ISO 3382-1 Measurement Uncertainty and Reporting
TL;DR
ISO 3382-1 Annex A provides guidance on measurement uncertainty. Key sources include spatial variation (dominant), instrument uncertainty, temperature effects, and background noise contamination. Spatial standard deviation of T30 in a well-designed concert hall is typically 3-5% (JND for RT is about 5%). Results should be reported as the spatial mean ± standard deviation for each parameter and each octave band. The number of measurement positions directly affects uncertainty — doubling positions reduces standard error by √2. Reporting must include room conditions (temperature, humidity, occupancy), equipment used, and measurement grade.
Sources of Measurement Uncertainty
ISO 3382-1 Annex A identifies several uncertainty sources for room acoustic measurements:
| Source | Typical magnitude | Mitigation |
|---|---|---|
| Spatial variation | 3-8% for T30 | More measurement positions |
| Source directivity | 1-3% for T30 | Better omnidirectional source |
| Background noise (INR) | 0-10% for T30 | Adequate INR |
| Air temperature | 0.1%/°C for T30 | Record conditions |
| Instrument | <1% for digital | Calibrated equipment |
Spatial variation dominates in virtually all practical measurements. The room itself has position-dependent acoustics, and no amount of equipment quality can eliminate this inherent variation.
Just Noticeable Differences (JND)
ISO 3382-1 Table 1 provides the just noticeable differences for each parameter, representing the smallest change a typical listener can perceive:
| Parameter | JND |
|---|---|
| T30, EDT | 5% |
| C80 | 1 dB |
| D50 | 0.05 |
| Ts | 10 ms |
| G | 1 dB |
Measurement uncertainty should ideally be less than 1 JND. Achieving this requires sufficient measurement positions — the spatial standard error of the mean equals σ/√N, where N is the number of independent source-receiver combinations.
Reporting Requirements
A complete ISO 3382-1 measurement report should include:
- Room description: dimensions, volume, surface materials, seating capacity
- Conditions: air temperature, relative humidity, occupancy state (empty/furnished/occupied)
- Equipment: source type, microphone type, recording system
- Measurement grade: survey, engineering, or precision
- Source and receiver positions (plan drawing)
- Results per octave band: spatial mean ± standard deviation
- Number of independent source-receiver combinations
- INR per octave band and the resulting evaluation range (T20 or T30)
Temperature and Humidity
Air absorption at high frequencies is strongly temperature and humidity dependent. At 20°C/50% RH, air absorption at 4 kHz is approximately 0.02 dB/m. A 10°C temperature change can alter high-frequency RT60 by 5-10% in large rooms. Always record conditions and note if the measurement was taken in significantly different conditions from the design operating state.
SonaVyx Reporting
The SonaVyx report generator includes all required reporting fields. Technical commissioning reports include room conditions, measurement positions, per-band results with standard deviation, and INR quality indicators. Results are exportable as JSON and CSV for integration with design software. See the broader ISO 3382-1 hub for the complete standard overview.
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Last updated: March 19, 2026