoustics Research & Development for outdoor sound propagation applying advanced
calculation methods for prediction and simulation purposes in a software application. The methodology makes use of
the image source method combined with visibility tracing techniques to implement a novel method of multiple path-
detection, taking into account reflections from finite impedance surfaces and finite-sized objects applying Fresnel zone
corrections as well as diffractions of unlimited orders from edges. These advanced methods are no longer used only in
the laboratory but are now available to engineers in the field, making theory available in practice. Some examples are
also presented.

Despite the rapid development in acoustics calculation software during the last couple of decades... more Despite the rapid development in acoustics calculation software during the last couple of decades, such advances have not been achieved uniformly. Various demands in different disciplines have shifted the focus to a number of different aspects of the calculations. Methods in game development have focused on speed and optimized calculation times to achieve interactive sound rendering, whilst engineering methods have concentrated in achieving accuracy for reliable predictions. This paper presents a flexible, expandable and adjustable framework for the development of fast and accurate acoustics calculations both for game development and engineering purposes. It decomposes the process of acoustic calculations for 3D environments into distinct calculation steps and allows third party users to adjust calculation methodologies according to their needs.

This paper examines the effect of sound diffraction in predicting sound propagation in ancient th... more This paper examines the effect of sound diffraction in predicting sound propagation in ancient theatres. Few simulation studies to date concerning ancient theatre acoustics were conducted with diffraction effects. While sound diffraction effects in ancient theatres are known qualitatively, rarely have they been quantitatively documented. In this paper, the ancient theatre of Kourion in Cyprus was acoustically modeled and simulated, in a commercially available software application which handles also sound diffraction to high orders. Sound measurements were also taken at the theatre for comparison purposes. All analyses were conducted in the frequency domain. Comparison of results of the variation of sound pressure level with distance and frequency shows that the contribution of sound diffraction is significant. It is proposed that future acoustical simulations of ancient theatres should include sound diffraction effects.

The process of performing an Environmental Impact Assessment includes the study of noise propagat... more The process of performing an Environmental Impact Assessment includes the study of noise propagation. Often, the path from a noise source to a noise sensitive location involves complicated mechanisms of sound transmission. These mechanisms may relate to diffraction & reflections from obstacles (natural or man made), ground properties, and meteorological conditions. The International Standards Organization proposes with standard ISO9613-2, methods by which to calculate these effects. While they are relatively easy to implement, they underestimate the true workings of the aforementioned mechanisms. In this paper, we present the OTL - Terrain software application, which accurately and precisely simulates outdoor sound propagation. The software application can be used for the prediction of environmental noise and the design of control measures. OTL - Terrain is an application which uses geometrical acoustics (GA) and models the propagation of sound in terms of rays. The tool makes use of the image source method (ISM) combined with visibility tracing techniques to implement a novel method of path-detection, taking both reflection and diffraction effects into account. Calculations utilize the predicted reflections from finite-sized objects with Fresnel zone corrections, an unlimited order of diffraction, and atmospheric turbulence. This paper presents a comparison of the predictions made by the OTL – Terrain application, the methods proposed by ISO, and the published results from experimental data.

Acta Acustica united with Acustica, 2013

The seat dip effect is considered to be one of the intractable acoustical phenomena in room acous... more The seat dip effect is considered to be one of the intractable acoustical phenomena in room acous-tical simulations. This phenomenon is mainly due to edge sound diffraction and scattering. Wave Based Geometrical Acoustics (WBGA), which originates from the image source method, spherical wave propagation, impedance discontinuities and sound pressure summation, accounts for wave phenomena such as reflection from planes, diffraction from edges, refraction due to strati-fication of mediums to mention a few. By applying WBGA, we demonstrate that the seat dip effect can be accurately calculated and predicted. This paper compares results of the seat dip effect calculated using WBGA with published and measured data.

Geometrical acoustics, using plane wave propagation and sound absorption coefficients, fail to ca... more Geometrical acoustics, using plane wave propagation and sound absorption coefficients, fail to calculate room resonances. Usually such wave phenomena are being calculated with numerical methods such as Finite Element Method or similar which are computationally heavy. The WBGA, which is based on the image source method, spherical wave propagation, impedance discontinu-ities and sound pressure summation, can accurately simulate room resonances both in the frequency and spatial domain. In this paper we present calculation results of room resonances using the WBGA compared to published data.

Until recently geometrical acoustics has been considered an approximate method of calculating the... more Until recently geometrical acoustics has been considered an approximate method of calculating the sound field within a 3D environment because of certain limitations in existing methods. Geometrical acoustics mostly refers to the use of ray tracing and image sources. Ray tracing is a pure energetic method, while the image source method, despite calculating complex sound pressures and theoretically representing a solution to the wave equation, has certain limitations. One of the limitations found in most of the image source implementations is the use of plane wave reflection coefficient and absorption coefficients, a fact that prohibited image sources to be an exact solution of the wave equation. In this paper we extend the image source method, using spherical wave reflection and diffraction coefficients as well as complex surface impedance. We compare the results of the calculations with published data and we conclude that the use of spherical wave coefficients and complex impedance can improve room acoustics predictions.

