The Fosi Audio IM4 offers the simplicity of wired earphones: no battery, no charging and no wireless pairing required. Using the included cable, it can be connected directly to a compatible audio source equipped with a 3.5 mm headphone output.

The open-back design, carefully tuned dynamic driver and customizable accessories deliver natural, balanced sound that remains comfortable during extended listening sessions.

The IM4 uses a 10 mm N52 dual-magnet, dual-chamber dynamic driver. The dual-magnet system provides powerful control, while the dual-chamber acoustic architecture helps produce balanced sound reproduction.

The PU-based, beryllium-coated diaphragm is designed to reproduce a wide soundstage and crisp details with precision. Its 20 Hz to 20 kHz frequency response covers the audible frequency range.

The open-back design reduces internal sound reflections and pressure buildup inside the housing, resulting in a more open, natural presentation and a more spacious soundstage.

Acoustic damping reduces resonance and excessive harshness, contributing to a more relaxed, less fatiguing sound. The design is intended to maintain a balanced sound signature during extended listening sessions.

The IM4 is tuned to deliver balanced bass, midrange and treble. Clear vocals, rich detail and smooth high frequencies make the in-ear monitor suitable for listening to a wide range of musical genres.

The open acoustic design and carefully controlled sound signature aim to reduce listening fatigue. This makes the IM4 a comfortable choice for both shorter listening sessions and longer, more immersive use.

The interchangeable aluminum and brass sound nozzles allow the IM4 sound signature to be tailored to individual preferences. The aluminum sound nozzle reduces sibilance and delivers a stronger sense of bass.

The brass sound nozzle, by contrast, is tuned for clearer midrange and treble. By easily switching between the two options, listeners can select the setting that better suits their music, audio source and personal listening preferences.

The IM4 offers three types of ear tips with different sound characteristics: Balanced, Bass and Deep Bass. The different designs allow the fit and perceived bass response to be refined further.

All three ear tip types are available in three sizes, making it easier to find the right option for the ear canal. The correct size can provide a more secure fit, greater wearing stability and more consistent sound.

The ergonomic IM4 housing was developed using data from millions of ear shapes. Its form is designed to provide a secure fit and all-day comfort while keeping the earphones firmly positioned in the ears.

The hollow structure reduces weight, bringing each earpiece to just 7 g ±0.5 g. The lightweight construction and smooth, skin-friendly metal finish help reduce pressure on the ears during extended use.

The IM4 housing is precision CNC-machined from a single block of 6063 aluminum alloy. The all-aluminum construction provides a solid structure, smooth feel and clean, minimalist appearance.

The distinctive orange metal grille and logo give the in-ear monitor an instantly recognizable appearance. The open grille structure is also a defining element of the IM4 acoustic design.

The detachable cable connects to the earphones using 2-pin 0.78 mm connectors. The replaceable design makes it easier to substitute the cable and also allows compatible alternative cables to be used.

The included four-core cable comprises a total of 392 strands of 5N-purity silver-plated OFC conductors and terminates in a gold-plated 3.5 mm plug. The combined weight of the earphones and cable is 38 g ±1 g.