It was once thought that the ocean was a silent place. However, if you were to drop a hydrophone, or underwater microphone into the water, you would soon discover that the underwater world is quite noisy. A hydrophone picks up acoustic signals and then transfers the sounds into a receiver that allows you to hear them. The following instructions allow you to inexpensively build your own hydrophone. Use this hydrophone to hear sounds in your aquarium or go down to the beach and drop it in the water.
How to Build a Hydrophone
How to Build a Hydrophone(Level: High School)