How to read a frequency response graph without a degree in acoustics.

Anatomy of a frequency response graph

A frequency response graph plots two things against each other, which frequencies the headphone plays (side to side) and how loud it plays each one (up and down). The line across the middle is the headphone's fingerprint. No two models share exactly the same shape, and that shape tells you a lot about what you'll hear.

The measurement goes like this. Somebody plays a precise test signal through the headphone, usually a sweep that glides from 20 Hz up to 20,000 Hz at a steady electrical level, and a measurement mic sitting in a fake ear picks up what would reach your eardrum at each frequency. That fake ear might be a simple coupler or a whole head and torso simulator (HATS for short), and the result gets plotted as one smooth line showing how the headphone strays from the signal going in.

A perfectly transparent headphone would play every frequency at exactly the same level, a flat horizontal line. No real headphone does that, and as you'll see in a minute, you wouldn't want one that did anyway. If you've ever stood at front of house watching an analyzer during a system tune, this'll feel familiar, and once you know what the shapes mean, you've got a real tool for shopping.

Reading the axes (don't skip this part)

These graphs follow a few conventions that throw first-timers off, so the axes are worth a minute before anything else.

The horizontal axis is frequency in hertz. It usually runs from 20 on the left (about the bottom of human hearing) to 20,000 on the right (about the top). The big thing to know is that it's logarithmic, so the stretch from 20 to 200 Hz takes up the same width as the stretch from 2,000 to 20,000 Hz, even though one covers 180 Hz and the other covers 18,000.

That's on purpose. Your ear works the same way. You hear a doubling of frequency as the same musical step, an octave, whether it's 100 Hz to 200 Hz or 1,000 Hz to 2,000 Hz, and the log scale draws it that way too.

In practice the bass (20 to 200 Hz) takes the left third of the graph, the midrange (200 to 2,000 Hz) the middle third and the treble (2,000 to 20,000 Hz) the right third. You get three slices of about equal width, even though the number of hertz in each one is wildly different.

The vertical axis is relative loudness in decibels (dB). The scale usually spans about 30 to 40 dB, with 0 dB set at some reference level, often what the headphone does around 1 kHz. Higher on the graph means louder at that frequency, lower means quieter.

Decibels are logarithmic as well, and the rules of thumb get mangled a lot. Every 3 dB is double the power, but your ear doesn't hear that as double the loudness. It takes something like 10 dB before most people say a sound got twice as loud. Even so, a broad 3 dB lift across a whole region is easy to hear, and a 10 dB bump is a big deal.

So when you compare two headphones, I'd zero in on broad differences of 3 dB or more. Narrow little wiggles of a dB or two rarely matter, while a 6 dB gap across the bass or the treble is the kind of thing that makes two pairs sound like different animals.

What "flat" really means (and why you don't want it)

New listeners often assume a flat line straight across the graph is the perfect tuning. It isn't, and a truly flat headphone would sound off, because your ears don't hear the world flat.

Picture good speakers in a well-treated room. The sound crosses the room, bounces off the walls, wraps around your head and shoulders, funnels through the folds of your outer ear and down your ear canal before it reaches the eardrum, and every step of that trip shapes it. Your outer ear and ear canal together build up a big boost centered around 3 kHz, right where speech is easiest to understand.

So a flat speaker in a treated room still lands at your eardrum with a bump in it, and that's just what your anatomy does. Your brain expects that bump and uses it to make sense of what it's hearing.

A headphone driver sits a few millimeters from your ear and skips most of that trip. To sound natural, it has to fake what your body would have done with speakers, which means it needs a raised output around 2 to 4 kHz, measured at the eardrum, to stand in for that natural ear gain.

So a graph showing a dead-flat line at the eardrum is actually showing a headphone that'll sound wrong, usually thin, distant and missing presence. A well-tuned pair shows a particular non-flat shape, called a target curve, that makes up for normal ear anatomy.

