A skeptic's guide to headphones
A bewildering array of headphones is now available, at prices
from a few pounds to sell-a-kidney. It's difficult to make an
informed buying choice, for two reasons.
First, the entire field is full of specialized jargon terms that mean little to most people. The skeptic in me wonders whether they mean anything to anybody. Second, whatever manufacturers say, there are no truly general-purpose headphones. No device will suit all applications, so many people will own more than one, or make compromises.
In this article I'll describe the characteristics of the various types of headphones that are currently available, without recourse to vague, audiophile silliness. All the specific headphones I mention cost less than UK£300 because, although I'm fussy, I'm not stupid.
A note about cost/benefit considerations
Whatever anybody else tells you, relatively cheap headphones offer better value for money than expensive ones. Thousand-pound headphones sound a lot better than ten-pound headphones, but they probably don't sound a hundred times better. Of course, it's difficult to assign a numerical value to how good something sounds, but common sense would suggest that thousand-pound headphones would have to sound staggeringly, bewilderingly good to justify the price. The Sennheiser HD800S (current price about £1300) sounds pretty darned good, and no mistake. But the Sennheiser HD58X sounds pretty good, too, and costs one eighth the price. If somebody left me his HD800S in a will I'd accept gratefully, but I'm not about to part with that amount of my hard-earned cash for such a marginal improvement in sound.
In fact, there are some great-sounding headphones in the £100-200 range. And, unless you use headphones exclusively for listening to music in a quiet room, the cheaper headphones are likely to be much more versatile. That's because the really expensive headphones are catering for the "audiophile" market, where extortionate pricing and single-minded lack of versatility are actually selling points.
I'm not saying that expensive equipment is bad -- only that, with the levels of technology and mass-production we have today, inexpensive equipment can be quite good. It's true that, in general, you get what you pay for; but with headphones over about £200 you'll pay an increasing amount for a diminishing improvement.
Headphones and headsets -- a digression
There was at one time a distinction between a "headset" and "headphones". A headset was a communications device -- a headphone with a built-in microphone. These days, almost all headphones have a microphone, because manufacturers know that most people will use them with a cellphone. So most modern headphones qualify as "headsets" in the original sense. Consequently, the word "headset" is now used to describe something boringly functional, probably designed for office use.
In fact, modern "headsets" are essentially light-weight headphones (with microphone), designed for all-day use. You shouldn't turn up your nose at the sound quality of some of these devices, particularly if all-day wear is important. The Sennheiser SC75 weighs almost nothing, has both jack and USB connections, and actually sounds pretty good for its current price of about £50. It's the headphone/set I use most often for music during the working day, simply because it's to hand all the time and I use it for business calls. To be sure, it won't win any hi-fi awards, but the sound is quite acceptable for anything other than the most critical listening.
There are also gaming headsets that offer excellent sound quality. These are usually more expensive than office headsets, but less expensive than branded "hi-fi" headphones.
In-ear, on-ear, around ear, bone conduction
"In-ear headphones" is the new, rather precious term for what we used to call "earphones". These push into the ear canal, usually providing good sound isolation and (necessarily) light weight. There are a few almost-in-ear phones, like most of the Bose in-ear range, that don't completely seal in the ear canal, but are held in place above it using soft flanges. The lack of sound isolation created by this arrangement is good for safety (you can hear traffic), and has a musical delivery that suits some people.
On-ear headphones clamp onto the pinna of the ear, so are usually smaller and lighter than full-sized, around-ear designs. However, the fit leads to an awkward compromise -- if the clamping force is too tight, the fit will generally be uncomfortable on the ears, and tend to cause overheating. But if it's too loose, the whole weight is carried by the headband. These headphones need a well-padded headband for long-term comfort, but often don't have one. The hugely popular Sennheiser HD25 range has a split headband, which can be adjusted to spread the weight in a satisfactory way. Still, the awkward weight distribution does reduce somewhat the benefit of light weight that on-ear headphones ought to offer.
Around-ear headphones completely surround the pinna of the ear and, as a result, clamp against the skull, not the ear. Most headphones that aim for optimum sound quality are of this construction. They're usually heavy, particularly if wireless, and restrict head movement. It's also been argued -- not entirely convincingly -- that some component of audio sensation is actually in the pinna, not the auditory apparatus of the ear. Around-ear headphones do not completely prevent the pinna responding to sound, and this is potentially an argument in their favour. Still, if you're looking for top-end sound quality, you're probably going to favour around-ear designs anyway, because that's what's available.
Both on-ear and around-ear headphones usually offer better sound quality than in-ear devices, in the same price bracket. Moreover, the larger designs aren't as dependent on fit to get decent sound. This is why reviews of in-ear phones vary so wildly, I think -- some people are lucky, and get a good fit; others less so. Bass performance is exquisitely sensitive to fit, and it's worth experimenting with whatever is provided to adjust the ear fit. Some people buy aftermarket foam sleeves and what-nots for their in-ear phones and, in fact, these aren't entirely snake oil -- changing the fit even slightly can hugely affect the sound. Whether it affects it for better or worse is, like everything in this field, a matter of personal preference.
