Sound insulation prediction models in European and International standards use the vibration reduction index to calculate flanking transmission across junctions of walls and floors. These standards contain empirical relationships between the ratio of mass per unit areas for the walls/floors that form the junction and a frequency-independent vibration reduction index. Calculations using wave theory show that there is a stronger relationship between the ratio of characteristic moment impedances and the transmission loss from which the vibration reduction index can subsequently be calculated. In addition, the assumption of frequency-independent vibration reduction indices has been shown to be incorrect due to in-plane wave generation at the junction. Therefore numerical experiments with FEM, SFEM and wave theory have been used to develop new regression curves between these variables for the low-, mid- and high-frequency ranges. The junctions considered were L-, T- and X-junctions formed from heavyweight walls and floors. These new relationships have been implemented in the prediction models and they tend to improve the agreement between the measured and predicted airborne and impact sound insulation.Peer ReviewedPostprint (author's final draft
The vibration reduction index K ij expresses the attenuation of the vibrational power flow through a junction. This quantity is important because it determines the contribution of the flanking transmission to the global sound transmission between rooms. It is used in acoustic building prediction models like that proposed in the standard EN 12354. Currently a draft exists to measure the K ij in laboratory. This draft, the prEN 10848, was prepared by the Technical Committee CEN/TC 126 and has been submitted for parallel enquiry. There are also prediction formulae available for the K ij, which are included in Annex E of the standard EN 12354-1 (2000). This article presents the K ij measured in a laboratory according to the draft prEN 10848 and documents an investigation in order to validate them for rigid junctions and junctions with a flexible interlayer. The observations focus on the comprehension and the quantification of the influence of some parameters like the modal overlap factor, the number of modes and the workmanship on the accuracy of the results. Furthermore, an extensive discussion tackles the problem of the determination of the parameter f l used in the prediction formulae for junctions with flexible interlayers and the effect of the applied load.
The more severe acoustic requirements imposed by the new Belgian standard for dwellings are a real challenge for the building professionals (architects, contractors, building elements manufacturers and suppliers, etc) and more particularly for the market of lightweight materials. An important brick producer in partnership with the BBRI has succeeded to propose efficient acoustic solutions for these kinds of materials by treating in particular the flanking transmission. Indeed, to obtain high sound insulations, the structural transmission paths of noise through the flanking walls cannot be neglected any more. By the application of resilient rubber interlayers at the junctions, these transmission paths are nearly eliminated. A large number of measurements was carried out in order to study in detail the effect of these flexible joints on the sound transmission. These measurements were made in a specially designed laboratory where vibration reduction indexes can be measured for all types of connections and for different loads. We present, in this paper, the measurement survey and the analysis of the results.
The prediction of the reduction of impact sound pressure level ΔL according to annex C of the standard ISO 12354-2 gives an acceptable estimation of the floating floor's performance for thin resilient layers. However, the performance is often largely overestimated for thick resilient
layers or for resilient layers combined with thermal layers. One reason for this is that the simplified model doesn't account for the thickness resonances in the underlays which can greatly affect ΔL. This is confirmed by comparing finite element and transfer matrix method simulations
with experimental results. This paper establishes the mechanisms leading to the development of these resonance waves and provides some guidelines to estimate their negative effects on the ΔL.
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