IEC 61672-1

IEC 61672-1 is the international specification for sound level meters. Almost every professional instrument in this database states conformance to it, and the class 1 or class 2 marking on a datasheet refers to its tolerance limits. The standard has three parts: Part 1 gives the specifications, Part 2 describes the pattern-evaluation tests used for type approval, and Part 3 describes the periodic tests a calibration laboratory performs on an individual instrument. National adoptions include ANSI/ASA S1.4-2014 in the United States, EN 61672-1 in Europe and JIS C 1509-1 in Japan, all of which are technically identical to the IEC text.

Scope and editions

The first edition, published in 2002, replaced IEC 60651 (sound level meters) and IEC 60804 (integrating-averaging sound level meters), whose type 0, 1, 2 and 3 grades had been used since the 1970s. The second edition of 2013 is current. It tightened several requirements, introduced the group X and group Z designations and clarified how an instrument is to be tested with its microphone. A datasheet should say which edition is claimed; “IEC 61672:2002 class 1” and “IEC 61672-1:2013 class 1” are not the same statement, and an instrument that only cites IEC 60651 type 1 has not been shown to meet either.

The standard covers three kinds of instrument: a conventional sound level meter that displays time-weighted levels, an integrating-averaging meter that also measures L_eq, and an integrating meter that measures sound exposure level. In practice, nearly every instrument sold today is of the second kind and offers the third as a parameter.

What it specifies

• Frequency weightings A, C and Z, each given as a design goal with class-dependent tolerance limits from 10 Hz to 20 kHz. The A weighting is mandatory; C and Z are optional in the standard but universal in practice.
• Time weightings F (125 ms) and S (1 s), with I (impulse) retained as an option. The standard notes that I is not suitable for assessing the impulsiveness of sound.
• Time-averaged (L_eq) and sound exposure levels, with requirements on the accuracy of integration for steady and tone-burst signals.
• C-weighted peak sound level, with tolerances on the peak detector’s response to short bursts.
• Level linearity: the range over which the indicated level tracks the input within tolerance, tested in steps at 1 kHz. This defines the linearity range quoted on datasheets.
• Self-generated noise, overload and under-range indication, directional response, and the effects of temperature, humidity, static pressure, vibration, magnetic fields and radio-frequency fields.
• Information the manufacturer must publish in the instruction manual, from the reference sound pressure level and microphone corrections to the effect of the windscreen and the configuration under which conformance is claimed.

Class 1 and class 2

The two classes share identical design goals and differ in the width of the tolerances and the range of conditions over which they apply. At the 1 kHz reference frequency the acceptance limit, which includes the laboratory’s measurement uncertainty, is about ±1.1 dB for class 1 and about ±1.4 dB for class 2. The limits widen towards the frequency extremes, considerably more so for class 2. Class 1 instruments must meet their tolerances from −10 °C to +50 °C, class 2 from 0 °C to +40 °C. The class applies to the complete instrument as tested, with a specified microphone, preamplifier and firmware. The guide Class 1 vs class 2 sound level meters discusses what follows for buyers.

Group X and group Z

The 2013 edition introduced two groups that describe how an instrument is to be tested. The distinction concerns whether the electrical tests of the frequency weightings can be carried out with the microphone replaced by an electrical input device, and how the acoustical tests account for the microphone. The group determines which procedures a laboratory follows under Parts 2 and 3; it does not indicate a difference in measurement performance and most buyers can disregard it.

What it does not cover

IEC 61672-1 says nothing about octave-band filters, which are specified by IEC 61260-1; about dosimetry, which is IEC 61252; about FFT, reverberation time or speech intelligibility; or about how a measurement should be made and assessed, which is the business of standards such as ISO 1996 and ISO 9612. It also sets no calibration interval. A meter may be class 1 and still have a high noise floor, limited memory or no logging; those are commercial specifications, discussed in Understanding sound level meter specifications.

Instruments stating conformance

The table lists every instrument in the database whose manufacturer-published standards list mentions IEC 61672, with the statement as the manufacturer makes it. Where the edition or class is not stated, that is because the manufacturer does not state it. Inclusion means the manufacturer claims conformance; only pattern approval or a laboratory test shows that a given instrument meets the limits.