Sound level meter calibration: how often, to which standards, and how
A sound level meter measures sound pressure level in decibels using a measurement microphone and standardized frequency and time weightings. It is used for occupational noise exposure, environmental noise, and product noise measurements. Because microphone sensitivity and electronics drift, periodic laboratory testing plus routine field checks with an acoustic calibrator are required for results to remain valid and legally defensible.
Also known as: SLM, noise meter, decibel meter, noise level meter, sound meter
How often should a sound level meter be calibrated?
Field check with an IEC 60942 acoustic calibrator (typically 94 dB at 1 kHz) before and after each measurement session; investigate and recalibrate if the levels disagree beyond the allowed tolerance.
Where this number comes from
IEC 61672-3 defines the periodic test procedure but not the interval; the interval is set by the regulations being followed. Guidance for UK and EU noise-at-work regulations calls for laboratory verification at least every two years, while annual calibration is commonly recommended for heavy use, legal work, or harsh environments.
Calibration intervals are a risk-based decision for the instrument owner, not a fixed rule: guidance documents such as ILAC-G24 and OIML D 10 describe how to set and adjust them from usage, criticality and calibration history. Treat the interval above as a starting point for your own quality system, not a compliance requirement.
What shortens or lengthens the interval
- Applicable regulation: some noise measurement regulations require verification every year, others every two years
- Use of results for legal or enforcement purposes, which demands current accredited periodic test evidence
- Microphone exposure to humidity, dust, wind, and temperature extremes in outdoor environmental monitoring
- Intensity of field use and transport, which increases risk of microphone and preamplifier damage
- Discrepancies observed during before and after field checks with the acoustic calibrator, which indicate drift between laboratory tests
Standards relevant to sound level meter calibration
Defines class 1 and class 2 performance requirements that the meter must meet
Defines the periodic test procedure used by laboratories to verify continued conformance to IEC 61672-1 for a limited period
Specifies requirements for the acoustic calibrators used for field checks and for the acoustical test in periodic testing
Standards are referenced by designation and title. For normative requirements, always work from the current edition of the standard itself.
How a sound level meter is calibrated
A typical sound level meter calibration, in an accredited lab or in-house, follows this outline. The exact points, tolerances and paperwork come from the applicable standard and your own procedure.
- Visually inspect the meter, microphone, and preamplifier, and record firmware and configuration details
- Perform an acoustical test by applying a class 1 or class LS sound calibrator per IEC 60942 at the reference level (typically 94 dB at 1 kHz) and record the as-found indication
- Apply electrical test signals via a microphone substitution device or electrical input adapter to test frequency weightings A, C, and Z against IEC 61672-1 tolerances
- Test level linearity across the measurement ranges and at range switch points
- Verify time weightings F and S and integrating functions (Leq) using tone-burst signals
- Check self-generated noise and overload indication behavior
- Compare all results to the class 1 or class 2 acceptance limits of IEC 61672-1, adjust the calibration factor if needed, and record as-left results on the certificate
Reference equipment typically used
- Acoustic calibrator or pistonphone conforming to IEC 60942 class 1 or LS
- Signal generator and electrical input adapter (microphone substitution capacitor)
- Precision measuring amplifier and calibrated voltmeter
- Reference microphone with traceable sensitivity
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Sources
- IEC 61672-3:2013, Electroacoustics - Sound level meters - Part 3: Periodic tests, IEC
Existence and scope of the periodic test procedure that verifies conformance to IEC 61672-1 for a limited period; basis for the procedure outline
- Sound Level Meter Calibration and Verification (FAQ), NoiseMeters Inc.
Interval claim: the applicable noise regulations set the period between laboratory calibrations, some requiring 1 year and some 2 years (UK and EU noise-at-work at least every two years), annual calibration recommended for legal or heavy use, plus the practice of field checks with a sound calibrator before and after measurements
- IEC 61672 - A Standard for Sound Level Meters Explained, Cirrus Research plc
The three-part structure of IEC 61672 and the role of Part 1 specifications and Part 3 periodic testing