1,721,002 research outputs found
Misura in situ del coefficiente di assorbimento acustico mediante segnale periodico pseudo-random binario MLS
No full textA 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
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 coefficient of polyester fibre materials. The parameters of the model have been adjusted to best fit the values of airflow resistivity and sound absorption coefficient 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 mu m, 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(2). (c) 2005 Elsevier Ltd. All rights reserved
REALIZZAZIONE E CALIBRAZIONE DI UNA APPARECCHIATURA PER LA MISURAZIONE DELLA RESISTENZA AL FLUSSO D’ARIA CON IL METODO A FLUSSO ALTERNATO A NORMA UNI EN 29053
No full textIn questo articolo è descritta la realizzazione di una apparecchiatura per la misurazione della resistenza al flusso d’aria dei materiali porosi e fibrosi di utilizzo acustico. E’ stato adottato il metodo a flusso alternato, previsto dalla norma UNI EN 29053 ma ancora poco utilizzato dai laboratori che eseguono misurazioni della resistenza al flusso d’aria. Si descrivono le procedure adottate per la calibrazione del sistema, le prove di ripetibilità eseguite per caratterizzare l’incertezza di misura della apparecchiatura ed infine una serie di misurazioni su diversi materiali fonoassorbenti presenti in commercio. Si rileva che nella versione italiana della norma è presente un’imprecisione di traduzione dal testo inglese originale che può indurre in errore nell’applicazione della procedura di calibrazione prevista per il metodo a flusso alternato
Mutual radiation into cavities: research oriented to the study of the thermal environment inside a motorcar
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