Decay Curve

A decay curve shows how sound energy in a room decreases over time after the source is stopped, plotted as level (dB) versus time (seconds). It is the primary data from which reverberation time parameters (RT60, T20, T30, EDT) are extracted. Per ISO 3382-2:2008, the decay curve is obtained from the impulse response using Schroeder backward integration, which provides a more reliable and repeatable result than the older interrupted noise method. An ideal decay curve is a straight line on a dB-time plot, indicating uniform exponential decay. In practice, deviations such as double slopes (indicating coupled volumes), early curvature (indicating non-uniform absorption), or noise floor limitations are common. The linearity and dynamic range of the decay curve are quality indicators of both the room’s diffusion and the measurement’s reliability.