Target curves and the Harman research

A few research groups have tried to pin down scientifically what shape headphones should have. The one with the most pull is the work done at Harman International by a team led by Sean Olive, which has probably shaped modern headphone tuning more than anything else.

Olive's team ran blind listening tests with a lot of listeners, trained and untrained, having them rate headphones with the response tweaked by EQ. Pooling all those ratings, they worked out target curves for over-ears and in-ears, the shapes that kept scoring highest across very different groups of people.

The Harman over-ear target has a few telltale features:

• A modest bass lift of roughly 4 to 6 dB below about 100 Hz (listeners like a little extra low end)
• A level midrange through roughly 200 to 800 Hz, which keeps vocals clear
• A big rise peaking somewhere around 3 kHz, roughly 8 to 10 dB depending on how it's plotted, standing in for natural ear gain
• A gentle slope down through the treble above about 4 kHz, which avoids harshness without dulling the detail
• A small lift up around 8 to 10 kHz for a bit of air

A pair that sticks close to that shape will sound good to most people, trained or not. Pairs that stray a long way from it get polarizing, with some folks loving them and others wanting to throw them across the room.

Not everyone signs up for Harman. Some audiophiles like the older "diffuse field" target, which has less bass and more treble. Mixing, mastering and other studio work often call for something flatter in the bass. RTINGS rebuilt its own target when it moved to a new test head, starting from that head's diffuse field response with a gentle downward tilt of 1 dB per octave, and it says flat out that one curve doesn't fit everybody. Still, for everyday listening, Harman is the closest thing to a target backed by real listener data.

The practical upshot is that when a site draws its target line on the graph next to the headphone, as RTINGS and plenty of others do, you can see at a glance where a pair strays. Gaps start to mean something once they pass about 3 to 5 dB in any region, as long as you know which target you're looking at.

The frequency regions and what they sound like

To read graphs by feel, you need to know what lives in each part of the range and what a bump or dip there actually sounds like.

Sub-bass and bass (20-250 Hz)

This is the bottom of the music, where the kick drum's fundamental lives along with the low strings of a bass guitar, synth bass and the rumble in a movie's explosions.

Sub-bass, from 20 to 60 Hz, is the deepest stuff, more felt than heard. Plenty of "bass headphones" fall down here. They pump up the mid-bass (which is easy) without really reaching the sub-bass (which is hard and takes a capable driver). Read this part carefully. A pair that stays within about 3 dB of its reference down to 30 Hz has real extension, and one that's already 6 dB down by 50 Hz is faking its bass with a mid-bass bump. I get into that difference in my picks for bass and EDM.

Mid-bass, from 60 to 150 Hz, is the thump. Kick drum body, the fundamentals of an electric bass and the punch of an 808 all sit here, and it's where most "bass headphones" do their work, as pushing up 80 to 150 Hz makes the low end sound big even when the sub-bass is weak. A modest bump of 3 to 6 dB here is about what the Harman target asks for. Go past 6 dB and it starts sounding bloated, and past 10 dB it gets boomy and fake.

Upper bass, from 150 to 250 Hz, carries bass guitar harmonics, the low end of a piano and the lower notes of acoustic instruments. Too much here makes a headphone sound muddy and thick, with male vocals going cloudy, bass lines blurring together and the whole thing feeling crowded. Cheap bass-hyped headphones often trip up right here, and most people prefer this area flat or dipped a touch.

Midrange (250-4,000 Hz)

Most of the music lives here. It holds vocals, piano, guitar, brass and the core tones of most instruments, and it's where our hearing is most sensitive, so small changes have an outsized effect on how natural a headphone sounds.

The low mids, from 250 to 500 Hz, cover the lower vocal range, the body of an acoustic guitar and low brass. Too much here sounds honky or boxy, with male voices going nasal and instruments sounding stuck inside their own bodies. Most well-tuned headphones run flat through here.

