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how does an earphone work?
Basics of Sound
The eardrum is a thin membrane that separates the outer ear from the middle ear. Repeated changes in air pressure vibrate the eardrum, and these vibrations travel through the small bones of the middle ear. This series of vibrations is interpreted by the brain as sound. Objects that vibrate, like the strings on a guitar or the shell of a bell, shift the air particles around them back and forth. This creates a wave of changing pressure that travels into the ear to vibrate the eardrum.

Headphone Speaker Construction
Headphones are small speakers that fit against or inside the ears. These headphone speakers have a few basic components. There is an outer shell, or enclosure, that holds all the speaker parts and amplifies sound. The back of the enclosure encases a permanent magnet. The front cover of the enclosure has openings in it to transfer the sound into your ear. (It may have foam covering it to protect the headphone and provide a cushion against your ears.) Underneath the front cover is a flexible, slightly concave plastic disc (diaphragm) attached to a metal coil that sits behind it. Electrical wires connect the stereo to the headphone speakers.

Electrical Energy To Magnetism To Sound
Electrical energy travels through the wires from the stereo to the headphones. This electricity charges the metal center coil and magnetizes it. The coil becomes an electromagnet. Electromagnets can reverse pole orientation repeatedly. This means the coil will alternately be attracted to and repelled by the permanent magnet at the back of the headphone. The back-and-forth movement of the coil continuously flexes the circular plastic diaphragm, creating pulsating waves of air that travel through the front of the headphone enclosure and into the ear canal to vibrate the eardrum.

Sound Frequency and Levels
Our ears determine pitch and volume according to the frequency and amplitude of the vibrations. When the headphone speaker diaphragm moves back and forth quickly, we register this as a higher pitch. Slower diaphragm movements create lower pitches. (High-pitched tweeter speakers on a full-size stereo system have tiny diaphragm cones, because they're easier to move at a faster rate.) The force of the vibration, and how much that force moves our eardrum, translates to volume. Just like hitting a man-made drum, the greater the force of the vibration, the louder the sound.

Stereo Sound
Stereo headphones work by transmitting slightly different elements of the music into each ear. The brain interprets and overlaps these elements, giving one a two-dimensional representation of the music that sounds like it's bouncing back-and-forth inside one's head. Depending on how the music was recorded, the jumping of sound from ear to ear can be subtle or dramatic.


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