Archive for November 11th, 2015

November 11, 2015

Whispering Gallery

whisper echo

A whispering gallery is a circular room in which whispers can be heard clearly across great distances. The sound is carried by waves, known as ‘whispering-gallery waves,’ that travel around the circumference clinging to the walls, an effect that was discovered in the whispering gallery of St Paul’s Cathedral in London. Other historical examples are the Gol Gumbaz mausoleum in India and the Echo Wall of the Temple of Heaven in Beijing.

The gallery may also be in the form of an ellipse or ellipsoid, with an accessible point at each focus. In this case, when a visitor stands at one focus and whispers, the line of sound emanating from this focus reflects directly to the focus at the other end of the gallery, where the whispers may be heard. In a similar way, two large concave parabolic dishes, serving as acoustic mirrors, may be erected facing each other in a room or outdoors to serve as a whispering gallery, a common feature of science museums. Egg-shaped galleries, such as the Golghar Granary in India, and irregularly shaped smooth-walled galleries in the form of caves, such as the Ear of Dionysius in Syracuse, also exist.