The number of social surveys regarding citizens’ disturbance from environmental noise in Greece is relatively low compared to other European countries, where such surveys constitute a useful tool for strategic plans that aim in competing environmental noise.
Such a survey was carried out in 2007 by the School of Architectural Engineering, Aristotle University of Thessaloniki. The aim of the survey was to assess the impacts of environmental noise on the residents of the study areas. The results of that survey showed that noise levels in those areas were significantly high, reaching, in some cases, levels hazardous for human health.
It is widely known that in economic crisis conditions, environmental protection is regarded a ‘luxury’ by the State as well as by the citizens. Taking this attitude in consideration and the ongoing Greek economic crisis, a second survey was conducted ten years after the first one in the same area and with the same participants, to assess the extent to which economic conditions affect the way citizens perceive environmental noise.
The comparison between the two surveys is rather interesting.

The purpose of this study, which emerged in the context of a diplomatic dissertation, was to develop a distributed system used to measure environmental noise remotely using a professional sound level meter. As an initial effort, a simple structure was used to implement the system with a single measurement station which the user can control from a webpage that is hosted in the servers of the electro-acoustics laboratory in Aristotle University of Thessaloniki. The system is composed of various smaller subsystems so that it becomes distributed and easily manageable. This way it becomes easier to further develop the system for future applications. Finally, after the evaluation of the resulting system, several related applications are described.

The proposed announcement is part of a broader undergraduate research (2016-17), which was held at the Department of Architectural Engineering of the Democritus University of Thrace, concerning the bioclimatic facilities in Edessa's outdoor spaces and negotiates the study of the acoustic comfort conditions in public spaces (gardens / parks) of the city.
The research initially focuses on Edessa's urban development and the concept of acoustic comfort. It is presented the methodology of the survey, the twelve (12) selected areas of the city, as well as the criteria for their selection. Finally, the analytical and aggregate data are recorded and the conclusions of the survey are given.

In an older paper (2007) we examined the noise pollution in the center of Thessaloniki, due to all-day café bars (period 2005-06). The proposed paper continues the survey (period 2016-17) and proposes a comparative evaluation of the problem. New research data, using the same methodology, refer to a sample of 26 all day café bars, in the same area of the city center where in recent years there has been a great increase in the number of entertainment installations. The purpose of the recent paper is to identify the deficiencies in the licensing/ supervision of the all- day café bars and to correlated the dimensions of urban noise pollution to certain urban spatial planning parameters.

Recent technological advances in both credit card sized PCs, in both performance and energy consumption, have opened new ways for a broader and more affordable research, by turning these computers into tracking devices through the development of wireless sensor networks. This paper describes and tests a low-cost acoustic sensor based on the Raspberry Pi 3 platform, which supports advanced sound field analysis functions. Besides presenting the system’s components, an evaluation of the audio recording capabilities of the nodes for the correct assessment of sound pressure level as well as of other acoustic parameters is carried out. Finally, the possibility of collaborative recording for sound source localization tasks, from a pair of nodes through the determination of the time difference of arrival of the sound, is studied and tested.

Ancient Greeks with their inventive mind had managed to design a bullhorn, a stentorphonic tube, with which they could transmit clear sound messages in big distances depended on the noise level of the environment of the receiver (dB) for a specific intensity level (dB) at the input of the stentorphonic tube. The name stentorphonic tube was given because it sounded very loudly, just like the screams of Homer’s hero Stentor. This bullhorn was used by Alexander the Great in order to lead the troops.

In Homeric poems many acoustic phenomena are described with such clarity that we are able to identify them with equivalents that can be described with scientific terms: Summation of sound pressure level of many sources, attenuation of sound pressure level, masking of sound and reverberation. The classification, apart from useful information of acoustic, literal, and archaeological interest, provides also the possibility of comparison: Iliad is characterized by the loudness of human voice and it’s masking by the battle noise, while the Odyssey is characterized by reverberation. This happens because Iliad takes place outdoors while Odyssey indoors. Τhe described sound phenomena follow this difference.

