ISO 3382-2:2008

Overview

ISO 3382-2:2008 - "Acoustics - Measurement of room acoustic parameters - Part 2: Reverberation time in ordinary rooms" specifies standardized methods to measure reverberation time (RT) in ordinary indoor spaces. The standard defines measurement procedures, required apparatus, measurement-position rules, evaluation of decay curves, uncertainty categories, and the required content of a test report. Results are used both to assess room acoustic quality and to provide correction terms for other acoustic measurements (e.g., sound pressure level, sound insulation, sound power).

Key topics and technical requirements

• Measurement methods:
  • Interrupted noise method (direct recording of the decay after noise cutoff).
  • Integrated impulse response method (reverse-time integration of squared impulse responses).
• Measurement accuracy levels: survey, engineering, and precision - differing mainly by the number of measurement positions and resulting uncertainty.
• Evaluation ranges: 20 dB and 30 dB ranges are defined; 20 dB is preferred for practical field work (better SNR, relates to early decay).
• Equipment and filters:
  • Omnidirectional sound source recommended; for precision work source directivity must meet ISO 3382-1 requirements.
  • Omnidirectional microphones (preferably ≤14 mm diaphragm; up to 27 mm allowed with appropriate response correction).
  • Octave or 1/3-octave filters conforming to IEC 61260.
• Signal processing and averaging:
  • Exponential averaging time ≲ T/30; linear averaging interval ≲ T/12.
  • Sampling interval between decay points < 1.5 × averaging time.
• Environmental and setup notes:
  • Rooms should be essentially unoccupied during measurement (up to two people allowed to simulate unoccupied state if specified).
  • For large volumes, measure temperature and humidity when air absorption may matter; air absorption negligible if RT < 1.5 s at 2 kHz and < 0.8 s at 4 kHz.
• Data quality and reporting:
  • Methods for evaluating decay-curve linearity and non-linearity (Annex B) to flag unreliable results.
  • Guidance on spatial averaging, uncertainty estimation (Annex A), least-squares fit formulas (Annex C), and test-report content.

Applications

• Verifying and specifying room acoustic performance for classrooms, offices, restaurants, sports halls, terminals, workshops and industrial spaces.
• Providing correction terms for sound pressure level, sound insulation (ISO 140 series), and sound power measurements (ISO 3740).
• Supporting design for speech intelligibility, occupant comfort, and compliance with building code RT requirements.

Who uses this standard

• Acoustic consultants and engineers
• Building designers and architects
• Test laboratories and certification bodies
• Facility and venue managers
• Researchers in room acoustics

Related standards

• ISO 3382‑1 (performance rooms)
• ISO 3382‑3 (open plan spaces - in preparation)
• ISO 18233 (measurement methods)
• IEC 61260 (octave/fractional-octave filters)
• ISO 354, ISO 140, ISO 3740 (related acoustic measurements)

Keywords: ISO 3382-2, reverberation time, room acoustics, reverberation time measurement, interrupted noise method, integrated impulse response, measurement uncertainty.