Field Story
Open Office: Where Secrets Travel
An open-plan office handling sensitive financial data failed ASHRAE speech privacy requirements with D2,S measured at only 4 dB per doubling of distance, versus the 9 dB minimum. RTA measurements confirmed that the low-frequency sound masking system was miscalibrated, producing masking noise 8 dB below spec. Recalibrating the masking system and adding absorption to the ceiling plenum achieved D2,S of 10 dB.
Open OfficeSPL Meter Measurement per ISO 3382-2
TL;DR
ISO 3382-2 covers reverberation time measurement in ordinary rooms such as offices, classrooms, and hospitals. Unlike ISO 3382-1 for performance spaces, this standard allows the interrupted noise method alongside impulse response techniques. Your SPL meter is essential for verifying that the interrupted noise source achieves adequate level above background noise, typically requiring at least 35 dB above the noise floor in each frequency band. SonaVyx SPL meter with octave band analysis lets you verify band-by-band signal-to-noise conditions. The standard also requires background noise documentation as part of your measurement report, making SPL measurement a mandatory step in every ISO 3382-2 session.
ISO 3382-2 Scope and SPL Role
ISO 3382-2 applies to reverberation time measurement in ordinary rooms, not performance spaces. These include offices, classrooms, hospital wards, restaurants, and industrial spaces. The SPL meter serves three functions: source level verification, background noise documentation, and decay range confirmation.
Interrupted Noise Method
The interrupted noise method is commonly used for ISO 3382-2 measurements. This requires:
- A broadband noise source (pink or white noise) capable of producing sufficient level
- SPL meter verification that the source level exceeds background noise by at least 35 dB in each octave band of interest
- Steady-state level must be established before interruption (at least 3 seconds of stable noise)
Background Noise Documentation
ISO 3382-2 requires that background noise levels are documented as part of the measurement report. Use your SPL meter to record:
- Overall A-weighted background noise level (LAeq over 30 seconds minimum)
- Octave band levels from 125 Hz to 4 kHz
- Note any dominant noise sources (HVAC, traffic, equipment)
- Measure with the room in its normal operating condition
Decay Range Verification
The evaluation range for RT60 determination depends on the signal-to-noise ratio. With the SPL meter, verify:
- T20 requires a 35 dB decay range (source must be 35 dB above noise floor)
- T30 requires a 45 dB decay range
- If T30 cannot be achieved, fall back to T20
Position Requirements
ISO 3382-2 requires a minimum of 2 source positions and 3 receiver positions for a minimum of 6 source-receiver combinations. Use SPL measurements at each position to verify consistent coverage.
Common Mistakes
- Not measuring background noise in each octave band separately
- Using T30 when the decay range only supports T20
- Forgetting to document HVAC operating state during measurement
- Placing the source too close to a wall, creating non-diffuse conditions
Using SonaVyx for ISO 3382-2
Start with the SonaVyx SPL meter for background noise survey and source level verification. The octave band display shows per-band SNR directly. Then switch to the RT60 tool for the actual decay measurement. For impulse response analysis, use the IR measurement tool. Check your transfer function to verify source-room coupling. Visit AcousPlan for predictive RT60 calculations. See the learning hub for detailed tutorials.
Standard Reference
ISO 3382-2:
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Last updated: March 19, 2026