T30 (Reverberation Time)

T30 evaluates a 30 dB portion of the decay curve (from -5 dB to -35 dB below the initial level) and extrapolates to a 60 dB decay. The wider evaluation range means T30 samples more of the decay, producing statistically more robust regression than T20. However, this advantage comes at the cost of requiring a higher signal-to-noise ratio during measurement. The 45 dB INR requirement for valid T30 is a practical challenge. In many occupied spaces — offices, restaurants, retail — HVAC noise and ambient sound may limit the achievable INR to 30-40 dB. In these situations, only T20 can be reliably measured. Purpose-built performance spaces (concert halls, recording studios) typically achieve INR well above 45 dB with a balloon pop or starter pistol source. T30 is the preferred metric for architectural acoustics design verification because its longer evaluation range better represents the statistical reverberation process. Building regulations and design targets typically specify T30 or simply "RT60" (which conventionally means T30 when the decay is linear). The Sabine and Eyring formulas predict a single exponential decay, which corresponds most closely to T30. Comparing T20 and T30 reveals decay linearity. ISO 3382-1 flags a potential issue when T30/T20 deviates from 1.0 by more than 10%. Non-linear decays often indicate coupled spaces (two volumes with different absorption) or focused reflections that create separate decay regimes. In such cases, both T20 and T30 should be reported with the non-linearity noted. SonaVyx displays T20 and T30 side by side with per-octave-band breakdown and r² quality indicators, highlighting any bands where the ratio exceeds the ISO threshold.