As proved by the studies carried out but also from practical situations, the acoustic behaviour of an enclosed performance hall is strongly dependent on occupancy level. This happens because human bodies and upholstered seats contribute significantly to sound absorption and in addition modify the modal structure of the acoustic field. This work presents a complex finite element method (FEM) simulation, conducted in ANSYS Workbench 2023, which compares the acoustic performance of a concert hall under three discrete occupancy scenarios: 57, 43, and 28 attendees. Seven humanoid solid models were used to represent audience members and extract the air volume accurately from the hall geometry. Key acoustic metrics were evaluated, including acoustic pressure distribution, Sound Pressure Level (SPL), A-weighted SPL (dBA), far-field SPL, frequency band SPL, and frequency response phase angle, at representative frequencies of 400 Hz, 10,800 Hz, and 20,000 Hz. The obtained results demonstrate that occupancy reduction from 57 to 28 persons increases the effective modal density, elevates low-frequency standing wave contributions, reduces broadband absorption, and shifts the acoustic pressure distribution toward higher spatial non-uniformity. The results obtained provide quantitative assistance for the design of adaptive acoustic scenarios in spaces with variable occupancy.