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Listening at home⏱️ Estimated reading time: 15 min
On this page: Overview
Key Takeaways
A dynamic driver uses a voice coil to push a cone-shaped diaphragm, much like a tiny loudspeaker, and moves a lot of air for its size. A balanced armature is a small sealed receiver, long used in hearing aids, in which a pivoting reed drives a diaphragm. It is small enough that several fit in one shell, each covering part of the frequency range.
In an IEM, an electrostatic driver (EST) works as a supertweeter for the highest frequencies. Sonion, which makes them, rates its EST for use “from 7 kHz and upwards”, with a miniature transformer built in, so it plays from an ordinary phone or player and needs no special amplifier.
A hybrid IEM combines two or more driver families in one shell, most often a dynamic driver for the bass with balanced armatures for the mids and treble. The 2HT (1 dynamic + 1 balanced armature) is a simple hybrid; models that add electrostatic and bone-conduction drivers carry four families.
Not automatically. A planar magnetic driver spreads the drive force across a thin film, but how a planar IEM sounds still depends on tuning, fit and how much power your source gives it. Unique Melody does not make a planar IEM, so we have no planar model to recommend here.
No driver type wins on its own. Dynamic drivers usually take the bass in an IEM because a larger diaphragm moves more air, which is why most Unique Melody hybrids give the low end to one. Balanced armatures can play bass too, and the ear-tip seal decides how much low end you hear from either.
Spec sheets for IEMs read like a parts list: 1 DD, 4 BA, 2 EST, 1 BC. Those letters are the IEM driver types, the tiny transducers that turn an electrical signal into sound. Most explainers stop at three or four families. This one covers all six you will meet, including the bone-conduction drivers that most guides leave out.
If you are new to the category, start with our explainer on what are in-ear monitors, and our guide to how in-ear monitors work follows the signal from cable to eardrum. Here we zoom in on the drivers themselves: how each family works, what it is good at, where it struggles and which Unique Melody models use it.
At Bollsen, we are a family-owned earplug company and the official UK & EU partner of Unique Melody, a maker that uses every one of these driver families in its range. We did not measure these drivers ourselves. The figures below come from the published product pages and from the companies that make the drivers, and anything not published is marked “not stated”.
What is a driver in an IEM?
A driver is the part of an IEM that turns the electrical signal from your phone or player into moving air, or, in one family, into vibration of the shell. Every driver does the same job by a different physical route, and that route sets how big it is, which frequencies it handles well and how many fit in one shell.
An IEM can carry one driver or thirteen. In the Unique Melody range the count runs from 1 per side (From The Start) to 13 per side (The Multiverse Mentor and Mason FS). When there is more than one, a crossover splits the signal so each driver plays the band it suits.
How does a dynamic driver work?
A dynamic driver, also called a moving-coil driver, works like a miniature loudspeaker: a voice coil fixed to a thin diaphragm sits in a magnetic field, and the music signal pushes the coil and diaphragm back and forth to move air. You will find one in most everyday earphones.
Its strength is low-frequency output. The diaphragm is large compared with other in-ear drivers, so it moves more air, and Sonion’s design guide for earphone makers sums up the moving coil as “large, linear” with “strong bass” (Sonion, Designing Earphones with Balanced Armature Receivers). Diaphragm material matters too. Makers use composites and carbon nanotube (CNT) films to keep the diaphragm stiff and light.
The limits come from the same size. A dynamic driver takes up a lot of room in a small shell, so few fit, and it usually needs a vent to manage air pressure behind the diaphragm. Some listeners notice “driver flex”, a faint crinkle as the diaphragm reacts to pressure when the IEM is pushed in.
In the Unique Melody range, From The Start uses a single dynamic driver, and the 2HT and MEST MKII each use one 10 mm dynamic driver for the low end. The Stardust gives two dynamic drivers separate sub-bass and bass jobs. The 3DT is all-dynamic, with two 7 mm composite-diaphragm drivers and one 10 mm CNT driver per side.
How does a balanced armature driver work?
A balanced armature (BA) driver is a tiny sealed box in which a coil magnetises a thin metal reed, the armature, balanced between two magnets. The signal makes the armature pivot, and a drive pin passes that motion to a small diaphragm. Researchers at the University of Illinois describe the BA receiver as “the oldest magnetic earphone” and the most widely used receiver in hearing aids (Kim and Allen, How a hearing aid transducer works).
Its main strength is size. A BA is small and efficient, which is why it moved from hearing aids into in-ear monitors; Knowles, one of the main makers, explains how its balanced armature design for earphones works. Because each BA is so small, a maker can put several in one shell and tune each one to a band of frequencies.
