The acoustic design of the Main Hall of the “ALMA MATER STUDIORUM”

The University of Bologna, which started in 1088, opened in 1988 the new Main Hall, after restoration of a former Jesuits church, which was founded in 1623 and partially modified in 1843, on the site where S Petronius founded a church devoted to S. Lucy, in 432. The new Main Hall showed strong acoustic defects since his opening. The church has one high nave, plastered walls and a reflecting pavement. The lateral chapels of the church, as well as the huge volume (about 30000 m3) provoked a very high reverberation in the church, which is not mitigated by the not upholstered seats in the hall. The acoustics was partially enhanced by means of an electroacoustic system, which was able to partially redirect the sound directly to the audience. However, acoustic design of the hall was required to improve the sound distribution, even though already repeatedly proposed in the past. In this paper a new acoustic design of the hall is presented. Starting from recent acoustic measurements, the proposed enhancements cover many components in the church, but still maintaining its peculiar architectural aspect: acoustic plaster, curtains, and a set of transparent, flexible acoustical panels, which could move and turn separately, redirecting sound propagation in the hall. Finally, the acoustic enhancements are presented by means of 3D Auralization.