On the face of it, headphones are simple objects. Plug in, put on, play music. But if you want to get the very best out of your headphones, you’ll need to know a little bit about how they work - that means you’ll know whether they sound best when matched with a smartphone, for example, or a dedicated amp. Knowing these terms means you’ll know how loud they’re likely to go, so you don’t plug them in, turn them all the way up and detonate your eardrums. But when even a simple dive into headphone tech terms can be utterly headscratching, this kind of thing can get annoying fast. Fortunately, that’s where we come in. We’ve put together a complete, simple guide to headphone specs and terms, explaining everything you need to know in the simplest way possible - with plenty of practical examples.
- Drivers Explained
- Impedance and Sensitivity
- Different Headphone Types
- Isolation Vs Cancellation
- But How Can I Tell If A Pair Of Headphones Are Good?
- Do I Need An Amp?
- Three Great Headphones You Can Buy Right Now
- Video Guide
When headphone companies refer to drivers, they're referring to the part of the headphone that actually makes a sound. This is usually a thin, disc-shaped bit of machinery located inside the left and right housing of your headphones. Drivers eat up the electrical current that travels from the sound source up through the headphone cord, and spit it back out into your ears as sound.
All being well, you will never actually see a headphone driver. It’s the kind of thing you only eyeball if you ever dismantle a pair of headphones, or occasionally, if you modify one by, say, swapping out ear pads. But just because you don’t see them very often doesn’t mean you don’t need to pay attention to them. In order to select the type of headphones that is best for you, you need to know a little bit about the sizes they come in, and their different types.
Let’s talk about size first. Despite most audio companies measuring things in inches, headphone drivers have always traditionally been measured in millimeters. Please don’t ask us why. Driver sizes can arrange from 6-12mm (in earbuds) to 40-100mm (in larger headphones). There is a perception that larger drivers equal more exciting bass and better dynamics, but this isn’t the case. While the bass may be a little cleaner, due to the increased size of the driver diaphragm, it’s no guarantee of thundering basslines. In addition, larger drivers often have difficulty reproducing high frequencies (like violins and snares), due to the fact that their shape changes and deforms more readily. Case in point: the Audeze EL-8 Titanium, which we reviewed in full on this site a little while back. It has very large drivers, at 100mm, but we didn’t feel the bass was particularly exciting or powerful. It’s also a massive pair of headphones that makes you look a little bit like Princess Leia, but that’s neither here nor there.
When it comes down to is this: driver size is not a good indicator of anything. There is so much else at play inside the headphones that it’s not really useful, outside of academic purposes. It’s far more illuminating to look at the different types of drivers, and what they are made of. Knowing these will give you a far better idea of what a pair of headphones is going to sound like. We’ll try keep this brief.
Dynamic Drivers are the most common kind. You will find them in almost all on-ear headphones, and many over-ears. They tend to be larger, and as a rule, are able to produce more effective bass, although they can lack subtlety.
Planar Magnetic Drivers - also called Orthodynamics if you’re old-fashioned - are a little different from dynamic drivers. They create sound using an electromagnetic field, and are renowned for being airy and subtle. You’re likely to get highly accurate sound through these, giving you a better idea of what the music sounds like, without too much additional color. They usually (but not always) cost more than dynamic headphones.
Balanced Armature Drivers are most commonly found in earbuds and in-ear monitors. They are a solution to a particular problem, which is that small drivers (such as ones that need to fit right into your ear canal) don’t displace much air, which is of course how sound actually gets to your eardrum. Instead of just a single driver on each side, many earbuds will have multiple balanced armature drivers, which allow them to do the job.
Finally, there are Electrostatic Drivers, which use a diaphragm that has been electrically charged. Headphones that use these are super-expensive, finicky, and require specialised amps to run. You are almost certainly never going to find them in your local Best Buy, and if you’ve already got a few, then you probably don’t need this guide. Suffice to say: they sound brilliant, with unbelievable accuracy.
Impedance, we’d argue, is the most important spec you need to know about. When we're evaluating headphones, it’s the first thing we look at. Not just because it tells us a little bit about the headphone’s character, but also because it tells us what we’ll need to actually play it. Understanding it is the single most important tool you can use in buying headphones.
Fortunately, it’s pretty easy to explain.
Impedance is electrical resistance – essentially, how well something resists an electrical current that passes through it. It’s a “measure of the opposition that a circuit presents to a current when a voltage is applied.” (Thanks, Wikipedia). Even if that makes no sense, headphone impedance is still very easy to interpret. It’s measured in ohms (Ω) and what it tells you is how much power your headphones will need to get to a reasonable listening volume. It tells you how much you’re going to have to crank the volume knob before things are comfortable.
