Notes on IEMs

These are my notes on what I have learned about IEMs (in-ear monitors) and wired headphones. It is an attempt to explain the concepts in simple language - enough to identify your own music taste and pick the gear that fits it. Beyond that, this is a genuinely rewarding hobby, and if you are just getting started with IEMs, these notes should be a good starting point.

The Only Graph That Matters

Every earphone has one defining property: how loudly it plays each frequency relative to the others - deep bass, midrange, highs. Plot it on a chart - frequency from left (deep bass) to right (highs), loudness up and down - and you get a frequency response graph. Reviewers lean on this graph heavily, and for good reason: research on listener preference keeps finding that this curve explains most of why an earphone sounds good or bad to people [1]. Not the driver count, not the cable, not the price tag. The curve.

The graph splits naturally into five regions, and once you know what lives in each one, you can read any earphone review chart like a menu:

One thing trips everyone up the first time: that big hill around 3 kHz. It looks like a flaw. It is actually your own anatomy. Your outer ear and ear canal naturally amplify frequencies in that range by roughly 10 dB before they reach your eardrum. An IEM bypasses part of the outer ear, so a good one has to build that boost back in. A frequency response that looks like a flat line would sound dull and wrong. The hill is the earphone doing your ear's job for it.

What Should the Line Look Like, Then?

For decades there was no evidence-based answer - you bought whatever the magazines liked. Then a research team at Harman International, led by Sean Olive, answered it with data: they put hundreds of listeners through controlled blind tests, let them tune bass and treble to taste, and measured what people actually preferred [1]. The result is the Harman target curve - a moderate bass lift, a clean midrange, and that natural ear-gain hill, followed by gently declining treble.

The follow-up studies are the interesting part. Roughly two-thirds of listeners preferred the Harman target as-is, while the rest split into a camp that wanted more bass and a smaller camp that wanted less [2]. In other words: the target is not a law of physics, it is a very well-tested crowd-pleaser - and your personal taste probably sits either on it or a nudge to one side. The audio community describes those nudges with a handful of named sound signatures:

Look at the graph above as you read these: Harman is the tested default - a touch of extra bass over neutral, with vocals kept clear. Neutral boosts nothing and plays the recording as it was mixed - the reference sound studios work with. V-shaped lifts both ends of the graph, bass and treble; vocals live in the midrange between them, so they take a step back. The result is exciting at first listen, which is why so many store demos are tuned this way. Warm adds extra low end and pulls the treble down a little - a smooth sound that is easy to listen to for hours. Bright does the opposite: it pushes the treble up, which brings out fine detail but tires your ears over long sessions. None of these is objectively best. They are flavors, and the graph is just the recipe written down.

Which One Is Yours?

The fastest shortcut to your signature is the music you already listen to. This is a starting point rather than a rule, but it gets you to “probably right” without buying five pairs:

The Technical Terms, Translated

Beyond the frequency response, reviews lean on a small set of recurring words. Here is the whole dictionary you actually need:

• Soundstage - how big the invisible room around your head feels. Open-back headphones excel here; IEMs are naturally more intimate.
• Imaging - whether you can point at each instrument in that room. Matters a lot for gaming footsteps.
• Detail / resolution - how many small textures survive: fingers sliding on strings, the breath before a verse.
• Timbre - whether instruments sound like themselves. A piano with off timbre sounds like a keyboard ringtone of a piano.
• Sibilance - the sharp, spitty edge on “s” and “t” sounds when treble misbehaves. Once you notice it, you cannot un-notice it.

Spec sheets also love advertising what is inside the shell. The four driver technologies are worth knowing - mostly so that driver-count marketing stops working on you:

Do You Need an Amp? (A Small One Helps)

You do not need a stack of amplifiers to enjoy IEMs. But since phones dropped the headphone jack, something has to sit between your USB-C port and your IEMs - a DAC (digital-to-analog converter), the chip that turns your digital music into the electrical signal the earphones play. That piece matters more than people expect: my own IEMs sounded noticeably better when I swapped a bare adapter for a proper dongle DAC. The $10 Apple dongle measures genuinely well and is the floor; dongles in the $20-100 range (Moondrop Dawn Pro, FiiO KA11) add cleaner power and a lower noise floor. Full desktop amps only matter if you later move to full-size headphones - high-impedance or power-hungry planar models that a dongle cannot drive.

One caveat: the chain is only as good as what you feed it. Bluetooth compresses the audio, and standard Spotify streams are lossy - compressed in a way that throws away detail. A wired IEM with a dongle DAC only pays off when the source is lossless. Apple Music includes lossless at no extra cost; Tidal, Qobuz, and Amazon Music have equivalents. Wired IEMs plus a lossless subscription is the cheapest genuine upgrade in this whole hobby.

My Go-To Picks

Everything below is a boring, community-consensus staple - the kind of pick that shows up in every “best under X” thread for years because it keeps being right. The signature chips reuse the colors from the chart above.

Before You Hit Buy

• Seal first, judge second. An IEM without a proper seal loses its bass entirely. If a pick sounds thin, try the next ear-tip size up before writing a bad review in your head.
• Look up the graph. Community databases like squig.link [3] overlay measured frequency responses against the Harman target for thousands of IEMs. Thirty seconds there beats thirty minutes of adjective-heavy reviews.
• Ignore driver-count marketing. A well-tuned single dynamic driver beats a badly-tuned eight-driver hybrid every time.
• Mind the volume. IEMs sit close to your eardrum. The old 60/60 rule - listen at under 60% volume, and take a break after 60 minutes - is crude but protects your long-term hearing.
• Respect diminishing returns. The jump from $25 to $100 is enormous. The jump from $100 to $1,000 is barely noticeable. This hobby is kindest to people who stop at “happy.”

That is the whole game: learn one graph, know your flavor, buy a boring consensus pick, get the tips to seal. The gear above will outresolve most people's source files long before it becomes the bottleneck - and if you catch yourself browsing graphs at midnight for fun anyway, welcome. It is a good rabbit hole.