IEC 61672-1: Electroacoustics — Sound level meters — Part 1: Specifications

Specifies the performance requirements for three types of sound measuring instruments: conventional sound level meters, integrating-averaging sound level meters, and integrating sound level meters.

IEC 61672-1: Sound Level Meters

IEC 61672-1 is the primary international standard governing the performance of sound level meters (SLMs). Published by the International Electrotechnical Commission, it replaced the earlier IEC 60651 and IEC 60804 standards, unifying the requirements for both conventional and integrating-averaging sound level meters into a single document. This standard is referenced by noise regulations worldwide.

Class 1 and Class 2

IEC 61672-1 defines two performance classes. Class 1 instruments have tighter tolerances and are required for precise engineering measurements, regulatory enforcement, and situations where legal decisions depend on the measured values. Class 2 instruments have wider tolerances and are suitable for general noise surveys, workplace screening, and educational purposes. The primary differences between classes are the allowable frequency response deviation (plus or minus 1.1 dB for Class 1 vs plus or minus 1.4 dB for Class 2 at reference frequencies) and directional response requirements.

Frequency Weightings

The standard specifies three frequency weighting networks. A-weighting approximates the sensitivity of human hearing at moderate levels and is used for most regulatory measurements (LAeq, LAmax). C-weighting is flatter and used for peak measurements and assessing low-frequency content (LCpeak). Z-weighting (zero weighting) provides an unweighted flat response from 10 Hz to 20 kHz and is used for detailed spectral analysis. The standard provides exact filter coefficients and tolerance limits for each weighting.

Time Weightings

Three time-weighting characteristics are specified: Fast (125 ms time constant), Slow (1000 ms), and Impulse (35 ms attack, 1500 ms decay). Fast weighting is the default for most measurements. Slow weighting provides a more stable reading in fluctuating noise. Impulse weighting captures fast transients and is used in some European noise regulations for assessing impulsive sound.

SonaVyx Implementation

SonaVyx's SPL meter implements all three frequency weightings and all three time weightings per IEC 61672-1 with Class 2 tolerance targets. The A-weighting filter uses a cascade of IIR biquad sections designed via bilinear transform from the analog prototype poles. Calibration support allows users to correct for microphone sensitivity variations to achieve the best possible accuracy with consumer hardware.