ANSI S1.4 and IEC 61672 define the same two-tier accuracy system for sound level meters, and the cross-mapping is mechanical: ANSI S1.4 Type 1 performance is equivalent to IEC 61672-1 Class 1, and ANSI S1.4 Type 2 to IEC 61672-1 Class 2 [S2][S8]. Both standards use the same reference sound pressure of 20 µPa, the same A- and C-weighting networks, and the same Fast (0.125 s), Slow (1 s) and Impulse time weightings; the practical differences live in declared tolerances, frequency span and what kind of pattern evaluation the manufacturer must submit [S1][S5].
Specifying engineers should treat the two designations as interchangeable in procurement language, but pin the document number that governs the project: European environmental work almost always names EN 61672, while US OSHA 29 CFR 1910.95(d) noise dosimetry and MSHA noise rule compliance still reference ANSI/ASA S1.4 by name [S2][S8]. Sper Scientific's Type 1 Sound Meter, for example, is sold as meeting both "IEC 61672-1:2013 Class 1 and ANSI S1.4:2014 Type 1" in the same spec block, which is the typical dual-marking pattern OEM datasheets now use [S3].
What the Type / Class Number Actually Bounds
ANSI S1.4 Type 1 and IEC 61672-1 Class 1 both impose a reference-tone tolerance of roughly ±0.7 dB under controlled laboratory conditions; Type 2 / Class 2 widens that to about ±1.3 dB at the 1 kHz reference [S2][S8]. That tolerance figure is what an acoustical calibrator at 94 dB or 114 dB has to read on a known microphone before and after a measurement run, and it is the number a calibration certificate from a NVLAP- or A2LA-accredited lab is actually verifying [S3][S4].
Frequency coverage is the second hard divider: Class 1 / Type 1 meters must hold their tolerance from 16 Hz to 16 kHz on the nominal frequency response, while Class 2 / Type 2 meters only commit to 20 Hz to 8 kHz [S4][S5]. Below 16 Hz the IEC 61672 curve cuts off entirely, while ANSI S1.4 still specifies a ±4 dB window at 10 Hz, a real difference for infrasound surveys of wind farms, HVAC plant rooms and blasting events [S7]. A second difference sits at the LF end of A-weighting: IEC 61672 tightens the –3 dB corner near 20 Hz against the older ANSI S1.4 shape, so a meter can pass one standard and still drift on the other at low frequencies [S7].
Class 1 / Type 1 vs Class 2 / Type 2: A Decision Matrix
Four criteria line the two tiers up cleanly. On tolerance, Class 1 / Type 1 holds ±0.7 dB against Class 2 / Type 2's ±1.3 dB at the 1 kHz reference [S2][S8]. On frequency span, Class 1 / Type 1 covers 16 Hz–16 kHz (with extended ±2 dB field tolerance to 20 kHz for some models), while Class 2 / Type 2 stops at 8 kHz on the upper end and 20 Hz on the lower [S4][S5]. On operating temperature, IEC 61672 Class 1 is specified across roughly –10 °C to +50 °C, while Class 2 narrows to about 0 °C to +40 °C unless the OEM publishes wider data [S5]. On linear operating range, Class 1 typically spans the full 23 dB(A) reference sensitivity to 140 dB without range switching, while Class 2 is often limited to about 30 dB–130 dB on a single range [S5].
For a defensible environmental survey under ISO 1996-2 or for EU Directive 2003/10/EC noise exposure mapping, Class 1 / Type 1 is the only safe call, because octave or 1/3-octave band data, A-weighted equivalent (LAeq) logging and audio event recording all assume the wider frequency and tolerance envelope [S2][S4]. Class 2 / Type 2 fits occupational spot checks, IEC 61672-3 periodic field tests, and short-duration workplace mapping where a tighter uncertainty budget is not required for legal review [S2][S4][S9].
When Each Standard Has to Be Cited by Name
US-side procurement under federal noise rules still names ANSI/ASA S1.4 directly: MSHA's noise rule and the OSHA hearing-conservation amendment in 29 CFR 1910.95(d) both expect a Type 1 or Type 2 SLM that satisfies S1.4, and that citation carries through into the calibration certificate wording [S2][S9]. European and most international tenders instead name EN 61672-1 (the CENELEC adoption of IEC 61672-1) plus EN 61672-3 for periodic testing, and a Class 1 or Class 2 certificate is the contractual evidence [S1][S8].