Why is this important? Because the higher the number in front of the Ω symbol, the more power-hungry the headphones will be. It means that certain things – like smartphones – simply won’t be able to pump enough power into the cans. That means that even at max volume, things will still be a bit quiet. You may even start getting weird artefacts in the sound, and… Yeah, we don’t want that.
Fortunately, interpreting this as easy. Any impedance up to 32Ω can be played quite happily off a simple portable device, like a smartphone. Impedance from 33-100Ω is a little bit of a grey area – you’ll probably be able to generate enough volume, but you could certainly improve things by adding in a portable headphone amp, which will both increase the power and sharpen the sound. Anything above 100Ω is almost certainly going to require an amplifier. These days, there are plenty of headphones that run from 100-300Ω, and even some that nudge the 600Ω mark. At the time of writing, we're testing a pair of Beyerdynamic Amiron Home headphones (here's our full review) which measure at 250Ω, and which perform so much better when they are plugged into an amplifier.
If, by the way, your little bit confused about what an amplifier is and how you use it, check the section below!
You might reasonably ask why you would bother with high impedance headphones anyway. After all, if all it means is that you need more power to drive them, then why get one in the first place? Just get a low impedance pair to run off your smartphone, and have done with it. Right?
The reality is that high impedance headphones, because of their ability to handle electrical signals, are able to more accurately and vividly reproduce sound. As a consequence, they are often more expensive. But: that does not mean that low impedance headphones are bad. One of our favorite pair of headphones ever, one we would save from a burning building, is the AudioQuest NightHawk Carbon (Full review here). It has an impedance of – wait for it – an enormous 25Ω.
Then there's the term sensitivity. It relates to impedance, but it’s not very helpful in deciding whether or not to buy a pair of headphones. Let’s explain it.
Essentially, sensitivity is a measure of how loud a pair of headphones will play at a given power level. If headphone A has a higher sensitivity rating than headphone B at a power level of one milliwatt, then the audio it produces will be louder at that volume. What that means in practice is that you will have to crank the volume knob less to get more volume out of something. And to give you an idea, a sensitivity rating of 86dB (decibels) is considered relatively low, while anything above 110dB is on the high end.
But the thing is: sensitivity isn’t very useful, mostly because manufacturers aren’t always consistent with how they measure it. Sennheiser, for example, may make different measurements to Sony (we don’t know if they actually do, we’re just using names we plucked out of thin air) and so it can be a little bit hard to tell whether a pair of headphones will be loud enough. Add in the millions of variances of sound source and amplifier, and the hearing abilities of the person in question, and you’ve got a term that is sort of useless. Take the HiFiMan Edition S (full review here) – which, for the record, we think is a fantastic and innovative pair of headphones. It’s got a relatively high sensitivity of 113dB, but in practical terms, we didn’t find that we needed far less volume than any pair of cans with lower sensitivity.
It’s far more important to find a pair of headphones that will play loud enough for your particular sound source. That’s where impedance comes into play. If all you’ve got is a smart phone, then what you need to be looking at is a pair of headphones of up to 32Ω. That way, you’ll always be able to get them loud enough.
You may also see sensitivity referred to as Efficiency, or Sound Pressure Level (SPL). Sound makes waves in the air, which is how you can hear it, and the higher the volume the higher the pressure. Ultra-high pressures hurt. Obviously.
This is an interesting one. 90% of the time you won’t need to pay attention to it, but it’s a good indicator of the character of the headphone.
Essentially, it’s a measure of how much the audio changes from when it enters the headphones to when it exits the driver in audible form. That change is referred to as distortion, although it’s not the kind of distortion that you get from guitar feedback, for example. In most cases, you want the Total Harmonic Distortion (THD) to be as low as humanly possible. The less a pair of headphones messes with the signal, the more accurate the audio is likely to be, and the better the sound quality.
That being said: these days, headphone technology is so good that THD is measured in decimal points. A THD of 0.1% (which means that the headphones distort no more than 0.1%) is not uncommon. Take a pair like the bulky Sennheiser HD630VB (full review here), which have a THD of 0.08%, measured at a frequency of 1kHz and a volume of 100dB. That’s so low as to be unnoticeable, and although it’s only a single measurement taken at a particular frequency, you can be relatively assured that the headphones are unlikely to dramatically change the sound.
We should say that simply because a pair of headphones has a low THD doesn’t mean that they won’t imbue the sound with a bit of character – which, after all, is the point of most headphones in the first place. You can think of THD as unwanted distortion, which could reduce your enjoyment of the music. It’s not a particularly important spec, and many manufacturers don’t even display it.
Welcome to the single most useless spec on this entire list. Even more useless than sensitivity. Companies occasionally put a lot of emphasis on the frequency of their headphones, and we’re here to tell you that it’s all nonsense.
Frequency, or Frequency Response, refers to the range of sounds a pair of headphones can play – how low and how high they can go, expressed in Hertz. Low sounds, such as basslines, might hover around the 500Hz mark, while crisp snare hits might dominate the 16-17,000Hz mark (also written as 16-17kHz, or kiloHertz; that is, a thousand Hertz). The wider the range is, the more sounds the headphones will be able to reproduce. You’ll see a number that looks something like this: 10Hz-23kHz.
And it’s absolute codswallop. Here’s why.
The human range of hearing, at its best – that is, when you’re a teenager and you haven’t sullied your ears with too much headphone listening – can hear sounds as low as 20Hz and as high as 17.4kHz. Anything lower or higher than that is simply inaudible – at best, you might be able to ‘feel’ really low sounds if they are at a sufficient volume, but you won’t be hearing them audibly. So while a pair of headphones might be perfectly capable of producing sounds at 23kHz, it means absolutely nothing, because you won’t be able to hear them.
That’s why it makes us laugh when we see that headphones like the Sennheiser HD630VB, mentioned above, have a frequency range of 10-42,000Hz. That is, they can generate sounds that are more than twice as high as the highest human beings can hear. We are not doubting that they can produce those sounds, but there’s absolutely no point in telling us that they can. It’s completely meaningless.
At a stretch, you can take it as a general rule that headphones with slightly wider frequency ranges – anywhere up to 22kHz – will be able to add a little more detail into their sound spectrum. But it’s a very general rule. Our advice here is that you ignore frequency response entirely when deciding which headphones to buy. The only time you should pay attention to it is if it gives a slightly narrower range than normal, which could indicate that the headphones aren’t capable of doing their job. Anything that can’t go down to below 30Hz or above 16kHz is something you should probably steer clear of.
Note that we're not talking about a Frequency Curve, a term which is a little different. A Frequency Curve, which some companies proudly display, shows how boosted or cut different frequencies are across the entire range a headphone can put out. If you know what you're doing, you can analyse one and see that, for example, a particular pair has a bump at 500Hz, meaning it's like to emphasise certain bass sounds. Our take? It's fine, but it's probably a little overkill for most people. If you're not inclined, you can ignore frequency entirely.
So, those are the main specifications you need to know about. But it’s still worth knowing a little bit about headphone types, and the most obvious of those are the three main ones: over-ear, on-ear, and in-ear. Here, we are going to dwell less on what they are, which is fairly obvious, and more on their advantages and disadvantages.
Over-ear Headphones go over the top of the head (which is what the word circumaural means, a term you will sometimes see with regards to these) and have housings and cups that completely cover the ears. They tend to have better and deeper sound quality than the two other types of headphones, but they are also bulkier and heavier, and less portable than the other types. The Bowers & Wilkins P7 Wireless are a good example of over-ears, although they tend to quite portable. We reviewed them in full here.
On-ears rest on top of the ears. They don’t possess the depth of sound, and often aren’t built to produce really good audio quality, but they are cheaper, more portable, and lighter. You don’t tend to see a lot of high-impedance on-ears, as they are most commonly used with things like smartphones. An excellent example of these – which also happen to be a phenomenal pair of cans – are the Thinksound On2s (full review).
Finally, you have in-ears. You can broadly split these up into two types: earbuds, which are simple single-driver units that slot into the ears, and in-ear monitors (IEMs), which are slightly more complex and usually offer multiple drivers – and, as a consequence, better sound. These days, the only disadvantages of in-ears is that they can be uncomfortable to wear for long periods. The good ones have such advanced construction that they can often compete with the sound quality of much bigger headphones, although they tend to be equally as expensive. An example of the two types: the MEZE 11 Neos (full review) are earbuds, while the Campfire Audio Andromedas are IEMs.
In addition, it's worth knowing about open-back and closed-back headphones.
Pick up any pair you have to hand, and turn them over. Take a look at the outside of the cups. If the surface is solid, then the headphones are closed-back. If there is what looks like a grille there, or you can see through to the driver, then they are open-back. Dead simple – and yet, they contain some crucial differences which you need to be aware of when you’re buying.
