Late Reverberation
Definition
Late Reverberation
Late reverberation is the diffuse, exponentially decaying sound field that persists after early reflections, typically beginning 80-100 ms after the direct sound. Composed of thousands of overlapping reflections that arrive from all directions, late reverberation determines the perceived "size" and "warmth" of a space. Its decay rate defines the reverberation time (RT60), the single most important room acoustic parameter.
After the direct sound and early reflections, the sound field in a room transitions into a dense, diffuse reverberant field. Individual reflections can no longer be distinguished — instead, the sound energy decays smoothly as it is absorbed at each surface interaction. This exponential decay is the late reverberation, and its duration (RT60) characterizes the room acoustically.
The Sabine equation predicts late reverberation: T = 0.161V/A, where V is the room volume in cubic meters and A is the total absorption in sabins. Larger rooms have longer reverberation (more volume to fill); more absorptive rooms have shorter reverberation (more energy lost per reflection). A small, carpeted meeting room might have RT60 = 0.3 s, while a large cathedral can exceed 6 seconds.
Late reverberation affects intelligibility, music quality, and noise levels. For speech, late reverberation is generally detrimental: it masks the temporal modulation patterns of speech, reducing the modulation transfer function and STI. For music, moderate late reverberation provides warmth, blending, and the perception of ensemble — but excessive reverberation smears temporal detail.
The diffuse field level (reverberant level) in a room is approximately: Lrev = Lsource + 10 × log₁₀(4/A) dB. This level is independent of distance from the source — it is the same everywhere in the room beyond the critical distance. This is why reducing reverberation (adding absorption) reduces the overall noise level in spaces like restaurants and open-plan offices.
The transition from early reflections to late reverberation is gradual, not abrupt. The "mixing time" — when the sound field becomes statistically diffuse — depends on room size and geometry. In a well-proportioned rectangular room, this occurs after about 3-5 mean free paths (average distance between reflections). In irregularly shaped rooms, the mixing time may be longer and the decay may be non-uniform.
SonaVyx captures the complete decay process from the impulse response and computes RT60 via Schroeder backward integration.
Try It Now
Open this measurement tool in your browser — free, no download required.