Delphine Bard

Characterisation of an Elastomer for Noise and Vibration Insulation in Lightweight Timber Buildings

Regulations regarding impact and airborne sound insulation for lightweight timber constructions have become increasingly stringent due in particular to complaints by inhabitants. Accordingly, some building techniques frequently use elastomers at junctions so as to reduce low frequency noise. Development of accurate predictive tools (involving exact material properties) by using numerical methods such as the finite element (FE) method is needed in tackling flanking transmission problems during the design phase of buildings. The present research concerns the characterisation of an elastomer, presenting an accurate method for extracting its material properties from the manufacturers data sheet (properties there being often linked to such structural effects as shape factors and boundary conditions of samples and tests). The properties were extracted by comparing results obtained by analytical calculations, FE simulations, and mechanical testing, separating geometry and material dependence and ultimately serving as input to commercial FE software for setting up the aforementioned prediction tools.

A Finite Element Solution of Structure-Borne Sound Attenuation for a Lightweight Timber Floor

Structure-borne sound attenuation of lightweight timber floor structures has been investigated by high-resolution numerical calculation methods. Two models have been studied both experimentally and numerically. The first considers a continuous chipboard plate and a supporting beam. The second considers two plates that are fastened on one beam. Damping effects, which arise from the two different discontinuities, are included. The real-valued modulus of elasticity is replaced with a complex value. In the calculations, the orthotropic material characteristics of the building material have also been taken into account. The results from the calculations and laboratory measurement confirm that the attenuation rate is highly dependent on the excitation location, if all the other parameters remain the same.

Reflection and transmission properties of a wall-floor building element: comparison between finite element model and experimental data

Lightweight structures made of timber material have a number of advantages; they may become cost effective in the future and they demand relatively short production duration. However, one of the main drawbacks is related to the sound transmission, as it is becoming an increasing nuisance. The differences in weight, stiffness, density and repartition compared to traditional materials have repercussions on how the sound propagates through the structures and problems of sound insulation in the low frequency range through the junctions may arise. This paper provides an investigation of the reflection and transmission properties of a wall-floor real-sized timber element, which resembles a section of a lightweight building. The latter investigation was carried out by comparing finite element simulations with experimental data. The fairly good match between the experimental results and the simulations point out at the applicability of the finite element analysis as a prediction tool during the design phase before buildings are actually put up in order to prevent future problems. (Less)

Review of acoustic comfort evaluation in dwellings—part I : Associations of acoustic field data to subjective responses from building surveys

Acoustic comfort is a concept hardly described in the literature. But it has been used in engineering typically to refer to low noise or annoyance in order to invoke no discomfort. Current standardized methods for airborne and impact sound reduction are deployed to assess acoustic comfort in dwellings. However, the measured sound pressure levels do not represent comfort. The latter should include further the human perception of the acoustic environment. Therefore, this article reviews studies that approached acoustic comfort through the association of objective and subjective field data, combining in situ acoustic measurements and survey responses from residents. We evaluated the studies using Bradford Hill’s criteria. Most researches focus on self-reported noise annoyance while some others on satisfaction responses. Many studies were found incomprehensibly described: often vital data of statistical evaluation or study design are lacking. The results indicate that noise is a significant issue in living environments, especially certain impact noise types. The use of extended low-frequency spectra down to 50 Hz was suggested for impact measurements in order to predict better self-reported noise response. Greater problems with low-frequency transmission are displayed in lightweight structures which perform inefficiently compared to heavyweight components. Harmonization of presented results and study design details should be taken into account for future articles.

Methods of field measurements of facade sound insulation

The purpose of this article is to describe generally usable methods to measure the sound insulation of a facade in cases where a setup according to standards such as ISO 140/5 or ISO 16283/3 cannot be achieved. The methods discussed use a loudspeaker as the source of a test signal since background noise on the interior receiving side in many cases prevents the use of traffic as a noise source. The measurements presented in this article have been made using two loudspeaker positions at different angles. Three different ways of placing the microphone are considered. The microphone can be placed in fixed points directly on the facade, in fixed points at the same distance in front of the facade, or swept in front of the facade. The data presented are all taken from actual field measurements. The results are shown as a comparison between the levels acquired and the uncertainty associated with the different methods

