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

Polarity Checker per ISO 3382-1

TL;DR

Correct polarity throughout the measurement chain is essential for valid ISO 3382-1 impulse response analysis. The impulse response polarity determines the sign convention for parameters like initial time delay gap (ITDG) and affects the accuracy of direct sound detection. An inverted measurement chain produces a negative-going first arrival, which can confuse automatic detection algorithms and lead to incorrect timing references. SonaVyx polarity checker verifies your complete measurement chain before you begin an ISO 3382-1 session, preventing subtle errors that could affect all subsequent parameter calculations.

Polarity in Room Acoustic Measurement

ISO 3382-1 impulse response measurements depend on correct polarity for proper time-domain analysis. The first arrival should be positive-going for consistent parameter extraction.

Impact on Parameter Extraction

  • Direct sound detection relies on identifying the first significant positive peak
  • An inverted IR shifts the detected arrival time by half a cycle at the dominant frequency
  • This timing error propagates into EDT, C80, D50, and Ts calculations
  • The effect is small for broadband impulse responses but can be significant for narrowband

Source Polarity Verification

  1. Verify that the dodecahedron source produces a positive initial wavefront
  2. Check with the polarity checker at 1 meter distance on-axis
  3. Some amplifier configurations may invert polarity
  4. Document the polarity check in the measurement report

Measurement Chain Consistency

Ensure the same polarity convention is maintained across all measurement positions. An inadvertent cable swap between positions would create inconsistent results across source-receiver combinations.

Common Mistakes

  • Not checking polarity before an ISO 3382-1 measurement session
  • Changing cables between positions without re-verifying polarity
  • Ignoring polarity inversion because RT60 magnitude appears correct

SonaVyx Workflow

Check polarity with the SonaVyx polarity checker. 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