3D Immersive Hydrophone Arrays

Over the years, I've recorded with several types of hydrophone arrays. I started by using a mono hydro (as a contact microphone) to record wind vibrations. 

Then I took a pair of Gladys hydros with me to Greenland. Those DIY hydrophones blew my mind. Read about that in this blog post – The DIY Hydrophone that Showed My Underwater Recordings Could Be Beautiful.

All the recordings shared in this article would not be possible without the amazing Gladys hydros designed by Jules Ryckebusch. Every recording you'll hear was made with a Gladys. Jules also designed and built the custom 3D Hydro arrays I've used in Hawaii and French Polynesia. He built them to the specific needs of these two expeditions and these projects would not have been possible without these custom arrays. 

It is impossible to make these sorts of 3D recordings with off the shelf gear from commercial hydrophone manufacturers. 

RECORDING UNDERWATER IN STEREO

In 2022, 2023, and 2024 did a lot of underwater glacier and iceberg recording in stereo with Gladys hydros (in Greenland, Iceland, and Patagonia). Highlights from those experiments include: underwater snow, melting icebergs, glacier lagoon ice lasers, and iceberg animals.  

THINGS I LEARNED FROM MAKING UNDERWATER RECORDINGS IN STEREO

• Sound moves 4-5 times faster underwater
• Subject and space matter immensely to the quality of the underwater recording (just like they do in the air)
• Hydros act like omnis underwater, so you need to have at least a 2 meter spacing between your hydros to get wide stereo image (to account for the faster speed of underwater sound)
• I often prefer at least 3-7 meters of spacing
• Water breaks gear way more than air. You need more redundancy. If I want to record in stereo, I bring 4 hydros. 
  

3D IMMERSIVE HYDROPHONE ARRAYS: 

• There are tons of underwater recordings that have been made by whale researchers. However, the researchers are often not optimizing for artistic sound quality. They are often optimizing for mono recording (and for the longest duration possible). 
• Therefore, whale recordings are often made with lo-fi hydros, in mono, at low bit rates, at low sampling rates, and with placements that make for terrible acoustics. That's like listening to one of the most beautiful sounds in the world, with only one ear...that has severe hearing damage.
  
• Underwater recordings can sound like you stuck eight Sennheiser MKH8020s underwater in a giant cube array. You just need the right tools, subject, and underwater space. 

WORLD'S FIRST 3D RECORDINGS OF HUMPBACK WHALES – MADE IN HAWAII

• With a custom array of eight Gladys hydrophones, I successfully made, what are probably the world's first 3D recordings of humpback whales in Hawaii in February 2025. 
• The arctic population of humpbacks swim to the warmer waters of Hawaii for their winter. 
• This is like being teleported to another planet and it is hard to believe that sonic wonderland was happening just below the surface.  
• The goal of the project was to capture isolated sounds of humpbacks (without snapping shrimp). This was done by recording the whales in deep water away from the reef, but with a water depth between 400-1000ft so there was still enough reflections from the bottom to have good acoustics. 
• It is almost impossible to find locations where the whales are singing and no snapping shrimp are present. 
• After much toil and experimentation (and lots of help from assistants and whale guides). I got the 3D hydro array to work in two configurations: 3D Cube, and 3D Rectangular prism. 
• The main lesson is don't try to built a PVC pipe frame to create an underwater cube for the 8 hydros. That is a nightmare. It works much better to create an underwater cube (or rectangular prism) by hanging the 8 hydros from the boat. 
• I've always wanted to hear whale recordings that are both conceptually captivating and artistically beautiful. That was my goal with this project. I achieved it for my audience of one. You decide for yourself. I hope you enjoy listening. 

