Miomir Mijić

Results of experimental validation of method for direct localization of acoustic impulse sources in outdoor environment, proposed previously by the authors are presented. Based on the ambiguity function formulated for the collocated and distributed antenna arrays, the ambiguity function of the microphone array was formulated as a tool for characterization of the non-uniform geometry of the microphone array in terms of ambiguous grating lobes and side lobe levels.

In literature, the "box-in-box" system is described as a solution for achieving the highest possible sound insulation in a room. The system involves double walls separating a room from the surroundings in all directions, without any lateral pass for sound. This approach doubles the number of discontinuities in the material through which sound energy travels, thus providing higher sound insulation. Based on such an idea, some dwelling houses were designed with massive cavity walls between apartments with the expectation of better sound insulation. The concept was further motivated by the need to achieve adequate thermal insulation between apartments using insulation material in the cavity. However, in buildings where this was implemented, residents complained about inadequate sound insulation. Measurements showed that the sound reduction index of the double brick wall was lower than expected, even less than that of a wall where the two thinner layers were combined into a single thicker brick wall without an internal cavity. This was surprising, leading to research aimed at finding an explanation. It was concluded that in buildings there is the influence of sound paths through the wall’s lateral junctions, which is more pronounced with two thinner layers. With a cavity wall, the transmission of sound energy through lateral junctions and further by flanking transmission is more pronounced than with a single wall of the same surface mass. Additionally, the high seismic zone in Serbia requires certain adjustments in construction, invisible in architectural drawings, that further diminish the effect of the increased number of discontinuities in the wall. All of this makes the massive cavity wall in the building, contrary to expectations, less effective than a single wall made of the same quantity of material, making it acoustically and financially unreasonable. Research also revealed that material in the cavity has no influence on the sound reduction index value of the wall.

Recent papers and studies over the course of last three years have shown that COVID-19 has a negative impact on the speech communication quality between people. This paper presents an influence analysis of the curvature shape of protective transparent shields on the speech signal. Five shields made of the same material and dimensions but with different curvatures were analyzed, from a completely flat to a very curved shield which has the same shape of curvature at its top and bottom and covers the entire face. The influence of the shield is analyzed with two types of experiments – one using dummy head with integrated artificial voice device, and the other using real speakers (female and male actors). It has been shown that usage of protective shields results in a relative increase in the speech signal level, in the frequency range of around 1000 Hz, compared to the situation when protective shields are not used. The relative increase in speech signal levels for large-curvature shields can be up to 8 dB. The possible causes of this phenomenon have been analyzed and examined.

This paper examines speech privacy in both residential and commercial spaces. The ASTM E2638 standard defines the Speech Privacy Class (SPC) parameter, which measures speech privacy based on the signal-to-noise ratio at the listener’s position. This paper proposes estimating the SPC value using relevant ISO parameters commonly used in European practice: the apparent sound reduction index in dB (defined by ISO 16283-1, 2 standards) and the equivalent ambient noise level in dBA (defined by the ISO 1996-1 standard). The estimated value of the SPC parameter in this paper is referred to as the Speech Privacy Index (SPI). A diverse range of situations, i.e., rooms, was analyzed in the field. These rooms varied in terms of purpose, organization, dimensions, furnishings, isolation from other spaces, and internal and external environments. The results of the experiments demonstrate a strong correlation between the SPC value estimated according to ISO parameters (the proposed method) and the SPC as defined in the ASTM E standard. This indicates that the proposed method can provide an indicator of the state of speech privacy in buildings. The significance of the proposed calculation method (i.e., the STI parameter) lies in its ability to be applied at the building design stage, as well as after its completion, during routine testing.

The presented work is the result of affirmation of synergistic work of experts dealing with architectural and acoustic design with the aim and purpose of finding an adequate solution for optimal correction of the effect of GHG systems installed on the facade of the subject (case study) office building in Belgrade. Measurements established that the noise of the constructed GHG systems affected the residential building in the immediate vicinity. The effect of the constructed devices (refers to the installed units) of the office building in question in the case when they operate at full capacity was measuring to be about 58 dB (A). The urban zone in which the building is located (Vracar-Belgrade) belongs to the category of "office residential area" in which the outdoor noise level permitted for the period of day is 60 dB (A), and for the night period is 50 dB (A). Taking into account the stated facts, it has been unequivocally established that GHG systems to a certain extent exceed the permitted noise levels and "endanger" the neighboring observed building. The subject of this professional scientific research is the design of atypical facade architectural elements as a barrier reducing noise on the example of an office building in Belgrade. The architectural challenge was reflected in the fact that, in addition to designing the facade element which, at the request of the investor must not compromise the architecture of the building, therefore, should be "atypical in architectural design", it must also provide flexibility in applying different variants of acoustic barriers, which in addition to architectonic requirement must provide an adequate response to acoustic requirements. To the satisfaction of the authors, the designed barrier confirmed a successful synergy solution. The adopted architectural-acoustic configuration of the barrier proved to be effective regardless of the type of installed air conditioners, which in some way justifies the initial idea of strong causality of acoustic and architectural design, as a synergistic principle.

This paper presents the method for prediction of some basic mechanical parameters of a wood specimen by using simple instrumentation. The standard acoustic method for assessment of modulus of elasticity using the impulse excitation is extended by using a recording in the very near field. In this way, visualization of vibration patterns of the analyzed sample was accomplished for all modes below 5 kHz. This enables detection of signals with a good signal-to-noise ratio over a wide frequency range which is then used for loss factor assessment.

Public entertainment premises are significant sources of urban noise pollution. In this paper, indoor sound level spectra for different types of entertainment premises have been analyzed. While most of the spectra lie between two standardized curves proposed by the ISO 717-1:2013 (The International Organization for Standardization) standard, spectra recorded in discotheques show a pronounced spectral level below 160 Hz as a result of an intensive use of subwoofers. This indicates potentially inappropriate rating of sound insulation against such specific low-frequency noise by standardized spectrum adaptation terms. A modified spectrum adaptation term for a single-number rating of sound insulation under such circumstances has been proposed.

The introduced requirements for thermal insulation between dwellings, as well as some practical reasons, initiated greater use of double walls in building design practice. The standard EN 12354 -1 did not defined a procedures for calculation of the apparent sound reduction index for such constructions. The paper suggests a possible approach for calculation of apparent sound reduction index based on the calculation methodology for the single partition defined by the standard. Some theoretical analyses of the sound energy transmission through direct and flanking paths in a case of double massive partition were presented. Verification of the proposed approach were done by laboratory measurement and by FEM numerical simulation. The analysis included a number of commonly used constructions and types of their junctions.

The new legislation in Serbia for sound insulation in buildings, currently in preparation, should introduce for the first time a national implementation of dwellings’ acoustic classification. There are some structural systems and building typology that are common in existing housing stock. Some of them are caused by seismic demands and some by architects’ routines. All that introduced realistically accessible range of apparent sound reduction index values at different positions in existing buildings. To achieve a sustainable classification scheme in prepared new legislation the analysis of sound insulation in existing buildings were performed and implications of possible boundary values between different classes on the housing stock acoustic score were analyzed. Based on such approach, the suggestions concerned with the classification scheme and class limits are presented.