Room Acoustics 101: RT60, EDT, Clarity & More Posted on September 25, 2026 Ever walked into a room and noticed how sound behaves differently depending on its size, shape, or materials? From lecture halls and auditoriums to clubs and studios, the way sound decays after the source stops plays a crucial role in how we perceive it. While studying and measuring the acoustics of a room, there are multiple metrics that allows engineers and designers to create spaces that sound just clear, natural, and immersive. In this post, we will break down the essential room acoustic metrics: RT60, EDT, Clarity, and more, and explain why they matter for speech, music, and performance spaces. Understanding Key Acoustic Metrics RT60 (Reverberation Time 60 dB) RT60 measures the time it takes for sound to decay by 60 dB after the source stops emitting a signal. Longer RT60 times can lead to muddled and unintelligible speech. Shorter RT60 times may give a feeling that the room is “dead,” and lacking warmth or presence. RT60 is a foundational metric in room acoustics. The intensity of RT60 in a room influences both speech intelligibility and musical richness. EDT (Early Decay Time) EDT focuses on the first 10 dB of sound decay, technically reflecting what humans actually perceive. A higher EDT gives a room a sense of “liveliness”, whereas a lower EDT makes a space feel tighter or more intimate. One can think of EDT as the listener’s first impression of a room’s acoustics. RT20 / RT30 Measuring a full 60 dB decay is not always always practical in large or noisy spaces. That’s where RT20 and RT30 come in. RT20 and RT30 extrapolate RT60 based on the first 20 or 30 dB of decay respectively. The RT20 and RT30 are useful for preliminary acoustic measurements and help guide designers and acousticians with material selection and appropriate treatment. Clarity (C80) Clarity, measured as C80, quantifies how clearly sound is perceived. A higher C80 value usually denotes crisp, intelligible speech or music within a particular space. A lower C80 value usually denotes that sound within a space feels blurred or overly reverberant. Clarity is especially important in spaces designed for speech, lectures, or live performances, where precise perception is key. Why These Metrics Matter These metrics are of high importance while designing rooms for a particular application. For speech & presentations, EDT and C80 ensure conversations remain intelligible across seating zones. With regards to music & performances, RT60 and C80 balance reverberation and clarity to ensure a rich auditory experience. For designers values such as RT20, RT30, and EDT guide the choice of acoustic treatments, speaker placement, and room materials. Case Study: Sheila Raheja Auditorium, Mumbai One of the standout examples of excellent room acoustics is the Sheila Raheja Auditorium, in Mumbai. By optimizing RT60 and ensuring strong clarity values, the design achieved: Clear speech intelligibility across all seating zones Controlled reverberation without making the room sound “dead” Even audio coverage via a well-designed distributed system This illustrates how balancing multiple acoustic metrics results in spaces that are both functional and immersive. How AudioTechnik Can Help At AudioTechnik India, we measure RT60, EDT, and Clarity to provide tailored acoustic solutions for your space. From speaker placement and material treatment to distributed audio systems, we ensure your room sounds exactly as intended. Great acoustics aren’t about hitting one number. They are about balancing multiple metrics to create spaces that feel natural, clear, and immersive. Takeaway Whether you’re designing a lecture hall, a performance space, or a club, understanding room acoustics helps create a space that’s comfortable, engaging, and sonically pleasing. Have you applied RT60 or C80 measurements in your projects? What insights did you gain?