After a few failed attempts, I’m feeling pretty good about this hydrophone design. Though this would probably work with a glass jar, Nalgene bottle, or similar but my plan is to use a water-tight aluminum cylinder. It might need some weights in the bottom, but I think the thin aluminum will pick up sounds really well.
I’m especially excited about the easily replaceable cable without soldering, meaning it can even be switched in the field.
I would think best used with a DI box to isolate the hydrophone just in case of leaks, though with some recent and unrelated tests I’ve been doing on the conductivity of water, even a small leak probably wouldn’t zap anything.
Hopefully I can finish up a final prototype in the next few weeks and get them on ContactMics.com for sale very soon.