Environmental noise monitoring programmes measure sound levels at or near noise-sensitive receptors — residential areas, schools, hospitals, or nature reserves — over days, weeks, or months. The data is used in planning inquiries, noise impact assessments, regulatory compliance reporting, and enforcement action. Because the results may be scrutinised long after the measurement period, the defensibility of the data depends critically on demonstrated calibration stability and documented measurement uncertainty throughout the monitoring period.
Instrument selection for environmental noise monitoring is governed primarily by the applicable standard or regulation. IEC 61672-1 Class 1 is the minimum requirement for most European regulatory work. ISO 1996-2 provides the methodology for description and assessment of environmental noise. National regulations in many countries specify minimum instrument class, calibration check intervals, and documentation requirements. PLACID instruments are used in permanent monitoring networks, temporary project-specific deployments, and building permit noise surveys.
PLACID Class 1 measurement microphones with outdoor housings are suitable for fixed monitoring mast deployment and for temporary campaign monitoring. ISO/IEC 17025 accredited calibration with stated expanded measurement uncertainty is available for all instruments used in this application.
The defensibility of environmental noise monitoring data depends on more than the instrument class. Calibration records must demonstrate that the microphone sensitivity was within specification throughout the monitoring period. This requires a pre-deployment accredited calibration certificate, field calibrator check records at the start and end of each monitoring period, and — for long-duration programmes — evidence that the sensitivity has not drifted between laboratory calibrations. The PLACID long-term stability programme provides this evidence for PLACID reference microphone models.