Vaults

Example of a vault

Description

Vaults are generated by the projection of the arch section on a plan, which is most of the time horizontal. A vault is an arch-shaped structure, usually of masonry, used as the ceiling of a room or other enclosed space, as the roof of a building, or as the support for a ceiling or roof. Masonry vaults are often composed of voussoirs, which are held in place, like the stones of an arch, by the pressure of the neighboring pieces. A temporary supporting structure must be erected within the vaulted area during construction, because a masonry vault does not become self-supporting until the central voussoirs or keystones are put in place. A number of different types of vaults are used architecturally. The simplest of these is the barrel, or tunnel vault, the roof of which is shaped like half a cylinder and is supported by straight walls. A groined vault is formed by the intersection of two vaults of the barrel type, usually at right angles to each other. The junctures at which the two vaults meet are elliptical ridges, called groins. A dome can be thought of as an arch which has been rotated around its vertical axis. As such, domes have a great deal of structural strength. A small dome can be constructed of ordinary masonry, held together by friction and compressive forces.

Details and experiences

ACOUSTICS OF VAULTED STRUCTURES

Vaulted structures are characterised by two acoustic phenomena: echo and reverberation. Echo is a disturbing phenomenon which happens only in domes which are generated by the portion of a sphere. The dome might be built on a circular plan or on a quadrangular one (i.e. dome on pendentives) but it will always have an echo if it has the shape of the portion of a sphere or a shape close to the portion of a sphere. Hemispherical domes have the strongest echo. Pointed domes have rarely any echo but they can have a high reverberation and/or amplify the sounds. Domes which are generated by the intersection of vaults (i.e. cloister or groined dome) don’t have any echo at all.

Vaults and domes always manifest a high reverberation, which represents the time needed for the sound to fade away. This reverberation is due to 2 factors:

1. The size of the volume created by the vaulted structure, which is generally larger than other ones.
2. The shape of the structure, which tends to hold the sound within itself.

Echo and reverberation can be limited by acoustic correctors. These correctors are called single resonator absorbers. A German engineer, Helmholtz, elaborated some formulas to calculate them. The human voice ranges from 100 Hz to 2 kHz, with an average frequency at 400Hz. Correctors of various sizes can be installed to absorb the desired frequencies.

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