Acoustic properties of agroforestry waste orange pruning fibers reinforced polypropylene composites as an alternative to laminated gypsum boards

The present paper investigates the acoustic properties of natural fiber reinforced composites. Fibers from orange tree pruning were obtained and subject to different treatments in order to obtain mechanical, thermomechanical and chemi-thermomechanical pulps. These pulps were used as reinforcement for a polypropylene matrix. The obtained composite materials were submitted to acoustical tests in an impedance tubes device. The transmission losses obtained against the fiber content were obtained and discussed. Latter it was researched the influence of the fiber treatments on the soundproof characteristics. A numerical method was used to preview the acoustic insulation of the materials against the sound frequency. Finally the results were compared with that of the most usual lightweight soundproof solutions. (C) 2014 Elsevier Ltd. All rights reserved.Reixach, R.; Rey Tormos, RMD.; Alba Fernández, J.; Arbat, G.; Espinach, FX.; Mutjé, P. (2015). Acoustic properties of agroforestry waste orange pruning fibers reinforced polypropylene composites as an alternative to laminated gypsum boards. Construction and Building Materials. 77:124-129. doi:10.1016/j.conbuildmat.2014.12.041S1241297

“Studio teorico-sperimentale delle proprietà acustiche di pannelli fonoassorbenti trasparenti microforati

Nella correzione acustica degli ambienti confinati si può verificare l'esigenza di co-niugare buone prestazioni di fonoassorbimento con altre proprietà di carattere estetico o funzionale, quali trasparenza alla luce, durabilità nel tempo, resistenza strutturale. Una possibile soluzione si può ottenere con tecniche di microperforazione di lastre di materiale plastico trasparente, evitando quindi il ricorso a materiali porosi. Dal punto di vista acustico, i pannelli microforati si comportano come array di risonatori, caratte-rizzati, in virtù del piccolo diametro dei fori, da buone prestazioni anche in assenza di materiali fonoassorbenti nell’intercapedine: ciò è dovuto alle elevate dissipazioni visco-se e termiche che si realizzano nello strato limite all’interno dei fori. Le prestazioni fonoassorbenti dei pannelli microforati sono note, sia a livello teorico che sperimentale, da vari decenni [1]. Applicazioni integrate di pannelli trasparenti mi-croforati sono state proposte più di recente, sia in ambiente confinato [2], sia in barriere antirumore per infrastrutture di trasporto [3]. Oggi sono commercialmente disponibili rivestimenti di pareti, in alternativa ai tradizionali materiali porosi, realizzati con pan-nelli e membrane microforati. Tali soluzioni, in virtù degli spessori richiesti per ottenere prestazioni fonoassorbenti elevate (inferiori ad 1 mm), richiedono strutture portanti e hanno scarsa resistenza strutturale. Inoltre, le dimensioni (diametri dell'ordine di 0,1 mm) e il numero dei fori richiesti richiedono processi di foratura relativamente com-plessi e costosi. Nel lavoro si sono studiate, sia a livello sperimentale sia numericamente, soluzioni fonoassorbenti per ambienti confinati, ricorrendo all’impiego di configurazioni a più lastre, in grado di coniugare buone proprietà di resistenza strutturale (spessori di 1-2 mm) e semplicità di foratura (fori di diametro non inferiore ad 1 mm)

Properties of transparent sound-absorbing panels for use in noise barriers

Sound absorption and optical transparency are among the most useful properties of noise barriers. While the latter is required to reduce visual impact and for aesthetical reasons, the former is required whenever conditions of multiple reflections and presence of close, high receivers occur. The technical feasibility of a transparent, sound-absorbing panel for outdoor antinoise devices is investigated in this paper. An analysis of acoustical performance of multiple perforated plates is performed employing an existing theory for microperforated absorbers under normal incidence and diffused sound field. An optimization of the geometrical parameters is carried out on the basis of the European classification criteria of noise barriers for roadways. An optimized three-layer configuration can achieve sound-absorption properties similar to nontransparent products with only a limited loss of visual transparency and appropriate mechanical strength. Experimental data obtained with an impedance tube on small test samples made of transparent polycarbonate and in a reverberation room on full-scale prototypes are reported, showing a rather good agreement with the theoretical predictions. The optical performance of a multilayered configuration is evaluated also

