For this year’s Science Fair, Introductory Physics student Zachary B. chose to explore whether a speaker, such as the kind you might find in a stereo or pair of headphones, could be converted into a working microphone. Zach began by researching the basic qualities of sound and how sound travels through mediums as waves. This led to the study of microphones, including the identification of each component and their functions. This led Zach to the discovery that microphones, as well as speakers, are able to convert sound energy into electrical energy and information using magnetism and magnetic fields. On display Zach presented his visitors with what looked to be an ordinary pair of headphones connected to a laptop computer. After being directed to speak into the headphones, visitors were pleasantly surprised to hear their own voice amplified back at them! As Zach was quick to point out, although they may not completely resemble one another, a loudspeaker is quite literally a microphone working in reverse. The following is Zach’s summary of his project, cleverly titled "Speak to Me".
Can you turn a speaker into a microphone?
I think you will be able to turn a speaker into a microphone because microphones are just loudspeakers working in reverse.
Sound is a form of energy.
Sound energy travels in the form of waves.
Sounds are caused by vibrations.
Microphones turn sound energy in to electricity.
There are different types of microphones.
As you can see, microphones and speakers are very similar, which is why it’s so easy to turn a speaker or headphones into a microphone. This has to do with the components that make up a speaker or microphone. In a microphone, the sound waves that the microphone picks up are felt by something called a diaphragm. This thin piece of plastic moves back and forth when the sound waves hit it. A coil is attached to the diaphragm, and moves backwards and forwards as well. A permanent magnet is created that cuts through the coil. As the coil moves through the magnetic field, created by the magnet, an electric current flows through it.
The electric current flows out from the microphone to a computer or other recording device, and you can hear it.
A speaker works in almost the same way, except that the process is reversed.