The Sound of the Space: RT60 Reverb Time
RT60 is the most important metric in architectural acoustics. It stands for the time it takes for a sound to decay by 60 decibels after the sound source has stopped. In simpler terms, it measures how 'echoey' or 'live' a room is.
Why RT60 Matters
- Speech Intelligibility: In a classroom or lecture hall, an RT60 that is too high (over 1.0s) causes words to blur together, making it difficult to understand the speaker.
- Musical Richness: In a concert hall, an RT60 that is too low (under 1.2s) makes the music sound 'dry' and 'dead.' A great hall typically has an RT60 of 1.8s to 2.2s.
- Recording Studios: Often aim for a very controlled RT60 of 0.3s to 0.5s to ensure the 'room sound' doesn't interfere with the recording.
The Sabine Formula
Developed by Wallace Clement Sabine in the late 1890s, this formula remains the industry standard for estimating reverb time based on room volume and the total 'Absorption Units' (Sabins) in the room.
RT60 = (0.049 * V) / (S * α)
Where:
V=
Total volume of the room in cubic feetS=
Total surface area of the room (walls, floor, ceiling)α=
Average absorption coefficient of all surfacesAbsorption Coefficients
Every material has an absorption coefficient (α) between 0 (perfectly reflective) and 1 (perfectly absorbent).
- Concrete/Glass: α ≈ 0.02 (highly reflective)
- Heavy Carpet: α ≈ 0.30
- Acoustic Foam: α ≈ 0.80 - 0.95