Acoustics in Dalby church in Middle Ages and today

The subject for the research is Dalby church in Sweden which supposes to be the oldest stone church in Scandinavia. There are holes in the ceiling of Dalby church. Behind these holes are ceramic pots. In Swedish Musicology studies, the relationship between acoustic pots and acoustic resonators is poorly documented. Similarly, there is limited information on the difference in reverberation time in churches from late Middle Ages compared to present time. In the late medieval churches, the reverberation time must have been different than it is in churches today. There were more visitors and they had clothes made of heavy fabrics which would have affected the reverberation time. Currently, the reverberation time measurements are made without visitors which affect the reverberation time itself. This investigation is based on theoretical studies combined with practical reverberation measurements in Dalby church and simulations in ODEON in a 3D-model of the church. Following questions will be answered: What was ...

Predicting structure-borne sound from railway traffic

Since noise exposure can disturb the well-being, acoustical comfort in the built environment is of great importance when constructing new dwellings. Population growth causes densification of cities, which together with space limitation issues, lead to buildings being constructed closer to existing vibration sources such as motorways and railways, and vice versa. Likewise, architectural trends, environmental benefits and cost result in increased use of lighter materials such as wood and hollow-core concrete slabs. Lightweight structures make the achievement of acoustical comfort in dwellings an increasing challenge. A major issue when designing buildings regarded as acoustically pleasant, especially in the low-frequency range, is the lack of reliable prediction models to be used during the design stage of the building. Predictions of structure-borne noise are nowadays mostly made based on measurements performed on existing buildings and engineers’ experience. Hence, it is of interest to develop tools that ...

Algebraic reflections in geometric acoustics

Stochastic Ray tracing is one of the most widely used geometric acoustic algorithms, and excels primarily for modelling the late room response in high frequencies. A significant bottleneck of the algorithm is the high computational cost of testing rays for intersection with geometry, and the high amount of rays required for convergence. Several methods exist to reduce this cost by means of reducing geometric complexity. This paper instead proposes using bidirectional reflectance distribution functions (BRDF) to algebraically compute transmission paths between receivers and sources, thereby decreasing the amount of total rays needed. For each ray-geometry intersection, transmissions paths are calculated recursively, and several transmission paths can thereby be taken into account for each intersection test, while allowing for point-like transmitters and receivers. The method has been implemented on a graphics processor, and calculated room acoustic parameters are comparable to commercial geometric acoustic...

Numerical Prediction Tools for Low-Frequency Sound Insulation in Lightweight Buildings

Lightweight wooden-framed constructions have steadily increased their market share in Sweden during the last two decades. Achieving acoustic and vibration comfort in wooden-based buildings is, however, still a challenging task. Wood is high in both strength and stiffness in relation to its weight, but its variability has repercussions on how sound propagates, this triggering sound insulation problems. Even if buildings comply with present-to-day regulations, complaints amid residents often arise due to low frequency noise, as it is outside the scope of the standards (where no analyses are performed below 50 Hz). In this investigation, laboratory acoustic sound insulation measurements carried out on a facade element according to the current standards, are intended to be reproduced and calibrated by means of the finite element method. In doing so, the first steps of a numerical predictive tool mimicking the real specimen, from 0 to 100 Hz, are presented. This will enable further research about phenomena occurring in the far low end of the frequency range, which is believed to be the cause of most nuisances reported by residents. Reliable predictive tools for addressing acoustic issues during the design phase avoid additional costs of building test prototypes and ensure a better acoustic performance. (Less)

The furniture industry needs a new evaluation standard for evaluation of sound absorption

Since decades the standard ISO 11654 are prevailing for evaluating sound absorption of products. The standard is developed and fully adapted to ceiling manufacturer, in particular mineral wool ceiling manufacturer. However, the standard is used independently of which interior product it is applied to, casing a lot of “misuse” and confusion amongst many manufacturer. In particular, when it comes to evaluation of various types of office screens, the ISO 11654 becomes a problem. There is no need, and probably not even possible, to calculate absorption factor for an office screen correctly. Therefore, Sweden decided to develop a new standard, SS 25269—“Acoustics—Evaluation of sound absorption of single objects.” Hence office screens should be treated as single objects to cover a wide range of variety. The standard specifies an evaluation method of the sound absorption using only sound absorption area for each object tested. It will simplify the evaluation and minimize risk for errors since there is no need to...