Headphones have three main parts: a voice coil, permanent magnet, and cone-like diaphragm. The diaphragm vibrates when electrical currents run through the voice coil, converting the electricity into sound waves. There are three main types - sound canceling which emit opposite sound waves, open back which have hard backs, and closed back which have holes in the back. Headphones were first used for radio work in 1919 and now serve purposes like listening to music on devices and airplane pilots communicating.

1. Headphones: small loudspeaker (earphone) held over the ear by a band or wire worn on the head. A presentation by: S. Sikora

2. How they work: Made of three parts: a voice coil a permanent magnet a cone-like diaphragm The diaphragm is connected to the voice coil and this is what makes the sound by vibrations. These come through the wires that change the electricity into sound waves

3. Types: Sound canceling: They let out a sound wave that is opposite of the sound that is trying to be canceled Open back: They have a hard back to not allow any sound to come through Closed back: They have holes in the back to allow the exterior noise to filter through

4. Scientific Principles: Electrical currents run through the wires to be converted to sound waves in the headphone piece Sound canceling – use the principles of opposite sound waves running against each other

5. Impact: Headphones were first used with radio work in 1919 Contributed to invention of handheld telephones Serve many purposes: Airplane pilots Telephones Recreational uses: iPod’s and MP3’s

6. References: headphone . ( 2010). In Encyclopædia Britannica. Retrieved February 3, 2010, from Encyclopædia Britannica Online: http://search.eb.com/eb/article-9039697 Harris, W. (n.d.). HowStuffWorks "Noise-canceling Headphones: Electrostatic and Dynamic". Howstuffworks "Electronics" . Retrieved February 3, 2010, from http://electronics.howstuffworks.com/gadgets/audio-music/noise-canceling-headphone1.htm Lebeau, R. (n.d.). How noise canceling headphones work - by Raven Lebeau - Helium. Helium - Where Knowledge Rules . Retrieved February 7, 2010, from http://www.helium.com/items/615460-how-noise-canceling-headphones-work

7. References: Google Image Result for http://leahbess.com/html/hotz95_files/HEADPHONES.jpg. (n.d.). Google Images . Retrieved February 7, 2010, from http://images.google.com/imgres?imgurl=http://leahbess.com/html/hotz95_files/HEADPHONES.jpg&imgrefurl The History of Headphones. (n.d.). EzineArticles Submission - Submit Your Best Quality Original Articles For Massive Exposure, Ezine Publishers Get 25 Free Article Reprints . Retrieved February 7, 2010, from http://ezinearticles.com/?The-History-of-Headphones&id=3246508