公害用振動ピックアップの接地共振とその制御

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A block diagram of the measuring system is shown in Fig. 1. The pick-up of acceleration type is set on the ground surface and at a point on the surface not far from the pick-up struck with a wooden hammer repeatedly. The output of the pick-up is amplified and recorded on an endless tape of a data-recorder. At laboratory the record is reproduced and analyzed by frequency-analyzer of continuously scanning type. We tried preliminary experiments by placing the pick-up on a surface plate. To change the contact condition some sheets of paper were inserted between the pick-up and the surface plate and the number of sheets was changed 1, 2, 4, up to 128. Fig. 2 and Fig. 3 show examples of the results obtained. The pick-up used in the above experiments was that of actual vibration level meter. Next, using a test pick-up as shown in Fig. 4, we examined the relation between the resonant frequency f_0 and the mass of pick-up m_0, and also the relation between f_0 and additive mass m_a attached as shown in the figure. Fig. 5 and Fig. 6 show examples of the results. Then placing a pick-up of actual use on the ground surface under various conditions, we carried out several experiments. (a) Table 1 shows the order of values of resonant frequency on ground surfaces under natural condition and hardened by foot. In some materials and under some conditions we could not expect to harden the ground surface by foot. (b) In some cases we could improve the conditions by scattering certain materials, for examples, a small amount of water on dry sand, and a small amount of soil or sand on deep wet mud. (c) Attaching some kind of frames or rims under the base surface of pick-up, we could also improve the conditions, and example being shown in Fig. 7 and Fig. 8. (d) Fig. 9 shows examples of measurement of ground vibration due to passing trains. The hardening effect of ground surface can be ascertained in the figure obviously.
社団法人日本音響学会の論文
1977-11-01

公害用振動ピックアップの接地共振とその制御

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