Premium Open-Back HiFi IEM Earphones for Audiophile Listening

The Fosi Audio IM4 Open-Back In-Ear Monitor is a high-performance audiophile IEM engineered for listeners who demand exceptional clarity, natural tuning, and long-lasting comfort. Featuring a powerful 10mm N52 dual-magnet dual-cavity dynamic driver with a beryllium-coated diaphragm, the IM4 delivers detailed sound, expansive staging, and fatigue-free listening for music enthusiasts, gamers, studio monitoring, and portable HiFi setups.

Designed with an advanced open-back acoustic structure, customizable tuning nozzles, and premium CNC aluminum construction, the IM4 combines reference-grade audio performance with modern minimalist aesthetics.

Dual Magnet & Dual Chamber Acoustic Design

The IM4 uses a specially engineered N52 dual-magnet dual-cavity dynamic driver system to deliver greater driver control, faster transient response, and improved sonic accuracy.

Core Audio Technologies:

• 10mm dynamic driver
• N52 dual-magnet structure
• Dual acoustic chamber design
• PU beryllium-coated diaphragm
• Open-back airflow architecture

This advanced driver configuration produces:

• Wide and spacious soundstage
• Powerful yet controlled bass
• Natural mids and vocals
• Smooth treble detail
• Excellent instrument separation

Perfect for:

• HiFi music listening
• Audiophile portable setups
• Lossless audio playback
• Gaming immersion
• Studio reference monitoring

Balanced Tuning with Fatigue-Free Listening

Unlike aggressive V-shaped tunings, the IM4 is designed for natural long-session listening comfort.

The open-back structure combined with acoustic damping wool minimizes:

• Resonance
• Treble harshness
• Ear pressure buildup
• Listening fatigue

The result is a relaxed, airy, and balanced presentation ideal for extended listening sessions across multiple music genres including jazz, classical, rock, electronic, vocal, and acoustic recordings.

Open-Back IEM Design for Wider Soundstage

The semi-open acoustic architecture helps create a more speaker-like listening experience with improved spatial presentation and natural airflow.

Benefits of the open-back design include:

• Larger perceived soundstage
• Improved imaging accuracy
• Better instrument positioning
• More natural vocal presentation
• Reduced enclosed-ear sensation

This makes the IM4 ideal for listeners seeking a spacious and immersive audio experience rarely found in traditional closed IEMs.

Lightweight Ergonomic Comfort for Daily Use

Built for extended wear, each earpiece weighs only 7g, making the IM4 exceptionally lightweight and comfortable for long listening sessions.

Comfort Features:

• Ergonomic shell contour
• Hypoallergenic smooth metal finish
• Lightweight aluminum construction
• Secure in-ear fit
• Reduced ear fatigue

Perfect for:

• Daily commuting
• Portable DAC setups
• Work sessions
• Music production
• Long gaming sessions

Premium CNC Aluminum Construction

The IM4 showcases premium craftsmanship with a precision-machined 6063 CNC aluminum alloy shell.

Design Highlights:

• CNC-machined aluminum body
• Durable metal construction
• Distinctive orange metal grille
• Minimalist audiophile styling
• Excellent long-term durability

The aluminum housing also contributes to improved acoustic stability and resonance control while maintaining a premium modern appearance.

Customizable Sound Signature

Tailor the sound profile to your personal listening preferences using the included tuning accessories.

Included Audio Tuning Options:

Ear Tips:

• Bass
• Deep Bass
• Balanced

Sound Nozzles:

• Brass nozzle
• Aluminum nozzle

This allows users to adjust:

• Bass response
• Treble energy
• Vocal warmth
• Overall tonal balance

A rare feature for audiophile IEMs at this level.

Detachable 2-Pin Audiophile Cable

The IM4 includes a premium detachable cable system for better durability and upgrade flexibility.

Cable Features:

• 2-PIN 0.78mm connector
• 4-core 392-strand cable
• 5N OFC silver-plated copper
• Low signal loss design
• 3.5mm gold-plated plug

The detachable design enables:

• Easy cable replacement
• Balanced cable upgrades
• Longer product lifespan
• Portable DAC compatibility

Technical Specifications

• Shell Material: 6063 CNC Aluminum Alloy
• Driver Unit: 10mm N52 Dual-Magnet Dual-Cavity Dynamic Driver
• Diaphragm: PU Beryllium-coated Diaphragm
• Sensitivity: 109dB
• Impedance: 21Ω
• Frequency Response: 20Hz–20kHz
• Connector: 2-PIN 0.78mm
• Cable: 4-core 392-strand 5N OFC Silver-plated Copper Cable
• Audio Jack: 3.5mm Gold-plated Plug
• Weight per Earbud: 7g ±0.5g
• Total Weight with Cable: 38g ±1g

Features

• Open-back audiophile IEM design
• Dual-magnet dynamic driver
• Beryllium-coated diaphragm
• Wide soundstage and detailed imaging
• Balanced fatigue-free tuning
• Detachable 2-pin cable
• CNC aluminum alloy shell
• Customizable sound nozzles
• Multiple ear tip options
• Lightweight ergonomic comfort

Select Options	IM4-Obsidian, IM4-Galaxy