Recent archaeoacoustic techniques, applied in ancient sacred grottos and other constructions, have paved the way for new research insights in ancient cult and ritual practice, offering the potential to enrich interpretations of how ancient buildings or natural spaces were perceived as loci of divine presence and worship. Here, the acoustic research was focused on selected examples of caves with known historic significance in ancient Greek societies. The caves were selected from a specific geographical region, Attica in Greece, where the combined worship of the hoofed-god Pan with his female companions, the Nymphs, was first organized and performed inside caves during the 5th century BC. The purpose of this inter-disciplinary research is to enhance our existing knowledge regarding the utilization of sound and acoustics during ritual ceremonies in caves, in an attempt to understand whether sound was a determining factor in the selection of caves as appropriate sacred sites. Although access to such caves introduces significant difficulties, acoustic measurements were obtained in two caves (Parnitha and Vari) at different source-receiver positions at locations where historic evidence indicates that such rituals were taken place. The single channel measurements were used for extraction of the acoustic parameters of the caves. For the same positions, binaural responses were recorded using a dummy head and these were later utilized via virtual listening scenarios for presentations and controlled evaluation of the cave acoustics by listeners in the laboratory using appropriate pre-recorded audio samples which according to the archaeological and historical data were reproduced during ancient rituals, made people believe that they were the abodes of these sacred spirits. The tests and analysis provide novel findings with regards to the suitability of cave acoustics for such ritual ceremonies.

In this work, new results are presented from wave-based simulations of the acoustics of the ancient theatre of Epidaurus, enabling the evaluation of paths with multiple reflections and diffractions. The study is based on two 3D models with different levels of geometrical detail. The parameters of the models were calibrated in accordance with existing measurements of the theatre’s impulse response in different auditory positions. The analysis highlights the contribution of diffracted sound in the theatre’s excellent acoustic performance, since diffracted paths appear to boost the mid-low frequencies, enhancing speech intelligibility, especially in the most remote auditory positions. It also becomes evident that the acoustic response of the middle auditory positions is the result of two distinct sound fields, one reaching the listener from the front (ascending field) and one from behind (descending field). Moreover, evaluations with different step geometries (leading to different tier inclinations) are carried out, showing the impact of the tier geometry to the theatre’s acoustic performance. Finally, it is shown that the placement of pillows in the front seating positions has a degenerative effect on the theatre’s acoustics.

The STORM research project aims to provide critical decision-making tools to all European cultural heritage actors in charge of managing the effects of climate change and natural hazards. In this context and aiming to enhance the protection of monuments and archaeological sites, a wireless acoustic sensor network was designed and developed. The paper presents the sensor hardware and embedded software and provides preliminary results on the fidelity of the audio signals recorded by the network nodes.

The STORM European research project aims in developing an integrated set of technological and organizational resources for monitoring and safeguarding cultural heritage sites. In this context, wireless acoustic sensor networks that detect and record sound samples are deployed over cultural sites. The features of the recorded samples are calculated and forwarded to a feed-forward neural network for classification in order to extract information about the potential hazardous effect of the activity or activities that generated the sounds. Implementation details about the classifier and the sound features are discussed in this paper. Sound features are grouped with respect to their scalar or time-frequency nature and results are presented regarding the classification accuracy of each subset. Results are also presented regarding the accuracy of the proposed approach when operated in noisy environments.

Acoustic coloration is the audible distortion of a sound’s timbre, rhythmic sensation or pitch, which comprise the sound’s color [1]. It is caused by sparse low-frequency resonances of small size rooms which correspond to their early, strong reflections. In this paper, we study the impact of coloration on audio features that describe the color of audio signals. Hence, we collected a set of anechoic (uncolored) signals, which was later colored by the early reflections of various rooms. Audio features were extracted from both these types of signals and the means of their values were compared with the use of paired samples t-tests. The results of. these tests led to feature evaluation and selection in terms of acoustic coloration. In the end, we conducted an analysis on the impact of coloration on values of features that were marked as statistically significant.

