Headphones use electrical impulses to bring music to your ears

Mat Gordon, 13, an eighth-grader at Aptakisic Junior High School in Buffalo Grove and a member of Boy Scout Troup 79, asked, "How do headphones work?"

Sound starts as movement of air molecules that ripple outward like the waves caused by pebbles tossed into a pond. The air molecules enter your ear canal and are directed to the ear drum. They trigger the ear drum movement that starts a stream of electrical impulses that help your brain to decode and analyze the information.

Recorded music releases sounds that mimic the original air fluctuations created by the music. Your MP3 or CD player routes the recorded signals to speakers or headphones. Headphones and speakers are designed to produce an accurate version of the original air fluctuations.

"An electrical impulse comes through the cable from the player. Ear buds are like speakers," said Paul Foschino, senior marketing manager at Sony Pro Audio in New Jersey.

"A magnet sits in the housing. When the electrical impulse hits it, it moves back and forth, moving a cone that pushes air and creates different frequencies. It has direct contact with the ear canal which sends the signal to the brain," Foschino said.

Electricity, either from the wall outlet or from batteries, gets the whole electronic sound process going. Inside the housing, alternating electrical current is fed through a coil, transforming it into an electromagnetic coil. The electromagnetic coil causes a magnet to attract and repel the electric force. This process pushes a diaphragm or cone back and forth, creating the air movement needed to make sound.

How come you hear the sound in stereo? Jim Anderson, president of the Audio Engineering Society and New York University professor of recorded music, said, "If the recording is in stereo (which is a two channel recording), the CD, or the file if it's MP3, has a left and right component. This is played back with two separate amplifiers, to two separate speakers, or in the case of headphones, two separate ear buds. There's only one wire coming out of the iPod, but if you look at the plug, you'll see three bands. That's the connection for left, right, and a common ground to complete the connection."

There are lots of reasons people use headphones, according to Foschino. "Recording engineers use them to monitor sound and to isolate the sound. Hi-definition headphones are designed to address the pounding bass of rap and hip hop."

Loud sounds can lead to hearing loss. "Sony is concerned about devices damaging ears and designs headphones so they don't harm ear drums," Foschino said.

Students interested in careers in audio technology - including home and studio sound recording, audio design, acoustics, mixing, broadcasting and forensic audio analysis - might seek colleges with Audio Engineering Society Student Sections or consider attending the October AES convention in New York City. For more information, see the AES Web site at aes.org.

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