Earphones are small loudspeakers designed to fit in or around your ears. They come in several different designs and accordingly are available on the market at a wide price range. Earphones are the best way to listen to audio in private. Other people can't listen in, and you won't be disturbing other people if, for example, you are listening to music on a bus or train.
Earphones consist of a speaker cone, an iron coil, a magnet and speaker cables. When earphones are plugged into a music-playing device like a stereo, electricity is sent along the speaker cables. The speaker cables feed this electrical current through the iron coil, which behaves as an electromagnet. The coil then attracts or repels the permanent magnet, depending on the electrical current sent by the music-playing device. This causes the coil to move, which subsequently pushes and pulls the speaker cone. As the speaker cone vibrates as a result of this movement, it creates sonic waves that resonate through the air and are transferred through small bones and membranes inside your ear.
Earphones exist in three main types. The first, ear buds, are small earphones that are pushed into the ears. Because the speaker cones in this type of earphone are closest to the ears, they don't need to move as much air and so they have the smallest components. Large headphones make up the other two types: open-back headphones, which to some sound superior but leak ambient noise, and closed-back headphones, which enclose the listener's ears completely.
Small ear bud-type earphones are designed to be lightweight and portable; however, this means the cables are thin and fragile. Frequent movement and tangling weakens the speaker cables, meaning ear buds need to be replaced more often.
Listening to loud music for long periods of time is dangerous, and puts the listener at risk of noise-induced hearing loss (NIHL). NIHL is irreversible, can happen at any age and, although the symptoms are temporary, the damage is permanent. If you can't hear your music because of loud ambient noise, invest in some sound-isolation earphones.
Sound isolation earphones prevent sound entering or escaping your ears. A couple of different methods provide sound isolation in earphones. The more simple method manufacturers use is to provide silicone ear tips that fit around the earphone, acting as a plug. The more complicated (and more expensive) method is mounting a microphone in the earpiece, which produces a signal of opposite frequency to the ambient sound, effectively cancelling out the unwanted noise.