Arne Dijckmans

Sound transmission through finite lightweight multilayered structures with thin air layers

The sound transmission loss (STL) of finite lightweight multilayered structures with thin air layers is studied in this paper. Two types of models are used to describe the vibro-acoustic behavior of these structures. Standard transfer matrix method assumes infinite layers and represents the plane wave propagation in the layers. A wave based model describes the direct sound transmission through a rectangular structure placed between two reverberant rooms. Full vibro-acoustic coupling between rooms, plates, and air cavities is taken into account. Comparison with double glazing measurements shows that this effect of vibro-acoustic coupling is important in lightweight double walls. For infinite structures, structural damping has no significant influence on STL below the coincidence frequency. In this frequency region, the non-resonant transmission or so-called mass-law behavior dominates sound transmission. Modal simulations suggest a large influence of structural damping on STL. This is confirmed by experiments with double fiberboard partitions and sandwich structures. The results show that for thin air layers, the damping induced by friction and viscous effects at the air gap surfaces can largely influence and improve the sound transmission characteristics.

Development of a hybrid wave based–transfer matrix model for sound transmission analysis

In this paper, a hybrid wave based-transfer matrix model is presented that allows for the investigation of the sound transmission through finite multilayered structures placed between two reverberant rooms. The multilayered structure may consist of an arbitrary configuration of fluid, elastic, or poro-elastic layers. The field variables (structural displacements and sound pressures) are expanded in terms of structural and acoustic wave functions. The boundary and continuity conditions in the rooms determine the participation factors in the pressure expansions. The displacement of the multilayered structure is determined by the mechanical impedance matrix, which gives a relation between the pressures and transverse displacements at both sides of the structure. The elements of this matrix are calculated with the transfer matrix method. First, the hybrid model is numerically validated. Next a comparison is made with sound transmission loss measurements of a hollow brick wall and a sandwich panel. Finally, numerical simulations show the influence of structural damping, room dimensions and plate dimensions on the sound transmission loss of multilayered structures.

Numerical investigation of the repeatability and reproducibility of laboratory sound insulation measurements

An extensive parametric study has been carried out with a wave based model to numerically investigate the fundamental repeatability and reproducibility of laboratory sound insulation measurements in the frequency range 50-200 Hz. Both the pressure method (according to ISO 10140-2) and the intensity method (according to ISO 15186-1 and ISO 15186-3) are investigated. The investigation includes the repeatability of the different measurement procedures, which depends on the influence of the microphone positions and the source position. The reproducibility of the sound insulation measurements in different test facilities is studied by looking at the influence of geometrical parameters like room and plate dimensions, aperture placement and aperture thickness. The results show that for small-sized test elements, the reproducibility of the intensity method is better. For heavy walls and lightweight double constructions, however, the predicted uncertainty is similar for the three measurement methods. The results of the reproducibility study are also used to investigate systematic differences between the pressure method and both

Reducing Railway Induced Ground-Borne Vibration by Using Trenches and Buried Soft Barriers

To reduce railway induced low frequency vibration, two mitigation measures - open trenches and buried soft wall barriers have been studied in this paper by using coupled finite element-boundary element models. These models were developed at KU Leuven and ISVR, and have been cross-validated within the EU FP7 project RIVAS (Railway Induced Vibration Abatement Solutions). Variations in the width, depth, location of trench and properties of soft barrier material are considered under various soil conditions. Results show that in all ground conditions, the notional rectangular open trench performs better than the other constructions. The width of an open trench has little influence on its performance, whereas increasing the width of a filled trench reduces the stiffness of the barrier, improving the performance of the trench. Likewise, fill materials with lower Young’s modulus give higher insertion losses.

Stiff Wave Barriers for the Mitigation of Railway Induced Vibrations

This paper studies the efficiency of stiff wave barriers for the mitigation of railway induced vibrations. Coupled finite element–boundary element models developed at KU Leuven and ISVR are employed; these models have been cross–validated within the EU FP7 project RIVAS (Railway Induced Vibration Abatement Solutions). A first mitigation measure consists of a block of stiffened soil embedded in a halfspace that acts as a wave impeding barrier. The existence of a critical frequency from which this mitigation measure starts to be effective, as well as a critical angle delimiting the area where the vibration levels are reduced, is demonstrated. Next, a sheet piling wall is considered, accounting for the orthotropic behaviour of this wall. Calculations show that the reduction of vibration levels is entirely due to the relatively high axial and bending stiffness in the vertical direction (along the profiles), while the bending stiffness for bending waves traveling in the longitudinal direction (perpendicular to the profiles) is too low to affect the transmission of vibrations. Field tests are being carried out in Spain and Sweden to confirm the conclusions of these numerical computations.

