Physics
Reverberation
Quick fact
The famous 'reverberation time' RT60, the time it takes for sound to decay by 60 decibels, was first quantified by Wallace Sabine in the early 1900s while optimizing the acoustics of Boston's Symphony Hall.
Why this is interesting
Have you ever clapped your hands in an empty gymnasium and heard the sound linger for a moment? Why does that same clap sound dead in a carpeted living room?
Read the full explanation
Understanding Reverberation
When you clap, the sound travels out in all directions. In an open field, most of it disappears into the distance. But indoors, sound waves bounce off walls, ceilings, and floors. Each bounce reflects energy back into the room, creating a dense 'cloud' of overlapping echoes. Unlike a single distinct echo (like shouting at a distant cliff), reverberation is a rapid succession of reflections that arrive so close together your ear blends them into a smooth, decaying tail. The time it takes for this tail to fade into silence defines the room's 'liveliness' or 'dryness'.
A deeper explanation
Reverberation arises from the physics of sound reflection and absorption. Each time a sound wave encounters a surface, part of its energy is absorbed (converted into heat) and part is reflected. The material of the surface determines the absorption coefficient (0 = perfect reflection, 1 = perfect absorption). In a typical room, after many reflections, the sound energy decays exponentially. The characteristic parameter for reverberation is the reverberation time (RT60), which depends on the room volume and total absorption. A larger volume and less absorption yield longer reverberation. Additionally, the frequency content of the sound matters: high frequencies are absorbed more readily by soft materials, so reverberation often colors the tonal quality. Understanding this mechanism allows engineers to design spaces for clarity (lecture halls) or richness (concert halls), and to calibrate audio systems to compensate for the room's natural decay.