The middle mids, from 500 to 2,000 Hz, are where most vocals and most instrument fundamentals sit. The Harman target starts climbing gently through this stretch on its way to the ear-gain peak. A big dip here sounds scooped, with vocals shoved back and the music feeling far away, and a peak here sounds forward and shouty.

The presence region, from 2,000 to 4,000 Hz, is where speech gets its clarity and a plucked string gets its snap. It's where ear gain peaks and where the Harman target rises the most. A pair that doesn't lift here sounds muffled or dull, and one that overdoes it sounds harsh and in your face.

Treble and air (4,000-20,000 Hz)

The top octaves hold cymbal shimmer, the S's in a vocal, the "air" around an acoustic recording and the fine detail that separates a great recording from a merely good one.

The lower treble, from 4,000 to 8,000 Hz, carries sibilance (the S and T sounds), the tick of a stick on a cymbal and the bite of a distorted guitar. Peaks here can sound harsh and wear your ears out over a long session, and dips sound smooth or warm. The Harman target slopes gently down through here after the presence peak.

The upper treble, from 8,000 to 12,000 Hz, brings cymbal shimmer, the high harmonics of strings and brass and a sense of detail and space. Pairs that push it sound detailed and airy, and pairs that roll it off sound intimate or warm.

The air band, 12,000 to 20,000 Hz, is the very top of what we can hear, and most adults lose a chunk of it with age. A small lift of a few dB here gives a pair a sense of openness, and a dip takes that away without changing much else.

Treble is the hardest part of the graph to read. Measurements up here swing around a lot, so different mics, mounting positions and test heads can give pretty different treble readings for the same headphone, and a small shift of the cup on the fixture can move a peak. I'd check more than one source before I trusted any single graph's treble.

Common headphone signatures

Once the regions click, a handful of common tunings jump out at you, and they line up with the labels headphones get sold under.

Neutral or reference tuning sticks close to the Harman target. Think of the Sennheiser HD 650, the HD 560S and Audeze's MM-100. The graph shows a modest bass lift, an even midrange, the big presence rise and a gradual roll-off up top, and it sounds balanced and natural, the way working engineers and anybody who cares about accuracy tend to like it.

V-shaped or "consumer" tuning boosts the bass and the treble and pulls the mids back. Bass-forward pairs like Sony's ULT Wear, which even has a button for piling on more, head in this direction. You'll see big bass peaks, a scooped middle that pushes the vocals back and then a raised treble, and it sounds exciting in a quick demo but can tire you out over a long session and leave the singer sounding a mile away.

Warm tuning raises the bass and rolls off the treble, as on Meze's 99 Classics (the 2nd Gen is the current one) or ZMF's Aeolus. The graph shows a lifted low end, a normal midrange and a gentle treble slope from about 5 kHz up. It's smooth and easy on the ears and kind to badly recorded music, though it can come up short on detail and air.

Bright or analytical tuning keeps the bass flat or a bit lean and lifts the treble. The Sennheiser HD 800 S and Beyerdynamic's DT 990 Pro are the classic examples. Expect lean bass, accurate mids and a noticeably raised stretch from 5 to 10 kHz, which sounds detailed and articulate, and thin or fatiguing if your ears or your recordings don't agree with it.

Studio tuning sits close to neutral with a bit more upper-treble bite to help you catch problems in a mix. The Sony MDR-7506, the pair that turns up on every truck I've worked out of, is the textbook case, with a lift up top that makes sibilance and edits jump out at you. That's great for tracking and editing and less fun for kicking back with an album, and my tracking and recording picks go into the rest of that family.

Bass-head tuning cranks the low end way up and pushes everything else back. Lots of "extra bass" consumer pairs and some DJ headphones go this way, with bass peaks 10 to 15 dB high that spill into the lower mids and bury the vocals. It's fun for loud EDM and pretty unkind to most other music.

Measurement sources you can actually trust

Where your graph comes from matters as much as how you read it. I'd take a maker's own graph with a big grain of salt. It's often measured under flattering conditions or is just a stylized drawing that never went near a test rig.

