Sound Transmission Loss Of Panels Research Articles

Mechanical and vibro-acoustic performance of sandwich panel with perforated honeycomb cores.

The effect of perforating the honeycomb walls of a honeycomb sandwich panel on the dynamic bending stiffness and sound transmission loss of the panel is investigated. The dynamic bending stiffness and sound transmission loss of several sandwich panels with different cores are calculated using a semi-analytical method, and the static bending stiffness and flatwise stiffness of these structures are also analyzed with the finite element method. Furthermore, the influences of the honeycomb shape, the hole shape of the perforated honeycomb wall, the number of perforations, and the wall thickness on the vibro-acoustic and mechanical properties of the sandwich panel are investigated. The results show that the static mechanical performance of the sandwich panel quickly reaches a high level when the ratio of honeycomb wall thickness to length t/l is about 5.3 × 10-3 and a square hole in the honeycomb wall can bring superior characteristics of "high static and low dynamic properties," significantly improving the sound insulation of the sandwich panel. This study makes an effective reference for the optimized design of the innovative sandwich structure in practical applications.

Effects of mounting positions and boundary conditions on the sound transmission loss of panels in a niche

The sound insulation performance of railway car body structures is critical for the control of rail vehicle interior noise. In sound transmission loss (STL) measurements, a niche with a large depth is necessary to allow for mounting the wide range of thicknesses of railway car body panels and for the mechanical isolation of the two rooms. In this study, two typical interior floor panels are tested in a series of mounting conditions and mechanical boundary conditions. The change of STL results during measurement is also predicted by an STL prediction model based on the finite element method. At lower frequencies, the STL results are influenced by both the mounting positions and the mechanical boundary conditions. At higher frequencies, the STL results are mainly influenced by the mechanical boundary conditions. Differences between the panel in the infinite baffle and niches at the resonance and off-resonance frequencies are different. Considering both the effects of mounting positions and mechanical boundary conditions, the existence of the cavity amplifies the STL difference caused by the mechanical boundary conditions.

A Combined Experimental and Analytical Approach for the Simulation of the Sound Transmission Loss of Multilayer Glazing Systems

In order to ensure acoustic comfort of living spaces, nowadays façade systems having high performance are required. Within such context the glazing systems play a key role in achieving high levels of sound insulation. The characteristics of sound insulation of such systems can be determined by analytical methods that make use of experimental characterizations of the physical and mechanical parameters of these systems. In this work a combined experimental and analytical approach for sound transmission loss prediction of glazing systems is presented. In particular, the mechanical properties of monolithic and multilayer glasses with viscoelastic interlayer made of polyvinyl butyral (PVB) are measured using resonance curve method of flexural waves on glass beams with different boundary conditions. In order to achieve reliable input mechanical data (Young's modulus and loss factor), tested beams are characterized in free-free and elastic constraints boundary conditions, respectively. The elastic constrain boundary conditions are realized following the same specifications of ISO Standard 10140 series for larger panels. Starting from the proposed mechanical characterization, the diffuse field sound transmission loss of glass panels has been predicted through an analytical model for solid elastic layers. Results from the above-mentioned procedure are compared with laboratory measurements. From the analysis it will be shown a better accuracy in determining the sound transmission loss of panels when the elastic constrain boundary conditions are applied to the representative beams.

Models and comparisons for the evaluation of the sound transmission loss of panels

The purpose of this work is to present the numerical evaluation of the sound transmission loss of some simple panel configurations and to compare them to the theoretical and experimental data found in existing literature. The numerical evaluations are carried out through the commercial software VA-One®. Specifically, single and double panels of different materials and configurations are investigated and thus the possibility to build good predictive numerical models is verified. The panels refer to the common automotive and aerospace configurations. An analysis of foam lined panels is presented, too. The numerous test cases can be considered as benchmarks for the simulations obtained with the statistical energy analysis. The agreements are very good and thus, statistical energy analysis represents a mature predictive methodology for this kind of simulations. Nevertheless, some care is always needed to select among the different simulation strategies for given specific configurations. The results are eventually cross-compared in order to highlight the configurations which are more promising for further investigations; this has been done by introducing a dimensionless frequency.

Adapting Simple Prediction Methods to Sound Transmission of Lightweight Foam Cored Panels

A common building product used in industrial buildings consists of thin steel or aluminium skins on each side of a foam plastic core such as polystyrene. Such panels have many attractive properties, they are light weight, have excellent capacity to span between structural supports, excellent thermal insulation and are pre-finished. They are used extensively in many countries, and in New Zealand these types of panels are commonly used in food processing plants which are often noisy and located close to residences. The sound transmission loss of these panels in their basic form is poor, usually less than a simple mass law prediction based on the mass of the components. The performance is characterised by a sharp dip in the sound transmission loss at mid frequencies which causes a big drop in Rw or STC rating. The work described in this paper has developed simple methods of predicting the sound transmission loss of panels both as single panels and more importantly when used as part of a system to achieve higher performance.

