Field Story
The Dome That Made the Imam Speak Twice
A mosque with a 14-meter dome created a strong acoustic focus point 8 meters from the mihrab, causing worshippers to hear the imam twice with a 120 ms delay. Impulse response measurement clearly showed the focused reflection. Applying diffusive panels to the lower dome surface and a thin absorptive layer at the focus zone reduced the reflection by 14 dB, restoring clarity.
MosqueSTI Measurement per ISO 3382-1
TL;DR
ISO 3382-1 room acoustic parameters directly influence speech intelligibility as measured by STI. Reverberation time (T30), clarity (C50), definition (D50), and center time (Ts) all correlate with the modulation transfer function. By measuring these ISO 3382-1 parameters first, you can predict STI performance and identify which acoustic aspects need improvement. SonaVyx integrates both measurement frameworks, allowing you to capture impulse responses for ISO 3382-1 analysis and automatically derive STI predictions from the same data. This dual analysis is essential for multipurpose performance spaces that host both music and speech events.
Room Acoustics and Intelligibility
ISO 3382-1 parameters and STI are complementary measures of room acoustic quality. While ISO 3382-1 characterizes the room independently, STI evaluates how the room affects speech communication specifically.
Parameter Correlations
- RT60 and STI: longer reverberation reduces STI. RT60 above 2 seconds typically yields STI below 0.45
- C50 (Clarity for speech): higher C50 correlates with higher STI. C50 above 0 dB generally indicates acceptable speech clarity
- D50 (Definition): D50 above 0.5 aligns with STI above 0.45
- Ts (Centre Time): shorter Ts correlates with better intelligibility
Multipurpose Space Design
- Concert halls (ISO 3382-1 optimized) typically have RT60 of 1.5-2.5 seconds
- This yields STI around 0.35-0.50 for unamplified speech
- PA systems are needed to achieve STI above 0.50 in these spaces
- Variable acoustics (curtains, moveable panels) bridge the design conflict
Deriving STI from ISO 3382-1 Data
The impulse response measured for ISO 3382-1 contains all the information needed to calculate STI via the indirect method. Filter into octave bands, compute the modulation transfer function from the squared impulse response, and apply the STI algorithm per IEC 60268-16.
Common Mistakes
- Optimizing RT60 for music without considering speech intelligibility requirements
- Not measuring STI separately when the space serves speech-critical functions
- Assuming C50 above 0 dB guarantees adequate STI
- Ignoring ambient noise contribution to STI degradation
SonaVyx Workflow
Measure the impulse response with the SonaVyx IR tool. Extract ISO 3382-1 parameters and STI simultaneously with the STI calculator. Review RT60 per octave band with the RT60 tool. Verify source levels with the SPL meter. Use the AI diagnostic for optimization recommendations. Follow the room analysis workflow for structured measurement.
Standard Reference
ISO 3382-1:
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Last updated: March 19, 2026