Influence of vegetation on acoustic properties of soils.

Possible influences of vegetation on acoustically relevant soil parameters, such as porosity and soil structure, were considered. In situ measurements of sound interference patterns were performed in seven plant communities by means of an inclined track method. Normal acoustical specific impedances were calculated with a plane wave outdoor sound propagation model. The impedances found generally showed a real part constant with frequency, and an imaginary part decreasing with frequency. It is concluded that forest floors have an acoustically detectable layer structure and that, for purposes of modelling of outdoor sound fields, much lower impedances have to be used than for institutional grass.