Key comparison CCAUV.W-K2: features of hydrophone calibration

The results of key comparison are the most convincing and objective indicator of confirmation of the correctness and accuracy of the newly developed measurement method. The results of comparison and measurement methods applied at the second key comparison of national standards of the unit of sound pressure in water CCAUV.W-K2, organized by the Consultative Committee for Acoustics, Ultrasound and Vibration of the International Committee for Weights and Measures, are described. A feature of the comparison is that the calibration range has been expanded into the low frequency region by two octaves compared to the first key comparison CCAUV.W-K1. The results of the CCAUV.W-K2 comparison were considered successful. Important scientific results of participation in the comparison were confirmation of: the correctness of the hydrophone free-field calibration methods developed at VNIIFTRI (at ultra-low frequencies for a sound-reflecting water tank and in the noise reverberant sound field of the water tank), the equivalence of the calibration results when radiating signals of various types: chirp, noise and ton-burst. In the process of performing control calibrations, the pilot laboratory discovered violations of the stability of the reference hydrophone of comparison. When comparing the results obtained by participants, there was an increase in the discrepancy between the results in the frequency range 60–100 kHz, which is considered the least problematic.