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Cone of Sound

Today I was playing with sound experiments, and had so much fun with this one that I thought I would share it.  It is based on the original phonographs, which used a very similar setup to play recordings of music or voices.  They used a large cone to increase the volume of the sound.

To try this, you will need:

  • 2 needles or pins
  • paper
  • a piece of cardboard
  • tape
  • (optional)  an old phonograph record.  Use one you don't mind damaging.

IMPORTANT!  Using this with a phonograph recording could damage it.  Do not try this with a recording that is important, valuable, or that will get you in trouble if it is scratched or damaged.  Flea markets are a good place to pick up an old record to try this with.

The first thing we need to do is to make a paper cone.  Roll the paper into a funnel shape.  Shape it so that the small end is almost closed, and the large end is as large as possible.  Use a piece of tape to hold it in place.

Stick one needle through the small end of the cone, about 1/4 inch from the end.  This will be your phonograph.

Let's start with the needle that is not through the cone.  Hold it in your fingers, and scratch it lightly across a piece of cardboard.  Listen carefully to the sound that it makes.  

Try the same thing with your phonograph, holding it by the paper cone, and trying to use the same amount of force that you did with the first needle.  You should hear a much louder sound.

Why is it louder?  Remember that things produce a sound by causing the air to vibrate.  The more air you can vibrate, the more sound you will produce.  As you moved the first needle across the cardboard, the point would catch on a rough place, and then spring free as you moved your hand forward, catching again and again.  This caused the needle to vibrate.  The vibrating needle caused the air around it to vibrate, producing a small sound.

When you tried the same thing with your phonograph, the needle also caused the paper cone to vibrate.  The paper cone has a much larger surface, which lets it vibrate more air, producing a louder sound.

If you have an old phonograph recording that you are willing to sacrifice, try moving the needle along the grooves in the record.  DO NOT USE YOUR PARENT'S RECORDS WITHOUT ASKING! You should hear the recording play.  Can you move the needle at the right speed to hear it correctly?

The early phonographs did not use electricity.  Instead, they worked just as your cone does, with a needle vibrating as it moves across a surface that has bumps and grooves, and a large cone to amplify the sound.

If you want to experiment some, try using a piece of paper that is not rolled into a cone.  Stick the pin through one corner of the paper, and try scratching it across the cardboard.  Does it work?  Compare the sound that it makes to the cone.  Is one louder?  Is one more directional than the other?  You could also try using a sheet of aluminum foil, a paper towel, a sheet of cardboard, and other materials instead of the paper.  What properties (density, stiffness, flexibility, etc.) give you the best sound?  With the proper approach, this could be turned into a very nice science fair project.  Hmmm.  I wonder how well it would work with one of those yummy sugar cones used for ice cream?  Sounds like a good excuse for a trip to the grocery!

Have a wonder-filled week.