A novel approach is proposed for maps illustrating the accuracy of image source position reproduced by stereo systems in various scenarios of listening rooms / loudspeakers. Based on previous work by the authors, the maps unify results derived from an image localization classifier and the sweet spot area metric estimating the direction of arrival angles (DOA) of all potential image source positions reproduced by the system via a perceptual model. The statistical analysis of these maps indicates the skewness and kurtosis of the DOA classification error and hence the consistency and robustness of the image definition along the plane of listener positions. Results utilize such parameter mappings to objectively illustrate the robustness of this qualitative aspect of audio reproduction in rooms.

Early components of the auditory evoked potentials (AEP) reflect the neural processing of acoustic stimuli in the brainstem and the sub-cortical regions. Relating AEP patterns to their stimulus characteristics is a notoriously difficult task, due to the variability of their morphology. In this study, tone-Burst evoked auditory brainstem and middle-latency responses from 7 normal hearing subjects were used to develop a neural network model for the classification of AEPs depending on stimulus intensities. The raw AEP data was obtained from the study of Silva and Epstein (2010). Overall, results from this preliminary study indicate an accuracy of 85.2%, suggesting that the methodology developed should be further tested on larger data sets.

This paper aims at presenting a comprehensive review of the factors affecting HRTF variability, by examining their combined and individual impact on the Interaural Time Difference. The analysis was based on data from the LISTEN, SADIE, and ClubFritz publicly available databases. According to the results, most of these factors caused perceptible ITD variations at least on a subset of the tested azimuth positions, fact which emphasizes the delicate nature of the acoustic HRTF acquisition procedure.

In this paper a low-complexity method for up-mixing two channel stereo signals for surround sound reproduction is presented. Based on a common stereo signal model, the panning coefficients and azimuth positions of the sources in the stereo mix are estimated. This information is then being used for the stereo signal decomposition and the re-synthesis to a multichannel signal for surround reproduction. The proposed method is evaluated through a subjective listening test.

The work presented here is focused on overcoming the above problems, by architecting one web extension encapsulating a Javascript audio plugin host, based on HTML5, Web Components and Web Audio API (WAA). The host UI allows the listeners to dynamically add an arbitrary number of the available audio plugins and connect them in any sequence. Multiple instances of the same audio processor are allowed (e.g. two equalizers – one for the left channel and one for the right one). The audio plugin host is currently focused on audio effects. Advanced plugins are implemented such as HRTF-based 3D audio via headphones and virtual surround over two speakers based on crosstalk cancellation. The challenges behind the approach are numerous related to both performance and the very nature of web extensions.

The area of research is the city of Volos. A city lacking in a main theatrical stage, hut with several community performance stages of smaller scale scattered in the urban fabric. The present paper attempts to summarize the methodology and criteria for assessing existing performance halls in the city. At the same time, it investigates and evaluates the case-study of the old Electric Company hall with the aim ofproposing a set of architectural and acoustical design solutions for the space, further resulting in a design and methodology> interventional strategy> that can be applied to similar halls and stages of the corresponding typology.

In this paper we attempt to prove that the effective acoustic design of a space with coupled rooms (through the prediction and dispersion of sound-absorbing zones, without diversifying the architect design) can achieve greater goals than the effective control of the reverberation in a large and variform area of gathering and public serving. The purpose of the acoustic correction of the atrium in the new Thessaloniki City Hall was the effective reduction of the reverberation time (from 4 - 4.7 sec at the average frequencies, to the tolerable limits of 1 - 1.6 sec) due to the functioning of an open and exposed space which is composed with various sizes coupled spaces with openings of different dimensions. Furthermore, occasionally the atrium also serves events of speech (with electro-acoustic support), or live music events, with gathering of artists and audience on the ground floor.

