Balanced-armature (BA) and dynamic drivers are the two main ways an in-ear monitor turns electricity into sound. A dynamic driver uses a magnet and voice coil to push a flexible diaphragm, the same principle as a full-size speaker shrunk down, and it moves a lot of air, so it does bass well. A balanced armature is a tiny, sealed transducer that pivots a metal reed between magnets to vibrate a much smaller diaphragm. It’s fast and precise in the mids and treble but moves very little air. Hybrids put both in one shell so a dynamic handles the low end while several BAs cover the detail up top. You’ll see them labeled by count, like “1DD+4BA.”
That’s the short version. Here’s how each actually works, and why the driver-count spec on the box matters less than people think.
How a dynamic driver works
A dynamic driver is a miniature loudspeaker. A coil of wire (the voice coil) sits in a magnetic field and is glued to a thin diaphragm. Feed the coil an audio signal and it becomes an electromagnet that gets pushed and pulled by the fixed magnet, dragging the diaphragm back and forth. That moving diaphragm pumps air, and moving air is sound.
The key trait is that a dynamic diaphragm is comparatively large, anywhere from about 6mm to 10mm-plus across in an IEM, so it displaces real volume. That’s why single-dynamic IEMs tend to have bass with weight and slam. It’s the technology in most affordable earphones and in plenty of excellent ones. Moondrop built its reputation partly on single-dynamic models like the Aria and the Kato, tuned to its VDSF target curve, which prove you don’t need a fistful of drivers to sound good. One well-engineered dynamic, tuned properly, will beat a badly integrated stack of drivers.
The trade-off is speed and the cost of precision. A larger diaphragm has more mass to start and stop, and covering the entire frequency range with one moving surface means compromises at the extremes.
What a balanced armature is
A balanced armature (BA) is a sealed, sesame-seed-sized transducer originally built for hearing aids. Inside sits a tiny iron reed, the armature, suspended between two magnets. When it’s centered, the magnetic pull on each side is equal, or “balanced,” which is where the name comes from. Audio signal running through a surrounding coil tips the armature one way or the other, and a stiff drive rod links that motion to a small diaphragm.
Because the moving parts are minuscule and the whole thing is sealed and precisely tuned, a BA is quick and resolving. It excels at midrange clarity and treble detail. But that small diaphragm moves almost no air, so a single BA can’t produce satisfying sub-bass on its own. Makers get around this by using several BAs, each tuned to a slice of the spectrum (a woofer BA, mids BAs, tweeter BAs) with crossovers and internal acoustic tubes routing sound to the nozzle. That’s why you see all-BA IEMs advertised with high driver counts.
Some designers have pushed BA design further. 64 Audio patented tia (Tubeless In-Ear Architecture), an openly radiating BA driver that ditches the traditional sound tube to reduce resonance, used in reference models like the U12t and the Fourte. It’s the same underlying transducer with cleverer plumbing.
Why hybrids (2DD+4BA and so on) exist
Because each driver type is better at one job. Ask a dynamic driver to do delicate treble and it’s fighting its own mass; ask a balanced armature to do room-shaking bass and it can’t move enough air. A hybrid assigns the work to the tool suited to it: a dynamic driver handles the lows, and multiple BAs handle mids and highs. A tribrid adds a third type, usually an electrostatic (EST) driver, dedicated to the very top octaves.
Moondrop’s Blessing 2 is a well-known hybrid that helped set the template for reference-style multi-driver tuning; its Variations is a tribrid pairing a dynamic, BAs, and electrostatic drivers. On the summit-fi side, brands like Empire Ears and Noble Audio use Sonion’s electrostatic drivers to extend treble in flagship IEMs such as the Noble Shogun.
The caveat worth repeating: driver count is not a quality score. A “2DD+4BA” label tells you the parts list, not how well the crossover blends them or whether the tuning is any good. Integration is the hard part, and it’s invisible on a spec sheet. Plenty of three-driver IEMs outclass eight-driver ones. Read measurements and trust your ears over the number on the box.
Who actually makes BA drivers
Almost nobody who sells you an IEM makes their own balanced armatures. It’s a specialized micro-acoustics business dominated by two suppliers.
Knowles is the original. The Illinois company, founded in 1946 by acoustical engineer Hugh S. Knowles, pioneered the miniature balanced armature receiver for hearing aids in the 1950s, and its BA drivers sit inside a large share of the IEM industry. It supplies makers including Campfire Audio, 64 Audio, Shure, and Westone, and co-develops custom drivers with brands (the EJ-33877 it built with FiiO for the FA9, for instance).
Sonion, founded in Denmark in 1974 and now owned by Novo Holdings, is the other giant. It makes BA drivers and the electrostatic receivers used in many flagship hybrids and tribrids. Between them, Knowles and Sonion supply most of the BAs in premium in-ears.
There’s a third name worth knowing. Bellsing, a Shenzhen maker founded in 2014, produces low-cost BA drivers that turn up throughout budget ChiFi IEMs (KZ and CCA among them), often with model numbers mirroring their Knowles equivalents. That resemblance became a legal matter. In 2021 the U.S. International Trade Commission found Bellsing had misappropriated Knowles’ trade secrets and issued a general exclusion order barring the infringing drivers from U.S. import, which is a big reason Bellsing BAs are common in Asia-market budget gear but scarce in U.S.-sold products.
Knowing who made the driver inside your IEMs, and what that supplier is good at, tells you more than any marketing bullet point. If you want to trace the parts behind the brands, browse our full directory of drivers and component suppliers.
