Acoustic characterization of porous substratum used in green noise control elements

摘要

Traditionally, acoustic treatment of external surfaces involved application of man-made materials such as rockwool, porous concrete or recycled rubber. Recently, it has been discovered that porous soil substratum which is used in green (living) walls exhibits very high values of the acoustic absorption coefficient. This acoustic performance is comparable to or better than that typically expected from a thick layer of rockwool or fibreglass. It has also been also found that the effect of foliage on the acoustic absorption coefficient of soil substratum is not negligible and can be highly pronounced particularly in the case when the soil is at a high degree of water saturation. The purpose of this work is to study the effect of moisture and vegetation on the acoustic absorption coefficient of soil substratum. This work relies on the laboratory data for the acoustic absorption coefficient obtained in a large impedance tube in accordance with the ISO 10524-2 method. The results show that the type of foliage, foliage density and its amount are the main factors which affect the absorption coefficient of a green wall system at a given degree of water saturation. The acoustic properties of these systems are modelled using the porous material theories.