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Acoustic correction using green material in classrooms located in historical buildings
Abstract and Figures
The acoustic correction inside classrooms located in historical buildings using absorbent panels is difficult for aesthetic reasons. Furthermore, architectural restrictions are often imposed to preserve the historical heritage. The acoustic measurements inside the classrooms show high reverberation time values, which imply an adverse environment for speech reception. In this paper the reverberation time in classrooms located in historical buildings was reduced by installing removable sound absorbent panels. The panels were made with “green material”. The absorbent material was obtained by crushing giant reeds of sweet water, a plant which grows quickly in wetlands. The crushed material was then put in jute sachets, installed in the wooden frames and covered with different colours jute cloth for aesthetics. Acoustic measurements were made in the classrooms with smooth plaster walls, without students. A virtual model of the classroom was drawn with 3D CAD. The surface area covered with green material absorbent panels was evaluated by the software Odeon. After the installation of the absorbent panels, comparisons between the virtual classroom acoustic properties and the real classroom acoustic properties were made to validate the effect of the green absorption panels.
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... The absorption coefficients for straw, hay, broom, plant litter, coarse-grained chestnut, wood chips, and fine-grained poplar wood chips show a doublepeak trendline, with maximum peaks recurring at constant intervals based on material thickness [12,13]. Since these green materials are loose and granular, some manufacturers have packed them in jute envelopes to create absorption panels for reducing reverberation in classrooms [14], as shown in Figure 1. frequencies-comparable to traditional porous materials. ...
... The absorption coefficients for straw, hay, broom, plant litter, coarse-grained chestnut, wood chips, and fine-grained poplar wood chips show a double-peak trendline, with maximum peaks recurring at constant intervals based on material thickness [12,13]. Since these green materials are loose and granular, some manufacturers have packed them in jute envelopes to create absorption panels for reducing reverberation in classrooms [14], as shown in Figure 1. Hydroponics is a method of growing plants without soil and serves as an efficient agricultural production system. ...
Hydroponics is a method of growing plants without soil and serves as an efficient agricultural production system. Compared to traditional farming, hydroponic crops offer significant water savings while also reducing the need for chemical pesticides by eliminating soil-borne diseases and pests. Additionally, hydroponic materials are being studied as a potential food source for space missions and as a substitute for industrially produced animal feed during winter. This paper explores the acoustic absorption properties of green materials derived from hydroponic systems. The roots of wheat grown in a porous layer formed a rigid skeleton structure. After drying, test specimens were prepared for acoustic measurements, undertaken using an impedance tube, to assess the material's sound absorption performance. The results indicate optimal absorption around 600 Hz and 2000 Hz, reaching α = 0.95-1.0, which is significant. A brief description of the substrate layers is also provided.
... The acoustic properties of historical buildings and the improvement of acoustic conditions are frequently investigated in the literature. In the research of Iannace et al. (2013), a classroom located in a historical building was analysed, the original vault form was preserved in the acoustic improvement proposal, and the application of portable absorbent panels on the classroom wall was suggested. Alonso et al. (2014) researched the acoustic evaluation of the cathedral of Seville. ...
... In literature research, it is seen that acoustic suggestions are presented in accordance with the original form of historical buildings. Iannace et al. (2013) examined the vaulted classroom and offered practical suggestions. They could not present the concave vault surfaces as absorbent. ...
In the restoration of historical buildings, the characteristics of the original period and the design decisions of the original period should be preserved. The rich interior volumes of historical buildings should not be reduced, the original ceiling height should not be changed and their original interior forms should be conserved. In addition, the requirements of current standards in the restoration of historical buildings should be met as much as possible. Providing auditory comfort conditions is also one of the important parameters in the restoration process. In this study, the meeting room in the historical building was analysed, the design decisions of the original period of the meeting room were preserved, and an acoustic improvement project was presented depending on the characteristics of the historical building. In the acoustic project proposal, the original room height, the richness of the interior volume, and the perception of the mirrored vault system were preserved to maintain original period design decisions. In the acoustic project proposal, auditory comfort conditions were improved by increasing the total absorption rate in the meeting room. Reverberation time analyses and delayed reflection analyses were performed. In addition, the homogeneous propagation of the sound in the space was examined by using the acoustic simulation program. With the acoustic project proposal, the reverberation time was controlled in line with the DIN18041 standard, the delayed reflections were greatly reduced, the homogeneous propagation of the sound in the space has been improved, and the intelligibility of speech in the meeting room has been increased.
