Archives of Acoustics

When we look at the history of AGH – University of Science and Technology, recognized as one of the best universities in the country, we find that for that success many people worked for several dozen years. However, the subjects, the methodology and directions of their work were shaped by units – outstanding personalities of science. Just to mention, among others Professors Stanisław Zuber, Władysław Takliński, Witold Budryk, Maksymilian Tytus Huber and Władysław Bogusz. These people have shaped our institution, marked its new path of development and permanent place in the history of Polish and world science. To belong to such a group is a great ennoblement, for which one works out for his entire life. Undoubtedly, such personality was also Professor Zbigniew Witold Engel, to whom we said goodbye on November, 6th, 2013, in the St. Clement’s church in Wieliczka. Professor was born on April 1, 1933, in Zawady near Zhovkva in the province of Lviv. After graduating from Jan Matejko Middle and High School in Wieliczka in 1950 earned a matriculation certificate. Then he began his studies at the Department of Communications of Polytechnic Departments of Academy of Mining and Metallurgy and involved with our university for the next 63 years. October 1, 1952 the Department of Mechanics of the University of Mining and Metallurgy was created, and soon after began professor’s adventure that was the work of science, education and organization. The history and fate of our university are inextricably linked with the person of professor who practically since the very beginning of the Faculty supported it in all areas of its activities, and has always actively participated in academic life.

Speaker‘s emotional states are recognized from speech signal with Additive white Gaussian noise (AWGN). The influence of white noise on a typical emotion recogniztion system is studied. The emotion classifier is implemented with Gaussian mixture model (GMM). A Chinese speech emotion database is used for training and testing, which includes nine emotion classes (e.g. happiness, sadness, anger, surprise, fear, anxiety, hesitation, confidence and neutral state). Two speech enhancement algorithms are introduced for improved emotion classification. In the experiments, the Gaussian mixture model is trained on the clean speech data, while tested under AWGN with various signal to noise ratios (SNRs). The emotion class model and the dimension space model are both adopted for the evaluation of the emotion recognition system. Regarding the emotion class model, the nine emotion classes are classified. Considering the dimension space model, the arousal dimension and the valence dimension are classified into positive regions or negative regions. The experimental results show that the speech enhancement algorithms constantly improve the performance of our emotion recognition system under various SNRs, and the positive emotions are more likely to be miss-classified as negative emotions under white noise environment.

Speech emotion recognition is deemed to be a meaningful and intractable issue among a number of do- mains comprising sentiment analysis, computer science, pedagogy, and so on. In this study, we investigate speech emotion recognition based on sparse partial least squares regression (SPLSR) approach in depth. We make use of the sparse partial least squares regression method to implement the feature selection and dimensionality reduction on the whole acquired speech emotion features. By the means of exploiting the SPLSR method, the component parts of those redundant and meaningless speech emotion features are lessened to zero while those serviceable and informative speech emotion features are maintained and selected to the following classification step. A number of tests on Berlin database reveal that the recogni- tion rate of the SPLSR method can reach up to 79.23% and is superior to other compared dimensionality reduction methods.

In spite of the fact that standardizing operations and increased awareness of hazards led to a significant improvement of vibroacoustic climate of operator’s stands of new machines, their long-term operation - often under difficult conditions - leads to a fast degradation of acoustic qualities of machines. Temporary operations performed during surveys and periodical overhauls are rarely effective, due to the lack of any guidelines. In this situation the authors propose the algorithm for selection of eventual screens or sound absorbing and sound insulating partitions, utilizing the measuring procedure aimed at identification, at the operator’s stand, of main noise components originated from various sources. On the basis of this procedure, the vibroacoustic energy propagation paths in the machine was estimated.

The goal of the studies undertaken in Polish national parks was to determine noise threats, examine the resources, assess the quality of soundscapes and identify the possibilities of their protection. The questionnaire method used in the studies made it possible to identify the awareness of noise threats and the value of soundscapes according to the park service staff. In addition, the semantic differential and description methods were used to learn how students assessed the soundscape quality of Polish national parks. Finally, avenues of further research on soundscape in environmentally valuable areas were indicated. The research findings indicate that each national park in Poland is characterised by diverse and unique soundscapes and is subject to the pressure of road traffic and tourism resulting in noise hazards. The conservation of the acoustic values of parks is necessary and possible.

