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.

Mosque

Coherence Measurement per ISO 3382-1

TL;DR

Coherence supports ISO 3382-1 measurements by indicating the reliability of the measured room response at each frequency. Low coherence in specific bands warns that the impulse response data in those bands may be corrupted by noise, yielding unreliable RT60, clarity, or definition values. SonaVyx displays coherence from the transfer function measurement, which can be captured alongside or before the impulse response. Using coherence to validate measurement quality is especially important in large performance spaces where achieving adequate signal-to-noise ratio at the farthest receiver positions is challenging.

Coherence as Quality Indicator

ISO 3382-1 defines quality metrics like INR for impulse response measurements. Coherence from the transfer function provides complementary quality information in the frequency domain.

Interpreting Coherence for Room Measurements

  • High coherence (above 0.8): the measurement system captures the room response reliably
  • Low coherence at specific frequencies: noise or reverberation dominates at those frequencies
  • Coherence drops at low frequencies in large rooms due to modal behavior
  • Coherence drops at high frequencies due to air absorption reducing signal level

Correlation with INR

  1. Bands with high coherence generally have adequate INR for RT60 extraction
  2. Bands with coherence below 0.5 may have insufficient INR for T30
  3. Use coherence as a quick pre-check before running the full impulse response measurement
  4. If coherence is low, increase source level or move the source closer

Common Mistakes

  • Ignoring low coherence and reporting RT60 values for bands where data is unreliable
  • Not using sufficient averaging to achieve stable coherence estimates
  • Confusing room modal behavior (expected low coherence) with measurement problems

SonaVyx Workflow

Check coherence with the SonaVyx transfer function. Capture IRs with the IR tool. Measure RT60 with the RT60 tool. Verify levels with the SPL meter. Predict room behavior at AcousPlan. Follow the room analysis workflow.

Standard Reference

ISO 3382-1:

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Last updated: March 19, 2026