Overview
IEC TR 61094-10:2022 - "Electroacoustics - Measurement microphones - Part 10: Absolute pressure calibration of microphones at low frequencies using calculable pistonphones" - describes an absolute calibration method for measurement microphones using a calculable pistonphone. The technical report is applicable to laboratory standard microphones (per IEC 61094-1) and other measurement microphones, and provides a reproducible, SI‑unit based basis for determining complex pressure sensitivity at low frequencies without reliance on a secondary microphone.
Key topics and technical requirements
- Principle: Calibration is based on generating a known sound pressure in a sealed cavity (coupler) driven by a piston with a calculable volume velocity. The microphone’s pressure sensitivity M is obtained from the measured output voltage and the calculated sound pressure.
- Acoustic transfer impedance (ZT): The sound pressure at the microphone diaphragm is derived from the cavity’s acoustic transfer impedance and the piston’s displacement/volume velocity.
- Piston displacement measurement: Rigid piston frontal area and displacement are measured (e.g., laser interferometry or other displacement techniques) to determine volume velocity.
- Corrections and limits: The report includes heat‑conduction corrections, operating frequency range considerations, and guidance on ensuring uniform pressure distribution within the cavity.
- Environmental reference conditions: Reference conditions are defined (23.0 °C, 101.325 kPa, 50 % RH) and all quantities are expressed in SI units.
- Influencing factors: Treatment of factors that affect pressure sensitivity such as polarizing voltage, shield configuration, static pressure, temperature, humidity, vibration and distortion.
- Uncertainty analysis: Framework for calibration uncertainty components, example uncertainty budgets, and combined/expanded uncertainties (informative Annex B).
- Design examples: Informative Annex A provides example pistonphone designs (including laser pistonphones) to aid implementation.
Applications and who uses it
- National metrology institutes (NMIs) and calibration laboratories performing absolute pressure calibration of measurement and laboratory standard microphones at low frequencies.
- Acoustic calibration labs needing a primary or absolute method alternative to reciprocity techniques (IEC 61094-2).
- Manufacturers of measurement microphones and pistonphones designing calibration hardware and validating low‑frequency microphone performance.
- Acoustics engineers and quality assurance teams requiring traceable, reproducible low‑frequency microphone sensitivity data for sound measurement systems.
Related standards
- IEC 61094-1: Specifications for laboratory standard microphones
- IEC 61094-2: Primary pressure calibration by the reciprocity technique (related calibration method)
Keywords: IEC TR 61094-10:2022, absolute pressure calibration, calculable pistonphone, measurement microphones, low-frequency calibration, acoustic transfer impedance, microphone sensitivity, calibration uncertainty.