IEC 61672-1 Class 1 vs Class 2: Tolerance Comparison
TL;DR
IEC 61672-1 defines two accuracy classes. Class 1 instruments have tighter tolerances across all specifications — frequency weighting (±1.1 dB vs ±1.4 dB at mid-frequencies), level linearity (±1.1 dB vs ±1.4 dB), and directional response. Class 1 is required for legal enforcement, precision laboratory measurements, and some building acoustics standards. Class 2 is acceptable for general-purpose field surveys, screening measurements, and occupational noise assessments in most jurisdictions. The key difference is not quality but acceptable measurement uncertainty.
Tolerance Comparison Table
The following table summarizes the key differences between Class 1 and Class 2 at representative frequencies for A-weighted measurements:
| Parameter | Class 1 | Class 2 |
|---|---|---|
| Frequency weighting (250 Hz – 4 kHz) | ±1.1 dB | ±1.4 dB |
| Frequency weighting (63 Hz) | ±1.6 dB | ±2.6 dB |
| Frequency weighting (31.5 Hz) | ±2.1 dB | ±3.5 dB |
| Frequency weighting (8 kHz) | ±2.1 dB | ±3.6 dB |
| Level linearity (1 kHz) | ±1.1 dB | ±1.4 dB |
| Directional response (1 kHz) | ±1.4 dB | ±2.4 dB |
| Operating temperature range | -10°C to +50°C | 0°C to +40°C |
Tolerances widen significantly at frequency extremes (below 63 Hz and above 8 kHz) for both classes.
When Class 1 Is Required
Several regulatory frameworks and standards mandate Class 1 instruments:
- ISO 3382-1 room acoustic measurements require Class 1 or better
- Building acoustics testing under ISO 16283 specifies Class 1
- Legal noise enforcement in the EU typically requires Class 1
- Airport and transportation noise monitoring standards
When Class 2 Is Sufficient
Class 2 instruments are acceptable for:
- Occupational noise screening per OSHA 1910.95 (OSHA accepts Type 2 / Class 2)
- General environmental surveys and community noise complaints
- Live sound system tuning and SPL monitoring
- HVAC noise assessment for comfort evaluation
Expanded Uncertainty
The class designation directly affects measurement uncertainty. A Class 1 instrument contributes approximately ±1.5 dB expanded uncertainty (k=2) to a single measurement at mid-frequencies, while Class 2 contributes approximately ±2.3 dB. When combined with environmental and positioning factors, total measurement uncertainty is always larger than instrument uncertainty alone.
SonaVyx Classification
SonaVyx implements Class 2 equivalent processing algorithms — the frequency weighting filters and time weighting detectors meet the mathematical specifications. However, overall system accuracy depends on the phone or interface microphone, which varies by device. Calibration against a known reference significantly improves accuracy. For periodic verification procedures, see IEC 61672-1 periodic testing.
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Last updated: March 19, 2026