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Loudspeakers: Magnetic Music

The venue’s sound system will add pep and power to the event. Learn how speakers let everyone feel the music or the wedding toast with Groupon’s look at a loudspeaker’s guts.

Whether they’re as tiny as earbuds or as huge as the loudspeakers once found at the Roman Coliseum, speakers work according to the same basic principles. All sound travels through the air in the same way that waves travel through the ocean, so speakers need to convert the electrical signals they receive into motion and thus sound. The mechanisms responsible for this translation are called drivers, which have three parts: a permanent magnet, an electromagnetic coil, and a cone. When the coil receives an electric current, it reverses polarity and is pulled toward the permanent magnet or pushed away from it. The cone moves accordingly, compressing the air inside the box and pumping amplified sound waves into the surrounding air. The frequency of the vibrations controls the pitch of the sound, and the amplitude controls the volume of the sound.

Top-quality speakers typically have multiple drivers dedicated to high, middle, and low frequencies in order to reproduce the full spectrum of audible sound. Woofers are the largest in order to move the volume of air necessary to make lower frequencies. Tweeters are the smallest, responsible for higher frequencies since they can vibrate fastest, and midrange drivers handle the frequencies in between. In most cases the boxes that house these are sealed—otherwise, the motion of the cones would produce sound waves in both directions—though it is possible to use vents to “tune” the box itself and produce additional resonance.