IEM Drivers, Impedance and Choosing by Signature

IEM listings lead with driver counts: “1DD + 4BA + 2EST”. That line tells you how the earphone is built. It does not tell you how it sounds. The tuning does that, and the tuning is what the part on sound signatures was about.

This post covers what the driver types are, what the impedance and sensitivity numbers on the box mean, and why some IEMs sound different on different players. It ends with picks for each signature.

The driver types

Driver	How it works	Strengths	Weaknesses
Dynamic (DD)	A small cone moved by a voice coil, like a tiny speaker	Natural bass with real weight; coherent from one driver	Treble detail depends heavily on the design
Balanced armature (BA)	A tiny reed balanced in a magnetic field drives a diaphragm	Small, precise, efficient; good for mids and treble	Usually covers only part of the range; bass can feel light
Planar magnetic	A thin film with a printed conductor sits between magnets	Fast, clean treble; low distortion	Less sensitive; small IEM planars are mostly used for treble
Electrostatic (EST)	A charged film between two plates; needs a step-up transformer inside the shell	Airy upper treble	Only used as a “super-tweeter” in IEMs
Bone conduction (BC)	Vibrates the shell, so some sound reaches you through the ear’s bone	Adds a sense of physical bass texture	Rare, and its effect is hard to measure
Piezoelectric (PZT)	A crystal that flexes when voltage is applied	Cheap way to extend treble	Can sound metallic if poorly tuned

Hybrids and tribrids

Most IEMs above about $50 mix driver types. A hybrid pairs a dynamic driver for bass with BAs for mids and treble. A tribrid adds a third type, usually EST or planar for the top octave. Some sets now use four types; makers call them “quadbrids”.

A crossover splits the signal between the drivers. Sometimes it is electrical (capacitors and resistors), sometimes acoustic (tube lengths and filters). Every split is a place where drivers can disagree on timing and level.

More drivers is not better

Adding drivers gives the designer more control over each band. It does not raise quality by itself.

• Coherence suffers first. One good dynamic driver plays the whole range with one timing. Eight drivers must be blended so you cannot hear the joins.
• The crossover makes impedance uneven. That ties the sound to the source (see below).
• Cost goes up faster than sound quality. Many of the best-measured budget sets use one dynamic driver, or one DD and a couple of BAs.

Choose by the frequency-response graph and the signature you want. Treat the driver count as a hint about how the IEM was engineered, not a score.

Impedance and sensitivity

Two numbers on the spec sheet matter for pairing.

Spec	Unit	What it tells you
Impedance	ohms (Ω)	How hard the IEM resists the current from the player. Most IEMs are low impedance, in the tens of ohms.
Sensitivity	dB/mW or dB/V	How loud the IEM plays for a given input. Higher means less power needed.

Almost any modern source can drive an IEM loud enough. A low-impedance, high-sensitivity IEM can even reveal background hiss from a noisy player. Volume is rarely the problem. The tuning change is.

The impedance curve

The single impedance figure on the box is measured at one frequency, usually 1 kHz. The real impedance changes across the range. That shape is the impedance curve.

• A single dynamic driver has a nearly flat curve. It sounds the same on almost any source.
• A multi-BA or hybrid set has a curve with peaks and dips, created by the crossover. As an illustration, a set could read 30 Ω in the bass and under 10 Ω in the treble.

Why multi-BA sets are source-sensitive

The player’s output has its own impedance, in series with the IEM. Together they form a voltage divider. Where the IEM’s impedance is low, more of the signal is lost across the player’s output; where it is high, less is lost.

With a flat-impedance IEM, that loss is the same at every frequency, so you just turn the volume up. With an uneven curve, the loss is different at each frequency, so the tuning itself changes. Bass can swell or treble can drop by a few decibels, enough to move an IEM one step along the signature table.

The rule of thumb, and how to check a player against it, is in the part on sources. The short version: a source with near-zero output impedance plays every IEM as tuned. An older player with a few ohms of output impedance is safest with a single dynamic driver or a small hybrid.

That is why I keep the iPod Video and a modern Sony Walkman in separate columns below.

Picks by signature

Prices are USD list prices found on 2026-10-26; check a retailer before buying. Driver layouts come from retailer or aggregator listings. Where sources disagree, the table says so.

Signature	Tier	IEM	Price	Drivers	Best on
Neutral / Harman	Premium	Softears RSV	$730	All-BA (count approx.)	Low-impedance source
Neutral / Harman	Value	Crinear Daybreak	$170	1 DD + 2 BA + 2 micro-planar	Both
Bass-heavy, quality	Premium	Thieaudio Origin	$849	1 DD + 4 BA + 2 EST + 1 BC	Low-impedance source
Bass-heavy	Value	Softears Volume S	$319	2 DD + 2 BA (some sources list 1 DD + 2 BA + passive radiator)	Both
V-shape	Value	Simgot SuperMix 4	$150	1 DD + 1 BA + 1 planar + 1 PZT	Both
Vocal / mid-forward	Value	Truthear Hexa	$80	1 DD + 3 BA	Both
Budget, neutral-bright	Value	Truthear Gate	about $22	1 DD	Both

I left out premium picks for bright, V-shape and vocal tunings. I could not confirm current prices and driver layouts for the sets I had in mind, and a guessed spec is worse than no spec.

How I would choose

• Purist who sometimes wants bass: start with the Daybreak. Use a gentle low-shelf on the player when you want weight. If you find yourself using that shelf every day, the Volume S or Origin is the next step.
• Older player with some output impedance: stay with the Gate, Hexa or Daybreak. Fewer crossovers means less tuning drift.
• Modern low-impedance player: the RSV and Origin become safe choices.
• Not sure what you like: buy the Gate first. At about $22 it is a cheap way to learn whether neutral suits you.

What comes next

The next part covers fit, eartips and cables. Tips change bass and treble more than most cable or source upgrades, so they come before spending more money on drivers.

Sources

• Crinear Daybreak, headphones.com
• Thieaudio Origin, headphones.com
• Thieaudio Origin specs, IEM Ranking
• Softears Volume S, headphones.com
• Softears Volume S review, The Metal Verse
• Softears RSV review, Headfonics
• Simgot SuperMix 4 review, Headphoneer
• Truthear Hexa specs, IEM Ranking
• Truthear Gate, SoundGuys