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.
How earbuds work
Taking broken things apart is a great way to find out how they work.
If you're a young person, ask an adult first to make sure what you want to
dismantle is really safe.
Here's my broken earbud and I've popped the back off it. You can see how the wires run up
through the main case to
the coil inside. We need two wires to make a circuit: one carries the
current into the coil from the stereo; the other carries it back again.
Next, I've tipped the earbud over and popped the front cover off.
The front cover is a plastic disc with holes in it to let the sound
enter your ear. Just behind it there's a very small cone. It's hardly
cone-shaped, though: it's a flattish, transparent disc made of very
thin and flexible plastic, and it's quite crinkly and crackly when you move it.
You can just see the tiny metal coil (colored red)
attached to it.
In summary, then, these are all the bits that make up your
Back case: holds everything together. The wires run up through a hole at the bottom.
Front case: This is the part that faces into your ear. Sometimes it's covered with a little fabric pouch to keep it clean.
Seal: This rubbery circle clips the front case to the back case, holding the two together.
Wires: Carry signals from the stereo to the speaker.
Magnet: The permanent magnet at the back of the speaker. This is the heaviest part of an earbud and makes up the vast majority of its weight.
Coil: This becomes an electromagnet when electricity flows through it.
Transparent plastic cone: This makes the sound when it moves.
How bigger headphones work
As you might expect there's nothing radically different inside bigger headphones: they're
just a scaled-up version of what you find inside earbuds.
As luck would have it, the arrival of my new Sennheiser headphones was followed quite
quickly by the final collapse of my old pair. I could have repaired them, my friends, but in the interests
of your curiosity, they've agreed to leave their insides to medical science!
Let's see what we find when we open them up:
This is one of the two earpieces from my old pair of open-backed headphones with the light foam cover
and the cable removed. Note that "open-backed" is a bit of an understatement for what you see here: the headphones
are almost completely open to the air and built around a kind of plastic spoke design. The diaphragm that makes the sound is in the center. The open spokes radiating outwards are there to make the
headphone the right size to cover your ear, without making it too heavy or uncomfortable.
Now I've popped out the central part that contains the loudspeaker:
Break off the protective plastic "spokes" and you can see the transparent plastic cone/diaphragm behind. You can also just see some small holes (beige dots) behind it that let sound out of the back and allow the diaphragm to move back and forth more freely.
Now the painful part. Break open the diaphragm cone (it's much thicker plastic than the ones in earbuds) and you can see the coil (red band) fastened on to it and the permanent magnet (silver and gold) behind. The coil sits in the slot like a band running loosely around the outside of the magnet:
Here's another shot of the diaphragm cone and the coil:
You can find bigger and clearer versions of these photos on our Flickr.
Who invented headphones?
And why? Early loudspeakers were pretty cumbersome things, and in the
late 19th and early 20th century, when audio equipment was equally cumbersome, there
was no obvious, immediate reason to shrink "sound reproducing machines" down to the size of your ear.
So how and why did headphones and earbuds come about? There were three reasons, essentially.
First, headphones and earbuds can reproduce sound with much less input power than big loudspeakers, so they work very well with unsophisticated, low-powered, audio equipment.
If you've ever built a crystal radio, you'll know you can do it without a battery or power
source of any kind providing you use what's called a crystal earpiece, which generates sound through
piezoelectricity using very little input energy (from the incoming radio waves).
Some early earpieces were even less sophisticated. You could listen to Thomas Edison's sound-recording phonograph (the forerunner of modern
record players) using either an amplifying "horn"
(ancestor of the loudspeaker) or stethoscope-like tubes stuffed in
your ears (ancestors of the earbud).
Second, despite the cumbersome nature of audio equipment, there was still a pressing need for portability.
Back in 1891, a Frenchman named Ernest Mercadier patented a
"bi telephone" (a pair of in-ear telephone receivers) that look strikingly like modern headphones,
"which shall be light enough to be carried while in use on the head of the operator, and, second, an improved means for securing the same in place." Portability was clearly a must for the
military; one of the key reasons for developing headphones was that pilots and battlefield soldiers had to hear sound clearly and discreetly. You couldn't put giant loudspeakers in the cockpit of a noisy, World War II fighter plane!
Photo: The military need for clear, effective, discreet comunication was a major driver of headphone development.
Photo by Joshua J. Seybert courtesy of
US Air Force.