... The growing awareness of health problems associated with the use of porous synthetic materials, such as glass wool, rock wool, polyurethane, etc., has also increased the attention paid to bio-based materials. Iannace et al. [1] have studied acoustically and aesthetically, the use of some green materials (giant reeds of sweet water) for the classroom acoustic corrections. Also, Glé et al. have treated the acoustic properties of plant particle materials (hemp) with several degrees of porosity [2]. ...
... The reed leaves are also used as fodder for livestock in most oases of Morocco. The reed can be also used in different forms in construction as bulk material packed in aesthetic bags for acoustic correction and thermal insulation, have illustrated by Iannace et al. [1]. The authors made aesthetic panels of jute bags filled with the reed that will be placed on the internal walls of reverberant rooms. ...
Sustainable materials tend to become an alternative to synthetic materials in the building sector for acoustical correction and thermal insulation. This research work is dedicated to the acoustical and thermal characterization of some sustainable materials derived from vegetable, agricultural, and animal wastes, i.e. date palm (trunk, petiole, pinnate leaves, bunch, and fiber mesh), reed, esparto, olive tree, fig tree, wood sawdust, chicken feathers, and sheep wool. All materials are characterized experimentally using standard methods: impedance tube and guarded hot plate for absorption coefficient and thermal conductivity measurements, respectively. The results indicate that the majority of studied materials exhibit good acoustical and thermal performances: absorption coefficient in the range 0.6–0.9 (medium frequencies) and thermal conductivity between 0.044 and 0.091 W/m.K. It is found that esparto, petiole, chicken feathers, and sheep wool meet the main properties required for acoustic correction and thermal insulation applications and have great potential to replace synthetic materials (glass wool: 0.95, 0.044 W/m.K). The measured absorption coefficient and thermal conductivity were (0.9, 0.065 W/m.K); (0.88, 0.072 W/m.K); (0.94, 0.045 W/m.K); (0.95, 0.044 W/m.K); for esparto, petiole, chicken feathers, and sheep wool, respectively.
... However, it is important to note that the developed bio-material is versatile and can be easily filled into various enclosures, such as non-woven casings, for installation in specific applications. This approach is consistent with similar methods used by other researchers in acoustic testing [66,67]. Afterward, the cavity was covered with jute fabric (256 GSM) from both ends for normal incidence SAC testing in a two-microphone impedance tube setup. ...
Among the most abundantly available bioresources, lignocellulosic biomass offers a ‘green renewable’ alternative resource for producing high-value biomaterials suitable for acoustic applications. In this study, a systemic process is developed to fabricate sound absorbing material using refined cellulosic microfibrils generated from natural deep eutectic solvent (NADES) pretreated rice straw. Physico-chemical characterization using FTIR and FESEM analysis confirmed substantial removal of the hemicellulose and lignin from the extracted cellulosic microfibrils. Moreover, the surface area after NADES pretreatment increased to 12.55 m²/g from 2.18 m²/g of raw rice straw, suggesting the enhanced potential of sound dissipation within the biomaterial. The noise reduction coefficient (NRC) of the NADES pretreated rice straw was increased to 0.55 compared to 0.41 with untreated rice straw. Sound absorption performance shows an increasing trend with the increase in sample thickness (25 mm to 50 mm); however, no significant improvement in sound absorption was observed with an air gap of more than 20 mm. Overall, the tested biomaterial shows comparable NRC to commercially available synthetic sound absorbing materials.
Graphical Abstract
... Interestingly, researches concerned with natural fibers-based absorbers managed to develop eco-friendly, acoustically efficient, cheap and aesthetically appealing FAPs through the usage of natural fibers as fillings into wooden frames enwrapped by natural acoustically transparent fabric [25]. Iannace at al. [26] utilized giant reeds fibers as a filling into jute bags as a practical acoustic correction in existing classrooms to promote local and sustainable acoustic design. In correspondence, this paper aims to develop a novel FAP that is based on one of the major local agricultural residues in Egypt, Date Palm Pruning Residues. ...
This paper presents an experimental study of acoustic absorption of novel fabric acoustic panels utilizing non-woven fabric cores and fabric facings made of date palm midribs-fibers; to be used as absorbent panels for spaces with privacy needs. Normal acoustic absorption coefficients of various configurations; different densities, thicknesses and facings; were measured using impedance tube. Findings showed that the highest absorption was exhibited by 50 mm- thick midribs-fibers cores. Additionally, 150 kg/m3 cores balanced between high tortuosity and porosity. Results of full assembly tests showed that 30 mm-150 kg/m3 and 40 mm-100 kg/m3 cores with woven midribs-fibers facings enjoyed significantly high absorption at low frequencies and high frequencies. Additionally, 40 mm-100 kg/m3 and 50 mm-200 kg/m3 cores with cotton facings provided competitive overall performances to commercial acoustic panels while providing flexible interior design options. Thus, interior designers can incorporate midribs-based fabric acoustic panels into their designs as local sustainable absorbent panels to enhance acoustical quality and complement space aesthetics.
