Reverberation time (RT) is a fundamental acoustic parameter that strongly influences speech intelligibility in enclosed spaces. Excessive reverberation causes temporal smearing of speech signals, reducing the clarity of consonants and degrading listener comprehension, while insufficient reverberation can result in speech sounding weak or unnatural. This presentation examines the relationship between reverberation time and speech intelligibility, with particular attention to occupied rooms used for communication‑critical functions such as classrooms, lecture theatres, and healthcare environments. Key speech intelligibility metrics, including the Speech Transmission Index (STI) and clarity measures, are discussed in relation to varying reverberation conditions. The analysis highlights optimal RT ranges for different room typologies and emphasizes the importance of acoustic design strategies—such as sound absorption, room geometry, and surface treatment—in achieving intelligible speech. The findings reinforce the need for performance‑based acoustic design to balance reverberation control with functional and architectural constraints.