Finally, not everyone can hear sound from loudspeakers as clearly as you might be
able to. Leafing through the patents in the US Patent and Trademark Office database,
it's clear that some of the earliest earbuds were actually earpieces attached to
hearing aids. If you want to amplify sound,
and do it portably and discreetly, using an earpiece makes a lot more sense than using a
loudspeaker. Apart from putting the sound directly in someone's ear, you also
separate the microphone from the speaker and so help to reduce "buzzing" and "whistling"
(where the speaker effectively feeds back into the microphone).
In 1943, for example, several years before transistors completely revolutionized
the power of hearing aids, we have Zenith Electronics offering a
hearing aid earpiece with just these aims in mind.
You can tell what a new pair of jeans will look like without even pulling them on. But how on Earth can you tell what a pair of headphones is going to sound like without listening first? Buying headphones involves guesswork and good luck, but follow these simple tips and you won't go far wrong.
Photo: Noise-isolating Etymotic earbud headphones. The rubbery gray flanges make a tight seal inside your ears and stop sounds getting in or out. The sound quality is far superior to that from normal earbuds. These earbuds come with different kinds of earplugs: the washable flanges you see here and disposable foam ends that are more comfortable but need replacing periodically. Both kinds have to be pushed into your ear canals to cancel background noise effectively—and they can get uncomfortable after a while.
Try before you buy
Inexpensive earbuds usually come heat-sealed in tough plastic, so even if you can try your new phones, there's no way you can return them if you don't like them. That's why it's best to buy headphones from a hi-fi shop if you possibly can. Quite often they have a few different demonstration pairs you can test out. There's nothing to stop you testing headphones in a shop and buying online later if you can get a better deal—though ask the store first if they'll match the price. Alternatively, ask a few of your friends what they use and listen to their headphones. Aim to try at least three or four different pairs.
If you're determined to buy online, remember that reviews can be misleading and unhelpful; they might even be planted by retailers or manufacturers. Sound is very personal and one person's idea of acoustic heaven might be another's idea of noisy hell. Different types of music exploit different parts of the sound spectrum (drum and bass will necessarily make heavier use of lower frequencies than classical music), so one pair of headphones might not sound equally good for everything you listen to. If you're going to go by online reviews, read widely and critically, and check well-informed professional reviews on audio sites as well as off-the-cuff amateur opinions.
Beware the bass
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).
Since Walkmans took off in the 1980s, there's been a trend for making headphones (and earbuds) sound very bassy at the expense of decent fidelity aross the entire range of frequencies; that biases people's expectations of how headphones should sound, which, in turn, prompts manufacturers to produce bass-heavy models that satisfy the demand (see, for example, Steve Guttenberg's article How do you like your headphone sound: Accurate or bassy?). Mass-market phones and earbuds may well be designed to emphasize bass frequencies—which is great if that's what you like and horrible if not. Beware of products that draw too much attention to their "bass response."
Listen to your own music on your own equipment
Both your hi-fi (or music player) and the headphones will affect the quality of the sound you hear, so if you're trying to compare headphones make sure you use the same stereo equipment in each case—and listen to familiar music. If you're trying expensive headphones in a hi-fi shop, take in your own equipment—even a portable CD player or MP3 player is better than nothing. The quality of MP3 tracks is always poorer than that of the same tracks played from a CD (because MP3 is a compressed digital format). In other words, a pair of headphones will sound worse with an iPod or MP3 player than with a CD player, even when they're playing the same track. So test headphones with a CD player if you possibly can.
Big headphones or small earbuds?
Think about where you're likely to use headphones—and how. Is the portable convenience of earbuds more important than the (likely) higher fidelity of headphones? Big headphones that sit over your ears generally sound better than small earbuds—that's why DJs wear "cans" (big phones). Having said that, there are high-quality, very expensive earbuds just as there are high-quality headphones. If you want some phones for listening mainly on the move (or for listening to a portable stereo or MP3 player at home), earbuds are generally the best bet; bigger headphones are usually better for "audiophiles" who want to listen to music or TV without disturbing (or being disturbed by) other people.
Open or closed headphones?
Open-backed phones usually sound better to me than closed-back ones, because they let sound move more freely with less distortion inside. If you're buying phones for private home listening in a room where other people will be chattering away or listening to the TV, you may prefer a closed-backed pair. Similarly, if you intend to use your phones on a train, bus, or plane, closed-backed headphones will reduce the background noise you hear and the disturbance you cause to other people—although noise-canceling headphones are generally better for travel use.
Normal or noise-canceling headphones?
