J. Alba

Noise effects of reducing traffic flow through a Spanish city

Abstract Towards the end of 1999, the building of one of the main communication routes in Spain was finished, the A-3 motorway, which connects Madrid and Valencia. So far, this road was running through the town Motilla de Palancar, province of Cuenca. The opening of the last section of the motorway on 3 December 1999, re-routes all the traffic passing through the town. This study makes a comparative of the noise levels before and after the opening of the motorway that goes through Motilla de Palancar.

Improvement of the prediction of transmission loss of double partitions with cavity absorption by minimization techniques

In this paper, a method based on the minimization of a quadratic error function is used as a tool to improve the predictions of noise transmission loss, and it is applied to the case of a double partition filled with an absorbent material. When experimental results are available, the method can be used to determine the value of the parameters of the materials composing the structure.

New absorbent material acoustic based on kenaf’s fibre

This project has been funded by the Ministry of Education and Science. DG Research (BIA2007-C02-01 y BIA2007-C02-02).

Modelling of impervious layers from measurements of the sound reduction index

Abstract In this work, developed algorithms are described to characterise impervious layers. It also includes measurements for their sound reduction indexes. These algorithms are based on the minimisation of the quadratic error and allow determining the parameters that characterise the impervious layer. To improve characterization, there is a revision of the classic model of impervious layer in matters of the bending stiffness, and different corrections on the total loss factor of the layer are introduced. This permits the to adjust with greater precision the prediction of the critical frequency. The use of this method is defensible considering that there are many ways of measuring the insulation of impervious layers and, through this particular method, they can be used to obtain the values for the mechanical characteristics of the layer, with the appropriate laboratory set-up conditions. Then, those values can be used in simulation algorithms for multiple layer partitions, obtaining predictions, which contain, implicitly, the set-up condition of each impervious layer.

Effect of Sodium Hydroxide Treatments on the Tensile Strength and the Interphase Quality of Hemp Core Fiber-Reinforced Polypropylene Composites

The formulation of greener composite materials by substituting glass fibers with natural fibers is a current field of research. If such natural fiber reinforcements come from industrial side streams, as hemp core fibers (HCFs) come from the extraction of hemp strands for the textile industry, an additional advantage can be identified. Nonetheless, such by-product fibers show some drawbacks, such as high lignin contents, which can make it difficult to obtain a good interphase between the fibers and the matrix and to obtain a good fiber individualization. A digestion treatment at different NaOH contents is proposed to eliminate soluble lignin and extractives from the surface of the fibers. At the same time, the use of a coupling agent solves incompatibilities between the fibers and the matrix. The composites were tensile tested and the impact of the proposed treatments is evaluated and discussed. Later, the Kelly-Tyson modified equation and a modified rule of mixtures—the micro-mechanic models—is used to study the impact of such treatments on the quality of the interphase between the polymer and the reinforcement. Both treatments showed a high impact on the tensile strength and the quality of the interphase, obtaining competitive composite materials reinforced with HCFs derived from a by-product.

Nuevos materiales absorbentes acústicos basados en fibra de kenaf

This project has been funded by the Ministry of Education and Science. DG Research (BIA2007-C02-01 y BIA2007-C02-02).

The Uncertainty in Absorption Coefficients Measured in Reverberant Chambers: A Case Study

The aim of this work is to study the uncertainties that are present in measurements of the sound absorption coefficients of acoustical materials by means of the determination of the reverberation time (according to ISO 354 [1]). A detailed study of the uncertainty in the measurements of sound absorption coefficients has been performed. As an additional feature we present a representation of the absorption coefficient and its relative uncertainty.

Characterization of Sheep Wool as a Sustainable Material for Acoustic Applications

In recent years, natural materials are becoming a valid alternative to traditional sound absorbers due to reduced production costs and environmental protection. This paper reports the acoustical characterization of sheep wool. Measurements on normal incidence and diffuse-incidence sound absorption coefficients of different samples are reported. The airflow resistance has also been measured. The results prove that sheep wool has a comparable sound absorption performance to that of mineral wool or recycled polyurethane foam. An empirical model is used to calculate the sound absorption of sheep wool samples. A reasonable agreement on the acoustic absorption of all sheep wool samples is obtained.

Vibration Reduction Index of a T-Junction With a Flexible Interlayer

This paper describes the procedure followed to evaluate the vibration reduction index for T-junctions with inserted flexible elements and proposes new equations to complement the standard EN 12354-1:2000. The experiment described in this work is based on a 1:3 scale model of a T-junction with a flexible interlayer. It was used to obtain a significant reduction in the cost of the configurations under study. We chose to carry out vibration measurements by near-field acoustic holography (NAH) in order to avoid the risk of accelerometer interference. Flanking transmission was determined for different elastic layers with the objective of quantifying the effect of the flexible interlayer and to compare the results obtained with predictive formulas. The results enabled us to propose new equations to complement EN 12354-1:2000 for the reliable prediction of the apparent sound reduction index. The uncertainty associated with the different average velocity levels is determined according to the Guide for the Expression of Uncertainty of Measurement (GUM).

Road traffic noise barriers based on recycled materials.

One of the main corrective measures taken to reduce environmental noise produced by roads is using sound barriers. However, the construction of miles of noise barriers implies a high cost. One solution to reduce the costs is using recycled materials in the noise barriers, for example, plastic wastes, which has great environmental benefits. According to EN 1793‐1 to 3:1998, the main acoustic characteristics of noise barriers are the sound absorption and the airborne sound insulation. On the other hand, the technical document CEN/TS 1793‐5:2003 gives guidelines for determining the in situ sound reflection index, which is an important parameter because the reflections from the barrier may increase the background noise in the surrounding area. This method has not been validated for noise barriers having a relatively low airborne sound insulation. In this study, sound reflection index using the impulse method is obtained in the laboratory for a wide frequency range. Environmental designs of road traffic noise ...