Contemporary tools which help to design technical objects refer to the conclusions drawn from studying the changes of physical processes accompanying the exploitation, especially to vibroacoustic processes. The main problem is to define such vibroacoustic measures, where their changes would model the analyzed physical phenomena in the best way. Basing on simple indicators which refer to occurring phenomena, it is possible to obtain accurate solutions with a satisfactory reliance level without using complex computing techniques needing detailed descriptors. According to the author, the indicators which are based on the analysis of vibroacoustic energy propagation are very useful in solving engineering problems. These indicators are useful while diagnosing the condition of technical systems, identifying and minimizing the vibroacoustic risks. The possibilities of using such indicators in order to find design solution are illustrated by sample results of the research of the structures with vibroacoustic elements which reduce the noise of rail vehicles by the rail vibration damping.

Recently, a new class of ceramic foams with porosity levels up to 90% has been developed as a result of the association of the gelcasting process and aeration of the ceramic suspension. This paper presents and discusses original results advertising sound absorbing capabilities of such foams. The authors man- ufactured three types of alumina foams in order to investigate three porosity levels, namely: 72, 88, and 90%. The microstructure of foams was examined and typical dimensions and average sizes of cells (pores) and cell-linking windows were found for each porosity case. Then, the acoustic absorption coefficient was measured in a wide frequency range for several samples of various thickness cut out from the foams. The results were discussed and compared with the acoustic absorption of typical polyurethane foams proving that the alumina foams with high porosity of 88-90% have excellent sound absorbing properties competitive with the quality of sound absorbing PU foams of higher porosity.

The use of periodic structures as noise abatement devices has already been the object of considerable research seeking to understand its efficiency and see to what extent they can provide a functional solu- tion in mitigating noise from different sources. The specific case of sonic crystals consisting of different materials has received special attention in studying the influence of different variables on its acoustic performance. The present work seeks to contribute to a better understanding of the behavior of these structures by implementing an approach based on the numerical method of fundamental solutions (MFS) to model the acoustic behavior of two-dimensional sonic crystals. The MFS formulation proposed here is used to evaluate the performance of crystals composed of circular elements, studying the effect of varying dimen- sions and spacing of the crystal elements as well as their acoustic absorption in the sound attenuation provided by the global structure, in what concerns typical traffic noise sources, and establishing some broad indications for the use of those structures.

When two pure tones of slightly different frequency are presented separately to each ear, the listener perceives a third single tone with amplitude variations at a frequency that equals the difference between the two tones; this perceptual illusion is known as the binaural auditory beat (BB). There are anecdotal reports that suggest that the binaural beat can entrain EEG activity and may affect the arousal levels, although few studies have been published. There is a need for double-blind, well-designed studies in order to establish a solid foundation for these sounds, as most of the documented benefits come from self-reported cases that could be affected by placebo effect. As BBs are a cheap technology (it even exists a free open source programmable binaural- beat generator on the Internet named Gnaural), any achievement in this area could be of public interest. The aim in our research was to explore the potential of BBs in a particular field: tasks that require focus and concentration. In order to detect changes in the brain waves that could relate to any particular improvement, EEG recordings of a small sample of individuals were also obtained. In this study we compare the effect of different binaural stimulation in 7 EEG frequency ranges. 78 participants were exposed to 20-min binaural beat stimulation. The effects were obtained both quali- tative with cognitive test and quantitative with EEG analysis. Results suggest no significant statistical improvement in 20-min stimulation.

For successful active control with a vibrating plate it is essential to appropriately place actuators. One of the most important criteria is to make the system controllable, so any control objectives can be achieved. In this paper the controllability-oriented placement of actuators is undertaken. First, a theoretical model of a fully clamped rectangular plate is obtained. Optimization criterion based on maximization of controllability of the system is developed. The memetic algorithm is used to find the optimal solution. Obtained results are compared with those obtained by the evolutionary algorithm. The configuration is also validated experimentally.

Vibrating plates can be used in Active Noise Control (ANC) applications as active barriers or as secondary sources replacing classical loudspeakers. The system with vibrating plates, especially when nonlinear MFC actuators are used, is nonlinear. The nonlinearity in the system reduces performance of classical feedforward ANC with linear control filters systems, because they cannot cope with harmonics generated by the nonlinearity. The performance of the ANC system can be improved by using nonlinear control filters, such as Artificial Neural Networks or Volterra filters. However, when multiple actuators are mounted on a single plate, which is a common practice to provide effective control of more vibration modes, each actuator should be driven by a dedicated nonlinear control filter. This significantly increases computational complexity of the control algorithm, because adaptation of nonlinear control filters is much more computationally demanding than adaptation of linear FIR filters. This paper presents an ANC system with multiple actuators, which are driven with a single nonlinear filter. To avoid destructive interference of vibrations generated by different actuators the control signal is filtered by appropriate separate linear filters. The control system is experimentally verified and obtained results are reported.

