The Amintore Galli theater in Rimini re-opened in 2018, after more than 60 years of inactivity. Its acoustics have been studied in depth, starting in 2009 until the reopening of the theater. This paper analyses the following different steps of the acoustic design of the Opera House: the analysis of the acoustics of similar other theaters, the design of the acoustics of the new main hall, the analysis of the acoustic characteristics of the diffusing panels in the theater, and the acoustic design of other rooms, including the rehearsal room. Moreover, this paper reports some of the most relevant results of the acoustic surveys conducted after the re-opening, comparing the values of some acoustic parameters obtained after the simulation processes, and the values of the same parameters during the final validation of the theater. © 2022 Free University of Bozen Bolzano. All rights reserved.