Hydrophone Construction Manual

This little guide will lead you to a simple and cheap home-made DIY hydrophone for the hobbyist. This hydrophone will enable records of underwater acoustic sources in your aquarium, like fish, shrimps, electrical pumps etc.

Of course, they do. Though their sounds are hardly investigated, especially those from freshwater fish (much better from marine fish). The best-known freshwater fish with acoustical capabilities is the croaking gourami Trichopsis vittata, but there are a lot of other species with sound from other families, not only gouramis can: Cichlids, cyprinids, characids, lots of catfish genua and, of course, cobitids.

Essentially there are two mechanisms of sound production, first the stridulation by rubbing harder bone parts or tooth, and second using the swimbladder with a cranial encapsulation called camera aerea Weberiana (CAW), this improvement enhances hearing capability as well. LADICH suggests that the naturally occuring sounds provide reliable information for acoustic communication.

A hydrophone is an underwater-microphone, a special device using piezoelectric elements to pick up acoustic energy (pressure changes) and convert into electrical energy. Hydrophones are an important part of the SONAR system used to detect submarines, they are used by geologists to detect seismic energy, or as a Bio-sonar to listen to cetacean sounds.

1. One piezo ceramic disc with brass-underlay, available from a musical greeting card, a buzzer or your electronics shop.
2. A sheet of polycarbonate or polystyrol about 4mm thickness from your building- or craftsmen-market, you'll need 2x60mm pieces in diametre
3. One o-ring seal 40mm in diametre and 4mm thick if possible (the thicker the better), a sanitary equipment from your craftsmen-market
4. Six screws and nuts 20mmx4mm, nylon or stainless-steel, neither iron nor brass (copper!) from same market
5. A suitable adhesive like acrylat-two-components-adhesive or a quick epoxy adhesive, available everywhere
6. A thin coaxial cable, the smaller the better, for example 2,5mm and 6 or more metres length, take a look to your electronics-shop
7. A suitable plug to connect to the soundcard of your computer, mostly 3,5mm (cut it off from your headphones )
8. Solder, soldering iron, different drills, screwdriver and other tools, sandpaper, coffee, cigarettes, …

This most important element is available from Piezo-buzzers, for example. The buzzers contain three main parts: the piezo-ceramic, the brass-base and two cables (if not, you have to solder a first time: positive=ceramic, negative=brass). You have to remove everything except the piezo, the brass and the cables. Be careful not to break the ceramic, remove rests of the old adhesive on the brass with sandpaper.

Prepare two polystyrol-plastic discs with 60mm in diametre (IMHO squares would work as well). Fix the piezo in the centre of the poly-disc and stick it with the brass' side down. Be sure not to scratch the plastic or to let adhesive float everywhere around. Lay the o-ring seal symmetrically on your disc an mark six points where the screwholes should be drilled in now. Make a mark to ensure correct alignment afterwards. Drill the holes.

As a warm-up solder your 3,5mm plug on the coaxial cable. Now you have to drill a hole for the coaxial cable near the centre (not outside the o-ring seal), then lead the cable by the hole and the o-ring, then solder the cable with the piezo on the lower surface. Adjust the three parts, testing their alignment for later screwing. Prepare a little bit of adhesive. Stick the cable and the upper plastic disc together, the cable must fit as good as possible.

When your adhesive has set you could assemble the parts with the six screws. Do not overscrew, the o-ring has to touch the plastic disc in a line of 1-2mm only. Now you have a microphone of minor quality, but underwater its quality will surprise you! You should check your device on short circuits with a multimetre before your hydro gets in touch with water. Now connect the plug to your sound card and put the hydro into your tank. Start your favourite recording tool.

If you want to connect the hydrophone to your headphones, or to receive a clearer signal, you have to install a preamplifier, because the hydrophone's output is too weak. A good choice is a product similar to these suggested ones:

Hama

Hama Stereo-Mikrofon-Vorverstärker PA 03

Neuling Electronics

Neuling Electronic CVS 908 - Phono / Mikrofon Entzerrer - Vorverstärker

Loughborough University Underwater Acoustics Research

Friedrich Ladich, University of Vienna, Department of Behavior, Neurobiology and Cognition

Ute Heidemann for improving this text

Eberhard Bundtzen

Was sich Fische zu sagen haben. Unterwasserreport

ISBN 392853002X

This work and its contents are copyrighted by Gerald Gantschnigg 2006. To obtain permission to use or reproduce parts of this material please contact.