How to Use a Sound Level Meter for Workplace Noise: Settings, Calibration, and OSHA Compliance

Updated March 2026  ·  29 CFR 1910.95  ·  11 min read

A sound level meter in untrained hands produces numbers that can mislead as easily as inform. Understanding what the different settings mean, when area measurements are appropriate vs. dosimetry, how to calibrate and verify your instrument, and how to interpret results correctly — this is what separates useful noise data from numbers that give false confidence.

Soundtrace integrates calibrated continuous noise monitoring into hearing conservation programs — replacing periodic manual sound level meter campaigns with always-current exposure data for every job classification.

What a Sound Level Meter Actually Measures

A sound level meter measures the instantaneous pressure fluctuations of sound waves in air and converts them to a decibel level. What the SLM number means depends critically on the settings used to produce it. The same sound environment measured with different settings will produce different numbers. Understanding which settings correspond to OSHA's noise exposure standard is essential for using SLM data in compliance decisions.

An SLM reading without documentation of measurement settings (weighting, response time, distance, duration) cannot be reliably interpreted for compliance purposes.

Type 1 vs. Type 2: Accuracy Classification and OSHA Requirements

ANSI S1.4 defines accuracy classes for sound level meters. Type 2 (General Purpose): accuracy tolerance of ±1.5 dB — the minimum accuracy class required by OSHA for occupational noise measurements. Type 1 (Precision): accuracy tolerance of ±1 dB, preferred for formal compliance determinations where results may be contested. Consumer-grade SLMs and smartphone apps do not meet either specification and should not be used for compliance decisions.

Key Settings: Weighting, Response Time, and Exchange Rate

Frequency Weighting: Always use A-weighting (dBA) for OSHA compliance assessments. Use C-weighting (dBC) for peak impulsive noise measurements. Time Response: Use Slow (1000ms) for steady or slowly varying noise in compliance assessments. Use Impulse/Peak for capturing short-duration impulsive peaks. Exchange Rate: Set to 5 dB for OSHA compliance measurements (OSHA standard). NIOSH uses 3 dB — using this for OSHA will overstate dose relative to OSHA's threshold.

For OSHA compliance: A-weighting, slow response for steady noise, 5 dB exchange rate. For impulsive noise peak: C-weighting, peak or impulse response. Document all settings for every session.

Calibration: Before, During, and After Measurements

Before each session, use an acoustic calibrator to verify the SLM is reading within 0.5 dB of the reference level. Repeat post-session — drift of more than 1 dB means measurements are questionable. Annual laboratory calibration is required as part of OSHA noise monitoring records. Never skip pre-measurement field calibration.

Measurement Technique for Accurate Results

Position the microphone at the height of the worker's ear (~1m for standing workers). Document measurement positions carefully. Use a windscreen near air sources. For variable noise environments, take multiple readings over a representative period. Variable exposures require dosimetry rather than SLM spot readings.

When SLM Is Appropriate vs. When You Need Dosimetry

Interpreting Results Against OSHA Thresholds

SLM readings are instantaneous or short-period averages — not 8-hour TWAs. For workers spending only part of the shift in an area, area readings must be combined with time-activity data for a dose calculation. Variable readings ranging widely in the same area require dosimetry for defensible compliance determination. Related: Sound Level Meter vs. Noise Dosimeter.

Documenting SLM Measurements

OSHA requires noise monitoring records to include: date, monitored task or location, instrument type, and results. Best practice also includes: measurement position, instrument serial number and calibration certificate reference, pre- and post-measurement calibration results, all instrument settings, and measured levels with observed variation.