Laboratory Test of Sound Absorption of Vegetation

In street canyons, with increasing absorption and diffusion of street boundaries and furniture, the sound attenuation along the length could be increased. Well designed and placed vegetation could have similar effects. Therefore, knowledge of such acoustic properties of vegetation is required to accurately predict sound propagation and optimise the use of green surfaces for reducing the noise impact. However, measurements and modelling of such acoustic properties of vegetation are still rather limited. In this study absorption properties of some typical vegetation samples used in European streets have been measured in a reverberation chamber in accordance with ISO 345:2003 and using a PU probe. It has been shown that for both bedding plants and evergreens the absorption is generally over 0.5 at middle and high frequencies, which is rather effective in noise control for urban environments. The effects of basic plant characteristics have been shown by comparing different plant types, although a more systematic study is still needed. For both the reverberation chamber method and the PU probe method, more development is still needed for producing robust results.