Akihiro Miyagi, Yasushi Minowa, Yuhka Mori, Akane Kaneda and Mao Kawamura: Physical attenuation effects of forest spaces on noises. Jpn. J. For. Plann. 54: 93~103, 2021 We used a sound test to determine the physical attenuation effects of forest spaces on noises. We selected a 10×50 m study area in a deciduous broad-leaved forest in Ohmi District, Sakyo-ku, Kyoto City. Oscillating sound was sampled at 80 and 95 dBs, and the sampling frequency comprised nine patterns : eight sine waves (125, 250, 500, 1,000, 2,000, 4,000, 5,000 and 8,000 Hz), and white noise. The sounds were oscillated from a set oscillation point and recorded at the heights of 1.3 and 5.0 m at five sound recording points. The sound pressure levels of the recorded sounds were then analyzed. A sound test was performed twice: before and after the falling of leaves. We created a standing tree map and a crown projection diagram based on tree census data, calculated the volume of the space occupied by the branches and leaves in the tree crowns, and established the presence and absence of leaves. The differences between the measured and theoretical values of sound-pressure levels(hereinafter, the “quantity of attenuation”)for every frequency band at the sound recording points showed almost positive values. Moreover, the volume of the space occupied by the branches and leaves in the tree crowns and the levels of attenuation between the oscillation point and the microphone were found to show a strong positive correlation. Overall, the quantity of attenuation hardly changed in the presence or absence of leaves. According to the frequencies, the quantity of attenuation for 95 dBs of oscillating sound were found to be higher before the falling of leaves than they were after the leaves had fallen. We thus inferred that the presence and absence of leaves had a significant effect on noise attenuation. In addition, the highest effect on noise attenuation was found in the levels of attenuation in the low-frequency band, followed by the middle and high frequencies. This study provides new information on the factors that influence the physical attenuation effects of forest spaces on noises.
View full abstract