Experimental assessment of different green wall systems: A comparative study on sound absorption and transmission loss measurements using impedance tubes

This research presents a comparative acoustic analysis of green wall systems by assessing their sound absorption and transmission loss properties. A novel classification is proposed based on potential differences in acoustic behavior, encompassing direct/indirect green façades, modular living wall systems (LWS), and continuous LWS. Both single-skin and double-skin configurations were assessed to examine the effect of an air cavity. Impedance tube measurements were conducted in accordance with ISO 10534-2 and ASTM E2611-24 standards using 100 mm and 30 mm diameter tubes to cover 63–6300 Hz. Samples were prepared with Euonymus fortunei ’Emerald Gold’ as the vegetation component and tested with and without growing medium, including soil or felt. To prevent spillage, the top and bottom sides of the 3D-printed sample holders were covered with tulle fabric. Preliminary tests were conducted to assess the acoustic impact of four different tulle, identifying Z-type tulle as the most suitable due to its negligible acoustic influence and near impermeability to soil. Results indicate that modular LWS offers a superior weighted sound absorption coefficient (α_w = 0.75), particularly at low frequencies, while continuous LWS performs better in terms of weighted sound reduction index (R_w = 16 dB). Green façade systems, by contrast, exhibited the lowest performance in both metrics. The addition of an air cavity (double-skin setup) generally enhanced acoustic behavior, especially for low-frequency absorption. These findings offer evidence-based guidance for the integration of green wall systems in urban environments where both aesthetic and noise-control functions are desired.