Experimental investigation of the effect of moisture on the acoustic properties of lightweight substrates used in green envelopes

• Published in: Applied acoustics 2021-09, Vol.180, p.108108, Article 108108
• Main Authors: Attal, Emmanuel, de l’Epine, Yorick Buot, Dauchez, Nicolas, Dubus, Bertrand
• Format: Article
• Language: English
• Subjects: Acoustic porous medium; Acoustics; Engineering Sciences; Green envelope; Lightweight substrate; Materials; Micro and nanotechnologies; Microelectronics; Moisture; Sound absorption
• ISSN: 0003-682X; 1872-910X
• DOI: 10.1016/j.apacoust.2021.108108

•Acoustic properties of moistened substrates are strongly influenced by their microstructure.•Impedance matching is essential to get high sound absorption in lightweight substrates.•Sound absorption of a green envelope may be improved with lower acoustic attenuation of the substrate. Substrates are used in green walls and roofs to supply air and water to the roots of the growing plants. These substrates are porous with micropores which store water and macropores which facilitate drainage and air entry. Effect of moisture on acoustic absorption is studied for two lightweight substrates: coir dust and perlite. Measurement of dry and moistened substrates are conducted to evaluate their effective speed of sound, attenuation, characteristic impedance, compressibility and density between 100 Hz and 1000 Hz using an impedance tube and the three microphone-two load method. Effect of moisture on these quantities is found to depend strongly upon the interaction between water and substrate particles at the microscale. Performance of rigid-frame and limp frame porous models is evaluated when applied to the characterization of dry and moistened lightweight substrates. Finally, sound absorption of substrate layers and composite plant-substrate samples is analyzed for different moisture contents.