Experience open, fatigue-free audio listening with the Fosi Audio IM4. Featuring a 10mm beryllium-coated dynamic driver housed in a 5-axis CNC-machined aluminum shell with an open-back architecture, the IM4 delivers punchy low-end impact, warm organic vocals, and an expansive soundstage.

Key Features

* Beryllium-Coated PU Diaphragm Dynamic Driver
Driven by a 10mm dual-magnetic, dual-cavity dynamic driver with high-strength N52 neodymium magnets, the beryllium-plated PU diaphragm provides rigid driver control, swift transient response, and low harmonic distortion.

* Open-Back Acoustic Shell Architecture
Incorporates open-back rear chamber venting that relieves ear canal pressure, expands soundstage dimensions beyond typical closed-back designs, and reduces long-term listening fatigue.

* Precision CNC 6063 Aluminum Alloy Cavities
Carved from solid 6063-series aluminum alloy using 5-axis CNC milling, the durable, lightweight earpieces offer an ergonomic pseudo-custom fit tailored for long listening sessions.

* Swappable Sound Tuning Nozzles
Customize your treble profile using interchangeable nozzle filters. The stock aluminum nozzles offer a smooth, balanced presentation, while the brass nozzles add extra clarity and upper-midrange presence.

* High-Purity Detachable Silver-Plated Cable
Includes a 4-core, 392-strand 5N oxygen-free copper silver-plated cable featuring standard 0.78mm 2-pin connectors and a gold-plated 3.5mm plug for stable signal transmission.

* Easy to Drive Across Mobile and Desktop Sources
With a high sensitivity rating of 109 dB and a 21 Ohm impedance, the IM4 plays cleanly directly from portable DAC dongles, smartphones, or dedicated headphone amplifiers.

What is in the Box

* 1 Pair x Fosi Audio IM4 IEM Earbuds
* 1 x 4-Core 5N OFC Silver-Plated Cable (0.78mm 2-Pin to 3.5mm)
* 2 Pairs x Interchangeable Tuning Nozzles (Aluminum and Brass)
* 3 Pairs x Balanced Eartips (Small, Medium, Large)
* 3 Pairs x Bass Eartips (Small, Medium, Large)
* 1 x Faux Leather Carrying Case
* 1 x User Manual

Technical Specifications

* Driver Unit: 10mm N52 Dual-Magnet Dual-Cavity Dynamic Driver
* Diaphragm Material: Polyurethane (PU) with Beryllium Coating
* Housing Material: 5-Axis CNC-Machined 6063 Aluminum Alloy
* Acoustic Structure: Dual Chamber Open-Back Design
* Frequency Response: 20Hz - 20kHz
* Impedance: 21 Ohms
* Sensitivity: 109 dB/V (92 dB/mW)
* Cable Connector: 0.78mm 2-Pin Detachable
* Plug Termination: 3.5mm Gold-Plated Single-Ended
* Earpiece Weight: 7 grams per earbud