Fosi Audio has been keeping busy in 2025. After recently rolling out the ZH3 all-in-one desktop unit, the brand’s first-ever subwoofer, the SW10, and even a new Luna3 turntable, the company is shifting gears again—this time into in-ear monitors. The new IM4 is Fosi’s first IEM release, and it’s available now at Amazon for $110.

For a company known mostly for amps, DACs, and desktop gear, jumping into the IEM market is a big step. The IM4 is designed to appeal to listeners who still prefer wired earphones, even as wireless earbuds dominate pockets and purses. High-end IEMs can easily reach into the thousands, but Fosi is taking a different approach by aiming for affordability without stripping away useful features.

So who’s the IM4 for? It’s aimed at people who want a solid wired listening option, a more natural sound, and some flexibility to adjust how their earphones perform—all without breaking the bank.

“The IM4 is a milestone in our journey of earphone development, our first step in this category made with sincerity and care,” said Ryan Huang, founder and CEO of Fosi Audio. “With its natural, open sound and lightweight comfort, the IM4 is ideal 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,’ a declaration of support and identity that reflects our spirit of openness and our commitment to listening closely to the feedback and ideas of listeners worldwide.”

The IM4 is built around a 10mm beryllium-coated diaphragm driver. That’s paired with an N52 dual-magnet system to give the drivers more control and consistency. Supporting it all is a dual-chamber acoustic design: one chamber has nine ports to help balance frequencies, while the other uses damping materials to tame distortion.

In simpler terms, the setup is there to keep the bass tight, the mids clear, and the highs smooth, something that can be tricky to pull off at this price.

What really stands out here is the open-back architecture. Most IEMs are closed, sealing you off from the outside world, but the IM4 is designed to let sound breathe a bit more. That creates a wider soundstage, closer to what you’d expect from a pair of full-size open-back headphones.

The trade-off, of course, is less isolation from outside noise, but for at-home listening or quiet spaces, the payoff is a more open, natural presentation.

Physically, the earpieces are CNC-machined from aluminum, weigh just 7 grams each, and are shaped to fit comfortably for longer listening sessions.

Fosi has also added a layer of customization. The IM4 ships with three sets of ear tips—balanced, bass, and deep bass—so you can nudge the sound in different directions depending on your taste.

On top of that, there are interchangeable nozzles in aluminum and brass. These further tweak the tuning, letting you shift toward smoother highs or more energetic treble and bass. It’s a simple but effective way to make the same pair of earphones work for different genres or moods.

Out of the box, the IM4 includes detachable cables that end in both 3.5mm and 4.4mm connectors. That means they’ll plug into just about anything—your phone (with the right dongle), a portable player, or a desktop amp/DAC.

The cables are made from oxygen-free copper (OFC) with silver plating, which helps reduce interference and maintain clean signal transmission. And because they’re detachable, you can replace or upgrade them if needed.

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.
• Ear tips: Three sets for balanced, bass and deep bass
• Cables: Detachable 3.5mm and 4.4mm connections.
• Frequency response: 20Hz – 20kHz.
• Impedance: 21Ω.
• Sensitivity: 109dB/mW.

The IEM space is crowded, but it tends to skew either very cheap or very expensive. With the IM4, Fosi is carving out a spot in the middle—an option for listeners who want more than budget earbuds but don’t want to dive into four-figure territory.

It also shows where Fosi is heading as a brand. With products now spanning turntables, amps, subwoofers, headphones, and IEMs, the company seems intent on building a lineup that covers every type of listening setup, from desktop systems to portable gear.

The Fosi Audio IM4 will be available in Black and Silver finishes, priced at $110 at Amazon. It joins a growing collection of 2025 releases that show Fosi is expanding beyond its roots and offering listeners more ways to enjoy their music.