If you're listening to headphones in a noisy place (on a plane or in a noisy home), background sounds can seriously reduce the quality of the experience. Noise-canceling phones can be a big help and they come in two main kinds. Passive noise-isolating earbuds (like Etymotics) have earpieces that make a seal with your ear canal, preventing unwanted sound from getting in. Active noise-reduction headphones and earbuds (such as Bose QuietComfort) have a little microphone on the outer case. The microphone samples the background noise and an electronic circuit inside the phones automatically compensates for it (read more in our article on how noise-canceling headphones work). Passive noise-isolating earbuds are very low-tech and very effective; active noise-canceling phones can be more comfortable to wear, but generally need their own battery power (so you have an added, ongoing cost if you're going to use them regularly). If you're listening in a quiet place at home, there's no real reason to buy noise-canceling headphones: they tend to be much more expensive and, for the same price as a pair of noise-canceling phones, you could probably get a much higher quality pair of normal phones.
For safety reasons, don't under any circumstances use them on a bicycle, skateboard, or while driving a car—you won't hear things around you. You can buy bone-conduction headphones for use on bicycles and boards, which work by transmitting sound through the bones in your skull, but I'm not sure I would risk it.
What sized jack plugs do headphones have?
Earbuds have small jack plugs (usually 3.5 mm or 1/8"), while bigger headphones typically have plugs about twice the size (typically 6.3mm or 1/4"). If you buy cheap earbuds, you won't be able to use them on a big stereo or TV unless you buy an adapter to go with them (those are relatively easy to find online or in hi-fi stores—just type "3.5 mm to 6.3mm headphone adapter" into Google). Conversely, however, most decent audio headphones with 6.3mm plugs come ready-supplied with 3.5mm adapters so you can use them on smaller equipment too.
Build quality matters
Earbuds and headphones almost invariably fail where the main cable meets the jack plug (and, occasionally, where the cable meets one headphone/earbud or the other). If I were cynical, I might suggest headphone makers deliberately engineer their products to fail by using poor-quality cables and connections. You can always tell a good pair of headphones: the makers will have devoted some time to making sure the connections are robust enough to cope with constant flexing of the cable. Though you can't easily detect headphones and earbuds with poor connectors, you can spot well-engineered connections. Look out for makers who draw attention to any efforts they've made to make their cables more durable. If your headphone cable does fail, and you know how to use a soldering iron, it's relatively easy to fit a new jack plug—you can double the life of your phones with about 10 minutes' work; repairing headphone cables at the other (earphone) end is much more tricky and often not worth the effort. Hi-fi shops can sometimes also do repairs for you. (See our article on how to repair headphones for more details.)
In my view, coiled cables are a mixed bag. On the positive side, they save you having to keep wrapping up your headphone cable. On the negative side, coiled cables are virtually always stretched open and that constant tension puts added strain on the weakest points of the cable, where they meet the jack plug and the two headphones. Generally, I prefer to use an uncoiled cable and an extension lead.
Photo: Sick of broken headphone cables? Here's the ultimate solution: buy headphones with a detachable cable. You can unplug the cable from the headphone end as well as from the other end. If your cable fails, you simply unplug it and buy a replacement! These are Sennheiser HD-485s.
You get what you pay for
The basic rule of buying things generally holds true of loudspeakers, headphones, and earbuds. If you study the wide range of phones offered by a decent manufacturer like Sennheiser, you'll notice a distinct correlation between quality and price: the low-end phones are good, basic, and relatively inexpensive; the high-end phones are recording-studio quality and cost many times more.
Portable music players come with their own "default" headphones, but there's no reason why you have to stick with them. Try some others and you might be surprised how much better—or different—your music sounds: you might hear instruments or effects you didn't notice before. Shortly after buying an iPod, I switched to using some expensive Etymotic earbuds (which cost almost as much as the iPod)—and they made a huge difference to the sound quality. But remember that MP3 players are inherently limited in audio quality by the compressed files they're playing. If you want to hear better quality sounds, go back to your CD player... or even vinyl LP records!
White noise by Jonathan Duffy. BBC News, 5 January 2006. Explains how lengthy use of earbud headphones may be damaging your hearing and the sensible precautions you can take to reduce the risk.
There are hundreds of patents covering all kinds of headphone and earbud designs—and they're well worth looking at for deeper technical insights. Here's a representative selection to give you a taste:
US Patent 1,601,063: Acoustic Device by Halsey A. Frederick. Western Electric, 28 September 1926. One of the earliest patents I've found for "earbud" headphones, designed either for hearing aids or telephone receivers. Despite the age of the invention, you can see that this earphone is built in essentially the same way as a modern one.
US Patent 2,353,070: Headphone by Roy Pitkin, 4 July 1944. A typical pair of sound-isolating, military headphones designed for aviators during World War II. They have large padded cushions to prevent outside noise from interfering with the noise generated by the loudspeakers.
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