It's now quite difficult to get on-ear, wired phones that offer really good sound quality, simply because it's difficult to get on-ear, wired phones at all. They have limited application, and few manufacturers still make them. The Audio Technica ATH-m60x is a notable exception, and not too expensive.
Bone conduction is a relatively new technology, which uses the direct mechanical conduction of sound from a transducer to the skull around the ear canal. It's taken a long time to design bone conduction phones that sound decent, but such designs are now available. The sound quality doesn't rival any of the more traditional designs, but it's still acceptable. Bone conduction designs don't isolate external sound at all, which is good if you want to be able to hear people or traffic around you. And, because they don't work on the ear canal at all, you can block all external sound using well-fitted ear plugs. In principle this makes bone conduction phones very versatile. These devices are invariably wireless, and usually light-weight and unobtrusive. I use Aeropex Aftershokz headphones in the gym with ear plugs, and often at home without. They are by no means my first choice for sound quality, but they are convenient and unobtrusive.
Another advantage of bone-conduction phones is that they can be made completely sealed and waterproof.
I find that bone conduction phones vibrate uncomfortably at high volumes -- it feels like I have a bug in my ear. However, reports that they can shake the fillings out of your teeth are probably exaggerated.
Wired or wireless
The convenience of wireless -- usually Bluetooth -- headphones can't be denied. However, the sound quality of wireless headphones only approaches that of wired headphones at the top end of the market. There has, until recently, been little motivation for manufacturers to emphasise sound quality in their wireless models, because the main limitation in quality was the Bluetooth interface itself.
Recently, however, Bluetooth audio coding methods like LDAC and AptX have, in principle, opened the way to the development of wireless headphones with plausible hi-fi credentials. The introduction of AptX HD has gone even further in this direction.
Unfortunately, all these coding methods are proprietary, and are not available in all headphones, or in all playback devices. A few cellphones support AptX HD, as do a few top-end portable music players. Some devices support both AptX and LDAC but, in practice, it's usually one or the other, because of licensing costs.
If your playback device is primarily a cellphone, you might find that the decreasing lack of support for wired headphones pushes you towards wireless. It's usually possible to connect wired headphones to a cellphone's USB socket, but results are variable, and somewhat unpredictable.
I think it's fair to say that, among wireless technologies, only AptX HD really comes close to the sound quality that can be achieved with wired headphones. But, frankly, LDAC and AptX are good enough for most people in most situations. However, the presence of these technologies in headphones is no guarantee that the rest of the device is up to the same standard -- the rest of the device has to be constructed accordingly.
In short, if you want decent sound quality from wireless headphones, you need to be willing to spend a bit of money, and look for support for at least AptX or LDAC. And, of course, you'll need a player (or cellphone, or whatever) that supports these standards.
Leaving aside sound quality, it's important to remember that wireless headphones (including in-ear) will be heavier than wired and, of course, will have a battery that needs to be charged. Wireless headphones are usually designed for use with cellphones, and have call controls and microphones built in; wired devices usually don't have these features. Top-end wireless headphones usually have active noise cancelling but, again, this adds weight to the device.
Wireless in-ear phones come in many different formats. Typically both ear units are connected to a common electronic module, either in a neck-band or slung between the ears. Neck-band designs usually offer the best battery life and Bluetooth range, and least weight in the ears, but the format does not suit everybody. These units have become very popular for sports and fitness activities, because they don't place a lot of weight on the head, and don't restrict motion much. Sports units are typically water-resistant, and have locking flanges to keep them in place during activity.
So-called "true wireless" or "free wireless" designs have independent electronic units for each ear. Designing these tiny devices has been a magnificent engineering effort, and they have become very popular, despite their profound disadvantages. The most obvious of these is that it's difficult to achieve both low weight and long battery life. Despite manufacturers' optimistic claims, 1-2 hours continuous use is common. Proprietary charging cases take away some of the sting, but you can't use the phones at the same time as charging them. Having said that, I should point out that the Samsung true wireless buds can be used singly, leaving the other free for charging. I'm not sure whether that's true of other models.
Personally, I do not much care for true wireless earbuds for anything other than listening to audiobooks. I have yet to find any that I would feel happy using to listen to music. I can only guess that the success of these devices has come about because their owners haven't heard anything better. It isn't even as if they're particular convenient, except perhaps for sports; and, even then, you'd probably need an (expensive) noise cancelling model if you don't want to blow your eardrums out.
Although it's not relevant to music, the issue of latency arises when using wireless headphones to watch video. There's often a small delay between the picture and the sound, caused by the time taken to encode, transmit, decode, and process the digital audio signal. In my experience, few modern wireless headphones are badly affected by latency, but I appreciate that some people may be more fussy in this area that I am.
