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 AuditoriumSpectrum Analyzer Measurement per ISO 3382-2
TL;DR
Spectrum analysis supports ISO 3382-2 measurements in ordinary rooms by providing octave-band noise assessment and source spectrum verification. In rooms like offices, classrooms, and hospitals, the background noise spectrum often has dominant HVAC components that vary by frequency band. A spectrum analyzer reveals which bands will have adequate signal-to-noise ratio for valid RT60 measurement. SonaVyx RTA mode with octave band overlay lets you quickly assess noise conditions and verify source coverage before committing to a full ISO 3382-2 measurement session, saving time and ensuring valid results.
Spectrum Analysis in Ordinary Rooms
ISO 3382-2 measurements in ordinary rooms face challenges that spectrum analysis helps address: variable background noise, limited source power, and frequency-dependent absorption that may prevent valid measurement in some bands.
Background Noise Assessment
- Capture the noise spectrum with octave band resolution
- Identify dominant noise sources by their spectral signature (HVAC typically peaks at 63-250 Hz)
- Determine which bands may have inadequate SNR for RT60 measurement
- Consider measuring during quieter periods if low-frequency SNR is insufficient
Source Spectrum Verification
- Verify that the noise source (for interrupted noise method) covers all required bands
- Check that the source output exceeds background noise by at least 35 dB per band
- For the impulse method, verify sweep or MLS spectral coverage
- Adjust source level or position if specific bands are deficient
Room Absorption Profile
The room spectrum under steady-state excitation reveals the frequency-dependent absorption characteristics. Rooms with heavy soft furnishings show rapid HF rolloff; rooms with hard surfaces maintain energy across the spectrum.
Common Mistakes
- Not checking the noise spectrum before starting RT60 measurements
- Assuming the source has flat spectrum when it may roll off at low frequencies
- Ignoring intermittent noise sources that affect specific frequency bands
SonaVyx Workflow
Use the SonaVyx spectrum analyzer for pre-measurement noise survey. Measure RT60 with the RT60 tool. Capture impulse responses with the IR tool. Monitor levels with the SPL meter. Predict treatment needs at AcousPlan. Follow the room analysis workflow for structured measurement.
Standard Reference
ISO 3382-2:
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Last updated: March 19, 2026