The Sound Book: The Science of the Sonic Wonders of the World by Trevor Cox

Author:Trevor Cox [Cox, Trevor]
Language: eng
Format: epub
Tags: Science, Acoustics & Sound, Non-Fiction
ISBN: 9780393350586
Google: rATGAgAAQBAJ
Amazon: 0393350584
Barnesnoble: 0393350584
Goodreads: 17986401
Publisher: W. W. Norton & Company
Published: 2014-02-10T00:00:00+00:00

Figure 5.9 Sound in a whispering gallery.

Imagine cuing a ball on a circular pool table so that it goes off almost parallel to the side wall. The ball then maps out how sound moves around the gallery when someone whispers along the wall. An unexpected effect becomes apparent: the ball hugs the wall, circulating close to the curve without ever going into the middle of the circle. The same thing happens with sound in a whispering gallery, as shown in Figure 5.9.

When I visited the listening station at Teufelsberg, I demonstrated the whispering-gallery effect to my tour guide, Martin. He had encouraged others to try out the acoustics in the center of the room but was unaware that the voices could skim around the edges. Later, in brief moments when the radome was empty, I made a measurement by bursting a balloon on one side of the dome, while my sound recorder was balanced next to the wall on the other. With such a loud bang, the sound can make many circuits around the edge of the dome before dying away to silence. For one burst I counted eight clear bangs. A plot from one of the recordings (Figure 5.10) shows four or five spikes at times when the bang passes the microphone.

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