Amir Khan

A series of reproducibility experiments on the characterization of acoustical parameters of selected samples of porous media is carried out on a range of porous samples in several independent laboratories in Europe and North America. The data on the characteristic acoustic impedance and complex propagation constant are presented in this work. In addition, the assessment of the related geometrical parameters required for modeling the acoustic performance of porous media, namely the steady-state flow resistivity, porosity, tortuosity, viscous and thermal characteristic lengths, and thermal permeability, is carried out. Detailed procedures related to sample preparation, and installation are discussed together with data on the material property variation observed between individual material samples and laboratories.

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 th...