Communicating arcs

Low level. We can all speak from any distance using mobile phone, but could you talk to a friend 50 meters away using... a building? In the Science Museum Príncep Felipe we will show that you can do it.
Los viandantes pueden disfrutar del efecto arquitectónico que producen los arcos comunicantes de la entrada del Museu de les Ciències

To do this, place yourself at the edge of our great arch, beside the entrances of the Museum and follow these steps:
1. Stand at one end while your companion is at the opposite side.
2. Speak naturally facing the wall. Start a conversation and wait for an answer.
3. Now place yourself in the centre of the arch while your partner stays in the same position and speaks again.

What is happening? How is it possible to hold a conversation without shouting 50 meters away, and you cannot do it if you put yourself right in the center of the arch?

The Sound waves of your voice are channelled through the arched structure, and reach directly into the ear of the other person. It is just this structure which allows waves not to be scattered in all directions. That's what happens when you place yourself in the centre of the arch or when we normally talk.