Noise cancellation and isolation
In most circumstances, we want headphones to block external sounds, at least to some extent. It's not really safe to crank up the volume to drown out the environment although, like most people, I find myself doing this from time to time. We can block external sound in simple, mechanical ways, like providing a good seal around the ears, or in fancy electronic ways. The Sennheiser HD25 is a master of "passive" (mechanical) sound isolation, but this effectiveness comes at the expense of tight clamping around the ears. Many in-ear phones are naturally isolating, because they block the ear canal.
For many years, Bose was the king of active (electronic) noise cancellation. The first time I switched on the Bose QC20i, in a noisy airport departure lounge, I felt that I had suddenly gone deaf. To be fair, this in-ear headphone wouldn't be my first choice for listening to music -- it's sound delivery isn't really to my taste -- but oh, my, the noise cancellation was awesome.
Since then, other manufacturers have caught up, and decent active noise cancellation is no longer limited to Bose. In full-sized headphones, the Sony WF-1000XM3 and Sennheiser Momentum 3 are viable challengers to the hugely-popular Bose QC35 in the noise cancellation contest. All three of these devices are wireless, heavy, and right at the top of my price range. As yet, I have not found an in-ear phone, at any price, that has active noise cancellation as good as the old QC20i.
Open back, closed back
Most headphones that aim for top sound quality are of an open-back design. A fully open back allows the loudspeaker diaphragm to vibrate freely in uncompressed air, which reduces many problems with unwanted resonance. However, as much noise leaves the back of the headphone as enters your ears, which makes them unsuitable for use at high volume around other people. Moreover, the open design does not block much, if any, external sound.
It is often claimed that the open design leads to an improved sound stage, that is, an increased feeling of openness and three-dimensionality. To get this benefit, you'll probably also have to go for an around-ear, rather than on-ear design.
My experience is that there is some truth in these claims. I've found that the AKG K702 (around-ear, open-back) is particularly good in this area (although not in all areas; such is the nature of headphones). Closed-back headphones, at any price, don't seem to offer any sensation of sound stage at all; the same is true for in-ear phones. At their best, closed-back designs will create a stereo image just outside your head. At worst, the stereo image will be a meaningless jumble.
Still, I've not found any headphones, at any price, that offer a sound stage that matches that of even modestly-priced loudspeakers. Since many open-back designs direct almost as much sound into the environment as loudspeakers would, their application is limited.
I use open-back headphones for listening in a quiet environment at home, when there are other people around, but not in the same room. For all other applications I use closed-back headphones. It goes without saying that open-back headphones are no use for travel, or in the gymnasium.
My favourite open-back headphones (in my price range) are the Sennheiser HD58x. They have a neutral sound delivery even at high volume, with no obvious unexpected resonances or distortion. However, they are big and heavy, even for a wired design. If there is a wireless open-back headphone design that sounds any good, I haven't heard it. All the decent wireless headphones have closed backs.
High impedance, low impedance
Impedance, measured in ohms, controls the amount of current that flows in an electrical device when a certain alternating voltage is applied to it. Impedance depends on frequency, so values quoted by manufacturers are only nominal. In the headphone context, a "low" impedance is in the range of 30 ohms, and a "high" impedance over 300 ohms.
Traditionally, the impedance of a headphone was determined mostly by the amount of wire in its speaker coils -- more wire, greater impedance. Lower impedance has (or rather had) the advantage that we can get more current in the speaker coil -- hence more volume -- for a particular voltage. This is a big deal when using portable music players and cellphones, because they are battery-powered. With mains-powered equipment, impedance could be higher, if there was any advantage to making it so.
And was there an advantage? Perhaps. If the headphone offers a high impedance, its response to an electrical signal will be less affected by the characteristics of the amplifier and the cable. The high impedance leads, in principle, to a more predictable electro-mechanical behaviour.
Whatever the notional advantages, using high-impedance headphones can be a nuisance with portable devices. You'll often see these headphones described as "hard to drive" or just "fussy". Most decent-quality portable music players will drive high-impedance headphones reasonably well, but most (all?) cellphones won't.
Most headphones currently on the market have nominal impedances less than about 70 ohms, simply because portable players are so popular. Even more traditional "hi-fi" vendors are now moving to low-impedance designs. If sound quality is a primary concern, then you should use low-impedance headphones with low-impedance cabling and connectors. The main symptom of poor-quality cabling is a lack of stereo channel separation but, frankly, the effect is not usually prominent. Cable upgrades are available for many popular headphones, but make sure you buy from a seller with a good refund policy, as you're unlikely to notice much difference.
It goes without saying that issues of impedance are irrelevant in wireless headphones, or in any headphone that has built-in electrical amplification.
Summary
There was a time -- not so very long ago -- when you had to spend a lot of money to get reasonable sound quality from headphones. It wasn't all that long ago that wireless headphones sounded awful, and were unreliable, at any price.
Things have changed. While there will always be people willing to spend a fortune chasing the tiniest improvement in sound quality, for most purposes it isn't really necessary.
What is, necessary, perhaps is to know how you intend to use your headphones, and choose a design that is suitable for that application. Headphone manufacturers present us with a lot of glossy silliness but, in the end, the principles are not that complicated.
