How Many Drivers Does an IEM Need? Why More Is Not Automatically Better

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Key Takeaways

How many drivers does an IEM need? As many as its design calls for, and sometimes that is one. One well-tuned dynamic driver can be all an in-ear monitor needs; extra drivers split the work into bands. Tuning, the crossover and the fit in your ear matter more than the number on the box.

At Bollsen, we are the official UK and EU partner of Unique Melody, and our range runs from 1 driver per side to 13. So we see where extra drivers help and where they mostly add complexity. New to the category? Start with what are in-ear monitors, and for what each driver family does, read IEM driver types explained. Here the question is just how many, and how they share the work.

In our view, a driver count is easy to print on a box and hard to hear. Two IEMs with the same count can sound nothing alike, and for some listeners one dynamic driver simply sounds better than a 13-driver design.

What does an extra driver actually add?

An extra driver lets the designer split the frequency range, so each driver plays a narrower band it suits instead of covering everything from deep bass to the top octaves. That can buy extension at either end, or let two drivers share one busy band.

Small parts made this possible. Sonion, a maker of balanced armature receivers, notes in its guide to designing earphones with balanced armature receivers that their small size makes it “possible to place multiple transducers in a single housing”. The same guide adds a warning: “A small mistake may cause inexplicable results.”

Count and family are separate things. The 3DT has 3 drivers from one family (all dynamic); the Mason FS has 13 from two, twelve balanced armatures plus one bone-conduction driver.

What is a crossover, and what do 4-way and 5-way mean?

A crossover is a small filter network that splits the signal into frequency bands and sends each band to the drivers built for it. The number of “ways” is the number of bands, not drivers. Our Stardust has 6 drivers per side (2 dynamic for sub-bass and bass, 4 balanced armatures) on a 4-way crossover.

Where two bands meet, both drivers play the same notes for a while, and if their outputs arrive out of step they partly cancel or pile up. Sonion’s guide puts it plainly: “Phase and delay issues resulting from the crossover can make the earphone sound muddy”. It notes that “6 and 12 dB per octave crossovers are common” and that “High order crossovers will not fit” in an earphone.

The timing window is tiny. Jerry Harvey of JH Audio said in an interview published by The Absolute Sound that “it is impossible to build a phase coherent IEM without making sure sounds from the drivers all arrive within .01ms of each other.” Every extra band is one more place where that has to hold. Done well, though, a crossover earns its place: in Sonion’s words, a good one will “keep the kick drum out of the vocals”.

How does the Unique Melody range go from 1 driver to 13?

Our range works as a ladder. From The Start (£179) has 1 dynamic driver per side and no crossover at all. The 2HT (£279) pairs a 10 mm dynamic driver with one balanced armature, the 3DT (£359) uses 3 dynamic drivers and the Stardust (£719) has 6 on a 4-way crossover.

Several models sit at 10. The MEST MKIII CF Blue has 10 drivers on a 5-way crossover, and the MEST Jet Black has 10 on a 4-way air crossover plus a separate 2-way crossover for its 3 bone-conduction drivers. The Maven III Moonshard carries 12.

At the top, The Multiverse Mentor (£4,049) and Mason FS (£7,649) each carry 13 drivers per side: twelve BAs and one bone-conduction driver, on a 5-way crossover. Reviewing the custom Mentor, Headfonics gave the split: “The precise grouping is 4 BA drivers for the lows, 2 for the mids, 2 more for the mid-highs, and 4 for the highs and ultra-highs with a 5-way crossover.”

So 13 drivers make 5 bands, with up to 4 armatures stacked on one. Count does not track price neatly either. The Maven III Moonshard has 12 drivers at £1,979, the MEST Fortune 10 at £2,429, and the two 13-driver models sit £3,600 apart.

How many drivers suit the way you listen?

No driver count suits everyone, but each band of counts tends to buy something and cost something. Our models are listed where one fits.

Read the middle column as possibilities, not promises. A 5-way design can be tuned in a way you dislike, and one driver in a way you love. On stage, in our view, a clear, stable mix and a good seal matter more than the count.

What decides the sound more than the driver count?

Tuning decides more than the count. That means the designer’s target, the crossover, the nozzle, tubes and dampers, and then the seal in your ear. Sonion’s guide notes that “2 pairs of earphones can have the same frequency response but still sound very different”, so even a measured graph does not tell the whole story.

A graph still tells you far more than a driver list. It shows where the bass sits and where the treble peaks, whatever hardware made them. Our guide on how to read an IEM frequency response graph shows where to look.

Fit comes first in practice. A pair that does not seal sounds thin whatever its count, so try every tip size in the box first.

What do more drivers cost you?

More drivers cost complexity first. Each extra band adds crossover parts and another hand-off to align in phase and time, and each extra driver takes space, which can push the shell size up. Impedance varies too: 11.7 Ω on the Stardust, 23.8 Ω on From The Start and 22 Ω on The Multiverse Mentor, so the count says nothing about how easy a pair is to drive.

Then there is price: £4,049 and £7,649 for our two 13-driver models against £179 for From The Start, though part of that gap pays for shells, cables and hand finishing as well as drivers. Our guide on how much to spend on IEMs breaks the tiers down.

Is a single dynamic driver IEM good?

A single dynamic driver IEM can be very good, because one driver needs no crossover and so has no hand-off between drivers to get wrong. Its limit is that one diaphragm has to cover the whole range, which puts the full weight on tuning and fit.

Crinacle’s In-Ear Fidelity IEM rankings state that “The IEMs are ranked purely by sonic performance”, and the list places single-dynamic designs such as the Sennheiser IE600 (setup “DD”, rank A+) in its A grades. Crinacle adds that “The letter ranks are NOT according to price-to-performance value”, so read it as one reviewer’s view.

Our From The Start is one dynamic driver at 23.8 Ω and 106 dB, with a 4.4 mm balanced cable only, so a phone needs a 4.4 mm dongle DAC.

How do you read a driver list on a spec sheet?

Read a driver list in four passes. Take a line such as “1 DD + 4 BA + 2 EST + 1 BC” as the example.

1. Count. Add up the drivers (8 here) and check whether the figure is per side or for the pair.
2. Families. Note which types are present: dynamic (DD), balanced armature (BA), electrostatic (EST) and bone conduction (BC).
3. Ways. Look for the crossover. A 4-way or 5-way figure tells you how many bands the drivers share; if it is not stated, the count alone cannot tell you.
4. What is missing. Tuning, dampers, impedance, sensitivity and fit are not in the list. Look for a frequency response graph and the tip options.

So how many drivers does an IEM need?

One can be enough, and 13 can be right too. Choose by the tuning you like, the fit and your source, and read the driver count as a description of the design, not a score.

If you are comparing models rather than counts, how to choose in-ear monitors in the UK walks through fit, plugs and budgets. When you are ready to listen, shop the Unique Melody range and compare the models side by side.