Since the mid-1950s, Stockhausen had been developing concepts of spatialization in his works, not only in electronic music, such as the 5-channel "Gesang der Jünglinge" (1955–56) and "Telemusik" (1966), and 4-channel "Kontakte" (1958–60) and "Hymnen" (1966–67). Instrumental/vocal works like "Gruppen" for three orchestras (1955–57) and "Carré" for four orchestras and four choirs (1959–60) also exhibit this trait (; ; ). In lectures such as "Music in Space" from 1958 , he called for new kinds of concert halls to be built, "suited to the requirements of spatial music". His idea was In 1968, the West German government invited Stockhausen to collaborate on the German Pavilion at the 1970 World Fair in Osaka and to create a joint multimedia project for it with artist Otto Piene. Other collaborators on the project included the pavilion's architect, Fritz Bornemann, Fritz Winckel, director of the Electronic Music Studio at the Technical University of Berlin, and engineer Max Mengeringhausen. The pavilion theme was "gardens of music", in keeping with which Bornemann intended "planting" the exhibition halls beneath a broad lawn, with a connected auditorium "sprouting" above ground. Initially, Bornemann conceived this auditorium in the form of an amphitheatre, with a central orchestra podium and surrounding audience space. In the summer of 1968, Stockhausen met with Bornemann and persuaded him to change this conception to a spherical space with the audience in the centre, surrounded by loudspeaker groups in seven rings at different "latitudes" around the interior walls of the sphere (; ). Although Stockhausen and Piene's planned multimedia project, titled "Hinab-Hinauf", was developed in detail , the World Fair committee rejected their concept as too extravagant and instead asked Stockhausen to present daily five-hour programs of his music . Stockhausen's works were performed for 5½ hours every day over a period of 183 days to a total audience of about a million listeners . According to Stockhausen's biographer, Michael Kurtz, "Many visitors felt the spherical auditorium to be an oasis of calm amidst the general hubbub, and after a while it became one of the main attractions of Expo 1970" .