We choose to use piezos thanks to their faculties to catch vibrations.
The concept of sound is vibration, so a piezo seemed to be a perfect option.
To make the box of the hydrophone, we had to find the perfect one. It had to be compact and watertight. On lunch break, we went to the supermarket and searched for the box (and something to eat). Our choice stopped on a Tarama Box. We killed two birds with one stone: we found something to eat and a box for our project.
First of all, we had to weld the piezo with a jack to listen to the piezo frequences on a pc. The copper part had to be soldered on the ground pin and the ceramic on the microphone branch of the jack.
Then, we took the cover plate of the box and we made a little hole in the center of it to pass the cable. Of course, the piezo had to be in the box, so we glued it on the right side of the cover plate whith a glue gun.
Here is the result on an other angle.
Then, we filled the box with vegetabel oil and sealed it with the glue gun.
We tried to seal it as well as we could, so we added ducktape on the top of the box, but, by experience, it is not necessary.
We tried our hydrophone in water to see if it was well sealed.
Of course, we tried a sound test in the water as well.
We went to the Paris Games Week and collected some goodies. One of them was this AMD candy box and it was the perfect size for our piezo, so we decided to make another hydrophone.
We repeated the same process just like for the first prototype.
And here is the final result!
Music Test in Water with watterproof Smartphone: (non emplified)
Test in air:
Test in air Clap and Tap:
Music Test in air:
Test in watter with speakers outside:
Test in watter with speakers inside: