Some Physical and Psychological Aspects of Noise Attenuation by Vegetation

-The physical mechanisms governing sound attenuation by foliage, stems, and ground are reviewed. Reflection of sound energy is found to be the primary mechanism. In addition, new experimental results are discussed that help to quantify the psychological effect of a plant barrier on perceived noise level. Listeners judged the loudness of noise transmitted through hemlock trees and through a minimal fence barrier to differ by as much as 7 dB even though the sound level at the listener was the same. CONSIDERABLE M E A S U R E MENTS O F NOISE muffling by plants have been made. To properly interpret these measurements, a firm understanding of the physical mechanisms of sound attenuation by plants is required. For example, many of the differences in sound attenuation by plants found by earlier workers (Eyring 1946, Wiener and Keast 1959, Embleton 1963) can now be reconciled by physics (Aylor 1972a). Besides physical effects, there can be psychological effects of plant barriers on the perception of noise. The visual shielding of a source by plants may have a beneficial effect for reducing the annoyance of noise (Kurxe 1974, Herrington 1974). So far , this potential psychological effect has not been quantified.