Jules Ryckebusch's Gladys Is a Do-It-Yourself Hydrophone That Outperforms Commercial Competition

Audio designer Jules Ryckebusch has penned a guide on creating a hydrophone, or underwater microphone — dubbed, and why not, the Gladys, and designed to build on lessons learned since he first started listening to the watery world.

"My first hydrophone Instructable is a few years old at this point. Many were built and used around the globe," Ryckebusch explains. "One of the first things I learned was that there needs to be a ground connection from the recorder to the water. That is facilitated by addition of a ground wire, which caused me to update the original Instructable. Now, based on personal experience and feedback from multiple users, I have made more improvements. Enough that it warrants a new Instructable. They cover ease of build, technical improvements and durability."

Gladys, like all hydrophones, is effectively a microphone — but rather than picking up vibrations in the air, it monitors pressure variations in water. "Cylindrical piezo elements are perfect for that," Ryckebusch says. "[But] one of the challenges is that they are pretty high impedance electrically. To best capture the signal they produce, we need a high impedance buffer. That is what both of the circuits [in Gladys] provide."

The Gladys design offers a change to the original circuit that protects the opamp from damage should anything impact the microphone and cause a nasty voltage spike — with the protection still working even when the hydrophone is unpowered. The circuitry is housed in a 3D-printed mold for silicone casting, providing the waterproofing required to have the hydrophone submerged without damage.

The changes aren't all about making the hydrophone more robust, however: Gladys also performs better than Aquarian, Ryckebusch's original design. "The Aquarians sounded less clear and muddy," he explains. "Although they do have about 12-13dB more initial gain. Opening the spectrogram in Audacity showed why: they have almost no signal above 10kHz, While the Gladys hydros easily go into the ultrasonic range. I am just super impressed with how these perform. They far exceed commercial ones costing many times more."

The full write-up is available on Instructables, with Ryckebusch selling a kit with buffer board, mold, piezo cylinder, and wire on JLI Electronics for $65.