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Sound absorption properties of tropical plants for indoor applications

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The paper presents the experimental results of sound absorption coefficient measurements of several tropical plants, including fern, baby tears, begonia, maidenhair fern and ivy. All these plants live in tropical underbrush in conditions of low lighting, warm temperature and high relative humidity, conditions that can be often found inside common buildings. A vertically mounted impedance tube with a diameter of 100 mm is used in accordance with ISO 10534-2 method to determine the absorption coefficient spectra. A substrate made of coconut and per-lite soil for hydroponics is used with all the samples. It is chosen because of its high porosity and, as a result, good sound absorption properties. The paper also presents the random inci-dence absorption coefficient spectra which were measured in a reverberating room in accordance with ISO 354. The aim of this research is to investigate the feasibility of introducing absorptive panels made of living plants as a replacement for conventional man-made acoustic treatment of surface used to improve the acoustic quality of indoor spaces.
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... Plants have been suggested as effective passive acoustic insulators, reducing sound levels through the reflection, dispersal, absorption or interference of sound waves by vegetation and growth media [1,18,19]. ...
... De Lucia et al. [33] * Han [23] * Salamone et al. [26] Real environment Gunawardena and Steemers [16] * Fernández-Bregón et al. [34] Ren and Tang [35] * Schempp et al. [31] * Smith and Pitt [32] Son et al. [36] Acoustics Lab environment Asdrubali et al. [18] * Salamone et al. [26] Real environment * Fernández-Bregón et al. [34] Mental health ...
... The category includes different attempts of quantifying greenery based on the leaf coverage of a plant. Aspects taken into consideration include (i) leaf "size" in terms of area or surface [11,13,18,21,22,24,25,[27][28][29][30]37], leaf length [33], and leaf volume [28]; (ii) leaf "quantity" in terms of mass [27] and volume occupied [36] (supposedly, by the leaf canopy including the air space between leaves). ...
Article
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The introduction of green plants in indoor spaces has raised a great amount of interest motivated by plants’ supposed capacity to improve the quality of indoor built environments. Subsequent studies have covered a broad range of topics, testing plants in indoor environments for their climate-mitigating effects, acoustic benefits, potential energy savings and the enhancement of the indoor microbial communities. Despite the diversity of focus in these studies, no major breakthroughs have been made involving the use of plants in indoor environments after nearly thirty years of research. To identify major inconsistencies and gaps in the research, this review, of an explorative nature, presents an analysis of plant-related parameters reported in 31 cases of experimental research involving the use of plants in indoor environments. The papers were identified by searching the online databases Google Scholar, ResearchGate, Scopus and MDPI and were selected based on their relevance to the topic and diversity of focus. Two classifications in table form provide an overview of the 38 plant-related parameters used in the reviewed research. The conclusions drawn from the analysis of the tables highlight a strongly anthropocentric frame of reference across the majority of the studies, which prioritize human and experimental convenience above plant physiology, and display an overall scarcity and inconsistency in the plant-related parameters reported.
... The study conducted by ALRahman, Ishak Raja, and Abdul Rahman (2013) investigated porous materials from date palm and coconut coir fibers. Asdrubali, D'Alessandro, and Mencarelli (2014) obtained the SAC measurements of ferns, begonias, ivy, and some tropical plants in a laboratory investigation. Berardi and Iannace (2015) measured the absorption coefficients and flow resistance of samples of kenaf, wood, hemp, coconut, cork, etc. with different thicknesses and reported their acoustic behaviors. ...
... For most species, a rather low absorption coefficient was measured at a low-frequency range, while an obvious increase was seen with increasing frequency. With a focus on the literature, the characteristic SAC peaks of the investigated tree trunks have hereby been shown to have comparable and high conformability with the previous experimental data of several natural fiber-based materials in the low-frequency and part of the medium-frequency regions (50-2000 Hz) (ALRahman, Ishak Raja, and Abdul Rahman 2013; Asdrubali and Horoshenkov 2002;Asdrubali, D'Alessandro, and Mencarelli 2014;Berardi and Iannace 2015;Berardi, Iannace, and Gabriele 2017;Ekici et al., 2012;Koruk and Genc 2015;Li et al. 2020;Reethof, Frank, and McDaniel 1976;Reethof, Mcdaniel, and Heisler 1977;Taban et al. 2019aTaban et al. , 2019b. ...
... The measurements confirmed that, as natural fibers, the untreated trunk samples absorb sound better at medium frequencies; they also possess SAC values of above 0.5 at both medium and high frequencies, on average. Comparisons with previous studies indicate a high accuracy for SAC peak values at a frequency range between 2000 and 6000 Hz (ALRahman, Ishak Raja, and Abdul Rahman 2013; Asdrubali and Horoshenkov 2002;Asdrubali, D'Alessandro, and Mencarelli 2014;Ekici et al., 2012;Koruk and Genc 2015;Taban et al. 2019aTaban et al. , 2019b. ...
Article
In recent years, noise pollution generated by increasing global urbanization has become an important issue. This study focused on determining the sound absorption coefficients (SACs) of untreated tree trunks as natural fiber-based materials and predicting their noise reduction coefficients (NRCs). It also evaluated the effects of noise reduction using numerical data. One of the most effective acoustic characteristics is the normal incidence SAC; this was obtained for trunks belonging to species of black locust, narrow-leafed ash, stone pine, silver lime, sweet chestnut, sessile oak, maritime pine, cedar, and plane in the frequency range of 50–6000 Hz using an impedance tube based on a two-microphone transfer function method. The absorbance of sound was found to correlate with the tree species, trunk diameter, bark shape, and the bark’s fibrous structure. The results confirmed that when compared with deciduous species, the trunks of coniferous species exhibit higher NRC values which were recorded as 0.302 ± 0.005 for stone pine and 0.233 ± 0.004 for cedar. Furthermore, the surface morphology of the outer bark of different tree species obtained via scanning electron microscopy revealed that significant variations exist in the microstructure of the bark’s fiber cells.
