(FILES) This photograph shows the South Rose window and organ of Notre-Dame de Paris cathedral, ahead of its official reopening ceremony after more than five years of reconstruction work following the April 2019 fire, in Paris on December 7, 2024. Alongside the stonecutters, carpenters and archaeologists who went to Notre-Dame after the 2019 fire, scientists looked at an intangible heritage: its acoustics. Sermons, organs, polyphonic chants... sound, and the way it propagates within its walls, is an essential element of the cathedral and throughout its 860 years of existence, this acoustic has been "dynamic, evolving", depending on architectural changes, but also modifications - sometimes subtle - in furniture and decor, Brian F. G. explains to AFP. (Photo by Ludovic MARIN / POOL / AFP) (Photo by LUDOVIC MARIN/POOL/AFP via Getty Images)