Throughout history, many cultural heritage buildings of important value have been lost due to natural disasters as well as human causes (e.g. fire, war destruction, change of use etc.). The needs to build a larger theatre, as occurred in Vienna, addressed the Carinthian Gate theatre to have different room functions, while currently is considered the house of Sacher cake at international level. This paper deals with the discovery of the acoustic response of one of the most important theatres of Vienna. The realization of a 3D model that reproduces the architectural features allows the authors to perform acoustic simulations that reveal the sound environment that would be perceived by the audience during artistic performances at the end of eighteenth century in Vienna. In addition, the simulated results of the main acoustic parameters have been compared with the values of other opera theatres provided with similar dimensions and architectural features, as already studied by the authors. The results indicate an overall acoustic response, as typical of horseshoe shape plan layout theatres with the values of clarity found very close or within the optimal range, the sound strength ranging between 4 and 11 dB, and the reverberation time close to 1.5 s, in line with the criteria of opera theatre based on the room volume of the main hall and finished materials applied to the surfaces of the 3D model.