Vibration Transmission Across Junctions of Double Walls Using the Wave Approach and Statistical Energy Analysis

The sound insulation between adjacent rooms in buildings is not only determined by direct airborne sound transmission through the common wall, but also by structure–borne flanking transmission. To quantify the flanking transmission, the determination of the vibrational energy transmission at a junction between plates is crucial. In this paper, statistical models are developed for the prediction of flanking transmission across rigid junctions composed of single and double walls. The coupling loss factors are determined from wave theory for semi–infinite plates under the assumption of diffuse vibration fields. In–plane wave transmission must be accounted for in the case of wave transmission across double wall junctions. In general, the vibration transmission across double walls shows similar trends as the vibration transmission across single walls. An initial assessment of flanking transmission across a double wall junction can therefore be made by use of an equivalent single wall junction model. The developed models can also be used to investigate structure-borne flanking transmission across two adjacent single wall junctions. It is shown that indirect coupling between non–adjacent plates is important and should be accounted for in statistical models.

New acoustic solutions for cross laminated timber based buildings

Cross laminated timber is becoming a popular building material for the construction of multifamily dwellings, offices, hotels, etc. The acoustic challenges are important: in contrast to light weight timber frame constructions, it is far more sensitive to flanking transmission and its equally relatively light weight and orthotropic character in comparison with traditional heavy stone requires special solutions for the direct airborne and impact sound insulation. The paper presents a new, special, and patented building system that almost annihilates flanking transmission and will detail optimized low frequency sound insulation solutions for floors.

Efficient modeling of sound transmission through finite-sized thick and layered wall and floor systems

Built-up wall and floor systems such as roof panels, floors with floating screeds, etc., have found widespread application in building construction. Achieving sufficient sound insulation with these systems is challenging because of their relatively low weight and complex vibro-acoustic behavior. A fast and sufficiently accurate acoustic design tool is needed. The semi-analytical transfer matrix method is able to efficiently compute the response of a thick or multilayered structure in the frequency-wavenumber domain but has important limitations. First, the system is assumed to be of infinite extent. At lower frequencies however, neglecting the modal behavior of the wall can lead to large prediction errors. Second, integration over all possible incident plane waves is necessary to obtain the diffuse transmission loss, resulting in a high computation time. The transfer matrix approach is therefore extended in two ways. The modal behavior of rectangular walls and floors with simply supported boundary conditi...

Numerical study on the repeatability and reproducibility of laboratory building acoustic measurements

An important issue in building acoustics is the significant variability in laboratory test results that numerous round robin tests have indicated. The current wish to include the frequency bands 50-80 Hz in the procedures to determine single-number quantities has prompted new discussions. In this paper, wave based models are used to numerically investigate the fundamental repeatability and reproducibility. Regarding sound insulation measurements, both the pressure method (ISO 10140-2) and the intensity method (ISO 15186-1 and ISO 15186-3) are investigated in the frequency range 50-200 Hz. Flanking transmission measurements (ISO 10848) are also studied. The investigation includes the repeatability of the different measurement procedures, which depends on the influence of the source and receiver positions. The reproducibility in different test facilities is studied by looking at the influence of geometrical parameters like room and plate dimensions. Increasing the number of source or receiver positions has ...

The repeatability and reproducibility of laboratory building acoustic measurements: Numerical study

An important issue in building acoustics is the significant variability in laboratory test results that numerous round robin tests have indicated. The current wish to include the frequency bands 50-80 Hz in the procedures to determine single-number quantities has prompted new discussions. In this paper, wave based models are used to numerically investigate the fundamental repeatability and reproducibility. Regarding sound insulation measurements, both the pressure method (ISO 10140-2) and the intensity method (ISO 15186-1 and ISO 15186-3) are investigated in the frequency range 50-200 Hz. Flanking transmission measurements (ISO 10848) are also studied in a broad frequency range. The investigation includes the repeatability of the different measurement procedures, which depends on the influence of the source and receiver positions. The reproducibility in different test facilities is studied by looking at the influence of geometrical parameters like room and plate dimensions, aperture placement and aperture...