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ブログ 2018-09-20

“Whispering Gallery” : Mysterious phenomenon seen in St Paul’s Cathedral (London)

Hello, this is Mr.I of Shizuka Co., Ltd..

Today, changing my preferences as usual, I’d like to tell you about some knowledge related to sound.
original article in Japanese (日本語の記事)

Whispering Gallery

Do you know the phenomenon called “Whispering Gallery”? This is a phenomenon in which reflected sound repeats reflection along the concave surface and travels far. 

As you can see, the sound that was talking in a low voice at a certain point of the building repeatedly reflects through the wall and it reaches the opposite side. As a condition under which whispering gallery phenomenon occurs, it is said that the building has a beautiful circular shape when looking at the average, and that the wall is made of a material that easily reflects sound.

St Paul’s Cathedral

The famous one is “St Paul’s Cathedral” in London.

At the St Paul’s Cathedral there is a corridor that can be totally under the vault ceiling. There is nothing in the center of the dome, you can see the person walking in the opposite corridor, but even if you make a loud voice to the other side, it does not reach at all. However, just by whispering toward the wall, the voice is conveyed to the other side without raising a loud voice. This phenomenon is well known for propagating in the horizontal direction along the wall, but it seems to occur also in the vertical direction on a large dome ceiling or the like.

Problems of reflected sound

Well, there is something mysterious and interesting about this phenomenon. However, it may be a problem from the viewpoint of architectural structure. In a space that emphasizes natural sound like a music hall, unnecessary reflected sound becomes a noise. In this case there is no direct problem, but depending on the purpose of the hall, it is required to pay attention. In that case, by applying sound absorbing material etc. to the wall, it becomes possible to reduce the reflected sound and it will be able to create a space where you can enjoy best music.

 

The story of this time is here.
Actually, there seems to be a place where whispering gallery phenomenon can be seen here in Japan, but I will decide this story again someday. See you soon again at the next article.

 

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