title: Sound absorption of porous substrates covered by foliage: experimental results and numerical predictions.
abstract: The influence of loose plant leaves on the acoustic absorption of a porous substrate is experimentally and numerically studied. Such systems are typical in vegetative walls, where the substrate has strong acoustical absorbing properties. Both experiments in an impedance tube and theoretical predictions show that when a leaf is placed in front of such a porous substrate, its absorption characteristics markedly change (for normal incident sound). Typically, there is an unaffected change in the low frequency absorption coefficient (below 250 Hz), an increase in the middle frequency absorption coefficient (500-2000 Hz) and a decrease in the absorption at higher frequencies. The influence of leaves becomes most pronounced when the substrate has a low mass density. A combination of the Biot's elastic frame porous model, viscous damping in the leaf boundary layers and plate vibration theory is implemented via a finite-difference time-domain model, which is able to predict accurately the absorption spectrum of a leaf above a porous substrate system. The change in the absorption spectrum caused by the leaf vibration can be modeled reasonably well assuming the leaf and porous substrate properties are uniform.
authors: Department of Information Technology, Ghent University, St.-Pietersnieuwstraat 41, 9000 Gent, Belgium.
authors: Lei
authors: L
authors: Ding
authors: Department of Information Technology, Ghent University, St.-Pietersnieuwstraat 41, 9000 Gent, Belgium.
authors: Timothy
authors: T
authors: Van Renterghem
authors: Department of Information Technology, Ghent University, St.-Pietersnieuwstraat 41, 9000 Gent, Belgium.
authors: Dick
authors: D
authors: Botteldooren
authors: School of Engineering, University of Bradford, Bradford, BD7 1DP, United Kingdom.
authors: Kirill
authors: K
authors: Horoshenkov
authors: School of Engineering, University of Bradford, Bradford, BD7 1DP, United Kingdom.
authors: Amir
authors: A
authors: Khan
mesh_terms: D065966:Absorption, Physicochemical; D003198:Computer Simulation; D003252:Construction Materials; D005160:Facility Design and Construction; D008962:Models, Theoretical; D009038:Motion; D009716:Numerical Analysis, Computer-Assisted; D018515:Plant Leaves; D016062:Porosity; D011312:Pressure; D013016:Sound; D013997:Time Factors; D014732:Vibration