Sound Level Meters (Class 1)
Precision calibrated instruments for measuring noise levels to IEC 61672 Class 1 standard.
What it is
About Sound Level Meters (Class 1)
Class 1 sound level meters — manufactured by Brüel & Kjær (now HBK), Norsonic, Rion, and NTi Audio — are the reference instruments for acoustic measurement in regulatory, planning, and occupational health contexts. Calibrated to IEC 61672-1:2013 Class 1 (the highest accuracy classification), they measure sound pressure level in decibels across a wide frequency range, with frequency-weighting filters (A-weighting for human hearing, C-weighting for impact noise, Z-weighting for flat response) and time-weightings (Fast, Slow, Impulse). A data-logging meter records Leq (equivalent continuous level), Lmax, Lmin, and statistical percentile levels (L10, L50, L90) over defined periods. For regulatory work — environmental noise assessments under BS 4142, planning noise surveys under NPPF, or occupational exposure surveys under the Control of Noise at Work Regulations 2005 — Class 1 measurement is typically required. Field use involves more than pressing record. The practitioner selects the correct measurement position, measurement duration, and weighting for the assessment being conducted; accounts for wind and background noise; documents meteorological conditions; and applies a calibration check at the start and end of each survey using a Class 1 acoustic calibrator (typically 114 dB at 1 kHz). Data is then downloaded to software (dBTrait, NovaStar, or the meter's companion software) for analysis, correction for background noise, and report writing. Brüel & Kjær 2250, Norsonic Nor150, and NTi XL2 are the most common instruments in UK acoustic consultancy practice.
What you can do with it
Capabilities
Perform a calibration check before and after a noise survey, documenting the calibrator level and any drift in the measurement record.
Set up a Class 1 meter on a tripod at the correct measurement position and height (1.2–1.5 m above ground, minimum 3.5 m from reflective surfaces) for an environmental noise survey.
Record a time-history log of Leq and percentile levels (L10, L90) over a defined measurement period, then download data for analysis.
Apply the BS 4142:2014+A1:2019 correction procedure by measuring background noise level separately and comparing against the specific noise source.
Write up a noise measurement report documenting instrument serial number, calibration certificate, meteorological conditions, measurement position, and results.
How to learn it
Learning Resources
Institute of Acoustics (IOA) Certificate of Competence in Environmental Noise Measurement — the standard qualification for regulatory survey work in the UK (ioa.org.uk)
Brüel & Kjær Academy — free online training modules on measurement fundamentals at bksv.com/academy
NTi Audio application notes — practical measurement guides available free at nti-audio.com
BS 4142:2014+A1:2019 — the standard itself is available from BSI; understanding the standard is as important as operating the meter
Pro Tip
Always perform the calibration check in the field at the measurement location — not just in the office before departure. A calibration drift identified after a long survey means the data may be unusable. Write the calibration readings and time stamps directly into your field notes at the time.
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