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.
MosqueTransfer Function Measurement per ISO 3382-1
TL;DR
Transfer function measurement supports ISO 3382-1 room acoustics by characterizing the linear relationship between sound source and receiver. While ISO 3382-1 primarily uses impulse response analysis, the transfer function provides complementary information: coherence indicates measurement quality, the magnitude response shows room resonances, and phase response reveals room mode behavior. SonaVyx transfer function analyzer is particularly useful for verifying source omnidirectionality requirements specified in the standard and for identifying problematic room modes that affect reverberation uniformity.
Transfer Function in Room Acoustics
ISO 3382-1 measures room acoustic parameters from the impulse response, which is mathematically the inverse Fourier transform of the transfer function. Both representations contain the same information, but each reveals different aspects of room behavior.
Source Verification
ISO 3382-1 requires an omnidirectional sound source. Transfer function measurement at multiple angles around the source can verify omnidirectionality:
- Measure transfer function at 0, 45, 90, 135, 180 degrees around the source
- Compare magnitude responses across angles
- Deviation should be within the tolerances specified in ISO 3382-1 Annex A
- Coherence at each angle should exceed 0.8 for valid results
Room Mode Identification
The transfer function magnitude response reveals room modes as narrow peaks and dips:
- Below the Schroeder frequency, individual room modes are visible
- Transfer function resolution must be sufficient to resolve mode spacing
- Use narrow smoothing (1/24 octave or less) to see individual modes
- Modal behavior affects the spatial uniformity of RT60 measurements
Coherence for Quality Control
The coherence function indicates how much of the measured response is due to the linear system response versus noise or nonlinearity. For ISO 3382-1 measurements, coherence below 0.8 at any frequency suggests that the impulse response data at that frequency is unreliable.
Common Mistakes
- Using too little averaging, resulting in noisy transfer function estimates
- Not checking coherence before interpreting magnitude response features
- Confusing transfer function peaks with room modes when they may be source artifacts
- Using transfer function when impulse response would be more appropriate for ISO 3382-1 parameters
SonaVyx Tools
The SonaVyx transfer function analyzer provides magnitude, phase, and coherence in a single measurement. For ISO 3382-1 parameters, use the impulse response tool for T20, T30, C80, and D50. Measure RT60 with the RT60 calculator. Check SPL conditions with the SPL meter. Predict room behavior with AcousPlan. See our learning hub for room acoustics tutorials.
Standard Reference
ISO 3382-1:
Try It Now
Open this measurement tool in your browser — free, no download required.
Last updated: March 19, 2026