Outdoor acoustic shells are architectural constructions placed in open public spaces to host music concerts. This work aims to highlight the importance of a holistic approach of acoustic design in auditorium's open air architecture, using characteristic examples of the evolution of acoustic shells’ design during the 20th century. The examples are examined on the basis of their architectural and acoustic quality and their construction characteristics.

The Lombard effect describes the phenomenon of background noise increase due to simultaneous verbal communication. The aim of this study is to discuss the Lombard effect in spaces for social gatherings. A literature review is presented as well various guidelines regarding its control.

Η παρούσα εργασία αποτελεί μέρος της πτυχιακής ερασίας του πρώτου εκ των συγγραφέων στη Σχολή Αρχιτεκτόνων ΕΜΠ. Σε αυτήν αναλύονται η σχέση της ακουστικής και της αρχιτεκτονικής studio ηχογράφησης μέσα από υλοποιημένα παραδείγματα αναγνωρισμένου κύρους. Επίσης προτείνεται συνθετική προσπάθεια σε σκαριφήματα ως εφαρμογή της ανάλυσης που προηγήθηκε.

This paper aims to examine the acoustical performance of drama theatres of modernity in postwar Hellas, in relation to their architecture. Acoustic measurements were carried out in seven theatres. Two theatre types are observed in this period, namely the type “less is more” and “detached” theatres. The first theatre type is usually hosted in the basement of multistory modern buildings. the other theatre type occupies an entire building in itself. It is demonstrated that the human scale which is adopted by the theatre type “less is more” works synergistically with good acoustics. by contrast the other theatre type needs additional building elements to achieve satisfactory sound performance. The present results illustrate the implications of architectural design on the acoustical performance of the theatres and demonstrate, by and large, the acoustical merits of the test auditoria.

We have implemented a client application to perform online music sessions with which the musician - user controls the start and transmission of audio to and from the server as well as point-to-point transmission and reception. We made measurements focusing on the mouth to ear delay and how this is affected by parameters such as the size of the Ethernet packet, the cache size, and we present the results for various audio compressions and uncompressed audio.

One of the main issues of radio broadcasters is content documentation and management. For this purpose, various techniques have been developed, utilizing machine learning algorithms for the segmentation, recognition and classification of sound events. Advanced deep learning methods and hybrid /combined approaches are currently deployed, pursuing more sophisticated semantic conceptualization and analysis outcomes. However, the limited availability of properly annotated datasets is undoubtedly one of the most critical problems in the training and evaluation of such smart systems. This paper proposes a novel web-radio automation system that, besides audio playlist and mixing management, it records events and actions of the streaming process, thus automatically producing suitable sound datasets with high quality and accuracy annotations.

The reproduction of audio signals with headphones often degrades due to spectral response deteriorations, colorization and attenuation or cancellation of different frequencies or frequency ranges, depending on the technical characteristics of each model. To address this problem, the practical application of the well-defined equalization method with pole fitting in the spectral responses of three different headphones using tree equalizer target functions, is studied in this work. The subjective and objective evaluation of the results demonstrates the satisfactory correction of the responses of the headphones with relatively low computational costs.

With the passage to the digital age and the tremendous evolution in microprocessors, many artists turned to electronic music. In our work, an open platform (set-up) of music creation through optical-electronic interfaces (sensors) is presented. It exploits man's kinesiology by combining laser beams and interfaces whereby, through a microcontroller, it creates or reproduces a multitude of musical joints as a real MIDI general controller. Sensors of metallic conductive materials, conductive pigments, as well as ultra-thin, transparent and flexible graphene films or graphene-related materials were studied. The results are quite satisfactory with high responses. The ease of creation and reproduction through this platform could make it a learning and entertainment tool, and maybe a music therapy tool.

