the more you know
After around four months or more determined to build a hydrophone (a microphone for use underwater) I finally completed one this weekend. The delay was not due to an enormously complicated build but more to my not being practically-minded enough to figure out a simpler build than the elegant but tricky one I'd tracked down online.
The build for which I'd bought components but which required quite precise work and inportantly a drill was more or less as follows:
Start with 2 hard plastic discs, 1 O-ring, 1 piezoelectric transducer, audio cable, epoxy glue, drill with a small bit, soldering iron and solder, and 4 screws.
1) Drill 4 holes round the outside of both plastic rings, ensuring that you will be able to align them.
2) Drill a hole in the centre of one of the plastic discs just big enough for the audio cable to pass through.
3) Solder the audio cable to the piezoelectric transducer as normal for manufacturing a contact mic. I was going to tell you to look it up yourself, but this link gives you the basic information. Normally though I'd buy the piezoelectric transducers separately. You can buy them sans plastic casing at a well known UK electronics store beginning with M, and probably elsewhere. I also find it more secure to remove the wires already attached and solder the audio cable directly to the piezo rather than splice together two wires. This is pretty much required with this build to make sure it's water tight, otherwise you have the piezo and the two wires to seal.
4) Place the O-ring in the centre of the other plastic disc and fix the underside of the piezoelectric transducer to that disc inside the O-ring.
5) Bring the two discs together with their holes aligned. With the screws tighten them enough that the O-ring forms a seal without being crushed.
6) Use the epoxy glue to fill in any space around the audio cable to prevent water getting inside.
It's neat but very fiddly and requires a lot of kit. To be honest I would probably never have managed to build this satisfactorily. I had all the parts and could have borrowed or bought a drill but just couldn't be bothered. Then a friend advised me on a much simpler build they'd been told about. After seriously botching the manufacture of a simple contact mic I had to wait a few days to get hold of some new piezoelectric transducers before I could have another go. Finally on the weekend I managed to successfully complete my first hydrophone.
In full that much simpler build is:
Start with a lid (jam jar, coffee jar - I used a plastic milk bottle lid although it may be a bit too soft to be ideal), make sure it's large enough to accommodate the piezoelectric transducer, 1 piezoelectric transducer, audio cable, epoxy glue, epoxy resin, soldering iron and solder.
1) Solder the audio cable to the piezoelectric transducer as before. As if making a contact mic. Which is what you're doing.
2) With the epoxy glue fix the piezoelectric transducer in the lid. If your soldering is as crappy as mine you might need to cut a gap in the side of the lid to allow the cable to pass through to avoid inadvertantly pulling it off the piezo.
3) If you like you can put epoxy glue over the back of the piezoelectric transducer. Then fill in the lid with epoxy resin. Be aware it's a potential sensitizer so you'd be well advised to wear a pair of gloves to work it.
4) To be sure there are no problems leave the epoxy to cure as per the instructions. When 24 hours or however long have elapsed you should have a basic functional hydrophone.
It's pretty ugly but it does the job and should take at most 15 minutes to build. Job done. You'll probably hear some recordings from my hydrophone in the next couple of weeks. I'm going to make another soon because I'm pretty sure this first one won't last very long.
The build for which I'd bought components but which required quite precise work and inportantly a drill was more or less as follows:
Start with 2 hard plastic discs, 1 O-ring, 1 piezoelectric transducer, audio cable, epoxy glue, drill with a small bit, soldering iron and solder, and 4 screws.
1) Drill 4 holes round the outside of both plastic rings, ensuring that you will be able to align them.
2) Drill a hole in the centre of one of the plastic discs just big enough for the audio cable to pass through.
3) Solder the audio cable to the piezoelectric transducer as normal for manufacturing a contact mic. I was going to tell you to look it up yourself, but this link gives you the basic information. Normally though I'd buy the piezoelectric transducers separately. You can buy them sans plastic casing at a well known UK electronics store beginning with M, and probably elsewhere. I also find it more secure to remove the wires already attached and solder the audio cable directly to the piezo rather than splice together two wires. This is pretty much required with this build to make sure it's water tight, otherwise you have the piezo and the two wires to seal.
4) Place the O-ring in the centre of the other plastic disc and fix the underside of the piezoelectric transducer to that disc inside the O-ring.
5) Bring the two discs together with their holes aligned. With the screws tighten them enough that the O-ring forms a seal without being crushed.
6) Use the epoxy glue to fill in any space around the audio cable to prevent water getting inside.
It's neat but very fiddly and requires a lot of kit. To be honest I would probably never have managed to build this satisfactorily. I had all the parts and could have borrowed or bought a drill but just couldn't be bothered. Then a friend advised me on a much simpler build they'd been told about. After seriously botching the manufacture of a simple contact mic I had to wait a few days to get hold of some new piezoelectric transducers before I could have another go. Finally on the weekend I managed to successfully complete my first hydrophone.
In full that much simpler build is:
Start with a lid (jam jar, coffee jar - I used a plastic milk bottle lid although it may be a bit too soft to be ideal), make sure it's large enough to accommodate the piezoelectric transducer, 1 piezoelectric transducer, audio cable, epoxy glue, epoxy resin, soldering iron and solder.
1) Solder the audio cable to the piezoelectric transducer as before. As if making a contact mic. Which is what you're doing.
2) With the epoxy glue fix the piezoelectric transducer in the lid. If your soldering is as crappy as mine you might need to cut a gap in the side of the lid to allow the cable to pass through to avoid inadvertantly pulling it off the piezo.
3) If you like you can put epoxy glue over the back of the piezoelectric transducer. Then fill in the lid with epoxy resin. Be aware it's a potential sensitizer so you'd be well advised to wear a pair of gloves to work it.
4) To be sure there are no problems leave the epoxy to cure as per the instructions. When 24 hours or however long have elapsed you should have a basic functional hydrophone.
It's pretty ugly but it does the job and should take at most 15 minutes to build. Job done. You'll probably hear some recordings from my hydrophone in the next couple of weeks. I'm going to make another soon because I'm pretty sure this first one won't last very long.
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