For the most part, open-backs are incredible. They allow air to interact with the driver, and this imbues the sound with some great qualities. It quite literally makes the sound feel ‘airy’ – open, wide, nuanced, with heightened detail and character. You’ll get a much wider soundstage (which means that the music will appear to be coming from all directions, rather than emanating from the center of your head). The downside? Bleed. Open-backs leak sound like crazy, meaning that anyone around you will be able to hear what you’re listening to, even at low volumes. The textbook case for this are Grado headphones; we have a pair of their SR325e cans in for testing at the time of writing. You can see right through to the driver, and every time we play them, people from miles around can hear what we’re listening to.
Closed-back headphones don’t have sound that is quite as open and detailed, as less air is allowed to interact with the driver. But that doesn’t mean that the sound is bad – far from it – and they are much better for listening to in environments where you’re not alone. And trust us: choosing between these two types of headphones is much easier and far more effective than divining things from specifications like the ones listed above. The Thinksound On2s are a good example of this. In their case, they use wooden housings, which provide the own internal resonances that help shape the sound.
We should also (briefly) mention the differences between wired and wireless pairs of headphones. It used to be that wired headphones would always win in terms of sound quality, but thanks to technology like Bluetooth aptX, the gap between the two of them in terms of audio quality has been getting smaller and smaller. Right now, we think that wired headphones are still superior; high impedance models need a separate amplifier to drive them, as the ones that are found in the housing of wireless headphones won’t do the job, and as such, wired cans are the ones to go for if you want better sound quality.
But: there’s no denying that wireless headphones are convenient as hell. Although you do need to charge them, and they can suffer from occasional dropouts, they definitely have their pluses. Go for wireless if you value convenience and simplicity over everything else, or if you find yourself on the go more often than not.
In the future, it will be interesting to see if headphone manufacturers actually managed to make a high impedance pair that also happens to be wireless. Technology is changing faster and faster now, so it’s entirely possible. You can bet that when they do, you’ll hear about it here first.
Headphone isolation refers to the ability of the cans to block out the world around you. If they can get a good ‘seal’ against your head, or the insides of your ear canal, they will have excellent isolation. There is no spec to measure this, unfortunately, but reviews will usually give you a clue.
A pair of Noise-Canceling Headphones (technically active noise-canceling headphones, as they use a powered system rather than a passive seal) actively work to block out the sound around you, using inbuilt microphones to capture the sound and then annihilate it. These are almost exclusively over-ear headphones, as the design lends itself to the increased amount of electronics necessary, as well as providing a decent seal that assists with the effect.
Sometimes they use batteries, and sometimes they can be recharged by USB or something similar. Either way, we love noise-canceling headphones – when they work well, that is – and think that if you’re looking for a new pair, these ones are worth considering. That being said, they do make things a little and sometimes a lot more expensive, so make sure you actually need them before you shell out.
You might also see the term Noise-Isolation Headphones. This is just noise-cancelation the relies on a passive seal round the ear, rather than any active electronics. It’s increasingly rare these days, so you shouldn’t have to worry about it too much.
Active noise cancellation is getting increasingly sophisticated these days. Take the Parrot Zik3s (full review here) which not only offer great cancellation, but also allow you to turn on a feature where you can amplify the sound of the world around you, essentially giving you super hearing. Kind of. Sort of. Well, we think it’s pretty neat.
Excellent question – and one that is asked frequently. How can you, as someone who doesn’t have access to a particular pair of headphones at a particular moment, tell if they are actually worth your time?
The best, simplest way to do it is to read the reviews. They’ll give you a good picture of what a particular pair does. Here are ours.
But let’s say you want to go further, by actually analysing the specifications headphone manufacturer gives. We’ve explained what the individual specs mean, so what we going to do now is bring them together with a practical example. For this one, we’re going to use a pair of headphones that we haven’t actually heard yet, for one reason or another – yes, we know, but there are a lot of headphones out there and we are still getting to a few of them. The AKG K712s are renowned by audiophiles, and still, we have yet to hear them. So what can we glean from their specs?
- Driver Size: Not given
- Type: Open-back, over-ear
- Impedance: 62 Ohms
- Sensitivity: 105 dB SPL/V
- Frequency Response: 10Hz – 39,800Hz
- THD: 0.1-1% / 100Hz (Not on AKG’s page, but measured by the good folks at Innerfidelity)
It’s not a lot of information, but it’s enough to give us a reasonable picture of what these headphones can do. Although AKG haven’t given a driver size for these (and we haven’t found a reliable source online that states it) it’s far more important for us to know that these are open-back, over-ear headphones, which means they are likely to deliver detailed, accurate sound with good isolation (although probably a lot of bleed). In addition, they have a high enough impedance that, assuming they are driven from a decent amplifier, will mean that the sound has even more detail, and will be relatively clear.