... The difference between the two parameters was discussed, and the application scenario of the new building material in the reconstruction of the ancient acoustic environment was constructed. Iannace et al. [48] used detachable sound-absorbing panels made of "green materials" such as reed and jute to acoustically modify a classroom in a historic building of the School of Architecture at the Second University of Naples. They measured reverberation time, speech clarity and other parameters under unoccupied conditions and compared the acoustic performance with the virtual model. ...
As a significant part of heritage building protection, an increasing number of researchers pay attention to the study of the acoustic environment. The purpose of this study was to provide a clear understanding of the status quo of acoustic environment research on heritage buildings and discuss future development directions through a systematic literature review. The PRISMA protocol was used to conduct a systematic evaluation based on 42 studies on the acoustic environment of heritage buildings retrieved from databases such as the Web of Science. Research on the acoustic environment of heritage buildings mainly focused on the following four aspects: the acoustic environment with different functions, the influence of building materials on the acoustic environment, the digitization of acoustic heritage, soundscape measurement, and perception of the historical area. Second, this study discusses the development trend of acoustic environment research of heritage buildings and the shortcomings of current research. Finally, this study provides a comprehensive overview of the acoustic environment research of heritage buildings and offers suggestions for future research.
... Also the scientific community has realized the potential of end-of-life materials [8], and several studies have investigated the properties of plastic bottles [9,10], cardboard and paper elements [11][12][13][14][15][16], Tetra-Pak panels [17], textiles waste [18][19][20][21][22], and egg boxes and trays [23][24][25][26][27][28]. More recently, so-called green and sustainable materials made of natural fibers have been investigated [29][30][31][32][33][34][35][36]. ...
Europe calls for a transition to the circular economy model based on recycling, reuse, the proper design of products, and repair. Recycling requires energy and chemical products for waste processing; on the contrary, reusing reduces the impact of transportation and expands the life of materials that cannot be recycled. This article highlights the characteristics of selected end-of-life materials; it aims to raise awareness among manufacturers to consider products’ conscious design to facilitate their reuse in different sectors. Panels 7 cm thick, realized by assembling cardboard packaging, egg boxes, bulk polyester, and felt, have been experimentally tested to understand whether they can be installed indoors to improve thermal and acoustic comfort. The panels’ equivalent thermal conductivity λeq measured through the guarded hot plate method is 0.071 W/mK. Acoustic tests have been performed in a sound transmission room and a reverberation room. The weighted sound reduction index Rw is 19 dB, the weighted sound absorption coefficient αw is 0.30, and the noise reduction coefficient NRC is 0.64. The measured properties have been compared to those of commercial materials, and the results show that the panels have interesting properties from the thermal and acoustic points of view. They could be employed in the building sector and in disadvantaged contexts where low-income people cannot afford commercial insulating materials. Although other factors, such as fire resistance, need to be evaluated, these results show that the proposed approach is feasible.
... Reed leaves are also used as fodder for livestock in most oases in Morocco. The reed can be also used in different forms in construction as bulk material packed in aesthetic bags for acoustic correction and thermal insulation as illustrated by Iannace et al. [27]. ...
This work aims to elaborate and characterize new ecological composite materials from cardboard waste and abandoned natural fibers for the manufacture of local acoustic absorbers/sound insulation panels and thermal insulation panels. For this purpose, twenty-eight samples were prepared by mixing a mass fraction of 60 % of cardboard waste and 40 % of natural fibers available in the south-east region of Morocco, i.e. Doum, Wheat straw, Reed, Esparto, Bagasse, Fig, and Olive. Firstly, the morphological analysis of the different fibers was carried out by scanning electron microscopy (SEM). Secondly, the acoustic and thermal properties were measured experimentally using standardized methods. In addition, bulk density, air flow resistivity and water absorption were measured. The experimental results showed that the studied panels have good acoustic and thermal performances. The sound absorption coefficient, sound transmission loss, bulk density, thermal conductivity, and heat capacity were in the range of 0.4–0.8; 20–45 dB; 278.6–343.8 kg/m³; 0.072–0.10 W/m.K; 1254.5–1807.5 J/kg.K, respectively. Consequently, the new panels developed in this study are good candidates for the development of local materials with the required acoustic and thermal insulation properties for applications in buildings. Their main advantages are: low environmental impact, low cost, and they can even compete with commercialized synthetic materials.
