We proposed a new method to evaluate noise reduction due to damping treatment by using the particle velocity of sound measured directly in the vicinity of a vibrating object. Moreover, the proposed method was verified based on the comparison between vibration and particle velocity reductions. In Japan, a procedure to revamp old railway bridges, which had no specific fissure damages or serious corrosions, by applying to composite remodeling process have been widely used. During the process of such composite remodeling, we have often used magnetic rubber damper or rubber-latex mortar to reduce remarkable large power of structure-borne sound radiated from steel bridge of railway. This proposed method enables us to estimate precisely noise reduction of these countermeasures, because we grasp the behavior of sound radiated from the vibrating object in detail. In this paper, we present the results of laboratory and field experiments on the effects of noise reduction by using two magnetic rubber dampers, type-A and type-B. In the field measurement, the type-B more significantly reduced the sound radiated from vibrating beam. However, the reduction of radiated sound and that of vibration did not coincide. The reason was clarified from comparison between vibration and particle velocity, which occur due to vibrating a steel plate of simulated beam of bridge in laboratory experiment. Thus, the proposed method enables us to evaluate noise reduction precisely.
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