Plants as Noise Control
Optimisation of the Acoustic Shielding Effect of Hedges and Woods
Hedges and woods have many important functions for our environment - especially in densely populated urban centres: They produce oxygen, filter the air, serve as visual protection or windbreak, are habitat for birds and insects, are used as structuring and limiting elements and contribute to balanced micro-climate by their ability to store humidity. But they are scarcely used for noise control in in urban development. Relevant design guidelines rank noise abatement by means of plants relatively low so that noise reduction can be computed only in case of large-area green spaces. The standard DIN ISO 9613-2 for example contains a noise abatement of α = 0.06 dB/m at 1000 Hz for all kinds of green spaces independent of the species of plants, their density of height. The result is a computed level reduction of 3 dB for a 50 m wide green space. However, it must be taken into account that the specifications stated in the guidelines are only minimum data, which can be clearly exceeded in practise.
Publiccations report on measurements, where sound attenuation is ten times higher than the values determined in standard DIN ISO 9613-2. These measurements were performed at natural green spaces, which were not optimized with regard to acoustic effiiency so that the potential of suitable hedges is expected to be even higher. Besides objective measurement data psychological argue for the use of plants for noise control in urban development. Local residents subjectively assess the noise control effect of hedges higher than that of noise barriers, althogh measured acoustic data prove the opposite.
Any knowledge of adequate design of hedges as noise control and their effectiveness is not available at present. Similary, the acoustic properties of hedges are still relatively unknown. Therefore, the aim of this study is to investigate, which plants are suited for noise control purposes from the acoustic point of view, how they should be planted, what dimensions these hedges must have, and how other influencing factors, e.g. the density of plants, surface area, form and thickness of leaves etc. have an impact on acoustic properties. The investigations will be performed by measurements under idealized laboratory conditions as well as by outdoor measurements at real hedges. In addition, computational models will be applied to determine the attenuation and absorption coefficients, to improve the noise control effect and develop a reliable basis of design for urban planning and ladscape design.
Prof. Dr.-Ing. Philip Leistner
Phone +49 (0)711 970-3314
Fax +49 (0)711 970-3406