The frequency response has a laughably high range, up to just under 40kHz, which, as we mentioned, is impossible for humans to hear. But the ability of the headphones to reproduce sounds this high means that it is likely that their quality is good, and it’s promising to see that they go as low as 10Hz.
We don’t, as a rule, perform scientific measurements here at TMS, but there are plenty of websites that do, like Innerfidelity. The link above has a whole range of data, and one graph that they helpfully supply is the THD. This varies at different frequencies but doesn’t go higher than about 5%, and only at very, very low frequencies. While that means that it’s bass may not be quite as accurate or precise as we would like, or it may be coloured a little, it’s not enough for us to worry about – especially when you look at the measurements at above 80Hz, which drop below 1% THD.
So from the stats – and bearing in mind that we haven’t heard these headphones ourselves – we can be confident that these are likely to be pretty good. They show all the signs of being able to provide accurate, detailed, rich sound which would benefit greatly from a good amplifier and DAC (Digital-to-Analogue Converter).
A headphone amp is a separate box that you place between your device and your headphones. It not only increases the overall volume of the music, but also improves the quality. A good headphone amp will be as much about the details of the music as it will be about making it as loud as possible.
It used to be that headphone amps were strictly not portable. They were huge boxes that sat somewhere and locked due to their location. No longer. You can now get a very decent headphone amp about the size of a cellphone, which you can easily carry around with you and which will do amazing, magical things to your sound.
So should you get one? We think they’re great, but we also know that the majority of listeners probably don’t need them. Ultimately, they’re nice toys for those who are super passionate about their music, and who want to experience it in the absolute best way possible. They really can be a huge advantage if you’re looking to do this, but conversely, they can also show up bad recordings audio that’s been compressed, like MP3s.
If you have the money to do so, then we strongly recommend taking a look at our roundup of the best headphone amps available. (That is, money to buy them, not money to look at our roundup. That’s free.) This is really what it comes down to. Headphones are an extremely personal thing, and only you can decide whether or not you need an amp to go with them. In any case, it’s never been easier to snag yourself a truly fantastic pair of headphones that you will love forever. We promise.
As far as we’re concerned, these are among the best headphones on the market. They are comfortable to wear for long periods, offer incredible sound – especially if driven by an amp – and offer a great range of extras, including a fantastic case. Furthermore, they are among the most forward thinking headphones around right now, with everything from liquid wood housing to 3D printer drivers.
In our review, we said: "Up until recently, only companies like Grado really nailed it. And their down-home, folksy Brooklyn family business charm is great…but somehow, we prefer these. And let’s be real: we didn’t just spend damn-near 3000 words of orgasmic, overblown prose to give the NightHawk Carbons nothing more than a perky thumbs-up. These get fireworks. These get the ticker tape parade. These get the goddamn key to the city, and a blowjob in the back of the limo.” We still stand by that. Including the part about the blowjob.
We’ve mentioned already, and we think they are among the best on-ear headphones available right now. The brainchild of sound engineer Aaron Fournier is light, portable, gorgeous – thanks to its wood housing – and it sounds fantastic. It’s not going to beat out bigger models, but it offers supreme value for money.
From our review: “It is really, really hard to find fault with the On2s. They have terrific sound, superlative design, excellent comfort and a compelling price point. Admittedly, they definitely aren’t going to satisfy fans of deeper bass…but really, that’s a subjective assessment. For what they are, they provide a genuinely fantastic experience, and if you’re in the market for a new pair of headphones – and want something that will give you maximum bang for your buck – then there should really be only one option: go wood.”
Straight out of Romania, a pair of all metal earbuds that blew us away. The 11 Neos are not only light and robust, but offer a warm and controlled sound that we fell in love with, even though it would have been nice to see a little bit more detail, and get a slightly less annoying in-line mic. Headphone designer Antonio Meze produces some great stuff, and in the earbud arena, he’s got a real contender here.
“If you do most of your listening with earbuds, you would be shortchanging yourself not to hear these,” we said in our review. “At less than $100, these are an absolute steal. They incorporate technology that we would expect to pay a lot more for, and show off a level of detail that is just wonderful to behold. Admittedly, they’re not perfect (thanks to that irritating in-line mic) but it’s a minor mark against an otherwise stellar product.”