@jaybarlow33 Yes, Alex Rogers (Open Acoustic Devices) pointed out that the airspace in the waterproof housing can cause resonance. I just got a quote back for the HTI-96-min (Marine Mammal) hydrophone and at $365 USD it's still within our project budget, fortunately! Thanks again for your helpful advice!

@jaybarlow33 That's really very helpful, many thanks. What is the main application of your set-up? Although I haven't yet been given a quote for the HTI-96-min, I anticipate its going to be significantly more expensive than the H2a, where the performance (from other comments) is quite disappointing at frequencies > 15KHz. In your research, have you come across any other hydrophones that might do a good job with capturing whale vocalisations across their spectra at a reasonable budget? Have you ever evaluated the standard Hydromoth set up? Sorry for more questions, but you do seem well ahead of the game! Thanks in anticiption!

Hi Jaybarlow33, I'm really interested in your hydrophone set-up with the HTI-96 Min (with the flat HF response to 30KHz). Thanks for the useful note. This is the same microphone used by the more expensive Soundtrap devices, and I want to set up a hydrophone system for recording whale vocalisations (song) for extended deployment. Can you provide further info on your application - battery type/configuration and housing? Thanks, Terry