The results show that the insertion loss of leafs can be described by limp mass behaviour. Therefore, the most relevant property of leafs regarding the insertion loss is the mass per unit area of the leaf. The artificial plant Bengal Fig gives similar insertion loss and sound absorption as natural plants and was used to study the influence of probe thickness, as it does not wilt and therefore provides better reproducibility as natural plants. For plant material (leafs and branches) the insertion loss depends on the filling density of the probes. The measurements on probes of two different plant species showed similar results, if the filling density was equal. For the sound absorption coefficient results were again dependent on the filling density. As before, probes of different species gave similar absorption coefficients at equal filling density. Further tests have to reveal, if the filling densities tested are representative for real hedges, and if the results can be reproduced on real hedged. Therefore measurements on real size hedges in the laboratory and in the free field are next steps in this project.
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