## 3 Methods
### Samples  
The analyzed samples were made putting together different types of EoLHM and are shown in Figures 7 and 8, where the sequence described in the caption starts with the material nearest to the sound source. The layers of the samples were only placed close to and not connected to each other. The samples were 50 mm long, except for samples 13 and 14 that had a length of 24.2 mm, and sample 26 that was 100 mm long. The weight of the samples is reported in Table 1. For each sample, three repetitions were performed and the results of the experimental tests were averaged. This has made it possible to evaluate how manual skills influenced the panel acoustic performances. \begin{table}
\begin{tabular}{l c c c c c c c c c} \hline Sample & 3 & 22 & 4 & 5 & 7 & 8 & 13 & 14 & 17 & 26 \\ Weight & 3.6 & 4.19 & 12.63 & 12.63 & 13.33 & 13.33 & 6.47 & 15.4 & 4.36 & 19.31 \\ \hline Sample & 27 & 28 & 29 & 30 & 32 & 33 & 34 & 35 & 36 \\ Weight & 12.53 & 13.81 & 8.45 & 17.41 & 8.91 & 20.07 & 29.03 & 21.83 & 21.83 Figure 8: Configurations analyzed with the impedance tube: (**a**) samples made of several layers of cardboard, (**b**) samples made of clothes (one fabric at a time), (**c**) samples made of egg-boxes and clothes. Figure 7: Configurations analyzed with the impedance tube: (**a**) samples made of egg-boxes and polyester, and (**b**) samples made of egg-box, polyester and a metallic element. Samples 04 and 05 are made of the same elements but in sample 04 the polyester faces the loudspeaker. Sample 08 has an additional perforated cardboard layer. Since the acoustic properties of egg-boxes have been questioned in a number of papers [51; 52; 56], to analyze this aspect, the first set of samples (03, 22) was made at least by one egg-carton 2.79 g in weight made of recycled paper with a density of 355 kg/m\({}^{3}\). In sample 03, the egg-carton facing the sound source was coupled with loose polyester. The egg-carton was perforated and the holes were less than 1 mm in diameter. This element was used for realizing the other samples that included egg-boxes, which exception of sample 22 that was made of two not-perforated spaced egg-cartons whose cavity faced the sound source. To improve the acoustic performance, in the following set of samples (04, 05, 07, 08) the perforated egg-carton was coupled to other EoLHM such as loose polyester, a metallic element and cardboard 197 kg/m\({}^{3}\) in density. The cardboard was made of two external linear boards 0.11 mm thick and an internal board with 130 flutes/m. The metal element was a steel sphere with an external diameter of 13 mm, and a weight of 8.95 g.  
In particular, samples 04 was made of a box-carton, polyester and a metallic sphere. Sample 05 was similar but had mounted reverse. Samples 07 and 08 were realized to exploit the double panel characteristics. Indeed, a plane wave impinging a double-panel system saw the impedance of the panel closest to the sound source, the impedance of the airspace, the impedance of the second panel, and finally the impedance of the air beyond. The cavity acted as a spring element reducing significantly the TL, especially at higher frequencies. In the cavity the absence of absorptive material contributed to the transmission of sound, while the addition of damping elements such as fibrous materials attenuated the modes of the cavity. For this reason, in samples 07 and 08 cardboard layers were added to create a sort of cavity. In sample 07, to reduce the permeability, only a cardboard was added on the back of the sample. In sample 08 a perforated layer was added in the front of the sample: the first panel being perforated allowed the passage of a certain quantity of sound and behaved like a Helmholtz resonator. To characterize cardboard panels, a third set of samples (13, 14, 17) was prepared. In the last few years, cardboard is largely available at domestic level as a result of the e-commerce. For this reason, highlighting its acoustic properties would encourage its conversion into a building element.