A laser pistonphone designed for absolute calibration of infrasound sensors from 10 mHz up to 20 Hz

Demand for calibration at infrasonic frequencies has emerged. It is supported by earth monitoring issues and particularly by the Comprehensive nuclear Test Ban Treaty Organization (CTBTO), which provides a global international coverage for nuclear testing ban, and requires for the IMS (International Monitoring System). In the presentation, a new laser pistonphone design is presented with the objective of establishing primary standards for sound pressure at very low frequencies down to 10 mHz. The piston is a modified accessorized loudspeaker driver whose diameter is equal to the diameter of the front pistonphone cavity. The volume velocity of the piston is measured through a laser interferometer and it was designed to have an upper frequency limit of 20 Hz, to overlap with the reciprocity method of calibration. Particular attention has been given with the-sealing to avoid the pressure leakage loss. The dimensions of the front cavity were designed to allow the calibration of a large variety of sensors, including microphones, barometers, manometers and microbarometers. Examples of calibrations for several sensors are presented with the uncertainty. Finally, the metrological performance of the laser pistonphone is demonstrated by comparing the calibration results with those obtained with alternative methods.