DIY Contact Microphone and Hydrophone
How to Make Your Own Contact Microphone and Hydrophone (Inexpensively)
By Jean-Paul L. Garnier
When building your field recording kit there are a few specialty items you might want to include to help you gain access to unique sounds. The contact microphone, and similar hydrophone, are easy to make on a budget, and will open up new worlds of soundscape that can be added to your library of sounds for use in professional sound design.
A contact mic adheres to surfaces (using poster putty or similar equivalent) and picks up sounds that might otherwise be impossible to hear, amplifying any material it comes into contact with (think of it as a microphone version of a stethoscope). A hydrophone can be used underwater, or any liquid, to record all types of aquatic sounds and great liquids foley. Both mics can be built in under twenty minutes.
The designs are similar and can be made for a few dollars each using piezoelectric sensors (see image 1). Piezos can be purchased from electronics supply companies such as Mouser Electronics, or even scavenged from old fire alarms. The rest of the materials used in the construction of these microphones should be fairly easy to come by, and some you probably already have lying around the house.
(Image 1, depicting a Piezo disc)
Here’s what you’ll need:
- Piezo disc
- 1/8” mono jack and cable
- Glue gun and several glue sticks
- Plastic lid from juice container (large enough to contain the piezo)
- Small drill
- Soldering iron and solder (optional, you can also use electric tape)
Construction:
Start by drilling a small hole on the side of the juice container lid and making sure that the cable that goes to the 1/8” jack can fit smoothly through the hole. You’ll want to thread the cable through the hole before soldering or attaching the wires (leads) to the piezo disk, bare wires running inward, jack facing out from the hole.
The mono cable will have two wires, one of these will have shielding and will need to be connected to the black wire coming from the piezo, the one without shielding needs to be connected to the red wire coming from the piezo. To connect the wires simply spin them together until they form a tight connection.
At this stage it is important to test the mic before permanently adhering the wires and housing, if you don’t get a signal then reverse your wires and try again.
Now, if you know how to solder, you’ll want to “tin” the wires together with a small bead of solder. If you do not know how to solder, that’s okay, you can also adhere a small piece of electric tape over the connected wires. It is important that the red and black wires do not come into contact, so be sure to cover all of the bare wire with tape, or heat shrink tubing (optional).
Put a thin layer of hot glue into the bottom of the lid and fold the remaining wire into the lid. Once the wires are secure you can now fill the lid to the brim with hot glue, as it begins to dry you can push it in with your finger to make sure that there are no air pockets (careful the glue can be hot).
When the lid is full push the piezo disk into the glue, brass side facing up and away from the glue. After the glue has partially dried, take the entire apparatus and push it glue-side down into a flat surface such as a desk to push the glue and disk down flush to the rim of the container lid.
Hydrophone:
Additional Materials:
- Small plastic jar
- Nonconductive weight
To start recording underwater you’ll only need to make a simple modification to your contact mic. Follow the same steps as above, but skip housing the disc in the plastic lid. Instead use a small plastic jar as housing, putting your nonconductive weight in the bottom of the jar before introducing the piezo disc, then fill with hot glue making sure to completely cover the piezo element and any exposed cable. When filling with glue make sure to tap it with every layer you add to remove unwanted air bubbles, as these will prevent the hydrophone from properly sinking.
With these additions to your field recording kit you’ll be able to explore the wonderful worlds of micro and aquatic sounds. Adhere your mic to fences, windows, anything that you can think of, and collect sounds that would otherwise go unheard.
Jean-Paul L. Garnier
Jean-Paul L. Garnier lives and writes in Joshua Tree, CA where he is the owner of Space Cowboy Books, a science fiction bookstore, independent publisher, and producer of Simultaneous Times podcast. In 2020 his first novella Garbage In, Gospel Out was released by Space Cowboy Books and in 2018 Traveling Shoes Press released Echo of Creation, a collection of his science fiction short stories. He has also released several collections of poetry: In Iudicio (Cholla Needles Press 2017), Future Anthropology (currently being translated into Portuguese), and Odes to Scientists (audiobook - Space Cowboy Books 2019). He is a two time Elgin Nominee and also appeared in the 2020 Dwarf Stars anthology. His new collection of SF poetry, Betelgeuse Dimming has just been released and is available as a free download audiobook / ebook at spacecowboybooks.bandcamp.com. He is also a regular contributor for Canada’s Warp Speed Odyssey blog. His short stories, poetry, and essays have appeared in many anthologies and webzines.