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 AuditoriumCoherence Measurement per ISO 3382-2
TL;DR
Coherence measurement supports ISO 3382-2 by validating the frequency-dependent quality of your room acoustic measurements. In ordinary rooms like offices and classrooms, HVAC noise and low source power can create bands where the measurement is unreliable. Coherence quickly reveals these problem bands before you invest time in a full impulse response capture session. SonaVyx coherence display in the transfer function view gives you immediate feedback on measurement quality, helping you optimize source position and level for the most reliable ISO 3382-2 results across all frequency bands.
Coherence in Ordinary Room Measurement
Ordinary rooms per ISO 3382-2 often have higher background noise and less controlled measurement conditions than performance spaces. Coherence helps you work within these constraints effectively.
Pre-Measurement Quality Check
- Measure coherence before starting the ISO 3382-2 session
- Identify bands where coherence is below 0.7
- Increase source level or reduce noise to improve coherence in weak bands
- If coherence remains low, those bands may yield unreliable RT60 values
Position-Dependent Coherence
- Check coherence at each planned receiver position
- Farthest positions will have lowest coherence
- Near-wall positions may show low coherence at modal frequencies
- Adjust positions if coherence is consistently low
HVAC Impact
HVAC noise in ordinary rooms creates broadband masking that reduces coherence. The effect is worst at low frequencies where HVAC noise is strongest. Consider measuring during HVAC off periods if coherence is unacceptable.
Common Mistakes
- Not checking coherence before committing to a full measurement session
- Reporting RT60 in bands where coherence was below 0.5
- Blaming the measurement system when low coherence is caused by environmental noise
SonaVyx Workflow
Check coherence with the SonaVyx transfer function. Measure RT60 with the RT60 tool. Capture IRs with the IR tool. Monitor noise with the SPL meter. Predict treatment at AcousPlan. Follow the room analysis workflow.
Standard Reference
ISO 3382-2:
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Last updated: March 19, 2026