It is well known that sound absorption and sound transmission properties of open porous materials are highly dependent on their airflow resistance values. Low values of airflow resistance indicate little resistance for air streaming through the porous material and high values are a sign that most of the pores inside the material are closed. The laboratory procedures for measuring airflow resistance have been stan- dardized by several organizations, including ISO and ASTM for both alternate flow and continuous flow. However, practical implementation of these standardized methods could be both complex and expensive. In this work, two indirect alternative measurement procedures were compared against the alternate flow standardized technique. The techniques were tested using three families of eco-friendly sound absorbent materials: recycled polyurethane foams, coconut natural fibres, and recycled polyester fibres. It is found that the values of airflow resistance measured using both alternative methods are very similar. There is also a good correlation between the values obtained through alternative and standardized methods.

Latest developments in international standardization of whole-body and hand-arm vibration are pre- sented. In addition, two German projects are presented that might have impact on international work programs in the next years.

The paper consists of study results of exposure to high frequency noise at metalworking workplaces. The study was carried out using objective methods (measurements of parameters characterizing the noise) and subjective studies (questionnaire survey). Metalworking workplaces were located in a steel structure (e.g. deck gratings) of the manufacturing plant. The results are equivalent sound pressure levels in the 1/3 octave frequency bands with center frequencies from 10 kHz to 40 kHz in reference to an 8-hour workday equal to approximately 81-105 dB at most of the tested workplaces and exceed permissible values. The questionnaire survey of annoyance high frequency noise (i.e. in the audible frequency and low ultrasound range) was conducted among 52 operators of machines. Most of the workers describe the noise as: buzzing, insistent, whistling and high-pitched squeaky. Respondents specify the noise levels occurring at workplaces as: loud, impeding communication, highly strenuous and tiring.

Research in termoacoustics began with the observation of the heat transfer between gas and solids. Using this interaction the intense sound wave could be applied to create engines and heat pumps. The most important part of thermoacoustic devices is a regenerator, where press of conversion of sound energy into thermal or vice versa takes place. In a heat pump the acoustic wave produces the temperature difference at the two ends of the regenerator. The aim of the paper is to find the influence of the material used for the construction of a regenerator on the properties of a thermoacoustic heat pump. Modern technologies allow us to create new materials with physical properties necessary to increase the temperature gradient on the heat exchangers. The aim of this paper is to create a regenerator which strongly improves the efficiency of the heat pump.

