Catherine Guigou-Carter

The role of studs in the sound transmission of double walls

Steel studs are used in double walls to provide structural stability. This creates a vibration transmission path between leaves that can often be more critical than the airborne path through the cavity. Some of the existing models for sound transmission consider the studs as elastic springs. The spring stiff ness may be taken as the cross-section elastic stiff ness of the stud, but this leads to an underestimation of the vibration transmission. A procedure to obtain more accurate parameters to be used in vibration and sound insulation models is presented. The results show that they must be obtained from dynamic models and/or experiments.

Prediction Method Adapted to Wood Frame Lightweight Constructions

When wood frame lightweight constructions are considered, both the standardized methods, EN 12354-1 and -2, for predicting building performances from the performances of building elements and the related standardized laboratory measurement methods for characterizing building elements and their junctions have to be reconsidered. In this paper, a prediction method based on Statistical Energy Analysis and adapted to lightweight constructions, is presented. It was applied to a two-storey four-room building where an analysis of the different transmission paths was required in order to understand and improve the acoustic performances of the building. Comparisons between results, expressed in terms of airborne and impact sound insulation between rooms, either directly measured or calculated using the prediction method, are given in the three cases of vertical, horizontal and diagonal transmission. A satisfactory agreement between calculated and measured results is obtained.

The prediction of flanking sound transmission below the critical frequency

Although reliable methods exist to predict the apparent sound reduction index of heavy, homogeneous isotopic building constructions, these methods are not appropriate for use with lightweight building constructions which typically have critical frequencies in or above the frequency range of interest. Three main methods have been proposed for extending the prediction of flanking sound transmission to frequencies below the critical frequency. The first method is the direct prediction which draws on a database of measurements of the flanking transmission of individual flanking paths. The second method would be a modification of the method in existing standards. This method requires the calculation of the resonant sound transmission factors. However, most of the approaches proposed to calculate the resonant sound transmission factor work only for the case of single leaf homogeneous isotropic building elements and therefore are not readily applicable to complex building elements. The third method is the measurement or prediction of the resonant radiation efficiency and the airborne diffuse field excited radiation efficiency which includes both the resonant and the non-resonant radiation efficiencies. The third method can currently deal with complex building elements if the radiation efficiencies can be measured or predicted. This paper examines these prediction methods.

Measurement Methods Adapted to Wood Frame Lightweight Constructions

When building elements of wood-frame lightweight constructions are considered, laboratory acoustic measurement methods have to be rethought. Indeed, because lightweight elements are often highly damped, the vibrational fields are no longer reverberant and existing standards often lose relevance, particularly in the case of mechanical excitation (such as in impact noise measurements or in vibration reduction index measurements of junctions). In this paper, standardized methods are identified or new methods are proposed for characterizing lightweight elements in order to obtain input data for prediction models such as that adapted from the standards EN 12354-1 and −2 and described in a companion paper. Moreover, it is shown that a new parameter (the radiation efficiency) is required when predicting the performance of lightweight buildings. Measurement results are shown for both wall and floor elements and the results are discussed, particularly in comparison with heavy building elements.

Measurement of the Sound Reduction Index as a Function of the Incidence Angle by Two Different Methods

Generally sound reduction index R is measured for an incident diffuse field, and does not take into account the angular dependency. However, the variation of reduction index with direction of incoming wave can be significant, and it may be necessary to consider the angular influence in acoustical transmission problems, especially when considering directional noise sources. This paper presents two experimental methods, developed to measure the sound reduction index as a function of the incidence angle. Two set-ups, implemented in standard acoustical transmission laboratories, have been tested. In the first system, the vibrating wall is excited by a sound source which simulates a plane wave, with a given incidence angle. This incident field is generated by an acoustical horn. The reduction index R(θ) is obtained sequentially, for different angular positions of the source, from both the measurement of the outside wall pressure level and the transmitted pressure level. In the second system, the studied structure is excited by a diffuse field, and a wave by wave decomposition of the radiated intensity yields the reduction index as a function of the angle of incidence. The decomposition of the radiated intensity is based on the use of an acoustical holography technique, NAH-Phonoscopy. The mathematical formulation of the two methods is detailed. Experimental results are presented and compared to theoretical data. Then, the advantages and limits of each system are discussed.

