How To Build a Hydrophone
Hydrophones enable us to record underwater, which is reason enough to worship and adore them. Better still you can make your own very easily and cheaply. For the Canal Music tour I wanted to make myself a new hydrophone which includes the pre-amp I made here. I have made hydrophones using piezo elements before, but I never tried using a pre-amp which tends to make piezos sound a lot better.
If you don’t know what the hell I’m talking about right now, have a look at these instructions on how to make the simplest possible contact mic. It’s exactly the same principle when making a hydrophone except you get to go underwater.
I decided to house the pre-amp in the same enclosure as piezo elements (to avoid noise entering the circuit). The challenge here is to find a decent enclosure. After having some delicious spicy chickpea and tomato soup I thought it would probably be possible to solder up some kind of tin-can casing which would be fairly strong and water-tight.
After a few experiments, I found you can quite easily solder steel (NB not aluminium!!) food cans together using a regular soldering iron and electrical solder. It works for water pipes so It should be watertight in this case.
I used a wire brush to rough up the surface of the can before super-gluing two piezo elements to the inside of the lid.
I drilled a hole in the larger of the two cans just big enough for my microphone cable to go through. I then made this little chimney out of a scrap piece of can. I used a wire brush to clean the coating off the can before soldering.
To hold the chimney into position while soldering I temporarily bolted it to the can. A few moments later and it looks like some kind of improvised smoking device.
I coated the mic cable with hot glue and pulled it through the chimney, then splurged lots more glue where the wires enter the can. This is the most likely place water will try to enter the capsule so make sure you seal it completely using ridiculous amounts of hot glue.
This shows the pre-amp connected to (and sitting atop) the piezo / hot-glue sandwich.
All leads soldered-up! It was really fiddly to do and I made a wrong connection initially which was easily fixed. It’s a very good idea to connect your hydrophone to a mixer and check it actually works before you close the case. Before closing the unit I covered the pre-amp circuit with a lot of hot-glue to seal it off from any stray water.
My girlfriend bravely held the two halves of the case closed as I carefully soldered around the seam. Again I used a steel brush to clean the surfaces before soldering. It was actually quite easy to do and I like the quasi-welded appearance. All that is left to do now is pop it in the sink and test it out.
It took half a day to make the case and the same to make the pre-amp. The whole thing cost less than £10 in parts and compares very well against hydrophones costing 10 x the price. I’m going to paint and varnish the casing, this is important if you don’t want your hydrophone to rust away.
Go forth and hydrophone!
Leafcutter John is a London based Songwriter, Electronic musician, and Artist.
Comments
This is some quality information, but only someone with the right technical know-how can attempt this. - Grease Trap Cleaning
http://www.demegamass.ru
Superb article - I was just googling for hydrophones and found this.
Just one thing which puzzles me, would the generous amounts of hot-melt glue (second only to araldite in its ability to repair the universe), not dampen the responsivity of the unit. I might be totally wrong here (happens often), but I would have thought that the fairly dense mass of hot melt would deaden many of the higher frequency vibrations.
On the same topic of dampening, if you were after high frequency sound and were worried that paint needed for anti-corrosion might not improve accoustic performance, I wonder if plonking the whole thing in a jat of copper sulphate and plating it may be an option? I realise plating onto solder is not quite so simple but a spot of googling found this http://www.larrylawson.net/plating.htm which might be useful both for this - and any other time that copper plated solder could be useful (!)
Very good article though - Going to see if there is a speaker version of the same thing now - and also most impressed with the rochelle crystal microphone, thank you.
Mark