What is the accuracy difference between Class 1 and Class 2?

Class 1 per IEC 61672-1 allows ±1.1 dB at 1 kHz reference and ±1.4 dB across the range. Class 2 permits ±1.4 dB at reference and ±2.3 dB across. Class 1 is required for regulatory enforcement, litigation, and ISO 3382 building acoustics measurements.

When should I use A-weighting versus C-weighting?

Use A-weighting for general noise assessment, occupational exposure, and environmental monitoring. Use C-weighting for peak SPL measurement and low-frequency evaluation. The dBC minus dBA difference indicates low-frequency energy content in the noise source.

How often should I calibrate my sound level meter?

IEC 61672-1 clause 8 requires calibration before and after every session. Drift must stay within 0.5 dB. Laboratory periodic verification per IEC 61672-3 should occur annually. Record all calibration values in measurement logs.

Can a smartphone meet IEC 61672 Class 2?

No smartphone has achieved IEC 61672 type approval. MEMS microphones lack required frequency flatness and dynamic range. Calibrated apps can achieve ±2-3 dB within 200 Hz to 8 kHz, useful for screening but not regulatory compliance work.

What is the accuracy difference between Class 1 and Class 2?

Class 1 per IEC 61672-1 allows ±1.1 dB at 1 kHz reference and ±1.4 dB across the range. Class 2 permits ±1.4 dB at reference and ±2.3 dB across. Class 1 is required for regulatory enforcement, litigation, and ISO 3382 building acoustics measurements.

When should I use A-weighting versus C-weighting?

Use A-weighting for general noise assessment, occupational exposure, and environmental monitoring. Use C-weighting for peak SPL measurement and low-frequency evaluation. The dBC minus dBA difference indicates low-frequency energy content in the noise source.

How often should I calibrate my sound level meter?

IEC 61672-1 clause 8 requires calibration before and after every session. Drift must stay within 0.5 dB. Laboratory periodic verification per IEC 61672-3 should occur annually. Record all calibration values in measurement logs.

Can a smartphone meet IEC 61672 Class 2?

No smartphone has achieved IEC 61672 type approval. MEMS microphones lack required frequency flatness and dynamic range. Calibrated apps can achieve ±2-3 dB within 200 Hz to 8 kHz, useful for screening but not regulatory compliance work.

SPL Measurement Guide — IEC 61672 Accuracy Standards

IEC 61672-1 Sound Level Meter Classes

IEC 61672-1 clause 5 defines two performance classes. Class 1 meters have tolerance of ±1.1 dB at 1 kHz and ±1.4 dB across 20 Hz to 12.5 kHz. Class 2 allows ±1.4 dB at reference and ±2.3 dB across the range. Class 1 is required for legal noise enforcement and building acoustics per ISO 3382.

Frequency Weighting Networks

A-Weighting (dBA)

A-weighting approximates the ear's sensitivity at moderate levels per ISO 226:2003. It attenuates low frequencies (-26.2 dB at 63 Hz) and peaks at 2.5 kHz (+1.2 dB). IEC 61672-1 clause 5.4 defines the transfer function using four poles.

C and Z Weighting

C-weighting is flatter, used for peak measurements per EU Directive 2003/10/EC. Z-weighting applies no correction across 10 Hz to 20 kHz, measuring true physical sound pressure for research and loudspeaker testing.

Time Weighting Constants

IEC 61672-1 clause 5.7: Fast (125 ms), Slow (1000 ms), Impulse (35 ms attack, 1500 ms decay). Fast captures transients. Slow stabilizes readings. Impulse highlights impulsive noise relevant to hearing damage assessment.

Equivalent Continuous Level (Leq)

Leq integrates energy over the measurement period. LAeq is the A-weighted equivalent level used in nearly all noise regulations. IEC 61672-1 clause 3.13 defines Leq as 10 log base 10 of the time-averaged squared pressure ratio.

Calibration

IEC 61672-1 clause 8 mandates field calibration before and after sessions using a 94 dB or 114 dB calibrator at 1 kHz. Drift must not exceed 0.5 dB for valid measurements.

SPL Measurement Guide — IEC 61672 Accuracy