An empirical model for the equivalent translational compliance of steel studs.

The effect of the resilience of the steel studs on the sound insulation of steel stud cavity walls can be modeled as an equivalent translational compliance in simple models for predicting the sound insulation of walls. Recent numerical calculations have shown that this equivalent translational compliance varies with frequency. This paper determines the values of the equivalent translational compliance of steel studs which make a simple sound insulation theory agree best with experimental sound insulation data for 126 steel stud cavity walls with gypsum plaster board on each side of the steel studs and sound absorbing material in the wall cavity. These values are approximately constant as a function of frequency up to 400 Hz. Above 400 Hz they decrease approximately as a non-integer power of the frequency. The equivalent translational compliance also depends on the mass per unit surface area of the cladding on each side of the steel studs and on the width of the steel studs. Above 400 Hz, this compliance also depends on the stud spacing. The best fit approximation is used with a simple sound insulation prediction model to predict the sound insulation of steel stud cavity walls whose sound insulation has been determined experimentally.

Numerical Method for Predicting the Sound Reduction Index of a Double Panel Including an Active Control System and Porous Material

In this paper, a numerical method for predicting the sound reduction index of a double wall including an active control system and a porous layer inside the double wall cavity is presented. The double wall is placed in a laboratory situation between an emission and a reception room. Active control sources and error microphones are distributed in two vertical planes located inside the double wall cavity. The secondary sources role is to improve the sound reduction index at low frequencies by reducing the acoustical pressure at microphone positions created by the primary source placed inside the emission room. The simulation principle is based on the decoupled Green method where the radiated pressure inside the reception room is deduced from the double wall velocity and from the reception room Greens functions. The double wall and the active control system are modelled by finite element method using Nastran software. The two rooms Greens functions are analytically modelled using a modal method. The model allows investigating effects of various parameters on active control efficiency, such as the effect of evanescent modes inside the double wall cavity, the double wall cavity thickness, the number of control channels as well as the effect of a porous layer inserted inside the double wall cavity placed between secondary sources plane and error microphones plane.

Prediction method for the acoustic performance of permanent form systems

Permanent form systems considered in this paper combine a layer of porous or fibrous material onto which a concrete layer is poured. Such systems allow the fulfillment of French thermal regulations. However, their acoustic performance is quite limited. Indeed, the acoustic performance of the concrete layer is usually reduced by the presence of the porous or fibrous layer. The modeling of such multi‐layered structures submitted to acoustic excitation is discussed in this work. The behavior of such a system is investigated by using a wave approach based prediction tool. The porous layer is modeled following Biots theory. The effect of the metallic anchors that connect the fiber and the concrete layers is also investigated. The acoustic performance of such systems is studied both experimentally and analytically. A parametric study is performed to identify the most determinant parameters. The model is thus used to obtain insight into the behavior of such systems in order to develop solutions that result in improved acoustic performance.

Prediction of vibration reduction index for junctions made of cross laminated timber elements

The new revision of standard EN 12354-1 will provide some prediction formulas for estimating the vibration reduction index (Kij) of junctions made of cross laminated timber (CLT) elements. These are based on laboratory and in situ measurements. At the same time, new Kij prediction formulas for heavyweight junctions have also been added to this revised standard, in order to include large amount of data generated by means of parametric numerical analysis. The goal of this research is to study if the same philosophy based on numerical models used for the heavyweight junctions can be extended to CLT elements junctions. This step is not direct because the modeling of CLT structures implies a list of non-trivial aspects to take into account: (1) the details of the junction construction (i.e., direction and type of screws, presence of steel angles and plates); (2) the orthotropy on the mechanical properties of CLT panels; and (3) the different range of material properties and how damping must be considered in th...

Catalogue of vibration reduction index formulas for heavy junctions based on numerical simulations

© (2017) S. Hirzel Verlag/European Acoustics Association. The definitive publisher-authenticated version is available online at http://www.ingentaconnect.com/contentone/dav/aaua/2017/00000103/00000004/art00011 and http//dx.doi.org/10.3813/AAA.919091. Readers must contact the publisher for reprint or permission to use the material in any form.