Transparant Concert Hall Acoustics

April 15, 2005 the new concert hall for symphonic music, Casa da Música in Porto, Portugal, has been inaugurated. The architectural concept of a transparent shoebox-shaped hall in combination with program requirements challenged the acoustics in many ways. By just pressing a button the acoustics of the hall is changed from excellent for symphonic music to adequate for amplified productions. All kind of technical provisions have been introduced in the design: lighting bridges, movable canopy, acoustic curtains, a moving bridge etc. In fact we believe a new type of multifunctional halls has been built. Will this be the future and, if so, what are the consequences for the field of acoustics? The main auditorium, with a capacity of 1250 seats, has a transparent vertically movable and cantilever canopy. Canopy positions have been studied to optimize the support on the stage with respect to the playing ensemble. QRD diffusers have been applied to create a diffuse and equally distributed sound field. Because of architectural issues the standard 734 diffusers have been modified. Instead of the 0- deep well in the sequence 0–1–4–2–2–4–1, a 7–deep well is used. This modification proved to have an impact on the acoustic performance of the diffusers, thus the acoustics of the hall.