We present a novel algorithm for room acoustic parameters calculation which addresses one of the ... more We present a novel algorithm for room acoustic parameters calculation which addresses one of the major uncertainties in room acoustics prediction, that of user defined termination criteria. One of the uncertainties in room acoustics predictions that take place using geometrical acoustics methods is the user defined termination criteria. Ray tracing algorithms require maximum length and number of rays to be send. Image source algorithms require maximum reflection orders and/or maximum sound attenuation. Our algorithm adjusts progressively its termination criteria until a correct result is approximated, based on an intelligent guessing, therefore removing this burden and risk from the user. We explain the algorithm's termination procedure and we compare with typical implementations. We show that the results approximate measurements equally well or better, having the benefit that the user does not need to worry anymore about these settings.

Ray-tracing software, which normally uses ISO 9613-2 to calculate outdoor sound propagation, is t... more Ray-tracing software, which normally uses ISO 9613-2 to calculate outdoor sound propagation, is typically used to model community noise from large facilities. It is computationally practical for large-scale models. While ray-tracing has been used successfully for designing industrial facilities, the accuracy of some empirical algorithms in 9613 is questionable. It is presumed that ground effects calculated using 9613 are generally accurate for grazing incidence of a ray to the ground, but their use at large angles of incidence and taller sources is of lesser but unknown accuracy. For example, at 100 m, a 100-m high stack has an angle of incidence of 45°, which is much far higher than grazing incidence. Full-wave software, such as Greens Function-Parabolic Equation calculates wave length-effects, and is nominally exact, but too computationally intensive for modeling large-scale industrial facilities. On the other hand, Olive Tree Lab OTL Suite software provides the wavelength effects needed to accurately calculate and model ground reflections, and is computationally practical to model large industrial facilities. The accuracy of excess attenuations of ground effects calculated using 9613 are assessed. Conclusions on the accuracy of 9613 for use in design are made.

We present a hybrid algorithm which combines image source method, ray tracing and intelligent pri... more We present a hybrid algorithm which combines image source method, ray tracing and intelligent prioritization for faster calculation of impulse responses to be used in real time sound rendering. We use the image source method to calculate sound reflections from specular surfaces and we use a prioritized ray tracing algorithm for fast detection and evaluation of valid image sources from the tree of candidate image sources. Our algorithm delivers improved acoustical results in most cases when compared to a non prioritized version of it, a ray tracing algorithm and a best first image source algorithms, indicating that prioritization can deliver performance gains in real time sound rendering methods.

20th International Conference on Virtual Systems and Multimedia , Dec 11, 2014

Sound propagation in 3D spaces is governed by similar physical principles as light. As a result,... more Sound propagation in 3D spaces is governed by
similar physical principles as light. As a result, sound rendering
in a 3D virtual environment can benefit from methods developed for graphics rendering and vice versa. In this review, we provide an overview of methods used for sound rendering that share concepts and techniques with graphics rendering. Firstly we describe geometrical propagation techniques where the computations are based on ray theory similar to ray tracing techniques in computer graphics. Secondly, we review numerical techniques. These techniques, similar to the idea of radiosity, are based on the subdivision of the space into elements. Then we describe acceleration techniques that can be used in combination with other methods to speed up calculations. Lastly, for the sake of completeness, a quick overview is given of sound computation techniques that simulate specific sound effects that do not apply on illumination. The aim of this survey is to share knowledge among the two disciplines using familiar and known concepts.

Ray-tracing software, which uses ISO 9613-2 to compute outdoor propagation, is practical, and has... more Ray-tracing software, which uses ISO 9613-2 to compute outdoor propagation, is practical, and has been used successfully for design. However, serious doubts exist regarding the accuracy of some of the various empirical algorithms used, such as algorithms for ground effects and reflections, source height, reflections by objects, and ground cover. Further, 9613-2 has no algorithms for turbulence, phase, and wave length (except barrier diffraction). New wave-based image-source software (Olive Tree Lab-Terrain by PEMARD) uses theoretically accurate 3-dimensional algorithms that agree more closely with measurements than 9613. It takes into account reflections from finite impedance surfaces and finite-sized objects, applying Fresnel zone corrections as well as diffractions of unlimited orders from edges. The new software also calculates constructive and destructive interferences that are not possible with simpler algorithms, including 9613-2. Full-wave solutions (such as Greens Function-Parabolic Equation), which can also calculate wave-length effects, are usually too computation-intensive for design. The new software is computationally practical for the very large number of sources and sub-sources that are typically modeled during design. This paper compares results of calculations using selected advanced calculation algorithms from OTL-Terrain with measurements and those from 9613-2 both as a function of frequency and distance.

