Miomir Mijic

Ambient noise in large rivers (L)

This paper presents the results of hydroacoustic noise research in three large European rivers: the Danube, the Sava, and the Tisa. Noise in these rivers was observed during a period of ten years, which includes all annual variation in hydrological and meteorological conditions (flow rate, speed of flow, wind speed, etc.). Noise spectra are characterized by wide maximums at frequencies between 20 and 30 Hz, and relatively constant slope toward higher frequencies. Spectral level of noise changes in time in relatively wide limits. At low frequencies, below 100 Hz, the dynamics of noise level is correlated with the dynamics of water flow and speed. At higher frequencies, noise spectra are mostly influenced by human activities on river and on riverbanks. The influence of wind on noise in rivers is complex due to the annual variation of river surface. The influence of wind is less pronounced than in oceans, seas, and lakes.

Analysis of Contribution of Acoustic Resonators Found in Serbian Orthodox Churches

A study of a number of Serbian Orthodox medieval churches, during their reconstruction or archeological investigation, revealed the presence of acoustical resonators. This paper offers a review of the resonators discovered to date. In addition, laboratory experiments were conducted on several resonators removed from churches in order to clarify their function. Based on the relevant literature, laboratory experiments, and analyses of acoustical characteristics of the worship spaces where resonators were found, it is concluded that the resonators found in medieval Serbian churches have not contributed to their acoustic quality. There are three reasons why the resonators were not effective. They were installed in very small churches where the additional absorption is not significant, their resonant frequencies were too low in relation to the frequency content of Serbian Orthodox worship service, and lastly, in some cases there were too few resonators to achieve audible changes in acoustic response of the church.

Microphone array geometry optimization for traffic noise analysis

This paper outlines an approach for obtaining microphone array geometry for use in traffic noise analysis. The designed array has a smaller number of microphones compared to existing solutions, thereby reducing the cost of system realization. The array geometry is irregular, consists of 24 microphones, and was obtained by an optimization procedure that minimizes beampatterns sidelobes. Microphone position optimization was performed in the frequency band from 300 Hz to 2000 Hz, defined by traffic noise characteristics. The designed array is used in ongoing research dedicated to the analysis of angular distribution of incident traffic noise sound energy impeding a facade in urban environment.

Measurement of reverberation gain in an urban environment

Multipath propagation within an urban area introduces a specific type of reverberation in response to sound excitation. That appearance affects the level of ambient noise produced by strong sound sources. In this paper, the signals recorded during the 1999 bombing of Belgrade were used to analyze the characteristics of reverberation in that urban environment. Six recorded signals were selected among more than 50 explosions recorded at that time. Due to the impulse nature of sound sources, the recorded signals represent the impulse responses of that area. The measured reverberation time T30 is about 7 ± 1 s in octaves between 31.5 Hz and 1 kHz. There is a variation of decay slope in time that is verified by differences between values of T10 and T30. The reverberation gain calculated from recorded signals is 2-7 dB, depending on the global position of the sound excitation point as well as its micro-location according to its position among the surrounding buildings. A variation of gain over octave bands is in the interval of approximately 3 dB. Information about reverberation gain in urban environment can be useful in a quick estimation of noise level produced by strong sound sources in a large area of urban environment.

The influence of absorption on statistical distribution of free path lengths in rooms

The ray tracing method in sound field simulation in a room allows the calculation of the free path lengths distribution (FPL) by superimposing all rays paths generated in the analysis. In room acoustics the statistical theory of sound field defined this distribution as an indicator of room geometrical properties which are independent of absorption. Accordingly, some commercial softwares for ray tracing simulation allow user to calculate that global distribution of FPL only. This paper is concerned with the analysis of the changes in the shape of FPL distribution as a consequence of nonuniform arrangement of absorption in room. Particularly is analysed the impact of absorptive auditorium in different global forms of the halls where all other interior surfaces are acoustically hard.

Acoustical characteristics of old wooden churches in Serbia

There are more than 50 churches in the central part of Serbia built entirely of wood. These churches were all built at the beginning of the 19th century. This paper presents the results of acoustical measurements conducted in these places of worship. In addition, the analysis of acoustical properties of different architectural styles and constructions within the same category of churches is presented.

Whispered speech recognition based on gammatone filterbank cepstral coefficients

This paper presents the results on whispered speech recognition using gammatone filterbank cepstral coefficients for speaker dependent mode. The isolated words used for this experiment are taken from the Whi-Spe database. Whispered speech recognition is based on dynamic time warping and hidden Markov models methods. The experiments are focused on the following modes: normal speech, whispered speech and their combinations (normal/whispered and whispered/normal). The results demonstrated an important improvement in recognition after application of cepstral mean subtraction, especially in mixed train/test scenarios.

Calculation of sound insulation according to EN 12354: Influence of type of the separating element junctions

Separating element junctions make a dual contribution in the calculations of sound insulation according to EN 12354 standards. Junction types and vibration reduction index values determine the amount of the vibration energy which will be transmitted from the separating to the flanking elements, and therefore the flanking transmission between the source and the receiving room. On the other hand, vibration reduction index values influence the structural reverberation time of the element, by quantifying energy losses at its junctions. The aim of this work is to quantify the influence of the separating element junction types on the calculated value of airborne and impact sound insulation.

Calculation of sound insulation according to EN 12354: Influence of sound reduction index of flanking elements

EN 12354 standards describe models for calculation of sound insulation in buildings. EN 12354-1 defines a model for airborne sound insulation, while EN 12354-2 describes the calculation procedure for impact sound insulation. Although the calculated value of sound insulation in both cases depends mostly on the insulation properties of the separating element, flanking transmission is also treated. The aim of this work is to assess the influence of sound reduction index of flanking elements (walls, floors and ceilings) on the calculated value of airborne and impact sound insulation.

Reverberation time in Serbian Orthodox worship spaces

Seven years ago, at the ASA Meeting in November 1990, this author presented some preliminary results of acoustical research realized in the Serbian Orthodox worship spaces. At that time the results for only seven churches were included in the paper. This research has been continued until now and nearly 60 churches were analyzed, different in volume, age, and the architectural style. Such a large number of measurements allow some more general conclusions about acoustical characteristics of orthodox worship spaces. Reverberation times obtained in realized measurements show the important influence of several specific factors such as strong orthodox rules in church interior design and volume shapes. These factors are influenced by traditional architectural styles accepted as unalterable even in the contemporary architectural design. Some differences in the frequency characteristic of the reverberation time according to different historical periods were also discovered.