Significant changes to Utzon's design
What is the reason for Utzon's designs being changed in the Sydney Opera House?
Sydney Opera House
 The major hall, which was originally to be a multipurpose opera/concert hall, became solely a concert hall, called the Concert Hall. The minor hall, originally for stage productions only, incorporated opera and ballet functions and was called the Opera Theatre, later renamed the Joan Sutherland Theatre. As a result, the Joan Sutherland Theatre is inadequate to stage large-scale opera and ballet. A theatre, a cinema and a library were also added. These were later changed to two live drama theatres and a smaller theatre "in the round". These now comprise the Drama Theatre, the Playhouse, and the Studio, respectively. These changes were primarily because of inadequacies in the original competition brief, which did not make it adequately clear how the Opera House was to be used. The layout of the interiors was changed, and the stage machinery, already designed and fitted inside the major hall, was pulled out and largely thrown away, as detailed in the 1968 BBC TV documentary "Autopsy on a Dream", which "chronicles the full spectrum of controversy surrounding the construction of the Sydney Opera House".  Externally, the cladding to the podium and the paving (the podium was originally not to be clad down to the water, but to be left open).  The construction of the glass walls (Utzon was planning to use a system of prefabricated plywood mullions, but a different system was designed to deal with the glass).  Utzon's plywood corridor designs, and his acoustic and seating designs for the interior of both major halls, were scrapped completely. His design for the Concert Hall was rejected as it only seated 2000, which was considered insufficient. Utzon employed the acoustic consultant Lothar Cremer, and his designs for the major halls were later modelled and found to be very good. The subsequent Todd, Hall and Littlemore versions of both major halls have some problems with acoustics, particularly for the performing musicians. The orchestra pit in the Joan Sutherland Theatre is cramped and dangerous to musicians' hearing. The Concert Hall has a very high roof, leading to a lack of early reflections onstage—perspex rings (the "acoustic clouds") hanging over the stage were added shortly before opening in an (unsuccessful) attempt to address this problem.