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How to Make a Hydrophone for Kids

Listening to sounds underwater doesn̵7;t work by getting your ear wet. To hear the sounds being transmitted through liquid, you need to use a microphone that can listen to the vibrations going on underwater. You can make your own hydrophone with parts purchased from a hobby store and supplies found around the home. No special skills are needed.

Things You'll Need

Battery
Battery-powered toy microphone listening device
Party balloon
Silicone paste
Heavy-duty resealable storage bag
Utility knife
Scissors
Plastic tubing, 1/4th-inch diameter, 1 foot long
Bonding glue

Instructions

- 1
  Turn the battery-powered toy microphone listening device over so that you can see the back. Remove the battery compartment lid. Insert a battery and close the lid.
- 2
  Stretch the neck of the balloon open. Insert the microphone of the battery-powered toy microphone listening device fully into the balloon. Push the amplifier attached to the microphone into the balloon as well.
- 3
  Pull the earbud cable attached to the amplifier out of the balloon. Pinch the neck of the balloon. Tie a knot in the balloon. Apply silicone paste around the knot. Let the paste set for three hours.
- 4
  Cut a hole in the side of the heavy duty storage bag with the point of a utility knife or scissors. Open the bag̵7;s resealable top. Place the balloon and earbud cable into the bag. Pull the earbud cable out through the hole in the bag.
- 5
  Close the bag's resealable top. Run silicone paste on the seam and both sides of the bag where the resealable opening is located. Apply bonding glue around the hole so it covers the sides of the bag where it meets the cable. Let the glue set overnight. Apply silicone paste around the hole so it covers the sides of the bag where it meets the cable. Let the paste set for three hours.
- 6
  Reach through the bag and find the power switch on the amplifier that is inside the balloon. Move the power switch to turn on the microphone. Place the bag that is now your hydrophone into water, such as a swimming pool or a bathtub. Put the earbud at the end of the cable in one of your ears. Listen to the sounds coming from under the water.

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