Problem on noise emitted from drain pipe has always been caused. In recent years, the number of apartment houses and hotels which have different plan at each floor is increased because originality for room design is regarded as important. So new problems on noise emitted from drain pipe have been arisen. It is supposed that the investigations on concrete reduction methods for noise emitted from drain pipe and the many applications have been carried out. But paper on these investigations is very few.
The experimental investigations on generation mechanism, basic characteristics and reduction method of sound emitted from drain pipe were carried out. From these results the followings were shown.
(1) Sound emitted from drain pipe is caused by vibration of pipe wall which is generated by excitation by water drop of drain.
(2) Emitted sound is different from material of drain pipe. And the magnitude depends on the driving point impedance of pipe wall.
(3) Relation between emitted sound and drain quantity is linear.
(4) Emitted sound is almost constant regardless of the height of drain because drain is running at inner wall of pipe.

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