Sound
Reverberation Time
RT60
How long sound persists in a space after the source stops, conventionally the time for the level to fall by 60 decibels. Defined for rooms large enough to sustain a diffuse sound field.
In more detail
Reverberation time is how long sound persists in a room after the source stops. The convention, RT60, is the time for the sound pressure level to fall by 60 decibels, in practice measured over a shorter decay range and extrapolated. It is reported per frequency band, because it is almost never the same across the spectrum.
Physically it is a ratio of room volume to total absorption. Large hard rooms reverberate for a long time; the same volume with upholstery, rugs and drapery does not. That is why a kitchen of stone, glass and no textiles is tiring to be in, and why the remedy is absorption placed where the reflections are rather than more of it everywhere.
The classical formulation assumes a diffuse sound field, which small residential rooms do not really provide. At domestic scale, reverberation time is a useful directional measure and a poor precision instrument: individual reflections and room modes often matter more to how a space sounds than the averaged decay figure does.
Why it matters
Reverberation is the acoustic property people describe without naming — a room that feels loud, conversation that takes effort, a hard-surfaced great room where the dishwasher dominates. It is also the most tractable acoustic problem in a finished house, because it responds to furnishings, rugs, drapery and panels rather than to construction. Interior finish decisions set it whether or not anyone is thinking about acoustics.
The common misunderstanding
That shorter is always better. Heavily absorptive rooms sound dead, and speech can feel effortful in a different way. Music rooms, dining rooms and living spaces have different appropriate ranges, which makes reverberation a property to tune to the use of the room rather than one to minimize.
Related terms
On Compound
Where this term does real work — and where the decisions get made.
Sources
Last reviewed July 2026 by Compound Editorial. Definitions are educational and not project-specific engineering or medical advice.