Each BA covers a narrower band than a dynamic driver, so multi-BA designs need a careful crossover. Sonion’s guide also lists BAs for “occluded applications only”: they rely on a sealed ear canal. Fit a loose ear tip and a BA design loses much of its bass.
BA counts in the range run from 1 (2HT) to 4 (Stardust, MEXT and every MEST model, plus Maven III Moonshard) and up to 12. The Multiverse Mentor uses 12 BAs and one bone-conduction driver per side with a 5-way crossover and no dynamic driver at all, and the Mason FS follows the same 12 + 1 layout.
What does an electrostatic driver do in an IEM?
An electrostatic driver (EST) in an IEM is a supertweeter: a very light charged membrane moves between perforated plates when the signal voltage changes, and it handles only the highest frequencies. Sonion’s data sheet for its EST65SA01 describes “electret technology for IEM applications, combined with a transformer” and an “application as supertweeter from 7 kHz and upwards” (Sonion EST65SA01 data sheet).
The membrane is so light that it can reach well beyond the range of human hearing; the same data sheet lists output “up to 70 kHz”. That figure describes the driver’s range, not something you will hear. Because the membrane uses an electret (a permanently charged film) and a “miniature transformer included for passive drive”, an EST IEM plays from the same phone or dongle as any other.
The limits are output and range. An EST plays quietly on its own and covers only the top octaves, so it always works beside BAs, and the tuning of that hand-off decides whether the treble sounds airy or sharp. On IEM forums, listeners also point out that an electrostatic tweeter is not the same as a full-range electrostatic earphone, which needs its own dedicated energiser.
Five Unique Melody models use ESTs: two per side in the MEST MKII, MEST Jet Black and MEST Fortune, and four in the MEST MKIII CF Blue and Maven III Moonshard. Headfonics describes the MKII’s layout as “a single 10mm dynamic driver for the lows, a dual BA driver unit for the mids and upper mids, dual BA for the highs, and dual Sonion electrostatic drivers for the ultra-highs” (Headfonics, Unique Melody MEST MKII review).
What is a bone-conduction driver in an IEM?
A bone-conduction (BC) driver inside an IEM vibrates the shell itself, and that vibration reaches you through the shell’s contact with your ear rather than only as sound in the air. It sits alongside the normal drivers and is a different thing from bone-conduction headphones, which rest on your cheekbones and leave the ear open. Eight Unique Melody models carry one or more, and where the band is published it is 200 Hz–7 kHz for the MEXT’s OBC coil and 500 Hz–16 kHz for the MEST MKIII CF Blue’s silver-palladium piezo driver. Reviewers describe the effect in their own words (Headfonics hears the MKII’s BC driver “adding an additional layer from around the upper bass to the upper treble”), and our guide to bone-conduction drivers in IEMs covers every type in the range.
What about planar magnetic and MEMS drivers?
A planar magnetic driver uses a thin, flat film with a conductive trace printed on it, held between magnets, so the drive force spreads across the whole surface instead of one coil. A MEMS driver (micro-electro-mechanical system) is a tiny driver made on a silicon chip, with the same chip-making methods as the microphones in many phones.
Planar IEMs exist from other brands, and forum guides often add that planars can need more power than a phone gives. Unique Melody does not sell a planar earphone. In the range, both technologies appear only in the Umbral open-back headphones, which pair a 96 mm planar magnetic driver with a MEMS tweeter rated to 80 kHz (65 Ω, 84 dB/mW).
What do hybrid, tribrid and quad-brid mean?
These labels count driver families, not drivers. A hybrid IEM mixes two or more families; a tribrid mixes three, usually dynamic + BA + EST; and “quad-brid” is an informal name for four families in one shell. Shops use the words loosely, so read the actual configuration.
Counted that way, the 2HT and Stardust are hybrids (dynamic + BA). The MEXT mixes three families, dynamic + BA + BC, but not the usual tribrid recipe. The MEST MKII, MEST MKIII CF Blue, MEST Jet Black, Maven III Moonshard and MEST Fortune combine all four: dynamic, BA, EST and BC.
Two models break the pattern. The Multiverse Mentor and Mason FS are hybrids with no dynamic driver (12 BA + 1 BC), while the 3DT has three drivers but only one family. Where a crossover is published, it is 4-way on the Stardust, 5-way on the MEST MKIII CF Blue, The Multiverse Mentor and Mason FS, and 4-way plus a separate 2-way for the BC drivers on the MEST Jet Black. More families do not mean better sound, and our guide on how many drivers an IEM needs explains why.
Which driver types does each Unique Melody model use?
