Acoustic Performance of Mesoporous Charcoal: A Comparative Study Using Impedance Tube, Anechoic Chamber, and Mass Law

Abstract

As the demand for sustainable materials in acoustic applications grows, mesoporous charcoal—produced via biomass pyrolysis—has emerged as a promising material for acoustic absorption and thermal insulation. This study investigates its acoustic properties using impedance tube and anechoic chamber measurements, alongside comparisons with mass law predictions. Charcoal samples, characterized by pore sizes ranging from 2 to 50 nm and fraction sizes from 1 to 4 cm, were tested across varying thicknesses (5 cm, 10 cm, and 17 cm) and frequencies (315 Hz to 5000 Hz). The Johnson-Champoux-Allard-Lafarge (JCAL) model was used to derive key acoustic parameters. These parameters were instrumental in explaining the material's behaviour in different acoustic environments. Impedance tube measurements revealed sound absorption coefficients below 0.1 for most samples, attributed to the material’s low porosity (ϕ = 0.19) and fine pore structure. In contrast, anechoic chamber tests demonstrated increased sound reduction, with a 17 cm thick construction (fraction size 1 cm) achieving a sound reduction index (SRI) of 35 dB at 5000 Hz, significantly exceeding the transmission loss (TL) predicted by mass law, which calculated a TL of only 8.28 dB under similar conditions. Statistical analysis further revealed that SRI increases with particle size and thickness, ranging from 9.17 for 1 cm particles to 18.38 for 4 cm particles. The highest SRI of 28.00 was observed for 1 cm particles at 17 cm thickness, while bulk density results highlighted an inverse relationship with particle size: 1 cm particles had a bulk density of 550 kg/m3 compared to 323.33 kg/m3 for 4 cm particles. These findings highlight mesoporous charcoal's potential in sustainable acoustic applications, particularly in the context of circular economy principles. Its production from biomass, combined with the eco-friendly properties it brings to noise insulation, aligns with the goals of sustainable material cycles. Optimizing parameters such as pore size, fraction size, and thickness can further increase its acoustic performance, making it a promising material for eco-friendly construction and noise control.