Well this turned out to be a disappointing experiment. I have been thinking about doing a lot more recording with the hydrophone as I have captured some great material and want to continue to see what interesting results I can come up with recording under water. I decided to see if I could capture the sounds of ice cracking as it froze and melted so I placed the hydrophone into a plastic container, filled it with water and put it in the fridge. I attached the H4N to the mains power supply so it could run without fear of battery failure and left it on all night. 5 hours worth of recording later I an have nothing at all except the background hum of the refrigerator. Ok, so maybe ice doesn’t make much noise while its freezing, but I thought at least it would crackle and snap as it thawed out. So the following night I took the whole lot out of the freezer and left it to melt, again with the recorder running. Sadly I recorded another 5 hours of absolutely nothing. I was disappointed, but more than that I was very surprised, I really thought there would be some sound generated as the ice melted. I am going to do some more tests on this, but so far it has been a bit of a failure.