Field Story
Failing BB93: The Auditorium That Could Not Graduate
A new school auditorium failed its BB93 acoustic assessment with RT60 of 1.9 seconds at 500 Hz against the 1.0-second requirement. The building could not receive its occupancy certificate. Impulse response measurements across 6 receiver positions confirmed the issue. Installing Class A absorbers on 35% of the rear wall and ceiling clouds above the seating brought RT60 to 0.95 seconds, passing the standard.
School AuditoriumDelay Finder Measurement per ISO 3382-2
TL;DR
The delay finder supports ISO 3382-2 measurements in ordinary rooms by identifying the direct sound arrival time, which is the reference point for all time-domain parameters. In smaller rooms, early reflections arrive quickly after the direct sound, making precise timing measurement essential for correctly separating direct from reflected energy. SonaVyx delay finder automatically detects the first arrival in the impulse response and calculates the propagation delay, enabling distance verification and early reflection analysis that support reliable ISO 3382-2 reverberation time measurements.
Delay Measurement in Ordinary Rooms
ISO 3382-2 rooms are typically small enough that early reflections arrive within 5-20 ms of the direct sound. Accurate delay detection is essential for separating these components.
Distance Verification
- Measure the propagation delay to verify the source-receiver distance
- In ordinary rooms, distances are typically 1.5-10 meters
- At 343 m/s, this corresponds to 4.4-29.2 ms propagation time
- Compare measured delay against physical distance for consistency
Early Reflection Detection
- In small rooms, floor reflections arrive within 3-5 ms of the direct sound
- Wall reflections arrive within 5-15 ms depending on room dimensions
- The delay finder helps identify the temporal structure of these arrivals
- This information supports ISO 3382-2 measurement quality assessment
Source-Receiver Spacing Requirements
ISO 3382-2 requires minimum source-receiver distance of 1.5 meters and minimum distance from boundaries of 1.0 meter. The delay finder can verify these spatial relationships from the timing data.
Common Mistakes
- Not verifying that the detected arrival is the direct sound (a strong reflection may arrive first in some room geometries)
- Ignoring early reflection timing when interpreting ISO 3382-2 results
- Using insufficient sample rate for accurate timing in small rooms
SonaVyx Workflow
Use the delay finder in the SonaVyx transfer function. Measure RT60 with the RT60 tool. Capture IRs with the IR tool. Check levels with the SPL meter. Predict room behavior at AcousPlan. Follow the room analysis workflow.
Standard Reference
ISO 3382-2:
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Last updated: March 19, 2026