ANSI S1.4 Type Classifications: Type 0, Type 1, and Type 2
TL;DR
ANSI S1.4 defines three instrument types with progressively tighter tolerances. Type 0 (laboratory reference) has ±0.7 dB tolerance at 1 kHz, used only for calibrating other instruments. Type 1 (precision) has ±1.0 dB at 1 kHz, equivalent to IEC 61672-1 Class 1, required for precision measurements and enforcement. Type 2 (general purpose) has ±1.5 dB at 1 kHz, equivalent to IEC 61672-1 Class 2, acceptable for most field surveys and OSHA compliance. The Type designation affects tolerances for frequency weighting, level linearity, directional response, and detector characteristics.
Type 0 — Laboratory Reference
Type 0 instruments are laboratory-grade reference standards not intended for field use. They serve as calibration references for verifying Type 1 and Type 2 instruments. Type 0 tolerance at 1 kHz is ±0.7 dB, with extremely tight requirements across the full frequency range. There is no IEC 61672-1 equivalent to Type 0.
Type 1 — Precision
Type 1 instruments are designed for precision field measurements and legal enforcement. The tolerance requirements align with IEC 61672-1 Class 1:
| Frequency | Type 1 tolerance | Type 2 tolerance |
|---|---|---|
| 31.5 Hz | ±2.5 dB | ±3.5 dB |
| 63 Hz | ±2.0 dB | ±2.5 dB |
| 125 Hz | ±1.5 dB | ±2.0 dB |
| 250 Hz – 4 kHz | ±1.0 dB | ±1.5 dB |
| 8 kHz | ±2.5 dB | ±3.0 dB |
| 12.5 kHz | ±3.0 dB | ±5.0 dB |
Type 1 instruments must also meet tighter directional response requirements (the change in reading as sound arrives from different angles relative to the microphone axis).
Type 2 — General Purpose
Type 2 instruments are the most common in practice. They satisfy requirements for OSHA noise monitoring, general environmental surveys, and community noise complaint investigation. The wider tolerances allow for less expensive microphones and electronics while still providing measurements adequate for regulatory compliance.
Level Linearity
All types must maintain accuracy across a specified dynamic range:
- Type 0: ±0.4 dB across 60 dB range
- Type 1: ±0.7 dB across 60 dB range
- Type 2: ±1.0 dB across 60 dB range
This ensures that measurements at 50 dB and 110 dB have consistent accuracy.
Detector Characteristics
The Fast, Slow, and Impulse time-weighting response must meet type-specific tolerances for tone-burst response, crest factor handling, and overload indication. Type 1 instruments must handle higher crest factors without error.
Choosing the Right Type
Select based on application requirements:
- Type 1: Legal enforcement, precision laboratory work, ISO 3382 measurements, building acoustics
- Type 2: OSHA compliance screening, community noise surveys, live sound SPL monitoring, HVAC commissioning
The SonaVyx SPL meter implements Type 2 equivalent processing. For frequency weighting details, see the next section. For calibration requirements by type, see the calibration section.
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Last updated: March 19, 2026