The present work deals with a new passive system for real-time detection, classification and direction of arrival estimator of Unmanned Aerial Vehicles (UAVs). The proposed system composed of a very low cost hardware components, comprises two different arrays of three or six-microphones, non-linear amplification and filtering of the analog acoustic signal, avoiding also the saturation effect in case where the UAV is located nearby to the microphones. Advance array processing methods are used to detect and locate the wide-band sources in the near and far-field including array calibration and energy based beamforming techniques. Moreover, oversampling techniques are adopted to increase the acquired signals accuracy and to also decrease the quantization noise. The classifier is based on the nearest neighbor rule of a normalized Power Spectral Density, the acoustic signature of the UAV spectrum in short periods of time. The low-cost, low-power and high efficiency embedded processor STM32F405RG is used for system implementation. Preliminary experimental results have shown the effectiveness of the proposed approach.

The current paper examines the technical approach as well as the results of the acoustic study conducted for the "Aris Garoufalis" hall of the historical Conservatory of Athens. Due to architectural design limitations, minimal but necessary construction interventions were proposed. Numerous acoustical measurements were performed in order to capture the project’s progress level and to highlight key issues that eventually emerged as a result of design deviations from the original plan. Particular emphasis was placed on the importance of the choice of the seats in the room as well as on the impact of the incorrect application of acoustic surfaces, demonstrating their considerable influence on the main indicators of acoustic quality. Finally, the paper demonstrates the "inevitable" comparison of the acoustic prediction model with actual measurement results as the room modelling process became an essential part of the design approach.

This paper presents the design of conversion of the reserved envelope of “Βuilding 24” of the industrial complex “Allatini” in Thessaloniki into a variable acoustics auditorium, capable of accommodating both music and speech events. Its shoebox design demonstrates variable accommodation capacity by its conversion into two smaller auditoriums, with appropriate variable acoustic behavior. The acoustic design is performed based on the combination of geometrical design of reflectors with the method of images and the statistical – energy calculation method of reverberation time. The variable acoustics behavior is achieved by the use of variable sound absorption on the inner side of the building envelope. The design is being validated with an acoustic behavior simulation with the use of CATT Acoustic.

The use of academic libraries has expanded in recent years to adapt to changes in technology and society. Hence, different acoustic requirements are necessary which are often not taken into account in the design process. This study is carried out with the aim of improving the acoustics of the existing library of the Technical University of Crete. In the library area, impulse response measurements were performed at three different levels and at a sum of six measurement points. Reverberation time was then calculated. Sound levels were recorded in the time domain as well with the main sources of noise (steps, speech etc.). From the results of the measurements two are considered the most important problems whose solution is a priority for the improvement of the library acoustics: the fluctuating sound levels and the high reverberation time. To address these problems, several solutions are proposed, the most important of which are: segregation of spaces into zones with the fitting of suitable frames and the placement of absorbent materials. In conclusion, the solutions proposed for the improvement of acoustics of the library of the Technical University of Crete and existing libraries include a framework of acoustic and non-interventions to achieve the best possible result.

The Stavros Niarchos Foundation Cultural Center has already opened since 2017 and acts a multidisciplinary landmark that accommodates the Greek National opera and the Greek National Library. This majestic complex resides in an ecological natural landscape hosting at the same time an extensive closed parking area. Along with the main performance hall the SNFCC holds a second smaller multipurpose hall (experimental stage), rehearsal rooms for the choir, the orchestra as well as ballet rooms and numerous individual warm up rooms for the musicians. During its design and construction the top notch specs infused in all the building’s parts, required the continuous, meticulous and responsible contribution of every single person involved in the project. Adding to the above the challenging time scheduling, the implementation of the acoustic design guidelines consisted of very demanding tasks the throughout the entire duration of the project. The present paper is discussing the role of the Acoustic Consultant in projects of such scale and function using examples from the personal experience of the authors who acted as the executive acoustic consultants of the project from conception to completion.

The specific work deals with the estimation of the mixing time based on room impulse response measurements, using statistical analysis methods. The studied methods are based on the temporal evolution of the statistical measures of normalized kurtosis, Fisher information, Shannon entropy and Tsallis entropy. Their estimation accuracy is evaluated and the conditions for their reliable application are discussed on the basis of the analysis of different room impulse responses and the comparison of their results with those produced by mathematical models suggested by the literature.