83 research outputs found
Acoustical Characterization and Modeling of Sustainable Posidonia Fibers
No full textThis article presents the results of an acoustic characterization of fibers obtained from Posidonia Balls (scientific name: Aegagropiles), produced by a marine plant (Posidonia oceanica) that is widespread in the Mediterranean Sea and can be found on beaches in large quantities, particularly following storm surges. The aim of this research is to evaluate the possible use of these fibers as eco-sustainable sound-absorbing materials and to define an acoustic model for the optimization of sound-absorbing panels made from these fibers. Experimental tests were conducted to measure airflow resistivity and sound absorption for different densities of loose fiber samples. From these experimental tests, the five physical parameters of the Johnson-Champoux-Allard model were calculated to obtain an analytical formulation of the acoustic behavior of the fibers depending on their density. To the author’s knowledge, this is the first time that an article has been published on acoustic data relating to the sound-absorbing performance of loose Posidonia oceanica fibers and that an analytical model has been presented that allows for the acoustical design of panels of different thicknesses and densities made with this material. An interesting aspect of this material is that the lignin fibers are ready for acoustic application due to the natural cleaning process of the waves and salt water. Furthermore, the methodology consists of a hybrid method between the experimental characterization of some parameters (i.e., different densities) and the numerical inversion of the acoustic data for other parameters. This is an effective solution that has rarely been adopted in other studies on sustainable materials
Acoustical optimisation of paints for porous material
No full textThis work deals with an experimental study for the optimisation of paints for application on sound absorbent porous materials. Several formulations of water paints have been sprayed on a melamine foam in different quantities and thickness: the effect of this layer has been tested in term of airflow resistance and normal absorption coefficient measurements. Results give evidence to an increment of sound absorption at low and medium frequencies, and a decrement of sound absorption at high frequencies (up to 2000 Hz), as a dependence of the formulation and the sprayed quantity. Relation between physical and acoustical aspect has been also investigated. Two types of paint present good acoustical and tasteful results and are recommended for practical applications with optimisation of sound absorption at low medium frequencies or high frequencies
A European inter-laboratory test of airflow resistivity measurements
No full textThis article presents and analyses the results of an Inter-Laboratory Test (ILT) of airflow resistivity measurements according to the ISO 9053 standard. The main result of the ILT is the determination of the repeatability and reproducibility standard deviation values typical of these measurements, for the first time since the ISO 9053 publication in 1991. Ten European laboratories took part in the ILT project; two melamine foam sheets of different thickness, taken from the same factory batch, were sent to each laboratory. The laboratories cut the test samples and carried out measurements in repeatability conditions, either on a single sample either on different samples, in order to take into account also the influence of the sample cutting and non-homogeneity of the foam. The data show that most of the laboratories have a good internal repeatability, particularly for single sample measurements. The overall reproducibility is not so good, mainly due to systematic deviations inherent in the current laboratory practice. Measurements conducted by some laboratories using different methods, in order to verify their effective equivalence, are also reported. Finally, remarks on the current measurement procedures and proposals of amendments to the ISO 9053 standard are presented
Caratterizzazione fisico-acustica delle fibre di Egagropili
No full textIn questo articolo vengono presentati i risultati di una indagine sperimentale condotta su fibre ricavate da Egagropili, molto diffusi sulle spiagge del Mediterraneo e derivati dai residui di Posidonia oceanica, una pianta marina che forma grandi praterie su fondali sabbiosi in prossimità delle coste. Scopo di questa ricerca è quello di valutare il potenziale utilizzo di queste fibre come materiale fonoassorbente ecosostenibile
Sustainable Materials of Marine Origin: Experimental Investigation on Sound-Absorbing Properties and Possible Applications
No full textThe sea represents 70% of the earth's surface and the possible use of sound-absorbing materials with this
origin is little investigated. The purpose of this article is to investigate the possible use of two materials of
marine origin whose presence in the sea and on the coasts creates considerable environmental and economic
problems: it is a marine plant (Posidonia Oceanica) very common in the Mediterranean and a seaweed float
(Pelagic Sargassum) very common in the Atlantic Ocean, especially in the Caribbean area.
