ANSI S1.4: Field Calibration and Laboratory Verification
TL;DR
ANSI S1.4 requires field calibration checks before and after each measurement session using a calibrator conforming to ANSI S1.40 (the US equivalent of IEC 60942). The calibrator produces a known SPL (typically 94 dB or 114 dB at 1 kHz). Drift between pre and post checks exceeding 0.5 dB (Type 1) or 1.0 dB (Type 2) invalidates the session. Annual laboratory verification with NIST-traceable reference standards is recommended. For OSHA compliance, calibration records must be maintained and available for inspection.
Field Calibration (Pre/Post Check)
Before every measurement session:
- Fit the calibrator over the microphone
- Note the displayed level (should read within tolerance of the calibrator's stated output)
- Adjust if necessary to match the calibrator level exactly
- Record the calibration reading
After the measurement session, repeat the check. The difference between pre and post readings indicates drift:
| Type | Maximum acceptable drift |
|---|---|
| Type 1 | 0.5 dB |
| Type 2 | 1.0 dB |
These limits mirror IEC 61672-1 requirements.
Calibrator Standards
The calibrator itself must conform to ANSI S1.40 (US) or IEC 60942 (international). Calibrator classes:
- Class 1: ±0.3 dB accuracy at reference conditions — required for Type 1 SLM verification
- Class 2: ±0.5 dB accuracy — acceptable for Type 2 SLM verification
Calibrators must themselves be verified annually against NIST-traceable reference standards.
Laboratory Verification
Annual laboratory verification tests the complete instrument against reference conditions:
- Frequency weighting response at multiple frequencies and levels
- Level linearity across the full operating range
- Time weighting response (tone burst tests)
- Peak detector response
- Self-generated noise level
- Overload indication threshold
The laboratory must be accredited (typically A2LA or NVLAP in the US) with NIST traceability.
OSHA Calibration Requirements
OSHA 1910.95(d)(2) requires: "Audiometric testing equipment shall be calibrated at least annually." For noise dosimeters and sound level meters used under 1910.95, the employer must calibrate before each day's use per the manufacturer's instructions. Calibration records are part of the required documentation that OSHA inspectors may review.
Multi-Frequency Calibration
Standard calibrators operate at 1 kHz only. For applications requiring verified accuracy across the frequency range (octave-band analysis per IEC 61260-1), multi-frequency calibrators or pistonphones with adapters can provide reference levels at additional frequencies.
SonaVyx Calibration
The SPL meter provides a 94 dB calibration workflow. Place your device near a sound calibrator and the tool calculates the correction offset. This correction is saved and applied to all subsequent measurements. Per-frequency calibration curves are supported when using multi-frequency references. For environmental effects on calibration stability, see the environmental section.
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Last updated: March 19, 2026