by Chris Woodford. Last updated: November 15, 2013.
If you've ever been to a rock concert and heard music thumping out of giant loudspeakers, you'll know sound can pack a powerful punch. Sometimes, however, we want to enjoy music more quietly and intimately or in places where others don't want to hear what we're listening to. Trains and planes are noisy enough—just imagine the cacophony there would be if everyone sat with massive stereo systems in front of them! For times like this, headphones let us retreat quietly into our own imaginary worlds. Let's take a closer look at what's inside them and how they work!
Photo: My open-backed Sennheiser HD-485 headphones. Most of what you see in this photo is cosmetic: it adds little or nothing to the quality of the sound you hear. But it's important to remember that headphones have to be comfortable to wear for a reasonable amount of time or they'll be a waste of your money. The softly padded earpieces and foam padding across the top of the headband make these very comfortable. The plastic they're made from is light enough not to press on your head, but strong and durable enough to withstand wear and tear. Another cool feature is the removable lead: there's a jack plug where the wire joins onto the body of the headphones, which you can easily remove and replace.
Headphones: miniature loudspeakers fixed to your ears
Headphones (which are often called "cans" by DJs and people who work in radio broadcasting) work in exactly the same way as speakers, so you might want to consult our article on loudspeakers if you're not sure how they use magnetism to turn electrical energy into sound.
The biggest difference between loudspeakers and headphones is, of course, size. A loudspeaker needs to set all the air moving in a room so you can hear the sound it's making, but the speaker in a headphone only has to move the volume of air inside your ear canal. That's why it can be so much smaller and more discreet.
Large headphones are essentially just two loudspeakers mounted on a strap that clamps firmly over your head. Earbuds work the same way but, as you would expect, everything inside them (the magnet, the coil of wire, and the diaphragm cone that makes sound) is shrunk down to a much smaller size.
Speakers tend to be built into "enclosures" (as engineers call them—the rest of us call them "boxes") to amplify their sounds and keep them safe from damage. If you look closely, you'll see speaker enclosures usually have openings at the front or the back so air can move more freely in and out of them to generate decent sound. The same is true of headphones and earbuds, which come in two main types. As their name suggests, closed-back headphones are sealed at the back so (theoretically) no sound escapes (or leaks in from outside) while open-back headphones are open to the air at the back as well as the front. Many people find that open-back headphones sound better but much of the noise will leak into the room around you and annoy other people, while "ambient" noise from the room can easily penetrate open-back headphones and annoy you too. If that's a problem, you need closed-back headphones or noise-cancelling headphones, which make it easy to cut yourself off completely.
Photo: A pair of earbud phones from an MP3 player. The metal gauze on the front is "acoustically transparent": it lets sound out without letting (too much) dirt and dust in. The backs of some earbuds are completely sealed to stop sound from escaping (so they're similar to closed-back headphones), though other earbuds do have small vent holes in them (making them equivalent to larger, open-backed headphones).