The acoustic quality of assembly halls is a key feature in the architectural design of such spaces. This challenge has long been a concern for architects of religious buildings. Due to the extensive mirror cladding covering the porticos of the Imam Reza (AS) Holy Shrine, designing a sound system for religious ceremonies in this space presents serious challenges and is highly complex. The Imam Khomeini (RA) Portico within the Imam Reza (AS) Holy Shrine is an acoustically highly complex environment, and given its special status in hosting programs at the Holy Shrine, conducting scientific research on its acoustic conditions is of great importance. In this study, an attempt has been made to first describe the acoustic conditions of the Imam Khomeini (RA) Portico, and then, based on simulation results, propose acoustic modifications to improve the existing conditions. Based on simulation results and field measurements, recommendations such as installing sound absorbers on side walls and behind the ceremony platform, as well as creating side corridors using decorative and sound-absorbing walls, were proposed, some of which were implemented. These modifications led to an improvement in the Speech Transmission Index (STI) from below 0.4 to approximately 0.6, and a reduction in reverberation time from about 10 seconds at frequencies below 500 Hz to less than 2.5 seconds—which is considered favorable for a hall with an approximate volume of over 60,000 m³ and fully mirrored surfaces.