... The further the distance between a speaker and a listener, the less speech is heard [22]. In a closed space like a classroom, sound reflection and absorption by the ceiling, floor, walls, furniture as well as people present, all integrate together with the sound directly emitted by a speaker to shape diverse characteristics of the sound field [23,24]. Consequently, the intelligibility of a teacher's speech signals fluctuates depending on where children are, even in the same classroom [25]. ...
In this paper, the importance of implementing good acoustic conditions in classrooms using sound amplification systems is investigated to support more effective English education for elementary school children. To date, the failure of educating English as a second language at Japanese schools has been demonstrated by poor English conversation ability of those who completed a compulsory six-year English language course at Japanese junior-high and high schools (age 12–18). To amend the situation, teaching English became compulsory at grade three (age 8–9) and above at most Japanese elementary schools in the 2020 academic year. We conducted acoustic measurements of two types of sound amplification systems, a pair of PC loudspeakers and another with a loudspeaker array, in a typical classroom at an elementary school in Japan. We also analysed English listening test results of 216 Japanese native children (age 11–12) who were learning English in their usual classes in Japan, to compare the effects of those two systems. Results of logistic regression analysis adjusted by the discrimination difficulty of word pairs demonstrated the statistically significant association between correct answer rate of the English tests and classroom acoustic factors. Although, on average, upgrading the sound amplification system had positive effects on the correct answer rate, it also had a negative impact when the word pairs had English phoneme contrasts that do not appear in Japanese phoneme structure. Combined with the acoustic measurements’ results, it was also revealed that heterogeneous sound fields that depend on seat positions could be compensated using sound amplification systems with loudspeaker arrays. Our findings suggest that improvement of both acoustic quality and teaching methods is required for children to acquire English communication skills effectively in their classroom.
... However, while the materials typically relied on for indoor acoustic control are typically derived from petroleum [12], recent years have seen a new focus on the utilization of sustainable green materials, including agricultural by-products, to fulfill this function [13][14][15]. In this spirit, a wide range of studies have been conducted of eco-friendly sound-absorption materials such as rice straw [16], rice husks [17], palm fibers [18], giant reeds [19], egg cartons [20], and wood paper [21]. ...
The continuing development of industrialization and increasing population density has led to the emergence of noise as an increasingly common problem, requiring various types of sound absorption and insulation methods to address it. Meanwhile, the recycling of resources to ensure a sustainable future for the planet and mankind is also required. Therefore, this study investigates the potential of corrugated cardboard as a resource for noise reduction. The sound absorption and insulation performance of non-perforated corrugated cardboard (NPCC) were measured, and modified corrugated boards were fabricated by drilling holes either through the surface of the corrugated board alone or through the corrugated board in its entirety. The sound-absorption/insulation performance both of perforated corrugated cardboard (PCC) and perforated corrugated cardboard with multi-frequency resonators (PCCM) were measured using the transfer function method and the transmission matrix method. To determine the effectiveness of NPCC, PCC, and PCCM in noise reduction, the sound pressure level was analyzed by applying it to a home blender. The results showed PCCM’s sound absorption and insulation performance to be excellent. On the basis of these findings, we propose the use of PMMC as an eco-friendly noise-reduction material.
Polyurethane foam waste is one of the residues of the manufacturing processes in textile industry, the disposal of which is becoming a severe environmental problem. In this paper the sound absorption properties of different materials developed from ground polyurethane foam waste are studied. Because these recycled materials exhibit good sound absorbing properties they are viable alternatives to conventional materials for practical applications. Experimental measures have been carried out to determine the characteristic wave impedance and propagation constant of these materials. Modelling of the acoustic behaviour has been done using the Dunn and Davern model and Voronina model. The first model presents deviations in the results so the experimental results have been used to report corrections to the empirical model. The Voronina model has been applied to verify that it serves to model the behaviour of these kinds of recycled materials. Both models converge and present acceptable results.
This article is devoted to the acoustical properties of hemp concrete, a “green” building material. In the study, hemp concretes made of different binders and different kinds of particles were characterised, and then modeled using equivalent-fluid models. Further, it is shown that the sound absorption of these materials can be controlled and significantly enhanced by means of suitable constituents and fabrication processes. Finally, good results are provided by the models.