Boundary element analyses for sound transmission loss of panels

The sound transmission characteristics of an aluminum panel and two composite sandwich panels were investigated by using two boundary element analyses. The effect of air loading on the structural behavior of the panels is included in one boundary element analysis, by using a light-fluid approximation for the eigenmode series to evaluate the structural response. In the other boundary element analysis, the air loading is treated as an added mass. The effect of the modal energy loss factor on the sound transmission loss of the panels was investigated. Both boundary element analyses were used to study the sound transmission loss of symmetric sandwich panels excited by a random incidence acoustic field. A classical wave impedance analysis was also used to make sound transmission loss predictions for the two foam-filled honeycomb sandwich panels. Comparisons between predictions of sound transmission loss for the two foam-filled honeycomb sandwich panels excited by a random incidence acoustic field obtained from the wave impedance analysis, the two boundary element analyses, and experimental measurements are presented.

Predicting the Sound Transmission Loss of Honeycomb Panels using the Wave Propagation Approach

The sound transmission properties of sandwich panels can be predicted with sufficient degree of accuracy by calculating the wave propagation properties of the structure. This method works well for sandwich panels with isotropic cores but applications to panels with anisotropic cores are hard to find. Honeycomb is an example of anisotropic material which when used as a core, results in a sandwich panel with anisotropic properties. In this paper, honeycomb panels are treated as being orthotropic and the wavenumbers are calculated for the two principle directions. These calculated wavenumbers are validated with the measured wavenumbers estimated from the resonance frequencies of freely hanging honeycomb beams. A combination of wave propagation and standard orthotropic plate theory is used to predict the sound transmission loss of honeycomb panels. These predictions are validated through sound transmission measurements. Passive damping treatment is a common way to reduce structural vibration and sound radiation, but they often have little effect on sound transmission. Visco-elastic damping with a constraining layer is applied to two honeycomb panels with standard and enhanced fluid coupling properties. This enhanced fluid coupling in one of the test panels is due to an extended coincidence range observed from the dispersion curves. The influence of damping treatments on the sound transmission loss of these panels is investigated. Results show that, after the damping treatment, the sound transmission loss of an acoustically bad panel and a normal panel are very similar.

Analysis of the sound transmission loss of panels with resonant systems on the basis of equivalent representations

Effects of increasing the sound transmission loss of panels with the help of resonant systems on the basis of equivalent representations are analyzed. Emphasis is placed on the least-studied resonant systems, the inertial bodies of which simultaneously interact with media on each side of the panels. A universal expression for the sound transmission loss of panels with an arbitrary system of resonant elements with one degree of freedom is presented. It includes the parameters common to all types of resonators (the total mass, compressibility, quality factor, and characteristic frequencies). The expression can be directly used to compare the efficiency of different types of resonant systems mounted on a panel and to determine their optimum parameters.

Sound Transmission Loss of Panels with Resonant Elements

Sound Transmission Loss of Panels with Resonant Elements

Sound Transmission Loss of Panels with Resonant Elements

Various types of resonant elements that can be used for increasing the transmission loss of panels in narrow frequency bands are analyzed. The main physical phenomena determining the transmission loss of sound waves in panels with resonant elements are studied. Three main principles of increasing the transmission loss realized in panels with resonant elements are described: the principle of soft reflection, the principle of hard reflection, and the principle of compensation. The relations for estimating the transmission loss of panels with resonant elements, which model the main physical phenomena governing the propagation of sound waves, are presented.

Factors Affecting the Comparison of Theoretical and Experimental Sound Transmission Loss of Panels

The sound transmission loss of homogenous isotropic panels is simply described theoretically from an infinite plate theory, in terms of the panel mass per unit area, bending stiffness per unit width and loss factor, and some a priori assumptions about the forcing sound field. In a typical transmission loss test, a number of additional factors are involved which may affect the test results. These effects include: (a) “diffusivity” of the incident sound field at the panel; (b) finite size of the test opening; (c) depth of the test opening; (d) inhomogenieties in the panel; (e) resonant response of the panel; (f) panel size compared with correlation length in the forcing sound field; (g) spectral shape of sound fields (when measured with filters of nonzero bandwidth). These variables are reviewed in view of the current state-of-the-art, and their range of effect in the region of the panel critical frequency is discussed.

The measurement of sound transmission loss of panels with small transmission loss

The transmission room method for the measurement of transmission loss is reviewed and the lower limits of validity established. An alternative method for measuring low loss panels is described.