... 17) [22], as they have a greater effect in mitigating noise pollution at higher frequencies. Additionally, Asdrubali et al. [23] researched the absorption coefficient of tropical plants in a hydroponic porous substrate. An impedance tube was used in accordance with ISO 10534-2 [24] to determine the normal incidence absorption coefficient. ...
... Second, a reverberation chamber was used to determine the diffuse field absorption coefficient. From the five plant species selected for the study, ferns (Nephroepis Exaltata) were found to work best, although leaves of the plants only slightly increased the sound absorption coefficient in the higher frequencies [23]. Unfortunately, the chamber dimensions were lower than those required by ISO 10534-2 [23]. ...
... From the five plant species selected for the study, ferns (Nephroepis Exaltata) were found to work best, although leaves of the plants only slightly increased the sound absorption coefficient in the higher frequencies [23]. Unfortunately, the chamber dimensions were lower than those required by ISO 10534-2 [23]. Nevertheless, the work demonstrated the main absorber material to be the substrate soil, where plants had a beneficial effect only when planted in a large density [23]. ...
... According to Asdrubali et al. [23], the most important part of the attenuation in a forest is provided by the ground surface. They stated: "the main absorber is the substrate soil ( … ). ...
Chapter
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In this chapter, a case study is presented on the evaluation of acoustic performance of a tree barrier. It is a eucalyptus barrier that was planted as a visual barrier to block an industrial plant. First, the depletion law of sound pressure levels (SPL) of the source was analyzed; a linear divergence was found. A calculation scheme similar to that of ISO 9613-2 was applied. When comparing the SPL measured at a specific receiver with the results of propagating the SPL from the source without considering the existence of the barrier, an extra attenuation of 12 dB appeared, reinforcing the idea that the plantation behaves as an acoustic barrier. Four different calculations were used to obtain its insertion loss (IL), including general equations and expressions developed for green barriers. The best fit was obtained using equations for solid barriers, although it was not the expected result. This finding could be explained by the great distance between the source and the receiver. It opens the possibility of successfully using IL prediction equations for solid acoustic barriers (both thin and thick) to estimate the acoustic performance of green barriers, at least under conditions similar to those of this case study.
... The reverberation room method (Asdrubali et al., 2014;Hughes et al., 2015;Smyrnova et al., 2010;ISO 345:2003) is described under ISO 345 standards (ISO 345:2003) and is widely accepted for testing large samples and calculating random incidence absorption coefficients (Prisutova et al., 2014) (Fig. 2b). Per the standards, the minimum recommended volume of the standardised reverberation room, 200 m 3 , and the surface area of the test specimen between 10 m 2 and 12 m 2 were utilised. ...
Article
Grass has a high leaf density and requires minimum space to grow. This experiment was designed to determine the sound absorption behaviour of six grass species (Zoysia matrella (L) Merr., Stenotaphrum dimidiatum(L.) Brongn, Panicum repens (L.), Eleusine indica (L.) Gaertn., Axonopus compressus (Sw) P. Beauv, and Ischaemum sp.) for their possible use as noise screens. The sound absorption of each morphological leaf structure was studied. For Sound Absorption Coefficients (SAC) (α) studies, the reverberation room method under ISO 345:2003 standards was followed. A B&K dodecahedron Omni-directional speaker, power amplifier, and 2250L handheld analyser were used for reverberation time and RT60 measurements. Microscopic images of grass leaves were analysed using ImageJ software. This study revealed that grasses with the highest and lowest SAC for higher noise frequencies (> 1500 Hz) are S. dimidiatum Brongn and A. compressus, respectively. The SAC of S. dimidiatum Brongn positively correlated with noise frequency. In general, the correlation of SAC (α) with noise frequency (f) is in the form of log10α = a1log10f + b1 where a1 and b1 are grass type-dependent constants. The morphological parameters like total leaf area, total sample area, plant height, and sample dry weight strongly correlated with the SAC. But leaf thickness, length, width, surface area, and the weight of the sample poorly correlated with SAC in the frequency range.
... The researchers tried at first a traditional treatment of a cement plastered roof, then with the sustainable material coir matts for floor and walls ,they concluded after measurement that the second solution reduced T o to fit the room function as the coir is a very good sound absorber, economic and sustainable. Asdrubali et al [12], demonstrated that even tropical plants used for the decorative purpose in the living buildings can also serve as good sound absorbers. Tropical plants, namely baby tears and fern shown to have average sound absorption coefficient of 0.9 from 900 to 1600 Hz. ...
... The researchers tried at first a traditional treatment of a cement plastered roof, then with the sustainable material coir matts for floor and walls ,they concluded after measurement that the second solution reduced T o to fit the room function as the coir is a very good sound absorber, economic and sustainable. Asdrubali et al [12], demonstrated that even tropical plants used for the decorative purpose in the living buildings can also serve as good sound absorbers. Tropical plants, namely baby tears and fern shown to have average sound absorption coefficient of 0.9 from 900 to 1600 Hz. ...
... Furthermore, Restrepo and González (2009) found vertical gardens able to significantly reduce sound levels. More recently, Asdrubali and Mencarelli (2014) sought to determine the absorption coefficient of tropical plants in a porous substrate used in hydroponics cultivation. First an impedance tube was used to determine the normal incidence absorption coefficient. ...
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