For both materials, an experimental investigation was carried out aimed at modeling the acoustic propagation
in the two media with the Johnson-Champoux-Allard equivalent dissipative fluid model. The study was
conducted with variable apparent density in order to optimize the acoustic performance of the materials as a
function of density and thickness
A simple empirical model of polyester fibre materials for acoustical applications
No full textA new empirical model has been developed by the authors to predict the flow resistivity, acoustic impedance and sound absorption coeffcient of polyester fibre materials. The parameters
of the model have been adjusted to best fit the values of airflow resistivity and sound absorption coeffcient measured over a set of 38 samples. Calculated results are compared with normal incidence measurements carried out using two different techniques: the transfer-function method in an impedance tube (ISO 10534-2) and the free-field impulse response method (ISO 13472-1). Measurements performed on polyester fibre materials with different density and thickness values, and diameter ranging from 18 to 48 lm, are in good agreement with the predictions of the new model. It is concluded that the new model can predict the basic acoustic properties of common polyester fibre materials with any practical combination of thickness and density
Ottimizzazione geometrica di un metamateriale per assorbimento a banda larga
No full textDiversi strumenti di analisi sono stati utilizzati nell’ottimizzazione geometrica di un risonatore multiplo coiled-up, con l’obiettivo di massimizzare l’assorbimento acustico a banda larga, partendo da una frequenza di 100 Hz. Utilizzando sia un modello
analitico [1], che un modello FEM 3D, è possibile prevedere il comportamento acustico del sistema indagato, poi confermato tramite misure sperimentali eseguite nel tubo ad one stazionarie, sia con risonatori singoli che in parallelo
Definition of analytical models of non-acoustical parameters for randomly-assembled symmetric and asymmetric radii distribution in parallel fiber structures
No full textFibrous materials for acoustical applications have been extensively studied over the past years. A consid-erable number of experimental tests have been carried out as a function of fiber geometrical character-istics (for example, overall density, fiber diameter and density, open porosity, etc.) in order to determineanalytical formulations for the prediction of physical parameters, primarily the airflow resistivity. Due tothe increase of computational capabilities micro-to-macro structure approach is the subject of currentresearch in order to determine transport and acoustic properties starting from certain arrangements offiber in space. Almost all research assumes fiber having the same radius with regular or random positionwithin a representative volume of material. To this end, the aim of the present paper is to provide a revi-sion of existing analytical formulations of non-acoustical parameters for two-dimensional structures hav-ing random positioning in space and symmetric and asymmetric distribution of radii. Proposedformulations will be compared with existing models and finite element simulation
Evaluation of noise from air conditioning systems - A draft proposal
No full textThis paper discusses the practical evaluation of noise levels generated by air-conditioning and ventilating systems inside buildings. The results of this work are incorporated in a Draft Italian Standard. The criterion for evaluation is based on the difference between the total sound pressure level in the room when the noise source is working, and the background noise level. The allowable difference must decrease with the value of the background noise level. The measured sound pressure level is corrected according to the type of noise and to the acoustical characteristics of the room; impulsive noises should not be present in the system. At present this Draft Proposal, which has been developed by a Working Group of the Italian Standard Institution (UNI), is under discussion. © 1980, All rights reserved
Geometric optimization of a multiple coiled-up resonators for a broad band acoustic absorption
No full textIn order to investigate new solutions to obtain high absorption at low frequency, the concept of quarter-wave acoustic resonators coiled-up metamaterial has been applied to limit the thickness thanks to the possibility of ”rolling” their channels. This study is based on a metamaterial made of n quarter-wave coiled-up resonators in parallel: once the minimum frequency of absorption (e.g. 100 Hz) and the second harmonic (300 Hz) have been defined, this frequency range is divided into n different resonators so that the envelope of the high-harmonics is such as to obtain a high broadband absorption. Starting from the study of a single resonator, an analytical model was defined to calculate the normal incidence absorption coefficient and then it was extended to systems with n-resonators in parallel using the parallel equivalent circuit theory. This models were validated with impedance tube measurements and then used for a geometric optimization: defined a metamaterial with 16 resonators in parallel (minimum frequency of 100 Hz), the geometry was varied to maximize the absorption coefficient. The optimized geometry was than simulated using a 3D FEM model to consider the real development of the channels. The results of both analytical and FEM models will be discussed
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