Electromagnets in Speakers and Headphones

Headphones and Speakers are typically associated by their shared ability to produce sound in different forms. Headphones create a personalized music system, while speakers loudly project their listener’s musical choices. From radios, to intercoms, to the new “airpod” trend, speaker technology is present in all aspects of our lives. The first practical usage of speakers was introduced by Alexander Graham Bell when he created the telephone. A telephone speaker works by converting audio into an electrical signal (dynamic microphone), while our typical loudspeakers build on this principle by transferring an electrical signal into and certain sound (dynamic speaker). The dynamic speaker wasn’t created until 1925, 49 years after the telephone, by Edward W. Kellogg. However, in both speakers, the sound comes from vibrations within the speaker that produce sound waves.

So how exactly do loudspeakers work? When you see a speaker, you’ll notice a fabric or cone on the outside (#1 in diagram, pictured in bottom righthand corner). This works like a megaphone to amplify the noise created from the electrical signals within the speaker. The cone is attached to a metal coil that is typically made out of iron (#2 in diagram, it’s also called a voice coil). This coil is the electromagnet in a headphone/speaker system. Behind the coil is a permanent magnet (#3 in diagram). When electrical signals flow through the electromagnet, the coil attracts (or repels) the permanent magnet, creating vibrations and air pulses that mimic sound waves and are then amplified to become sound.
Still confused? This video on speakers will clarify how each piece of a speaker system works. Watch at the beginning of the video how the cone visibly pulses and moves from the vibrations of the voice coil and electrical signals.