Whispering gallery

As Flüstergewölbe or whispering (English Whispering Gallery) is colloquially referred to a place at which people can talk about an unusually large distance at a normal volume. For this effect, there are several causes:

  • Speaker and listener are located at the foci of facing parabolic " sound mirror " ( see picture). Even the small reflection area of ​​2 m in diameter is sufficient to transmit words softly spoken over a distance of about 80 m. Outside of the two foci is not to hear the sound. In principle, it is in this structure, an acoustic radio link, which is used eg in science centers to demonstrate the function of Flüstergewölben in elliptic spaces.
  • Speaker and listener are in the focal axes of a room with an elliptical ground plan or even better at the focal points of a rotary Elliptoids. In these cases, all emanating from the speakers sound waves are reflected from the walls of buildings so that they are located in the second focal point, the listener, reunite. In the cathedral of Agrigento in Sicily this effect in the past even had a special significance: it has inside the shape of a rotational ellipsoid, and a confessional was positioned there in one of the foci. This confession at another point was clearly heard in the room for other people, which led to some discord.
  • Speaker and listener are in a dome with respect to the center of which mirrored positions, the hemispherical dome is a special case of an ellipsoid in which both foci unite in the center. A standing in the center speaker hears therefore echo of his own voice in an unusual volume. Away from the center of the dome of the speaker, the sound waves are reflected from the walls at a point at an equal distance from the center on the opposite side of the dome. It is thus, in principle, to any person standing in such a bubble possible to talk with a partner on the other side, and succeed at the same time for many different dialogues. However, the effect with increasing distance from the center of the dome is weakening, because then increasingly resulting phase differences in the converging sound fronts. This phenomenon had, moreover, earlier in the Statuary Hall in Washington negative impact, as MPs from different parties in this room undesirably " Flüsterpartnern " were
  • Speaker and listener are in a vaulted passage or near the wall of a dome. Someone speaks against the curved wall, the noise is successively smoothly collected by multiple reflection, and guided in a direction parallel to the wall surface. The normal three-dimensional sound propagation with the typical decrease in volume with the square of the distance is limited by this effect. In a vaulted passage created by the additional sound reflection of the floor and the ceiling a kind of " acoustic waveguide ". In this case, the sound energy is not distributed with greater distance to an increasing area of ​​the sound front, so that the wave attenuates less and accordingly can continue. This mechanism is not very difficult regarding uniformity and smoothness of the curved wall, and produces, for example, the whispering gallery in the walkway of the Moorish Garden Wilhelma.
  • Speaker and listener are in the vicinity of a smooth and homogeneous in the interior wall. If the sound at a certain angle to the wall, it can then develop a so-called Rayleigh wave. This type of wave has been predicted theoretically by Lord Rayleigh later for stress-free boundaries and demonstrated experimentally in the dome of Saint Paul 's Cathedral in London. This acoustic wave style, is located directly at the interface between the wall and air and can also be completely flat or convex surfaces arise, so that the resulting effect is not limited only to a vault. The intensity of a Rayleigh wave, perpendicular to the wall will in dependence on the sound frequency rapidly, whereby a substantial portion of acoustic energy within a wall distance focus, which is smaller than the wavelength of the sound ( for example, 0.3 m to 1000 Hz or m is 3 100 Hz in air). Thus, the high frequencies of whispering vergleichswseise be particularly closely guided along the wall and carried sufficiently far, where also was originally the name " Whispering " stirred. The famous Whispering Gallery of St Paul's Cathedral made ​​possible by this effect, a whispered conversation along the entire gallery, which has a diameter of 32 m.

Flüstergalerien

  • Saint Paul 's Cathedral, a church in London, in the whispered words are audible from one side of a gallery in the dome on the other side.
  • BUSSTOPS, an arty tram stop in Hanover, transfer the sound of those waiting in the parabolic reflectors on the opposite side of the street.
  • Oldenburg ( Oldenburg), sound transmission between parabolic reflectors in Hörgarten at the " House of Listening"
  • Colonnade of Moorish garden Wilhelma in Stuttgart
  • Cathedral of Agrigento in Sicily
  • Flüstergewölbe in Görlitz
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