UNDERWATER SOUNDSCAPES FROM HAWAII

• These clips were all made using the Gladys 3D Hydro (V1) array. Here are stereo versions for listening:

HAWAII – 4.0.4 HYDRO ARRAY SPECS

• These are the specs for sounds included in AMB95 Hawaii: Humpback Whales
• 3D – these recordings were made with either a 3D-Cube or a 3D-Rect Prism:

• 3D-Cube: 10ft x 10ft x 10 ft (LxWxH). Made with PVC pipe frame. 
• 3D-Rectangular Prism. Made by hanging 8 separate hydros from boat.
  • Channels 1-4: 8ft x 12ft (LxW)
  • Channels 5-8: 8ft x 8ft (LxW)
  • 50ft Height between channels 1&5, 2&6, 3&7, 4&8.
  • This offset was done so the cables didn't rub against each other for channels 1&5, 2&6, 3&7, and 4&8. 
• Note that in the 3D-Rectangular Prism recordings there is much more wave sound in channels 5-8 because they are much closer to the surface at 20ft (versus channels 1-4 down at 70 ft). This gives a strong vertical element to the ambiences because you hear the waves above. 
• Channel Layout: L (1),R (2),Ls (3),Rs (4),Ltf (5),Rtf (6),LTr (7),Rtr (8)
• All 3D files are delivered as 8-channel WAVs that can be mixed into the 3D format of your choice, for example, a 7.1.4 Atmos mix. 

FRENCH POLYNESIA – 4.0.4 HYDRO ARRAY SPECS

• In October 2025 I traveled to the island of Moorea in French Polynesia to record the Antarctica population of Humpback Whales as they winter in warmer waters. 
  
• On this expedition I took a much improved V2 design of a custom Gladys Hydro 3D setup. No more PVC pipe frame madness. 
• The main improvement was the use of stereo microphone cables (with two hydros per cable). This enabled me to only have four cables (vs 8 in Hawaii). Each cable ran to the corner of the boat and then down into the water. This is so much better.

• I used Mogami W3106. This is an audio cable (not designed for submersion). So it won't last for years of use, but its main feature is that it is so flexible. This makes it possible to record in heavy seas without insane cable buffeting that ruins the recordings. The commercial hydros I've tried have much stiffer cables (that are designed for years of use in salt water), but that cause soooo much cable buffeting that the recordings are unusable. 
• One hydro is at the end of the cable (at 30 meters depth) and the second breaks out 7 meters above (at 23 meters depth). The top hydro has a 3D printed splitter that spaces the hydro and keeps it from banging against the cable. The splitter snaps on to the cable (and then I wrap a bit of electrical tape around it for extra security). 
• With four stereo cables, of 2 hydros each, I built a 7 meter x 7 meter x 7 meter cube of eight hydrophones that hung from the hull of a large catamaran sailboat. 
  
• I designed this array specifically for the width of the sailboat I planned to be using. The boat was 7 meters wide, so I could use it as the frame to create the cube, and hang the hydros right off the side of the boat.  
• I was also using the latest version of the Gladys hydro that uses a new resin with a much slower potting time. This greatly reduced the failure rate of the hydros in the field.
• Here are two examples stereo pairs: 1&5, 2&6

• I also experimented with making stereo recordings with Cetacean Research CRT-90P and Ambient ASF-MKII hydros and I'm happy to report that I could make beautiful recordings with both of these hydros (under some, but not all conditions). I'm happy to now have those hydros in my toolkit, in addition to the Gladys ones I primarily use.

UNDERWATER SOUNDSCAPES FROM FRENCH POLYNESIA

• These clips were all made using the Gladys 3D Hydro (V2) array. Here are stereo versions for listening:

3D IMMERSIVE SOUNDSCAPES TO DOWNLOAD: 

1. Thanks for reading this far. 
2. If you'd like to listen to one these 8 channel recordings, here's an immersive whale soundscape. Download it using the WeTransfer link – here.
3. That soundscape is for personal listening only. If you'd like to use my underwater recordings commercially, please purchase the sound libraries – here. 

I wrote and edited this blog post myself. See my full Made by a Human page – here. 

Thanks for listening, 

Tom