Acoustical optimization of a roller blind box

Roller blind boxes, also know as blind boxes or roller casings, are quite popular elements in Italian buildings, as total enclosures for the roller blinds. The boxes quite frequently show a removable face, for reasons of access, and in some cases air ventilation vents. The peculiar acoustical behaviour of the boxes is due to the presence of apertures and leaks and for this reason manufacturers are focusing their attention on the improvement of their sound insulation performances. An experimental investigation was carried out by sound intensity measurements in a reverberation room to determine the sound insulation of various steel blind boxes. The initial design showed not satisfying sound insulation ratings. A light, sound absorbing inner lining of the casing demonstrated to be even more efficient than a traditional, denser sound insulating treatment, particularly when noticeable leaks were present at the access faces of the box. Suitable absorbing materials such as mineralized wood fibres and polymeric foams were chosen and compared achieving up to 5 dB of improvement for Rw. Analyses of the frequency behaviour of the sound insulation and of the intensity maps were performed. The influence of leaks was finally estimated, demonstrating that a proper sealing could lead up to a further 10 dB performance rise

Acoustic intrinsic performances of novel sustainable noise barriers: laboratory and in situ measurement techniques

Laboratory and in situ methods have been used for measuring intrinsic performances of noise barriers, as prescribed by the European standard series EN 1793. The use of in situ techniques is promising, but their accuracy has to be duly verified, even in comparison with well-known standardized procedures. Sound insulation and reflection properties have been measured through a MLS-based technique in an outdoor test field. The paper analyzes the procedures that mainly influence the accuracy: correction for wave spreading and time windowing. Repeatability of the in situ method for sound insulation is satisfying and its results look consistent with simple prediction models. Nevertheless, in situ data can be overestimated at low frequencies, due to the overlapping of the transmitted and diffracted components. The method has to be carefully employed when the sample shows apertures as slits or holes, unless a different kind of sound propagation is assumed at the receiving side. A good agreement was found between in situ and laboratory sound insulation data, while in situ and laboratory absorption properties show poorer correlation

Transmission Loss Measurement of Consolidated Granular Media (L)

The normal incidence transmission loss of a new class of sustainable acoustic materials, i.e. consolidated granular media, has been measured to determine their sound insulating performance. Tests performed on different samples in a standing wave tube suggest that the traditional method employing an anechoic termination assumption can yield serious errors because its accuracy depends significantly on the properties of both the termination and the tested sample. Since it is not possible to implement a perfect anechoic termination over a wide frequency range, a well-developed alternative approach has been adopted. A simple theoretical analysis has been carried out to compare these two methods. It has been shown that the two-load method, based on two sets of measurements with different boundary conditions at the tube termination, can give more reliable and predictable results. Greater discrepancies have been observed in the case of the anechoic termination method applied to samples with higher values of flow resistivity. Results of the two-load method match well with predictions based on a simple model for acoustic transmission through a porous plate

Optimization of in situ noise barrier intrinsic characteristics measurements

Noise barriers intrinsic characteristics evaluation is fairly complicated if one aims at simulating barrier operating conditions. One of the most successful methods consists of in situ impulse response measurement, in particular by means of MLS signals combined with cross-correlation techniques. This has been adopted by a new CEN Technical Specification. Anyway, such a method has shown limitations and drawbacks. The aim of the research is first of all to investigate the influence of various parameters, such as source characteristics, measurement apparatus geometry and signal processing technique, on the final results of the measurements. Correlation has been found between errors due to subtraction technique, used to isolate the reflected component, and differences observed in subsequent measures. Particular attention is also paid to barrier materials and shape; reflection coefficient measurements on low- as well as on high-absorptive barriers were performed. Finally, method repeatability and reproducibility were taken into account

Prestazioni acustiche intrinseche di barriere di tipo innovativo: metodi di valutazione in laboratorio e in campo libero simulato

Nell’ambito di un Accordo di Programma tra CIRIAF e Ministero dell’Ambiente, inerente la sperimentazione di sistemi innovativi integrati di abbattimento del rumore e sfruttamento delle fonti rinnovabili di energia, si sono misurate le proprietà acustiche intrinseche di campioni di barriere antirumore ed elementi antidiffrazione; le misure sono state eseguite sia nelle camere riverberanti del Laboratorio di Acustica dell’Università di Perugia che in campo libero simulato, in un sito appositamente predisposto. Si sono valutate, ai sensi degli standard EN 1793, le seguenti grandezze: S, R, RI, SI e DI. Il lavoro riporta i risultati ottenuti e alcune osservazioni sulle metodologie di misura in situ. In particolare, le misure in situ di Reflection Index RI presentano una maggiore difficoltà di caratterizzazione per i campioni aventi geometria complessa e superfici composite. In tali casi, solo un maggior numero di posizioni di misura sembra adeguato al fine di ottenere risultati rappresentativi. La ripetibilità dei metodi in situ appare soddisfacente per SI, inferiore per RI. I valori di Sound Insulation Index SI appaiono congruenti con quelli forniti da modelli teorici di fonoisolamento; si osserva una discreta correlazione tra grandezze omologhe misurate in laboratorio e in situ. Sono infine riportati i risultati di misure preliminari per la caratterizzazione di un elemento antidiffrazione