有限障壁(衝立)による騒音の回折 : 障壁(塀)の遮音設計に関する実験的研究 第2報
Acoustical Science and Technology
Noise Reduction Brought about by a Finite Plane Screen
AcousticalSociety ofJapan 1 ff. g -igMscag CblS) l[ ,kswagoAth vees (m) totsEtcst(ceeir6Rwtthmes en2va ]e-us As the first experiment, the sound level distribution in the shadow zone of a long screen extending on the ground has been measured by produeing the lf3 octave band noise ranging from 2.5 kcfs to 10 kcls radiated from a non-directional speaker. The receiving points were moved along horizonta1 lines perpendicular and also not perpendicular to the screen, and the sound pressure level was
... ressure level was recorded with ahigh speed level recorder. The results thus obiained (Fig. 8) show that the calculation method of the sound level in the shadow zone described in the previous paper is applicable to any point not enly on the two-dimensional plane crossing perPendicular to the screen, but also in the three-dimensienal space. As the second experiment, noise reduction brought about by a finite screen (61 cm high, 128 cm long, 2cm thick) set up on the ground has been measured by the same method as mentioned above. The receiving points were moved along the horizonta1 and vertical lines para11el to the screen within the shadow zone of the screen, and the sound pressure levels were recorded. Also the theoretical calculations have been made under these conditions in the following way in accordance with the Kirchhoff's diffraction theory : 1) The sound pressure at the receiving point was given as an integral of a certain function over the blank p]ane on which the sereen was situated. /2) Then, that blank plane was divided into several zones bya number of convenient straight lines. The integral over each zone has beeri easily obtainea from the chart (Fig. 11 ) given in the previous paper. 3) The contribution of each divided zone to the sound pressure at the receiving point has been superposed together neglecting their phase since they were noises. 4) Similarly, the sound waves reflected from the ground were calculated at the image of the receiving point assuming that the ground reflects them perfectly. [[1ie results of measurement and calculated values have been shown in Fig. 10. From the practical point of view, the measured values are in pretty good agreement with the calculated values.