IEC 61672 is the international standard that specifies performance requirements, tolerance limits, and verification procedures for sound level meters. It defines two accuracy classes — Class 1 (precision) and Class 2 (general purpose) — used for environmental noise, occupational exposure, and regulatory noise measurements.
IEC 61672 is published in three parts by the International Electrotechnical Commission. Part 1 specifies the performance requirements for sound level meters. Part 2 defines pattern evaluation tests that manufacturers must pass for their instrument to earn a Class 1 or Class 2 designation. Part 3 specifies periodic verification procedures that laboratories and users follow to confirm ongoing conformance with the Part 1 requirements.
The standard replaced IEC 60651 and IEC 60804 in 2002 and has been updated periodically — the current edition is IEC 61672-1:2013 (Part 1), IEC 61672-2:2013 (Part 2), and IEC 61672-3:2013 (Part 3). IEC 61672 is referenced worldwide by regulators including OSHA (US workplace noise), the EU Environmental Noise Directive, and national noise-at-work regulations. Compliance with IEC 61672 is typically required to demonstrate legally defensible noise measurements.
Class 1 sound level meters have tighter tolerances than Class 2 — for example, A-weighted level accuracy at 1 kHz is ±1.1 dB for Class 1 versus ±1.4 dB for Class 2, and Class 1 is specified over a wider frequency range (10 Hz to 20 kHz) compared to Class 2 (20 Hz to 8 kHz). Regulatory bodies generally require Class 1 for environmental impact assessments and expert testimony, while Class 2 is acceptable for routine workplace surveys.
In environmental noise consulting, IEC 61672 Class 1 conformance is the gatekeeper for defensible measurements. A traffic-noise study for a highway expansion EIS requires Class 1 instruments with current IEC 61672-3 verification; measurements from a Class 2 meter will not be accepted by most state DOTs. In occupational safety, IEC 61672 Class 2 compliant instruments satisfy OSHA and EU noise-at-work regulations for routine 8-hour dose assessments. Common findings during audits include expired periodic verification, incomplete A/C/Z weighting test data on the calibration certificate, and missing linearity verification across the full measurement range. Labs sometimes deliver certificates showing only a 94 dB acoustic calibrator check — this is a field check per IEC 61672-3 Section 16, not a periodic verification, and does not satisfy annual recertification requirements.
OSHA 29 CFR 1910.95 (US occupational noise exposure) and the EU Physical Agents Directive 2003/10/EC require sound level meters to meet IEC 61672 (or the equivalent ANSI S1.4) with at least Class 2 accuracy. The EU Environmental Noise Directive 2002/49/EC and most national environmental noise regulations (e.g., UK's BS 4142) specify Class 1. ISO/IEC 17025 accredited laboratories performing IEC 61672-3 verification must include pressure, random incidence, and free-field corrections, frequency weighting tests, level linearity, self-generated noise, and time-weighting verification on the calibration certificate. Missing any of these items is a common audit finding. NIST provides primary-standard free-field calibration services for the reference microphones that underpin the traceability chain down to end-user instruments.
CalibrationOS manages IEC 61672 periodic verification with a dedicated template that captures every required test parameter: A, C, and Z weighting responses at standard frequencies, level linearity across the full range, time-weighting response (Fast, Slow, Impulse), inherent noise floor, and reference-frequency accuracy. The certificate generator automatically formats output per IEC 61672-3 Section 17 reporting requirements, including Class 1 or Class 2 conformance statement, measurement uncertainty with coverage factor, and pass/fail decision rule per ILAC G8. The out-of-tolerance workflow triggers reverse traceability when any weighting or linearity check fails, listing all noise measurements performed with the suspect instrument since its last verified calibration. Interval optimization uses multi-cycle drift trending to recommend evidence-based intervals consistent with ILAC G24 staircase analysis.
IEC 61672 covers the design, performance, and verification of sound level meters. Part 1 sets the performance requirements, Part 2 defines pattern-evaluation tests for type approval, and Part 3 specifies periodic verification procedures used by calibration laboratories and end users to confirm ongoing compliance.
Class 1 instruments have tighter tolerances (e.g., ±1.1 dB at 1 kHz) and cover a wider frequency range (10 Hz to 20 kHz) than Class 2 (±1.4 dB, 20 Hz to 8 kHz). Class 1 is required for regulatory environmental noise measurement and expert testimony, while Class 2 is acceptable for general workplace surveys and screening.
IEC 61672-3 does not mandate a specific interval, but accredited laboratories and most regulators require periodic verification every 12 to 24 months. Field checks using a Class 1 or Class LS acoustic calibrator per IEC 60942 should be performed before and after each measurement session.
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