The "green materials " are spreading in the architectural acoustics applications. These materials are completely biodegradable and they have the advantage that they are easily disposed at the end of useful life. The goal of this paper is to evaluate the application of the "green materials" into classrooms for the acoustical correction. Among available "green materials " the giant reeds of sweet water (Arundo donax) was chosen for its wide diffusion in the area of south of Italy. The "green material" was dried and crushed in an appropriate way and it was subsequently placed in jute sacks to build up uniform sound absorbing panels. The "green material" was characterized by measuring its acoustic properties (absorption coefficient, porosity and resistivity) and the same were compared with those of acoustical commercial materials. The "green" panels were placed in an university classrooms to evaluate the efficiency of the acoustic correction and the acceptability by the students.
The use of material waste, coming from the fibers of fluff (a textile residue from grounded end of life tires, ELTs), in the manufacture of sound absorber products, can help to combat two different kind of problems, the disposal of this kind of waste and the noise control. This paper presents the results of a new absorber material obtained through thermal compression, using a residue that is currently used for its high calorific value. Through this process, a product with a higher added value and a lower cost has been obtained. Through testing of samples made with fluff, results for absorption coefficients and acoustic impedance have been obtained. In addition, composite samples have been tested. One of these samples is a composite made with a layer of ground tire rubber (GTR), obtained by sintering and adding another layer of fluff.
This research aims to study the acoustical and flammability properties of biodegradable and easily disposable natural fibre jute and its composite for noise reduction in house hold appliances, automotive and architectural applications. Acoustical properties of jute fibre and felt (natural rubber latex jute composite) were measured in terms of normal specific sound absorption coefficient and sound transmission loss whereas fire retardant tests included limiting oxygen, flame propagation and smoke density test. The results illustrate that low density jute is a better sound absorber as compared to high density jute material, moreover natural rubber latex jute composite gives higher sound transmission class value than jute felt/cloth. Results were also compared with commercially available synthetic, non-biodegradable, glass fibre which indicates that the noise reduction coefficient value and sound transmission class rating of natural rubber latex jute felt are comparable to that of the popular fibre glass. Fire retardant tests show composite’s high limiting oxygen index value as compared to fibreboard and other natural sound absorbing material, wool, low smoke density rating and low light absorption with respect to fibre glass as well as self fire extinguishing ability.
Acoustical measurements were performed in 30 randomly chosen, unoccupied classrooms at the University of British Columbia (UBC). Tests had previously been done in 46 unoccupied UBC classrooms, as well as in 10 of these when occupied by students. The results for the 10 classrooms were used to correct the “unoccupied” results to the half-occupied and fully occupied conditions. The objective of the work was to characterize the 30 classrooms, which were used in subsequent studies, to determine the acoustical quality of the UBC classroom stock and how this depends on the classroom design and the presence of students, and to elucidate characteristics of classroom acoustics relevant to optimal design. The results showed that the UBC classroom stock is of far from optimum acoustical quality when unoccupied, but is much better in the occupied condition. Generally, many classrooms have excessive reverberation and result in low speech levels, especially at the back of the rooms; in addition, they have excessively noisy ventilation systems.
Worldwide research has demonstrated the influence of bad acoustic conditions inside primary schools on pupils' learning and achievements and on teachers' stress. It has been also demonstrated that noise levels during school activities can be over 75 dB(A). Although the lack of sound insulation and sound absorbing units is of main concern for the phenomena, social and environmental context of the school can have also a dominant effect. In this paper are presented the results of a pilot study named "Sshh…school" conducted in two schools located in different places (a strongly urbanized area and a small village). The pilot study had the aim to sensitize all school actors (management, teachers, parents, pupils) to the problem and to find together the possible remedies to control it. Among others the effects of an information and instruction campaign and the introduction of friendly shared and sustainable absorbing materials were investigated.
Coir fiber from coconut husk is an important agricultural waste in Malaysia. Acoustic absorption coefficient of the fiber as a porous material is studied in this paper. Two types of fiber are investigated, fresh from wet market and industrial prepared mixed with binder. Moreover two analytical models, namely; Delany–Bazley and Biot–Allard are used for analysis. Experimental measurements in impedance tube are conducted to validate the analytical outcomes. Results show that fresh coir fiber has an average absorption coefficient of 0.8 at f > 1360 Hz and 20 mm thickness. Increasing the thickness is improved the sound absorption in lower frequencies, having the same average at f > 578 Hz and 45 mm thickness. Delany–Bazley technique can be used for both types of fiber while Biot–Allard method is compensated for the industrial prepared fiber considering the binder additive. This form generally shows poor acoustical absorption in low frequencies. Inevitably, fiber has to be mixed with additives in commercial use to enhance its characteristics such as stiffness, unti-fungus and flammability. Hence other approaches such as adding air gap or perforated plate should be used to improve the acoustical properties of industrial treated coir fiber.