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.
You can put sea sand into the capsule. This allows the capsule to sink in water.