Understanding sound level meter specifications
By soundlevelmeter.review editors, practising acousticians. Published . Neutral by policy: no brand pays for placement.
Sound level meter datasheets are written by different companies for different markets, and the same word does not always mean the same thing. This guide goes through a datasheet heading by heading, explains what each specification actually tells you, and points out where to read carefully. The database uses one template for every instrument so that figures can be compared line by line; this guide explains what those lines mean. Short definitions of each term are in the glossary.
Class and standards
The class marking refers to IEC 61672-1 and applies to the complete instrument with a named microphone. A datasheet should say which edition (2002 or 2013). Conformance to the older IEC 60651 and IEC 60804 is often listed as well; those are not equivalent. Separate standards govern filters (IEC 61260-1), dosimetry (IEC 61252) and speech intelligibility (IEC 60268-16), and pattern approval is a separate statement again. See Class 1 vs class 2 for what the class does and does not tell you.
Measurement range, linearity range and peak range
Three ranges appear on datasheets and are easily confused. The measurement range (or display range) is the span from the lowest level the meter will show to the highest before overload. The linearity range is the IEC 61672-1 term for the span over which the indicated level tracks the input within the class tolerance; it is tested at 1 kHz and is the range to rely on. It is typically a few decibels narrower than the measurement range at the bottom, because the lowest few decibels above the noise floor are not linear. The peak range is the span over which LCpeak is within tolerance; its upper limit is usually higher than the RMS range because the peak detector has headroom.
A modern meter normally has a single range covering 100 dB or more; some designs switch between ranges, which complicates unattended logging. Check whether the figures are given with a specific microphone.
Noise floor
The noise floor, or self-generated noise, is the level the meter indicates with no sound at the microphone. It should be stated as an A-weighted level with the microphone fitted; an “electrical” figure measured with a dummy microphone is lower and not comparable. A signal should be at least 10 dB above the floor, where the floor adds 0.4 dB. The floor depends on microphone sensitivity: a ½-inch 50 mV/Pa microphone gives a floor in the mid-teens of dB(A), a 12.5 mV/Pa high-level microphone 10 dB or more higher. A meter with a 20 dB(A) floor cannot measure a 25 dB(A) rural night-time background.
Frequency and time weightings
The A, C and Z frequency weightings are defined by IEC 61672-1 and every conforming meter has them; what varies is whether all three are measured simultaneously or one at a time, and whether all parameters are available for each. G weighting for infrasound (ISO 7196) and the obsolete B weighting are extras. The F (fast, 125 ms) and S (slow, 1 s) time weightings are likewise universal; the I (impulse) weighting is retained in IEC 61672-1 as an option and is still required by a few national procedures. Look for “simultaneous” or “parallel” measurement of all weightings and all time constants: it means a run does not have to be repeated because the wrong setting was chosen.
| Specification | What it tells you | Check that it states |
|---|---|---|
| Linearity range | Span over which readings are within class tolerance | Lower limit at 1 kHz with the named microphone |
| Noise floor | Lowest credible level | A-weighted, with microphone, not electrical only |
| Frequency range | Where class tolerances are met | Not the raw microphone response |
| Octave bands | Spectral analysis capability | IEC 61260-1 class, band range, real-time or sequential |
| FFT | Fine-resolution analysis | Lines, span, window functions, averaging |
| Logging | Time-history capability | Shortest interval, parameters per interval, memory, markers |
| Battery life | Field endurance | Conditions: backlight, logging, spectra, temperature |
Octave-band filters
Spectral analysis in 1/1 or 1/3-octave bands is specified by IEC 61260-1, which has its own class 1 and class 2 limits for filter shape. Datasheets should give the filter class, the band range, whether bands are measured in real time in parallel with the broadband values, and whether Leq, Lmax and percentiles are available per band. A few lower-cost models step through bands sequentially, which is unsuitable for anything that changes with time.
FFT
FFT analysis is not covered by any instrument standard, so the datasheet carries the whole specification: the number of lines, the frequency span and hence the resolution, the window functions available, the averaging modes and whether the FFT runs in parallel with the sound level meter functions. FFT is used for identifying tones and their sources, for tonality assessment under ISO 1996-2 and ISO/PAS 20065, and for machinery work; in environmental and building acoustics it is an occasional tool.
Logging and data
Logging is where instruments differ most and datasheets say least. The useful numbers are: the shortest logging interval (1 s is common; 100 ms or shorter matters for impulsive sources); which parameters and spectra are stored at each interval; the memory in days at a given setting; whether markers can be added; the audio format if sound is stored; and how data leave the instrument and in what file formats.
What manufacturers omit
Reading what is absent is a skill. Common omissions, each of which should prompt a question to the supplier:
- A linearity range, where only a measurement range is given.
- A noise floor with the microphone fitted, where only an electrical figure or none is given.
- The conditions behind a battery-life figure.
- Whether the class applies with the outdoor kit, extension cable or alternative microphone.
- The IEC 61260-1 class of the filters.
- Whether a function is standard or a licence, and what the licence costs.
- The sample rate used for percentile statistics, which affects L90 and L10.
- The edition of the standard conformed to.
This site records only what the manufacturer publishes and leaves the rest blank, so a blank field on an instrument page is itself information. The comparison tool makes gaps visible by placing instruments side by side, and the category tables can be filtered to the instruments that do publish a given value.
Frequently asked questions
- What does the measurement range on a sound level meter mean?
- The span of levels the manufacturer says the meter can display, from a lower limit set by inherent noise to an upper limit set by overload. It is a headline figure. The linearity range, defined by IEC 61672-1, is the part of that span over which the indication tracks the input within class tolerances, and is usually narrower at the bottom.
- Why do two meters with the same class have different noise floors?
- Class tolerances apply to the accuracy of the indication, not to the lowest level the meter can resolve. The noise floor depends on the microphone (a 50 mV/Pa microphone is quieter than a 12.5 mV/Pa one), the preamplifier and the converter. The standard only requires that self-generated noise be stated.
- Is a wider frequency range better?
- Only if you need it. IEC 61672-1 tolerances run from 10 Hz to 20 kHz; a microphone that extends further is useful for infrasound (G weighting, ISO 7196) or ultrasound and otherwise adds nothing to an A-weighted measurement. Check the range at which class tolerances are met, not the raw microphone response.
- What is the difference between 1/3-octave and FFT analysis?
- Third-octave filters have constant relative bandwidth, about 23 percent of the centre frequency, matching how hearing works. FFT has constant absolute bandwidth, for example 1 Hz, which resolves individual tones and harmonics. Acoustics standards are written in octave bands; FFT is for diagnosis, tonality and machinery.
- What do manufacturers typically leave off a datasheet?
- Commonly: the linearity range as distinct from the measurement range; the noise floor with microphone fitted; the conditions behind the battery-life figure; whether the class applies with the outdoor kit; the octave filter class; and which functions are licences. A blank on this site means the manufacturer did not publish the value.
Related tables: Handheld sound level meters, Noise dosimeters, Noise monitoring stations. Terms are defined in the glossary; the standards referred to are explained under Standards.
More guides
- How to choose a sound level meter · Class 1 vs class 2, integrating vs non-integrating, parameters by application, options and licences, calibration.
- Class 1 vs class 2 sound level meters · IEC 61672-1 tolerances, what the classes do and do not say, and where each is typically required.
- How to choose a noise dosimeter · IEC 61252, exchange rates, criterion levels, badge vs cable, intrinsic safety, logging and audio.