DIY hydrophones

A few weeks ago I was talking to Dave Burraston about microphones and he strongly encouraged me to start building my own – specifically, hydrophones.

Hydrophones are microphones used for the purpose of recording sound in water and often consist of a transducer housed in a water resistant membrane or ceramic enclosure which facilitates the capture of vibratory phenomena. Since hydrophones aren’t conventional microphones and are confined to a specialist area of sound recording they are relatively expensive and can be difficult to acquire.

Following my discussion with Dave I knocked out a couple of inexpensive hydrophones and took them down south on a roadtrip down to Milang, South Australia earlier this month.

#1 “Bob”

– Film canister
– Male RCA plug
– Audio cable
– Small piezo transducer
– Vegetable oil
– Cling wrap
– Lots of hot glue
– Rubber bands.

Dear old Bob. What I’ve done here is taken a small piezo connected to an audio cable (wrapped it in cling wrap sealed with a small rubber band) and housed it in a film canister filled with vegetable oil. The lid of the film canister needs to have a hole punched in it to allow the audio cable to pass through. Once this has been done, several sticks of hot glue are used to seal everything up. It looks pretty ugly, but you have to make sure everything’s absolutely watertight. At the end of the audio cable I’ve connected a male RCA plug for input to a portable amplifier. The amplifier’s a must (esp. with DIY equipment like this) as you’ll want to boost/balance the signal in order to get a good signal to noise ratio.

How’s it sound? Pretty good. It’s got a reasonably good response but has the tendency to be a bit unstable in heavy water motion (lots of clunks/clipping, etc). Here’s a recording I made off a small jetty in Milang.

#2 “Nancy”

– Plastic pill box
– Male RCA plug
– Audio cable
– Medium piezo transducer
– Lots of hot glue.

Glorious Nance! This is a simpler design to Bob as it consists of just an enclosure, piezo, cable, RCA plug and a few less sticks of hot glue. I took my inspiration for this one from Leafcutter John’s Tin Can Hydrophone. It follows a similar principle and you could use practically any container to house to piezo providing it’s got a reasonable surface area for the piezo to sit (in this instance it’s been grafted to the base of the pill box with hot glue.)

I think I prefer this design to Bob as I’m able to get a more immediate and dynamic response. Here’s a recording that made with Nancy buried beneath a layer of sand on the banks of Lake Alexandrina (near Milang.) Hydrophones are used principally for recording in water but can be utilised in more unconventional ways! – as Chris Watson demonstrates in a video here

Nancy gets put to the test under a layer of sand. Thanks to Chris Watson for the inspiration!

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3 thoughts on “DIY hydrophones”

    1. G’day Robb,

      Ah – this was a few years ago. At the time I was sending a Mono input into an Edirol (Roland) HR-09 hand-held recorder, and I’ve since upgraded to an Olympus LS-100 which is much better. I haven’t listened to these recordings in a long time, but I do recall there were some interference issues mostly due my rudimentary connections and – more specifically – choice of cable. This was later fixed by EQ-ing/filtering out undesirable sounds. Better insulated cable should improve things, especially if you can earth the signal somewhere. In addition to this, the HR-09 had a fairly dubious preamp when using external inputs (piezos, etc) and this would often result in light static, interference (it didn’t help that the metal mount for the built-in mics attracted peripheral signals!) Hopefully that helps you out. If you get stuck, send me through some pics/diagrams of your set-up. I’ll probably revisit these DIY hydrophones at some point. I’ve had a couple of JrF hydrophones for the past couple of years but I’m really not that happy with them – considering what I paid for them.

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