Building a Hydrophone for the ROV


I am currently working on designing a hydrophone for OpenROV. My starting point will be the following guide from NOAA.

My initial thought is to use a cheap microphone and encase in a small container filled with mineral oil. However if anyone in the community has any tips, tricks, or would like to follow along and give advice feel free!


Looked at this hydrophone?

I was thinking either more piezos to make lower impedance or a impedance matching transformer/preamp (like for an acoustic guitar) for better frequency response, but I think they cover that in later builds. The mechanics for making it waterproof were what I was looking for. Lots of interesting information on his site!


regarding enclosures you get started with the battery tube + endcaps. Gives us approx. 1 1/8” inside diameter. Without the batteries in, the tube would flex or collapse under pressure. You could go with a short tube or add plugs (or actual batteries for power) for structural support.

Another simple approach would be to sandwich together (with maybe 5 to 6 brass bolts) a couple of acrylic disks (like the endcaps) with a center section with an o-ring sealed thicker disk (would 3/8” be enough to fit electronics?), that has it’s center cut out (smaller diameter circle) like a donut. The cut out section would be large enough for the electronics and batteries. Wires would be run through a potted hole and the transducer would be mounted at the center outside surface.

A friend of mine built a simple hydrophone using a piezo disk this way.

I have the unit if you want to give it a try (use from the surface only with amp - like a radio-shack mono amp)

I would like to do an enhanced version of the hydrophone as an add on to the ROV for listening to ocean/marine animal sounds. Would have to sample and stream audio to the surface.
With FET pre-amp like this:


YES Jim! This would be a good starting point for me to get started with experiments and possibly reverse engineer something that will work well with our beaglebones…THANKS!


I just used this basic hydrophone and a Radio Shack mini AMP to receive my first test tones from a potted 40KHz piezo-ceramic transducer and the wideband power amp that we have been designing - see other blog for details


Suggestions for a DIY hydrophone?

Link to other blog -