FiiO FH9 Knowles 7 Driver Hybrid In-Ear HiFi Earphone

The FiiO FH9 is a flagship hybrid in-ear monitor and the result of two years of intensive research into getting the most from hybrid designs. Each titanium earpiece holds seven drivers: a 13.6mm dynamic driver with FiiO’s second-generation DLC diaphragm for the bass, and six Knowles balanced armatures for the mids and highs. FiiO’s patented S.Turbo bass tube, a semi-open design and a notch filter against sibilance shape the sound, and three interchangeable filters let you choose the tuning. A pure silver Litz cable with twist-lock 2.5mm, 3.5mm and 4.4mm plugs completes it. The FH9 is Hi-Res Audio certified and won a VGP 2024 Summer Life Style award.

One dynamic driver and six balanced armatures

The 1 dynamic + 6 BA design (seven drivers in total) combines the strengths of each type: a big dynamic driver that reaches the lowest frequencies with ample punch, and a custom set of Knowles balanced armatures that reproduces every last detail. Together they give a rich, detailed soundscape befitting a flagship. As the chief engineer of FiiO’s IEM R&D centre explains, the wide frequency coverage and high energy density of a multi-driver design matter most for the small details, such as the air around strings and percussion, and make instruments and voices sound more solid and more real.

Second-generation DLC bass driver

The FH9 is FiiO’s first hybrid IEM with its self-developed second-generation DLC (diamond-like carbon) bass driver. Compared with the first generation, the magnetic circuit has been redesigned for 20% higher magnetic density, to drive the large 13.6mm diaphragm with even more dynamism. Because DLC is very rigid, with a high damping coefficient, the diaphragm follows the voice coil precisely rather than rippling as weaker materials do, for very fast transients and minimal distortion.

A custom Knowles balanced armature set-up

All six balanced armatures in each earpiece are from Knowles. The highs are handled by Knowles’ proven SWFK-31736. For the midrange drivers, FiiO worked with Knowles for more than two years on how best to combine multiple drivers in perfect harmony, for an absolutely coherent sound.

Supercharged bass with S.Turbo

The bass sound tube uses FiiO’s patented S.Turbo acoustic design (patent ZL2018211416279), which guides sound waves through a turbine-shaped tube to strengthen the bass, making it deep and powerful without being bloated or muddy. It also filters out unwanted higher-frequency sound from the other drivers, for a smoother join between bass and mids.

A notch filter against sibilance

Harsh sibilance often comes from putting drivers into a shell without considering how they interact, which creates unwanted resonances. Using finite element analysis, FiiO designed the FH9’s shell with a notch filter cavity that removes resonances generated in the shell, sound tube and cavity, for a purer, more transparent sound.

Semi-open, for fatigue-free listening

The semi-open acoustic design uses FiiO’s balanced pressure relief between the front and rear cavities. The result is a more natural sound and more comfortable long sessions, with much less pressure on your eardrums.

Three sound filters

The FH9 comes with three interchangeable sound filters, each with its own damping and filter density, so you can choose between three sound signatures:

Titanium, machined to flagship standards

Each earpiece is precisely made from titanium with five-axis CNC machining to tight tolerances. Titanium is beautiful, and its extreme rigidity greatly reduces unwanted harmonics and resonances. The shells feel pleasant against your skin, so you can settle into long listening sessions. Choose black or silver (which FiiO calls grey).

Pure silver cable, twist-lock plugs

The cable is high-purity monocrystalline pure silver, with 8 strands of 28 wires (224 in all), each wire individually insulated and braided in Litz style. Its transparent TPU sheath is environmentally friendly and resists yellowing with age and stiffening in the cold. Twist-lock swappable plugs (2.5mm, 3.5mm and 4.4mm, using a design licensed from FABRILOUS) suit almost any source. The angled stainless steel MMCX connectors make the earpieces easier to connect and more comfortable to wear, with blue and red markings for left and right.

Good to know

• A wealth of ear tips to find your fit: three pairs each of bass, balanced, vocal and SpinFit tips (S, M, L), plus two pairs each of foam and double-flange tips (M). SpinFit tips and the black filters come fitted.
• In the box: FH9, pure silver cable with 2.5mm, 3.5mm and 4.4mm plugs, HB5 carry case, ear tips, red, green and black filters, cleaning brush, MMCX removal tool and magnetic cable clip.
• For FiiO’s four-driver hybrid with tuning switches, see the FiiO FH5s.