Fosi Audio, known for its affordable hi-fi audio solutions, has announced the IM4, the company’s first-ever in-ear monitors. With an open-back architecture, lightweight CNC aluminum shell, and extensive customization options, the IM4 delivers natural sound and all-day comfort at an accessible price point.

“The IM4 is a milestone in our journey of earphone development,” said Ryan Huang, Founder and CEO of Fosi Audio. “With its natural, open sound and lightweight design, the IM4 is perfect for everyday listening—whether you are unwinding at home or discovering detail on the go. The name IM4 resonates with the phrase ‘I am for,’ reflecting our spirit of openness and our commitment to listening closely to feedback from users worldwide.”

Fosi Audio IM4

Natural, Spacious Sound

At the heart of the IM4 is a 10mm beryllium-coated diaphragm driver paired with an N52 dual-magnet system and dual-chamber acoustic design. This combination produces smooth highs, detailed mids, and deep, controlled bass with a natural balance suited for music, movies, gaming, and streaming. The open-back design expands the soundstage well beyond typical IEMs, creating an experience closer to full-size headphones while remaining portable.

Comfort and Customization

Each earpiece is CNC-machined from aluminum and weighs just 7 grams, ensuring a secure, pressure-free fit that adapts comfortably to different ear shapes. For added flexibility, the IM4 includes:

Fosi Audio IM4
  • Three sets of ear tips (balanced, bass, and deep bass) for sound and comfort customization
  • Swappable aluminum and brass nozzles to fine-tune highs, mids, and bass response
  • Detachable cables in both 3.5mm and 4.4mm versions for wide device compatibility

This level of personalization allows the IM4 to adapt to different genres, listening styles, and user preferences, from relaxed detail-oriented sessions to powerful bass-driven playback.

Technical Specifications

  • Driver: 10mm beryllium-coated diaphragm
  • Magnet: N52 dual-magnet system
  • Acoustic design: Dual-chamber, open-back
  • Housing: CNC-machined aluminum
  • Weight: 7g per earpiece
  • Tuning options: Interchangeable aluminum and brass sound nozzles; three ear tip sets (balanced, bass, deep bass)
  • Cables: Detachable, 3.5mm and 4.4mm connections
  • Frequency response: 20Hz–20kHz
  • Impedance: 21Ω
  • Sensitivity: 109dB/mW

Pricing and Availability

The Fosi Audio IM4 is available from September 30, 2025, in black and silver finishes at an MSRP of $99 USD / CA$135.99 / £89.99 / €99.99.

For more information, visit www.fosiaudio.com

Fosi Audio IM4