Acoustic Characterization of Grass-cover Ground.

摘要

A custom designed acoustic impedance tube was used to measure acoustic properties of nonconsolidated materials, specifically soils and grass-covered ground. The tube was configured vertically for studying acoustic properties of granular materials i.e. soil and dirt. Software was developed to collect data and calibrate the impedance tube. An equivalent fluid model for describing sound propagation in rigid frame porous media was used to model acoustic behavior of dry and wet soils as well as grass-covered and -uncovered ground. The model requires six parameters, i.e. porosity, tortuosity, flow resistivity, thermal permeability and viscous and thermal characteristic lengths. are measured separately. While flow resistivity was measured, the remaining five parameters were found by fitting procedure (optimization process). Theoretical models of sound propagation in porous media and acoustic measurements were used to explore the effects of water and vegetation (grass blades and roots) on the sound absorption and reflection of grass-covered ground. The acoustic and flow resistivity measures show that there is minute differences between the acoustic-soil interaction behavior between a root substrate with and without grass. Particularly with the soil samples, moisture encouraged broadband absorption in the higher frequency limits of the acoustic impedance measurements system compared to dried soil.