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 AuditoriumRT60 Measurement per ISO 3382-2
TL;DR
ISO 3382-2 defines reverberation time measurement in ordinary rooms such as offices, classrooms, and healthcare facilities. Unlike ISO 3382-1 for performance spaces, this standard allows fewer measurement positions and simpler source requirements. You need a minimum of 2 source positions and 3 receiver positions for 6 combinations, or you can use the engineering method with more positions for higher precision. SonaVyx RT60 tool supports both the interrupted noise method and the impulse response method specified in the standard. The tool automatically extracts T20 and T30 with regression quality verification, ensuring your results meet the ISO 3382-2 evaluation criteria.
Scope of ISO 3382-2
ISO 3382-2 applies to ordinary rooms, defined as enclosed spaces used for speech, music, or other activities where the acoustic environment affects the experience. This includes offices, classrooms, conference rooms, restaurants, hospitals, and similar spaces.
Measurement Methods
The standard allows two methods for RT60 measurement:
- Interrupted noise method: steady-state pink or white noise is abruptly switched off, and the decay is recorded
- Integrated impulse response method: an impulse response is captured and the Schroeder backward integration is applied
- Both methods yield equivalent results when properly executed
Position Requirements
- Survey method: 1 source, 3 receivers (minimum 3 decays per combination, 9 total)
- Engineering method: 2 sources, 3 receivers (minimum 2 decays per combination, 12 total)
- Precision method: 2+ sources, 6+ receivers for detailed spatial mapping
- Source and receiver must be at least 1 meter from walls and 1.5 meters apart
Evaluation Parameters
ISO 3382-2 specifies T20 and T30 as the primary reverberation time parameters. T20 uses the decay from -5 dB to -25 dB below the initial level, while T30 uses -5 dB to -35 dB. The regression line must have a correlation coefficient r squared of at least 0.95.
Frequency Bands
Measurement should cover octave bands from 125 Hz to 4 kHz as a minimum. For the single-number quantity, average the 500 Hz and 1 kHz octave bands. Extended measurements from 63 Hz to 8 kHz provide additional insight.
Common Mistakes
- Using too few source-receiver combinations for the chosen method
- Placing source or receiver too close to room boundaries
- Not verifying that the decay range supports T30 before reporting it
- Averaging T20 and T30 values together instead of reporting them separately
Using SonaVyx
The SonaVyx RT60 tool automatically computes T20 and T30 with regression quality indicators. Capture impulse responses with the IR measurement tool. Verify background noise conditions using the SPL meter. For design-stage predictions, use the AcousPlan RT60 calculator. Check frequency response with the transfer function. Follow the room analysis workflow for guided measurements.
Standard Reference
ISO 3382-2:
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Last updated: March 19, 2026