C50 vs D50 relationship?

Same ratio, different forms. C50 = 10 log(early/late) in dB. D50 = early/total as %. D50 50% = C50 0 dB. Complementary perspectives on the same physical measurement.

Why both C50 and C80?

C50 (50 ms) for speech: reflections within 50 ms integrate with direct. C80 (80 ms) for music: later reflections still positive. Different temporal integration for different content types.

Omnidirectional source with known power. Compare measured SPL to free-field at 10 m (anechoic reference). G shows room reinforcement effectiveness through reflection patterns.

Typical concert hall values?

T30: 1.8-2.2 s. EDT: 1.5-2.0 s. C80: -2 to +2 dB. D50: 30-50%. Ts: 80-130 ms. G: 4-8 dB mid-frequency. EDT/T30 near 1.0 indicates balanced energy distribution.

C50 vs D50 relationship?

Same ratio, different forms. C50 = 10 log(early/late) in dB. D50 = early/total as %. D50 50% = C50 0 dB. Complementary perspectives on the same physical measurement.

Why both C50 and C80?

C50 (50 ms) for speech: reflections within 50 ms integrate with direct. C80 (80 ms) for music: later reflections still positive. Different temporal integration for different content types.

Omnidirectional source with known power. Compare measured SPL to free-field at 10 m (anechoic reference). G shows room reinforcement effectiveness through reflection patterns.

Typical concert hall values?

T30: 1.8-2.2 s. EDT: 1.5-2.0 s. C80: -2 to +2 dB. D50: 30-50%. Ts: 80-130 ms. G: 4-8 dB mid-frequency. EDT/T30 near 1.0 indicates balanced energy distribution.

ISO 3382 Parameters — Complete Reference

ISO 3382 Room Acoustic Parameters

ISO 3382-1:2009 defines eight parameters from the impulse response: T20, T30, EDT (reverberation), C50, C80 (clarity), D50 (definition), Ts (centre time), and G (sound strength). Together they characterize how a room supports speech and music.

ISO 3382-1:2009§3.1-3.7, 6, Table 1ISO 3382-2:2008§4

Reverberation

T30: -5 to -35 dB, 45 dB INR. EDT: first 10 dB, correlates with perceived reverberance. When EDT differs from T30, early reflections shape perceived impression.

Clarity

C50: 50 ms boundary (speech). C80: 80 ms (music). Both early/late dB ratios. D50: same as percentage. C50 = 10 log(D50/(1-D50)). JND = 1 dB per Table 1.

Centre Time Ts

First moment of squared IR. Lower = clearer. Less sensitive to integration limits than C50/C80. Range: 20 ms (very clear) to 200 ms (very reverberant).

Sound Strength G

SPL relative to free-field at 10 m. Concert halls: 4-8 dB typically. Quantifies room amplification through reflections.

Try It Now

Measure all ISO 3382 parameters

Open Tool

ISO 3382 Room Acoustic Parameters

Reverberation

Clarity

Centre Time Ts

Sound Strength G

Frequently Asked Questions

Related Articles

Related Articles

→Complete Guide to Room Acoustics Measurement — ISO 3382

→RT60 Measurement — T20, T30 & EDT per ISO 3382-1

→Impulse Response — Measurement & Analysis