Наушники — Fosi Audio IM4

The IM4 is an open-back in-ear monitor from Fosi Audio, the first earphone the company has released, and it is priced at USD 99.99. Each earpiece is machined from 6063 aluminium alloy by CNC and has a vented rear, which relieves pressure inside the housing rather than sealing it. Two colour versions are offered, Obsidian and Galaxy.

Key specs that matter

A single 10 mm dynamic driver sits in each shell. It uses a PU diaphragm with a beryllium coating, driven by a dual-magnet system with N52 magnets inside a dual-cavity structure. Fosi rates sensitivity at 109 dB and impedance at 21 ohm, with a frequency range of 20 Hz to 20 kHz. Each earpiece weighs 7 g, plus or minus 0.5 g, and the complete set with cable comes to 38 g, plus or minus 1 g. The cable detaches at a standard 0.78 mm 2-pin connector and ends in a gold-plated 3.5 mm plug.

Engineering and use context

Two sets of screw-on nozzles change the acoustic output of the housing. The black aluminium pair is fitted as standard, and a gold brass pair is supplied in the box as the other option, so the owner can switch between them without tools beyond the fingers. The supplied cable has four cores with 392 strands of 5N oxygen-free copper plated in silver. Ear tips come in three styles, labelled balanced, bass and deep bass, each in three sizes, which lets the fit and seal be matched to different ear canals. The shell shape was developed from a large set of ear scan data, and the hollowed structure keeps weight low for long sessions at a desk or on a commute. Because the rear is open, the IM4 lets outside noise in and leaks some sound out, making it better suited to quiet rooms than trains or open offices. The package also includes a carrying pouch, a user manual and a quick start guide. No microphone or remote is fitted to the cable, and no wireless module is offered, so the earphone draws no battery and needs no charging.

Pairing

Being sensitive and easy to drive, the IM4 runs from phones, laptops and compact USB dongles, and Fosi itself suggests its MD3 DAC dongle as a plug-and-play partner. At home it also works from the 6.35 mm or 4.4 mm outputs of a desktop unit such as the Fosi ZH3, using an adapter for the single-ended jack or an aftermarket balanced 2-pin cable, and the lowest gain step keeps volume control usable. Any 2-pin cable of the same standard from other makers fits the sockets if a longer lead is needed.

Alternatives

Fosi Audio currently makes no other in-ear monitor or headphone model, so the IM4 has no same-brand alternative in this category.