The table sums up each driver family: how it works, the job it usually does in a shell and the Unique Melody models that use it. For the full model-by-model picture with prices and plugs, see our range guide on which Unique Melody IEM suits you.
| Driver family | How it works | Typical role | Unique Melody models using it (per side) |
|---|---|---|---|
| Dynamic (DD) | Voice coil pushes a diaphragm in a magnetic field | Bass, or full range in single-driver designs | From The Start (1, size not stated), 2HT (1 × 10 mm), 3DT (2 × 7 mm + 1 × 10 mm CNT), Stardust (2), MEXT (1), MEST MKII (1 × 10 mm), MEST MKIII CF Blue (1), MEST Jet Black (1), Maven III Moonshard (2), MEST Fortune (1) |
| Balanced armature (BA) | Pivoting armature drives a small diaphragm in a sealed box | Mids and treble, or every band in multi-BA designs | 2HT (1); Stardust, MEXT, MEST MKII, MEST MKIII CF Blue, MEST Jet Black, Maven III Moonshard, MEST Fortune (4 each); The Multiverse Mentor, Mason FS (12 each) |
| Electrostatic (EST) | Charged electret membrane moves between plates, fed by a miniature transformer | Supertweeter, top octaves only | MEST MKII, MEST Jet Black, MEST Fortune (2 each); MEST MKIII CF Blue, Maven III Moonshard (4 each) |
| Bone conduction (BC) | Driver vibrates the shell | Adds a band felt through the shell (band per model, where stated) | MEXT (1), MEST MKII (1), MEST MKIII CF Blue (1), MEST Jet Black (3), Maven III Moonshard (2), MEST Fortune (3), The Multiverse Mentor (1), Mason FS (1) |
| Planar magnetic | Flat film with a printed conductor between magnets | Full range in headphones | None of the earphones; only the Umbral open-back headphones (96 mm) |
| MEMS | Silicon-chip micro driver | Tweeter | None of the earphones; only the Umbral open-back headphones (to 80 kHz) |
Does the driver type decide how an IEM sounds?
Only in part. The driver type sets what is physically possible, but tuning, the crossover, the shell’s acoustic design, the ear tips and the fit in your ear decide what you actually hear. A common line on IEM forums puts it simply: two dynamic-driver IEMs can sound completely opposite.
Published frequency ranges show the same thing. The MEST MKII, MEST MKIII CF Blue and MEST Jet Black state 20 Hz–70 kHz, The Multiverse Mentor 20 Hz–40 kHz and the 3DT 20 Hz–20 kHz. These numbers say how far a driver can reach, not how good it sounds, and the shape of the response inside the audible band tells you far more. Our guide on how to read an IEM frequency response graph shows where to look.
Fit comes first in practice. A BA-heavy IEM with a poor seal will sound thin whatever its driver count, so try every tip size in the box before you judge any driver.
What does this mean when you buy?
What it means when you buy
Choose a sound, not a driver count. A single dynamic driver can suit you better than twelve BAs. Use the driver list to understand a design, then decide on tuning, fit, plug and price.
Want to hear each family on its own? The 3DT is all-dynamic, the 12-BA designs (The Multiverse Mentor and Mason FS) show BAs plus bone conduction, and the MEST models combine all four families.
Check the plug. Five models ship with a 4.4 mm balanced cable only, so a phone needs a 4.4 mm dongle. Our guide on how to choose in-ear monitors in the UK covers fit, plug and source step by step.
Prices run from £179 (From The Start) to £7,649 (Mason FS) incl. UK VAT. To compare every model with photos and full UK terms, see our page for Unique Melody in-ear monitors (UK).
Which IEM driver type is right for you?
Pick by the sound you want and the source you own, not by the letters on the spec sheet. If you love weight in the low end, a design that gives the bass to a dynamic driver is the obvious place to start. If treble detail is your thing, look at the EST models, and if you are curious about the shell-borne layer reviewers write about, look for bone conduction.
Then get the fit right with the tips in the box and judge the result with your own music.
His connection to hearing protection stems from personal experience with sound sensitivity during live events and work in noisy environments, an issue that made him more aware of the long-term risks of unmanaged noise exposure. Today, as both a communicator and a user of BOLLSEN products, he is passionate about raising awareness around the importance of proactive hearing care.
At BOLLSEN, he develops data-driven marketing campaigns, writes SEO-focused articles, and manages communication channels that connect customers with practical knowledge about hearing protection. His work ensures that BOLLSEN’s message—prioritizing health, performance, and sustainability reaches a global audience in an engaging and trustworthy way.
Passionate about writing since childhood, Timotej combines creativity with a strong analytical approach, continuously testing new ideas in digital marketing, performance advertising, and social media. He believes in learning through innovation and collaboration, balancing leadership with openness to new perspectives.
Beyond his professional role, Timotej is committed to a healthy lifestyle and finds inspiration in fitness, sports, and quality time with friends. His personal passion for well-being aligns with BOLLSEN’s core values, making his work not only a career but also a cause he deeply believes in.