A major category of algorithms for simulating sound propagation in three dimensional environments... more A major category of algorithms for simulating sound propagation in three dimensional environments is the category of geometrical acoustics which are based on various tracing techniques. All tracing techniques are essentially tree traversals throughout a tree of candidate sound paths which could potentially affect the sound field at a given receiver location. Even though there is significant literature for speeding up tracing in three dimensional spaces for use in real time applications, the type of these algorithms has barely been discussed. In this work, we implement an image source method variant and we compare three different tree traversal approaches, depth-first, breadth-first and best-first. We examine their performance in respect to time and we highlight the advantages and disadvantages of each one and evaluate the applicability of each in real time sound propagation calculations.

DAGA 2014

The path from a noise source to a receiver involves complicated mechanisms such as diffractions a... more The path from a noise source to a receiver involves complicated mechanisms such as diffractions and reflections from ob-
stacles, ground and material properties, as well as meteorological conditions. In this paper, we present the methodology
applied by P.E. Mediterranean Acoustics Research & Development for outdoor sound propagation applying advanced
calculation methods for prediction and simulation purposes in a software application. The methodology makes use of
the image source method combined with visibility tracing techniques to implement a novel method of multiple path-
detection, taking into account reflections from finite impedance surfaces and finite-sized objects applying Fresnel zone
corrections as well as diffractions of unlimited orders from edges. These advanced methods are no longer used only in
the laboratory but are now available to engineers in the field, making theory available in practice. Some examples are
also presented.

Despite the rapid development in acoustics calculation software during the last couple of decades... more Despite the rapid development in acoustics calculation software during the last couple of decades, such advances have not been achieved uniformly. Various demands in different disciplines have shifted the focus to a number of different aspects of the calculations. Methods in game development have focused on speed and optimized calculation times to achieve interactive sound rendering, whilst engineering methods have concentrated in achieving accuracy for reliable predictions. This paper presents a flexible, expandable and adjustable framework for the development of fast and accurate acoustics calculations both for game development and engineering purposes. It decomposes the process of acoustic calculations for 3D environments into distinct calculation steps and allows third party users to adjust calculation methodologies according to their needs.

This paper examines the effect of sound diffraction in predicting sound propagation in ancient th... more This paper examines the effect of sound diffraction in predicting sound propagation in ancient theatres. Few simulation studies to date concerning ancient theatre acoustics were conducted with diffraction effects. While sound diffraction effects in ancient theatres are known qualitatively, rarely have they been quantitatively documented. In this paper, the ancient theatre of Kourion in Cyprus was acoustically modeled and simulated, in a commercially available software application which handles also sound diffraction to high orders. Sound measurements were also taken at the theatre for comparison purposes. All analyses were conducted in the frequency domain. Comparison of results of the variation of sound pressure level with distance and frequency shows that the contribution of sound diffraction is significant. It is proposed that future acoustical simulations of ancient theatres should include sound diffraction effects.

The process of performing an Environmental Impact Assessment includes the study of noise propagat... more The process of performing an Environmental Impact Assessment includes the study of noise propagation. Often, the path from a noise source to a noise sensitive location involves complicated mechanisms of sound transmission. These mechanisms may relate to diffraction & reflections from obstacles (natural or man made), ground properties, and meteorological conditions. The International Standards Organization proposes with standard ISO9613-2, methods by which to calculate these effects. While they are relatively easy to implement, they underestimate the true workings of the aforementioned mechanisms. In this paper, we present the OTL - Terrain software application, which accurately and precisely simulates outdoor sound propagation. The software application can be used for the prediction of environmental noise and the design of control measures. OTL - Terrain is an application which uses geometrical acoustics (GA) and models the propagation of sound in terms of rays. The tool makes use of the image source method (ISM) combined with visibility tracing techniques to implement a novel method of path-detection, taking both reflection and diffraction effects into account. Calculations utilize the predicted reflections from finite-sized objects with Fresnel zone corrections, an unlimited order of diffraction, and atmospheric turbulence. This paper presents a comparison of the predictions made by the OTL – Terrain application, the methods proposed by ISO, and the published results from experimental data.

Sound propagation in 3D spaces is governed by similar physical principles as light. As a result, ... more Sound propagation in 3D spaces is governed by similar physical principles as light. As a result, sound rendering in a 3D virtual environment can benefit from methods developed for graphics rendering and vice versa. In this review, we provide an overview of methods used for sound rendering that share concepts and techniques with graphics rendering. Firstly we describe geometrical propagation techniques where the computations are based on ray theory similar to ray tracing techniques in computer graphics. Secondly, we review numerical techniques. These techniques, similar to the idea of radiosity, are based on the subdivision of the space into elements. Then we describe acceleration techniques that can be used in combination with other methods to speed up calculations. Lastly, for the sake of completeness, a quick overview is given of sound computation techniques that simulate specific sound effects that do not apply on illumination. The aim of this survey is to share knowledge among the two disciplines using familiar and known concepts.