Some double curvature structures are known for the echo or the reverberation phenomena they create. These are due to the size of the spaces and the materials exploited for the structure or the finishing (usually hard and with small pores). The shape does a lot in preventing or enhancing the effect. Cross or cloister vaults do not generate an echo. Pointed domes easily create reverberation more than echo. At the same time, spherical surfaces are highly reflective due to their concavity. Indeed, hemispheres, paraboloid, or similar surfaces are effective at reflecting and redirecting sound, sometimes constituting a whispering gallery. Examples of whispering galleries can be found in well-known architectures like St Paul's Cathedral in London, where the phenomenon has been studied by Lord Rauyleigh or the Archbasilica of Saint John Lateran in Rome, but also in caves like the Ear of Dionysius in Syracuse, Sicily, which has been treated by Wallace Clement Sabine.