Abstract: The force on eleetroacoustie transducers in coupler and the reciprocity parameter of the coupler for the calibration of hydrophone have been deduced as the projeetor, receiver and reciprocity transducer are installed in different situation and when the field in the coupler is ununiform.
Derivated the formulae for calibration of sensitivity of hydrophone in coupler calibration method when the pressure in liquid column of coupler was ununiform. The new parameter and formulae just proposed may carry out a theoretical estimate of the oeeuracy of reciprocity calibration in coupler. According to these formulae and parameter, we may modify the ealeulation of sensitivity by conventional count, and then the frequeney range of the coupler calibration can be extended.