In the work, the problems of the beam structural modification through coupling the additional mass or elastic support, as well as the problem of diagnostics of the beam cracks, are discussed. The common feature for both problems is that the material parameters in each of the discussed cases change only in one point (additional mass, the support in one point, the crack described by the elastic joint). These systems, after determination of the value of additional element and its localization, should have a given natural vibration frequency. In order to solve the inverse problem, i.e. the problem of finding values of the additional quantities (mass, elasticity), the beam inverse model was proposed. Analysis of this model allows finding such a value of additional mass (elasticity) as a function of its localization so that the system has the free vibration frequency, which is desired in the modification problem or measured on the object in the diagnostics.

The paper concerns the eigenanalysis of acoustic cavities with the use of radial basis functions (RBF). The Kansa collocation method was used for determination of the natural frequencies and eigenvectors of 1D, 2D and 3D acoustic elds. Due to validation analysis of the proposed method, in simple examples like 1D, 2D rectangle and 3D rectangular parallelepiped all calculated eigenferquency and eigenvectors were compared with exact (analytical) results. All results indicate that using of multiquadric radial basis functions provide a results with very high accuracy in comparison to analytical results. In the paper a new method for determining the shape parameter of the multiquadric radial basis functions is described.

In this paper, an automated measurement system was proposed that uses a probe hung below a remotely controlled balloon to measure parameters of the acoustic eld in the whole volume of a room. The study was conducted to estimate distortions that such system may cause in the acoustic eld at the measurement point. The most signicant source of the distortions will be the buoyancy element one large balloon or a number of smaller ones. This paper considers dierent spatial congurations of spherical balloons with regards to alterations they cause in the acoustic pressure levels measured below them. Interior of a room without and with a group of spherical balloons was modeled using the boundary element method. Using a larger number of smaller spheres instead of a single large one did not signicantly reduce the related distortions. However, using two spheres slightly decreased distortions when the distance between the balloons and the recording point was relatively small.

The article presents the model of sound insulation of single homo-geneous baffles based on the Statistical Method of Energy Analysis. The determined frequency characteristics of airborne sound insulation of the baffles obtained from the calculation model with the results of experimental tests were compared. Calculations using the Statistical Method of Energy Analysis and laboratory tests were performed for plates made of plexiglass and acrylic.

Critical and coincidence frequencies of panels are important in studying their behaviour under acoustic excitation Expressions for critical and coincidence frequencies of thin and thick homogeous isotropic panels are derived. Characteristics of critical frequency values in function of panel thickness for five different construction materials are shown.