Here are the sources I'd trust, roughly in order of how useful they are.

RTINGS has about the biggest headphone measurement database online. It now tests on a Brüel & Kjær Type 5128-B head and torso simulator, publishes its methods in detail and covers hundreds of mainstream and audiophile headphones, with its target drawn on the graph so you can spot the gaps. One thing to watch is that it rebuilt its target for the new rig, and a few older reviews still use the old method. For almost any headphone in mass production, it's the first place I'd look.

Crinacle runs a big measurement database focused on IEMs and audiophile headphones. His IEM graphs come off an IEC 60318-4 coupler (the "711" coupler that's the standard for in-ear measurement) in a clean format that's easy to compare. For IEMs specifically, it's the best source going. He also keeps a ranking list that stirs up plenty of arguments in audiophile circles but is worth a look.

Audio Science Review is a forum built around objective measurement. Graphs come from the site's own testing and from a lot of members, so the quality varies, but the arguments over methods are rigorous and odd results get picked apart fast. It's strong on audiophile and reference gear and thinner on mainstream consumer stuff.

Reference Audio Analyzer is a Russian site with one of the largest databases of headphone measurements anywhere. The methods are well documented and consistent, and while the layout can be a slog for English speakers, the data is solid.

oratory1990 is a Reddit user and acoustic engineer who posts careful measurements on calibrated gear, along with EQ settings to pull popular headphones toward a target. He's strong on premium audiophile headphones and has fewer mainstream models than RTINGS.

Other places can still help, just with more caveats. SoundGuys publishes its own measurements and has changed its methods over the years, InnerFidelity is gone but its archived graphs still float around, and YouTube reviewers range from great to guesswork.

Steer clear of graphs published by the maker itself, sites that won't say how they measure, and any graph that's suspiciously smooth with none of the normal wobble a real measurement has.

What frequency response graphs don't tell you

Frequency response is the single best measurement for predicting how a headphone will sound, but it doesn't show you everything. A bunch of things that shape what you hear never show up on that line.

Distortion is the first. The graph shows how loud the headphone plays each frequency, but not how cleanly, so two pairs with the same graph can distort very differently. Good dynamic and planar headphones usually keep it low, while cheap ones can get gritty when you turn them up, and a separate total harmonic distortion (THD) measurement is what to look for.

Transient response, how quickly the driver starts and stops, doesn't show either. A pair that's slow there can sound smeared even if its graph matches a quicker pair, and planar and balanced armature drivers tend to be faster than dynamics (my rundown of driver types explains why). It sometimes turns up separately as an impulse response measurement.

Soundstage and imaging, the sense of where each instrument sits in space, can't be pinned down by any single graph. Open-backs usually sound wider than closed-backs, and the whole design (cup shape, where the driver sits, the damping) plays a part.

How a pair reacts to the source and amp is another blind spot. Some headphones, especially high-impedance audiophile models, can feel different on different amps, while the same pair on the same rig will measure about the same whatever amp feeds it. My guide to impedance, sensitivity and amps covers when that matters.

Comfort and fit are obviously nowhere on the graph, and a pair that hurts after half an hour won't get worn no matter how it measures. I'd always read comfort reviews right alongside the graphs.

Build quality and how long a pair lasts don't show up either. The graph can't tell you whether the cups will crack in 18 months or whether you'll be able to buy replacement pads, so check long-term owner reviews and parts availability before any big purchase.

Then there's unit-to-unit variation. The graph shows one sample measured one way, and your pair might measure a bit differently because of manufacturing, age or worn pads, which matters more on cheaper headphones. Some sources measure several samples to show how much they vary.

Questions people ask about frequency response graphs

Why do different sites show different graphs for the same headphone?

A handful of reasons. Different rigs (a B&K 5128 head, an IEC 711 coupler, a GRAS fixture) measure a bit differently, especially in the treble. Pad wear changes the seal, where the cup sits on the test head shifts the bass, and units vary. The upshot is that good sources can disagree by a few dB in places. The overall shape should match across the reputable ones, so I'd only worry when the shapes are really different, which usually points to a method problem.

Can a graph really predict what I'll hear?

For tonal balance, mostly yes. It's good at telling you whether the bass will be heavy, the mids forward or the treble sparkly. It won't tell you how distortion behaves when it's loud, how the soundstage feels, whether they'll be comfortable or what you personally like. I'd use the graph as the foundation, then add reviews and, if you can, your own listen.

Why don't manufacturers publish honest graphs?

A few reasons, I'd guess. Real measurements often look worse than a marketing drawing, and most companies don't want to hand buyers an easy way to compare. There's also no one standard, so what looks flat on one rig looks lumpy on another. And independent sites like RTINGS and Crinacle will measure the thing anyway, so the makers don't feel much pressure. The result is that people trust the independents and treat the makers' graphs as advertising.

Should I EQ my headphones toward the Harman target?

It can help, and plenty of enthusiasts like the result. But EQ can't fix what the driver can't physically do, so a pair that runs out of steam below 30 Hz won't get there no matter how much you boost it. The free AutoEQ project (on GitHub, from Jaakko Pasanen) has presets that nudge lots of popular headphones toward a target. Give it a try if you're curious, and expect an improvement more than a transformation.

Why doesn't RTINGS' graph match Crinacle's for the same pair?

They use different gear and different targets. RTINGS measures on a B&K 5128-B head and compares against its own target, while Crinacle's IEM graphs come off an IEC 711 coupler and get compared to his own preference targets. The headphone is the same, it's the rig and the yardstick that change. For over-ears, I find RTINGS' presentation easier to read, and for IEMs, Crinacle's lines up better with the rest of the IEM world.

Are graphs for wireless headphones harder to read?

A little. Wireless pairs often have built-in EQ or processing that changes the sound with the app settings or the noise cancelling mode, so the graph you see reflects one particular setup that may not match how you'll use them. RTINGS usually spells out its test conditions, so check them and line them up with how you plan to listen.

Is there one perfect tuning?

Harman is the closest thing to a preferred neutral that research has come up with across lots of listeners, but people still differ, and some want more bass, some more treble and some less of that ear-gain peak. The perfect tuning is the one that fits your ears, your music, your gear and your room, and Harman is a great place to start before your own taste takes over.

My bottom line

A frequency response graph is about as close to hard evidence as headphone reviewing gets. Once you understand the axes, can spot the common tunings and know which sources to trust, you've got a real way to size up a pair before you buy.

The skill builds up as you go. At first you'll be able to tell bass-heavy from neutral from bright at a glance, then you'll start reading individual regions (a scooped midrange, a presence peak, a treble roll-off) and hearing them in your head, and before long you'll spot the small differences that set a Sennheiser HD 600 apart from an HD 650.

When you're shopping for anything over about $100, find at least one independent measurement (RTINGS first, then Crinacle, ASR or oratory1990) and hold it up to a target. Look at where it strays and ask whether that matches what you're after. A pair with about 6 dB of bass lift and a gentle treble roll-off will sound warm and punchy, and one with flat bass and a raised treble will sound analytical and detailed. Neither one's better across the board, but knowing which you're getting saves you from opening a box of headphones that sound nothing like you hoped.

The graph isn't everything. Comfort, build, the driver, distortion and your own taste all count. But it's the most useful single measurement there is, it's free for almost any headphone you'd look at, and ten minutes with it before a big purchase is about the best return on your time you'll find in this hobby.

There's plenty of folklore in headphone land. The graphs are where the data's solid enough to train your ears against, and if you want to practice, pull up RTINGS' graphs for the HD 600 and HD 650 side by side and see how many differences you can pick out between two pairs that have been rivals since 2003.