Jules Ryckebusch's Gladys Is a Do-It-Yourself Hydrophone That Outperforms Commercial Competition
"If you are at all interested in underwater recording," Ryckebusch says of his successor to the Aquarian, "you will not be disappointed."
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.