Stefan Schoenwald

Predicting sound radiation efficiency and sound transmission loss of orthotropic cross-laminated timber panels

In the last decades, new materials and new technologies which satisfy sustainability and energy efficiency demands have been developed for the building construction market. Lightweight structures are becoming increasingly popular, but it has been shown that they cannot provide satisfactory sound insulation to meet the regulation requirements. Therefore a proper acoustic treatment needs to be specifically designed, considering both airborne and structure-borne sound sources. Cross-laminated timber (CLT) elements, for example, have had great success in the last twenty years, both in Europe and North America. CLT plates, due to their peculiar sub-structure, very often exhibit an orthotropic behavior: they have different stiffness properties along their two principle directions. In this paper two prediction models to evaluate the radiation efficiency, due to mechanical excitation, and the sound transmission loss of an orthotropic CLT plate are presented. The main purpose of these simplified models is to provi...

Numerical analysis on applicability of measurement method according to ISO 16283 in small rooms at low frequencies

The robustness of the new measurement method for sound pressure level in small rooms with less than 25 m3 room volume at low frequencies from 50 Hz to 80 Hz that was recently introduced in the ISO 16283 series on sound insulation measurements in buildings was investigated in an experimental study. This restricted study revealed some potential problems with the method that were already presented, but unfortunately, a further experimental investigation was not possible because of the time- and labor-intensiveness of the conducted experiments. Now the sound level distribution in the room was predicted with a simple analytical modal model and an excellent agreement with the available experimental results was found. With the prediction model, it was possible to refine the results of the experimental study, to extend it to other room geometries, and to revisit and to analyze the identified potential problems on a much more detailed and broader database. In the conference paper, the experimental study and its ou...

Low frequency bandgaps in lightweight metamaterial panels using rotation inertia multiplication

Of all possible features of structural metamaterials, the formation of bandgaps is the most studied one due to its direct application for sound and vibration isolation. While achieving low frequency values for the position of the first bandgap is, in general terms, not an unsurmountable challenge, the combination of material properties such as high stiffness, low density, and reduced size of the unit cell, with low (in absolute terms) frequency bandgaps, may well require some careful consideration. In previous work, we designed panels with a 3D network of resonators, clearly improving the vibration isolation compared to a homogeneous panel with the same weight. Recently, we have devised a novel implementation of inertia amplification, based on coupling the energy of longitudinal waves into the rotational oscillation of inertia elements within the unit cell. In this contribution, we present examples of phononic crystals based on this approach, and we discuss the interaction of acoustic waves with the discu...

Predicting sound radiation and sound transmission in orthotropic cross-laminated timber panels

In the last decades, new materials and new technologies which satisfy sustainability and energy efficiency demands have been developed for the building construction market. Lightweight structures are becoming increasingly popular, but it has been proved that they cannot provide satisfactory sound insulation. Therefore a proper acoustic treatment needs to be specifically designed, considering both airborne and structure-borne sound sources. Cross-laminated timber (CLT) elements, for example, have had great success in the last twenty years, both in Europe and North America. CLT plates, due to their peculiar sub-structure, exhibit an orthotropic behavior; they have different stiffness properties along their two principle directions. This paper investigates prediction models for orthotropic plates designed to evaluate sound radiation due to mechanical excitation, and sound transmission due to acoustic excitation. Particular attention is paid to the influence on sound radiation of non-resonant vibration, or ne...

Advanced methods to determine sound power radiated from planar structures

In building acoustics, the most fundamental aim is to determine the sound power radiated by building elements. In this paper, two methods that are more sophisticated than the conventional measurement of sound pressure in a receiving room are presented and discussed. Both methods, the Discrete Calculation Method and the Integral Transform Method, require only the surface velocity measured in a grid on the radiating surface as input data. Thus the sound power is univocally associated to the considered element. The first assumes a series of radiating piston sources on the surface that move with same velocity and phase relationship as the structure. The second uses spatial Fourier Transformations to determine the radiated sound power in the wavenumber domain, analogous to Nearfield Acoustic Holography. The Integral Transform Method additionally obtains the angle dependent flexural wavenumbers of the structure, which is essential for the analysis of the element dynamics, and as input data for the prediction of...

Prediction of the Sound Transmission Loss of Multi‐layered Small Sized Elements

In this paper an improved method for the prediction of the sound transmission loss of multilayered finite structures, like glazing will be presented. The sound transmission loss of an infinite structure is predicted with a common transfer matrix as a function of the angle of the incident sound wave. Then Villiots spatial windowing method is applied to take into account the finiteness of the element. Usually an ideal diffuse distribution of the incident sound power is assumed and the prediction results are integrated over all angles of incidence. The obtained prediction results tend to underestimate sound transmission loss due to the dominance of the small values for gracing incidence. Often simple ad-hoc corrections are used for improvement, like Beraneks field incidence, that fail for multilayered structures. Kang suggests that the incident sound power on a surface of a room generally is Gaussian distributed on the angle of incidence and introduces a weighting function for the integration of the prediction results over the angles of incidence. New in this paper is that spatial windowing as well as a Gaussian distributed sound power is considered for the prediction of the transmission loss. The results of the prediction are validated by experiment.