The Sibelius Museum is rectangular in shape and has two centres, the Sibelius Hall and the Atrium. The slightly sunken concert hall seating 150 people is not built as a separate space but serves as a central point encircled by the exhibition spaces. The walls of the concert hall consist of concrete elements with visible holes from the casting process. The ceiling, on the other hand, is a concrete shell in the form of four concrete hyperbolic paraboloids. Their vault-like structures are cast-in-place and the pattern of their shuttering is subtly visible. Rainwater from the roof runs down into water butts via the four weight-bearing pillars. The Sibelius Hall is known for its original acoustics designed by T. K. Laakso. The acoustics are said to be especially ideal for chamber music and soloists.