Research in termoacoustics began with the observation of the heat transfer between gas and solids. Using this interaction the intense sound wave could be applied to create engines and heat pumps. The most important part of thermoacoustic devices is a regenerator, where press of conversion of sound energy into thermal or vice versa takes place. In a heat pump the acoustic wave produces the temperature difference at the two ends of the regenerator. The aim of the paper is to find the influence of the material used for the construction of a regenerator on the properties of a thermoacoustic heat pump. Modern technologies allow us to create new materials with physical properties necessary to increase the temperature gradient on the heat exchangers. The aim of this paper is to create a regenerator which strongly improves the efficiency of the heat pump.Polish acoustical community mourns the loss of Professor Marian Urbańczyk who passed away on July 10, 2013. Professor Marian Urbańczyk was born on February 2nd, 1948, in Katowice (Poland). There he attended the Silesian Technical College (Śląskie Techniczne Zakłady Naukowe), where he was a student of the electrical engineering and electronics class and in 1967 completed his secondary education with school-leaving examination and a honorary mention. In 1973, he graduated successfully (again with distinction) from the Faculty of Electrical Engineering at the Silesian University of Technology (Politechnika Śląska) in Gliwice. The same year he has joined the SUT’s Institute of Physics as a university teacher at the newly created Faculty of Mathematics and Physics. The late Professor Urbańczyk remained connected with the Institute until 2009, from 2007 to 2009 performing the function of its Deputy Director for Students’ Affairs. The scope of the Professor’s scientific interest comprised electronics of solid state, metrology, and technical physics, with special attention paid by him to acoustics, including acoustoelectronic systems and their applications in technology and metrology. In 1981, Marian Urbańczyk delivered his doctor’s dissertation concerning technical acoustics at the Institute of Fundamental Problems of Technology Polish Academy of Sciences (IPPT PAN) in Warsaw. In the year 1999, he was granted the post-doctoral degree (habilitation) by the Council of the Faculty of Electronics at the Wrocław University of Technology. In 2012, Marian Urbańczyk was made full professor by the President of Poland. The Silesian University of Technology in Gliwice remained the scene of Professor Urbańczyk’s scientific activity to the very end of his life. Since September 1, 2009, Professor had been working at the Department of Optoelectronics at the SUT’s Faculty of Electrical Engineering, acting as its Deputy Director. Professor Marian Urbańczyk was a promoter of several doctor’s dissertations and numerous master theses. In the framework of his didactic work, he has organized many students’ laboratories and workshops. He was also the author of a wide variety of teaching curriculums (syllabuses). The late Professor Urbańczyk was highly valued both by his students and coworkers. Professor Marian Urbańczyk was an unquestionable authority in the field of technical acoustics, metrology, and electronics, and an internationally acknowledged author (and co-author) of more than 200 scientific publications, nearly 50 of them having been included in the ISI list. His papers were published in highly-ranked journals and frequently cited by other authors. He was also the co-author of numerous patents and patent applications. The Professor was a member of Scientific Committees of many conferences, both domestic and international. Professor Marian Urbańczyk was a member of many international and Polish scientific societies, including the European Acoustical Association (EAA), the International Optical Engineering Society (SPIE), the Polish Acoustical Society (PTA), the Photonic Society of Poland, the Polish Physical Association (PTF), and the Polish Association of Sensor Technology (PTTS). Since 1975, Professor Urbańczyk was a member of the Polish Acoustical Society (PTA), elected later the Member of the Main Board of this organization and the Chairman (Local President) of the Board of Upper Silesia Branch of the PTA. The Professor acted also as a co-organizer of annual international conferences, including the Winter School on Wave and Quantum Acoustics and the Workshop on Acoustoelectronics. For his scientific achievements, Professor Urbańczyk has been awarded state orders, medals, and scientific rewards. Professor Urbańczyk’s death is an irreparable loss to the Silesian University of Technology, the Polish Acoustical Society, and the whole Polish scientific community. Professor Marian Urbańczyk was an extraordinary person, always very kind-hearted and understanding for others. For those who knew him personally, he was a Friend and a Master. And as the Friend and the Master we will retain him in our fond memory.

Mikołaj Łabowski, Professor Emeritus at the Institute of Acoustics, Adam Mickiewicz University in Poznań, passed away on the 8th of October, 2013. Professor Mikołaj Łabowski was born on the 17th of December, 1935, in Florynka in the southern part of Poland. He graduated from the Faculty of Mathematics, Physics and Chemistry of the Adam Mickiewicz University receiving his Master of Science degree in physics in 1962. Eight years later he obtained his PhD title from the same university. In 1981, on the basis of the book “Ultra- and hypersonic properties of selected liquids and critical mixtures” he obtained the degree of habilitated doctor. The President of Poland awarded him the titles of Associate Professor in Physics in the year 1991 and Full Professor in 1999. From 1985 to 1987,Mikołaj Łabowski held the post of Vice-Dean for Students’ Affairs at the Faculty of Mathematics and Physics of the AdamMickiewicz University. In the years 1996–1999, he was the Director of the University’s Institute of Acoustics. He held many posts in the Polish Acoustical Society, of which he was a HonoraryMember. He always served with advice and assistance in scientific matters to the Committee of Acoustics of the Polish Academy of Sciences. Professor Łabowski was an outstanding scientist, one of the founders of ultrasonic physics in Poland. After returning from scholarship in the Lomonsov University in Moscow, he became an expert in the field of ultrasonic studies of liquids and liquid mixtures. His groundbreaking works on ultrasonic properties of critical binary mixtures opened up new perspectives in the research of dynamic phenomena in the vicinity of critical temperatures. Professor Łabowski’s outstanding scientific achievements were recognized by rewarding him the Minister of Education Prize in the years 1981 and 1987. Throughout his whole professional career associated with the Adam Mickiewicz University in Poznań, Professor Łabowski has published over 100 papers, mostly in renowned international scientific journals, and carried out an intensive teaching activity. Through his profound knowledge and enthusiasm, Professor Mikołaj Łabowski continuously inspired colleagues and collaborators and decisively shaped the development of ultrasonic physics in Poznań. With the death of Professor Mikołaj Łabowski, Polish acoustics has lost a great researcher, teacher, and scholar.