The frequency and angular dependence of the absorption coefficient of common types of living plants

The frequency and angular dependence of the absorption coefficient of specimens of several types of plants used in living walls and noise barriers is investigated. The reported data are obtained by placing the specimens in a large impedance tube which frequency range has been extended significantly beyond the frequency of the plane wave regime. The multi-modal sound pressure field in the tube is measured with a microphone array. A theoretical model is adopted to determine the reflection coefficients for the individual modes. This information is used to estimate the frequency and angular dependent absorption coefficient for the plant specimens. The absorption coefficient data are compared against the predictions made with an equivalent fluid model which is based on the leaf area density and dominant angle of leaf orientation.