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

Impulse Response Measurement per ISO 3382-1

TL;DR

ISO 3382-1 defines how to measure and analyze impulse responses in performance spaces to derive reverberation time, clarity, definition, and other acoustic parameters. The standard accepts both the log sine sweep (Farina method) and MLS techniques for impulse response capture. SonaVyx implements both methods with automatic deconvolution and Schroeder backward integration. The key quality metric is the impulse-to-noise ratio (INR): at least 35 dB for T20 and 45 dB for T30. SonaVyx automatically calculates INR and warns you when the measurement quality is insufficient for the desired evaluation range.

ISO 3382-1 Impulse Response Requirements

ISO 3382-1 specifies that the impulse response must be measured with sufficient quality to extract acoustic parameters reliably. The standard defines requirements for the measurement signal, source, receiver, and analysis method.

Measurement Signals

Two primary methods are accepted:

  • Log sine sweep (Farina method): generates a swept sine from 20 Hz to 20 kHz over 5-20 seconds. Deconvolution via inverse filter yields the impulse response with excellent SNR.
  • MLS (Maximum Length Sequence): pseudo-random binary sequence deconvolved via circular cross-correlation. Faster but more susceptible to time-variance.
  • Exponential sweep is generally preferred for its superior harmonic rejection and time-invariance tolerance.

Quality Criteria

  1. INR must exceed 35 dB for T20 extraction
  2. INR must exceed 45 dB for T30 extraction
  3. The regression line r-squared must exceed 0.95
  4. Multiple measurements should be averaged to improve reliability

Source and Receiver Requirements

ISO 3382-1 requires an omnidirectional source. The source must produce sufficient energy across all octave bands from 125 Hz to 4 kHz minimum. Receiver positions must represent the audience area with adequate spatial sampling.

Parameter Extraction

From the impulse response, ISO 3382-1 defines: T20, T30, EDT (Early Decay Time), C80 (Clarity), D50 (Definition), Ts (Centre Time), and G (Sound Strength). Each parameter is calculated per octave band.

Common Mistakes

  • Using sweep duration too short for the room size
  • Not checking INR before reporting T30 values
  • Measuring during high background noise conditions
  • Placing source or receiver too close to reflecting surfaces

SonaVyx Tools

Use the SonaVyx impulse response tool with automatic INR calculation. Extract RT60 with the RT60 calculator. Verify background noise with the SPL meter. Check system linearity with the transfer function. Predict target values at AcousPlan. Follow the room analysis workflow for guided measurement.

Standard Reference

ISO 3382-1:

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Last updated: March 19, 2026