A unique theatre has opened up in Zwolle. The theatre is suitable for both classical concerts and stage plays. This dual use produces a unique acoustical problem. The amount of sound produced by an orchestra is different than the sound that is produced during a play. Thereby only when the sound is in proportion with the space the sound can be heard well. De Spiegel deals with sound distortions by using a moving ceiling. Because an orchestra produces loud sounds, the ceiling will be fixed at the highest position during a concert. For stage plays it works the other way around. Voices may fade away in the large space and therefore the ceiling will be fixed at the lowest position.

In its most compact form the theatre has a capacity of 850 seats. By raising the ceiling 6 metres and enlarging the theatre opening of 14 x 8 metres to 18 x 14 metres, extra space can be added to the acoustic volume which makes the auditorium suitable for concerts. By raising the ceiling the gallery can be connected to the auditorium, which results in a larger capacity of 1000 seats. The exterior of the auditorium is recognisable by its spherical geometry made of titanium and zinc. The round shape is sunk down into a box shaped volume. This is realised by two parts: the brick laid auditorium and the foyers. The theatre house consists of brickwork and the foyer is made of aluminium/wooden lower fronts. The foyers are spacious and designed to promote interactions between people. At several places seats are placed to encourage intimate conversations. The façade consists of long strips of glass between wooden pillars. Magnificent views from within are achievable due to the minimal pillars and tall glass. Distances between pillars vary creating an asymmetrical facade.