How to choose a sound level meter

A sound level meter is bought for a job, and the job decides almost every specification. This guide walks through the decisions in the order that practising acousticians take them: class, measurement principle, parameters, frequency analysis, options and licences, and finally calibration and support. Each section says what to look for on a datasheet and where the database can help. Our specifications guide explains the individual terms in more depth.

Class 1 or class 2

IEC 61672-1 defines two performance classes. Both are built to the same design goals; the difference is the width of the tolerances around them and the range of conditions over which the tolerances apply. At the 1 kHz reference frequency the class 1 acceptance limit is about ±1.1 dB and the class 2 limit about ±1.4 dB, and the gap widens at low and high frequencies. Class 1 instruments are specified from −10 °C to +50 °C, class 2 from 0 °C to +40 °C. A longer discussion is in Class 1 vs class 2 sound level meters.

The practical rule is simple. If the result may be challenged, buy class 1. Environmental noise standards such as ISO 1996-2 and most national planning guidance expect class 1, and several European countries require a pattern-approved class 1 instrument for measurements with legal effect. Workplace noise regulations generally accept class 2, because the uncertainty of where and how long a worker is exposed dwarfs the instrument tolerance. Many manufacturers sell one hardware platform in both classes, the class being set by the microphone fitted, so the choice need not be final.

Integrating or not

A conventional sound level meter shows a time-weighted level (F or S) that rises and falls with the sound. An integrating-averaging meter also computes the equivalent continuous level, L_eq, over a measurement period, together with sound exposure level and peak. Every assessment standard written in the last thirty years works with L_eq-based descriptors, so a non-integrating meter is of limited use beyond quick spot checks. The question to ask is whether the instrument measures all the parameters you need simultaneously, with all frequency weightings at once, or whether it has to be set up for one at a time.

Which parameters matter, by application

The table lists the descriptors that each field of work normally requires, so that a datasheet can be checked against it line by line. Definitions of each are in the glossary.

Environmental acoustics

Long unattended runs are the norm, so look at logging interval, memory, battery life and whether the meter can be left outside in a kit. Percentile statistics are normally computed from fast time-weighted samples taken ten or more times a second; check that the datasheet says how they are derived. Tonality assessment to ISO 1996-2 or ISO/PAS 20065 needs 1/3-octave or FFT data stored for the whole run, not just the overall level.

Occupational acoustics

A handheld meter is used for task-based surveys and for mapping; a dosimeter is worn by the person. Many handheld instruments now offer a dosimetry mode with both exchange rates, which is enough for ISO 9612 strategies. For shift-long measurements on moving workers, read How to choose a noise dosimeter.

Building acoustics

Sound insulation and reverberation measurements need 1/3-octave filters to IEC 61260-1 class 1, a reverberation time routine that handles both interrupted noise and impulse methods, and enough dynamic range to measure a 100 dB source room and a 30 dB receiving room with the same microphone. A dedicated building acoustics licence saves hours of post-processing; check that it exports to the software you already use.

Options and licences

Modern instruments are software-defined. Octave filters, FFT, audio recording, reverberation time, STIPA and dosimetry are typically licences, sometimes tied to the serial number and sometimes transferable. Three questions settle most purchase decisions: which licences are included in the quoted price, whether a licence can be added later without returning the instrument, and whether firmware updates are free for the life of the product. The category table shows which functions each instrument supports; the instrument page lists what the manufacturer publishes about options.

Hardware options matter too: an outdoor microphone kit, a detachable preamplifier with an extension cable so the operator need not stand beside the microphone, a windscreen with a published correction and a case that fits the calibrator.

Calibration and support

Budget for an acoustic calibrator of the same class as the meter (IEC 60942 class 1 for a class 1 meter) and for periodic laboratory calibration of both. Calibration costs recur for the life of the instrument and vary with the laboratory and the scope; ask for a quotation at purchase. Also ask where the nearest service centre is, how long a typical repair takes and whether a loan instrument is available. The calibration guide covers field checks, IEC 61672-3 periodic tests and what an ISO 17025 certificate shows.

Making a shortlist

1. Fix the class and the parameter set from the table above.
2. Filter the handheld sound level meters table by class and status, and open the instruments that list the spectra and functions you need.
3. Put up to four candidates in the comparison tool; it highlights every specification that differs.
4. Request quotations that itemise licences, calibrator, outdoor kit and first laboratory calibration.
5. Ask for a demonstration unit; handling and display readability in sunlight are not on any datasheet.