Fosi Audio is expanding its affordable Hi-Fi range with the introduction of its first ever IEMs. The IM4 buds are made of aluminium alloy, with 10mm dynamic drivers and an open-back design.
Remarkably for their tech, they are currently priced at £59 / $79 / €68.
Fosi Audio is expanding into another sector of the Hi-Fi market: headphones. And like its headphone amps and turntable, the goal is to deliver high-end specs without a sky-high price.
The Fosi Audio IM4 IEMs are its first in-ear monitors (IEMs) and are currently available to preorder on Kickstarter with a price in Hong Kong dollars that works out at roughly £59 / $79 / €68 / AU$119. That's an early bird discount, but the full price is still-low at £82 / $99 / €85 / AU$149.
These IEMs are open-backed, which is relatively uncommon among rivals in this price bracket. The upside is the promise of a wider, more natural sound stage and the downside is more dirty looks if you're listening loud on the bus.
Fosi Audio IM4: key features
The IM4 IEMs are made from CNC-machined aluminium alloy and each ear gets a single, dual-magnet 10mm dynamic driver with a PU beryllium-plated diaphragm. This, Fosi says, delivers low distortion, great detail and "a balanced, fatigue-free sound". They also feature "sparkling" treble and tight bass.
Fosi says that its tuning means that the single-driver setup performs just as well as rival multi-driver designs. The rear of the inner chamber is sound-damped to eliminate harshness and resonance peaks and the tuning features a "subtle treble lift".
The two-pin cable is braided with 4 strands of 392-core 5N high-purity OFC silver-plated wire and features a gold-plated connector. And including that cable, the total weight is just 38g, with each IEM weighing a mere 7g.
The package includes two sets of nozzles: aluminium and brass. And there are three sizes of ear tips in three different flavours: balanced, bass and deep bass.
The Fosi Audio IM4 are available to preorder now for shipping in November 2025.
