The low-frequency limit normally imposed by a confined water tank in u
nderwater acoustic transducers is prominently reduced by applying Pron
y's model to the sampled transient data. A new concept to improve the
calibration accuracy of transducers with an uneven transmitting respon
se is presented, i.e. that variation of transmitting characteristics o
f transducers with frequency can be compensated by using devised minim
um phase signals. Its effectiveness is demonstrated in the experiments
.