Noise Measurement Instrumentation and Calibration
Domain 2: Noise Measurement Instrumentation and Calibration
This domain examines whether you can select, set up, calibrate, and verify instrumentation so that readings are defensible. Items often hinge on instrument class, calibration acceptance, and field technique.
Core rules
- IEC 61672-1 defines Class 1 and Class 2 sound level meters; ANSI S1.4 uses the older Type 1 and Type 2 designations. Class 1 has tighter tolerances and is preferred for enforcement and research.
- A field calibrator typically produces 94.0 dB at 1000 Hz; some provide 114.0 dB. Perform a before-and-after calibration check and record as-found and as-left values.
- A common acceptance criterion is +/-0.5 dB. If drift exceeds the criterion, flag or invalidate the data unless a documented correction is justified.
- Use a windscreen, mount the meter on a tripod, and orient the microphone according to the manufacturer and standard. Record microphone height, distance from reflecting surfaces, time weighting, frequency weighting, and logging interval.
- Octave and third-octave filters should meet IEC 61260. Verify clock time and battery status before deployment.
Worked example
A meter reads 93.8 dB before measurement against a 94.0 dB calibrator and 94.6 dB afterward. The before drift is -0.2 dB, which is acceptable; the after drift is +0.6 dB, which exceeds a +/-0.5 dB criterion. The measurement is suspect. The correct response is to flag the run, check coupling and battery, recalibrate, and repeat if the data are needed for compliance. Do not silently apply an arbitrary correction.
Traps
Calibrating with the windscreen in place; hand-holding the meter; failing to record serial numbers and calibration dates; using a phone app as an enforcement instrument; and confusing frequency weighting with time weighting.