I don't think a hydrophone is needed, or desired. If the effect you describe is audible in the air (and I'm guessing it is), then it should be possible to record it using conventional microphones.
Food for thought:
A hydrophone's output would sound very different, but making a 'bass capable' one probably wouldn't be all that difficult - use a peizo transducer fitted to the inside of a disc of perspex or similar, having a matching disc to form the back, and a ring or two of perspex to act as spacers in between, with 'O' rings to seal the sections, bolting the whole together around the edge outside the 'O' ring margin. Feed the output of the transducer into a very high impedance (JFET) 1 - 10 megohms, and you'll get the lows. (The FET should be housed within your hydrophone.) Experiment with more compliant or thinner case materials, but be aware of water pressure effects on the casing.
Remember, sound waves in water are very different than in air - water is virtually incompressible - and therefore even an apparently rigid diaphram material (by air standards) will work well in water.
Food for thought:
A hydrophone's output would sound very different, but making a 'bass capable' one probably wouldn't be all that difficult - use a peizo transducer fitted to the inside of a disc of perspex or similar, having a matching disc to form the back, and a ring or two of perspex to act as spacers in between, with 'O' rings to seal the sections, bolting the whole together around the edge outside the 'O' ring margin. Feed the output of the transducer into a very high impedance (JFET) 1 - 10 megohms, and you'll get the lows. (The FET should be housed within your hydrophone.) Experiment with more compliant or thinner case materials, but be aware of water pressure effects on the casing.
Remember, sound waves in water are very different than in air - water is virtually incompressible - and therefore even an apparently rigid diaphram material (by air standards) will work well in water.
The sound is audible, but the environment would not be friendly to open air recordings. The microphone placement would either be out on the frozen surface of a windswept lake, or inside a 6x8 wooden icehouse. Which in addition to sounding like the inside a 6x8 wooden box, it has its own creaks, pops and wind noise to contribute to such a recording.
I'm hoping that getting a mic underwater and under 36" of ice will cure most of that.
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