For global projects, the cleanest procurement line is "sound level meter conforming to IEC 61672-1 Class 1 (EN 61672-1 Class 1) and ANSI/ASA S1.4 Type 1, with pattern evaluation per IEC 61672-2 and periodic testing per IEC 61672-3" [S1][S3]. This wording avoids the trap of a meter that is only marked to one of the two standards, and it gives the receiving inspector two independent compliance paths to check against the shipped certificate.
Pattern Evaluation vs Periodic Test: Two Different Documents
IEC 61672-2 (and the older ANSI S1.4 Part 2) defines a pattern evaluation, a one-time laboratory test on a representative instrument that establishes whether the design family can meet Class 1 or Class 2 at all [S1]. That certificate stays with the model, not the individual unit, and it is what a manufacturer's "IEC 61672 Class 1" claim on a datasheet is actually backed by [S1][S3].
IEC 61672-3 (and ANSI S1.4 Part 3) instead covers periodic testing, the per-instrument check at acquisition and after any repair, typically done with a Class 1 sound calibrator at 94 dB and 1 kHz [S1][S3]. Many buyers miss that "ANSI S1.4 Type 1" on the case is a design-class claim, not evidence the specific unit in the box currently passes; the only way to confirm pass status is a current 61672-3 field test against an acoustic calibrator such as a Sper Scientific 850016, a Svantek SV 33 or equivalent [S3][S4][S9]. Re-calibration intervals commonly run 12 months for laboratory use and 6 months or before/after each measurement campaign for environmental field work [S4].
Typical Microphone, Weighting and Range Trade-offs
Class 1 / Type 1 meters are usually built around a ½-inch pre-polarized free-field microphone with a nominal sensitivity near 50 mV/Pa and a flat response from 16 Hz to 16 kHz within ±1 dB; Class 2 / Type 2 units use a similar capsule with relaxed response limits and a 20 Hz–8 kHz window [S3][S4][S5]. Beyond the microphone, A- and C-weighting are mandatory on both tiers, with Z (linear) available on Class 1 models for unweighted spectral work; Z is optional on Class 2 and rarely fitted on economy units [S4][S5].
Most Class 1 / Type 1 instruments also support 1/1- and 1/3-octave band filters, AC and DC time-weighted output, peak hold (C-weighted or Z-weighted peak for hearing-damage risk) and data logging, while Class 2 / Type 2 models often drop the octave filters and peak-hold channels to hit a lower price point [S2][S3][S4]. For a sound level meter used in occupational noise surveys, the deciding extras are usually Leq/LEPd integration, a logging interval short enough to capture short transient events, and a peak C channel rated to 140 dB or above for impact-noise sources [S4][S9].
Choosing the Right Tier for a Given Job
Class 1 / Type 1 is the right call for environmental noise mapping under ISO 1996, EU Directive 2003/10/EC noise exposure, building acoustics per ISO 16283, NFPA 72A/72B emergency-signal intelligibility tests, and any measurement that may end up in a courtroom or public comment file [S2][S4][S5]. Class 2 / Type 2 covers OSHA-style spot surveys, general workplace walk-arounds, school and office background-noise checks, and post-construction verification where a less stringent uncertainty budget is acceptable [S2][S4][S9].
Two practical signals to track before purchase: confirm the calibration certificate lists the specific serial number, the IEC 61672-3 test date, and the test points used, not just a model-level claim [S1][S3]; and confirm the OEM publishes both an ANSI S1.4 pattern-evaluation certificate and the IEC 61672-2 certificate on request, because some low-cost Class 2 units are self-declared only and fail formal tender review [S1][S2]. For comparison work against an installed acoustic calibrator, a level measurement rig with a known 94 dB reference lets the engineer back-compute any drift on a previous survey; the same rig is what a level switch type trip-amplifier setup borrows from when validating alarm thresholds.
See also our earlier report, Smoke Detector vs Combustible Gas Detector: What Each Sensor Actually Sees.