Class 1 vs Class 2 Sound Level Meters: What's the Difference and Which Do You Need?
IEC 61672 defines two performance classes. Here is what actually separates them, when each is required, and why the microphone matters as much as the meter.
If you are specifying a sound level meter, one of the first questions you will meet is whether you need Class 1 or Class 2. Understanding the difference matters both for choosing the right instrument and for making sure your measurements will be accepted by the relevant authority.
What Class 1 and Class 2 mean
The classification comes from IEC 61672, the international standard for sound level meters. It defines two performance classes based on measurement accuracy and tolerance limits.
Class 1 has tighter tolerances. It is required for precision measurements, legal proceedings and regulatory compliance in many jurisdictions.
Class 2 has wider tolerances but remains suitable for most field measurements, occupational noise surveys and general environmental monitoring.
An important caveat: the tolerance limits in IEC 61672 are not a single number. They vary with frequency, level, weighting and test condition. At 1 kHz the acceptance limits are approximately ±1.1 dB for Class 1 and ±1.4 dB for Class 2, but quoting a single figure across the whole frequency range would be misleading. The correct summary is that Class 1 has tighter tolerances than Class 2 throughout.
Where the classes differ
- Tolerances. Class 1 is tighter across the frequency range, and the difference widens at the extremes of the spectrum.
- Temperature range. Class 1 instruments are typically specified over a wider environmental range.
- Price. Class 1 costs more, reflecting the manufacturing precision required.
- Application. Class 1 for legal and regulatory work; Class 2 for routine surveys and screening.
When you need Class 1
Choose Class 1 when:
- your measurements may be used as legal evidence or in a noise nuisance dispute
- local regulations specifically require Class 1, which is common in environmental impact assessment
- you need the highest achievable accuracy for research or calibration work
- you are performing building acoustics measurements to ISO 16283 or similar
When Class 2 is sufficient
Class 2 is appropriate for:
- occupational noise assessment under ISO 9612, which explicitly permits Class 2 instruments for most workplace measurements
- routine environmental noise screening and monitoring
- construction noise monitoring where high precision is not required
- general industrial noise surveys
- education and training
The microphone is part of the classification
The classification applies to the complete measuring system, not the meter body alone. A Class 1 instrument requires a Class 1 microphone (IEC 61094 WS1 or equivalent). Fitting a Class 2 microphone to a Class 1 body effectively downgrades the system to Class 2 performance. This is a common and expensive mistake when replacing a damaged microphone.
Our recommendation
For most occupational health and safety professionals, environmental consultants and industrial hygienists in ASEAN, a Class 2 sound level meter with data logging and octave band analysis is the most practical and cost-effective choice. If you regularly work on projects requiring legal defensibility or environmental impact assessment, invest in a Class 1 instrument.
If you are uncertain, the deciding question is simple: could this measurement ever be challenged by a third party? If yes, specify Class 1.
Placid Asia supplies both Class 1 and Class 2 sound level meters with full technical support and accredited calibration. Contact us for instrument selection advice.