TAS Commitment
Product Snapshot
🎧 10mm Beryllium-Coated Dynamic Driver – Fast, detailed, and natural sound
🧲 N52 Dual Magnet + Dual Chamber – Better control & wider soundstage
🌬️ Open-Back Design – Airy, fatigue-free listening
🪶 Ultra-Lightweight (7g per ear) – Long-session comfort
🛠️ CNC Aluminum Shell – Premium build with minimalist aesthetics
🎚️ Tunable Sound – Swappable nozzles & multiple eartips
🔌 Detachable 2-Pin Cable – Easy replacement & upgrades
Description
Fosi Audio IM4 Open-Back IEM – Audiophile Clarity, Tuned Your Way
The Fosi Audio IM4 Open-Back IEM is engineered for listeners who crave natural tonality, wide soundstage, and long-session comfort. Built around a 10mm PU beryllium-coated dynamic driver, the IM4 uses an N52 dual-magnet, dual-chamber architecture to deliver fast transients, controlled bass, and articulate mids with airy, detailed highs.
Its open-back acoustic design, combined with internal damping wool, minimizes resonance and listening fatigue—resulting in a relaxed, spacious presentation that feels closer to high-end open headphones than conventional in-ear monitors. Whether you’re a critical audiophile, a music enthusiast, or a creator seeking realism, the IM4 offers a refined yet engaging Hi-Fi sound.
Precision-machined from 6063 CNC aluminum alloy, the IM4 showcases premium craftsmanship with a minimalist aesthetic. The lightweight, ergonomic shells (just 7g per earpiece) ensure all-day comfort, while the striking orange metal grille adds a distinctive visual identity.
Sound personalization is at the core of the IM4. With interchangeable brass and aluminum nozzles and three types of eartips (Balanced, Bass, Deep Bass), you can fine-tune the sound signature to match your music and preferences. A detachable 2-pin 0.78mm cable with high-purity silver-plated OFC conductors ensures reliable connectivity and future upgrade flexibility.
📋 Specifications
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Shell Material: 6063 CNC Aluminum Alloy
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Driver Unit: 10mm N52 Dual-Magnet, Dual-Cavity Dynamic Driver
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Diaphragm: PU Beryllium-Coated
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Sensitivity: 109dB
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Impedance: 21Ω
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Frequency Response: 20Hz – 20kHz
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Cable: 4-Core, 392-Strand 5N OFC Silver-Plated Copper
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Connector: 2-Pin 0.78mm
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Audio Jack: 3.5mm Gold-Plated Plug
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Weight (Per Earbud): 7g ±0.5g
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Weight (With Cable): 38g ±1g
📦 What’s in the Box
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Fosi Audio IM4 Open-Back IEMs
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3.5mm Detachable Cable
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Carrying Pouch
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User Manual & Quick Guide
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Brass Nozzle
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Balanced Ear Tips
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Bass Ear Tips
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Deep Bass Ear Tips
📋 Specifications
Shell Material: 6063 CNC Aluminum Alloy
Driver Unit: 10mm N52 Dual-Magnet, Dual-Cavity Dynamic Driver
Diaphragm: PU Beryllium-Coated
Sensitivity: 109dB
Impedance: 21Ω
Frequency Response: 20Hz – 20kHz
Cable: 4-Core, 392-Strand 5N OFC Silver-Plated Copper
Connector: 2-Pin 0.78mm
Audio Jack: 3.5mm Gold-Plated Plug
Weight (Per Earbud): 7g ±0.5g
Weight (With Cable): 38g ±1g
📦 What’s in the Box
Fosi Audio IM4 Open-Back IEMs
3.5mm Detachable Cable
Carrying Pouch
User Manual & Quick Guide
Brass Nozzle
Balanced Ear Tips
Bass Ear Tips
Deep Bass Ear Tips
Warranty Period: 1 Year from the date of Invoice
Covered: Manufacturing Defects Only
Warranty Form: https://www.theaudiostore.in/pages/warranty-claim-form
Cable: 1-month warranty only for manufacturing defects only
Fosi Audio is a dynamic brand dedicated to providing the most comprehensive range of Hi-Fi audio products in the market. We cater to passionate audiophiles by offering Hi-Fi products, DIY kits, and expert guidance, ensuring an immersive audio experience. Beyond a mere transaction, we foster enduring relationships with our clients, supporting them throughout their audio journey.
Our diverse product lineup includes the Hi-Fi power amplifier, pre-amplifier, headphone amplifier, DAC, music player, Bluetooth receiver, DIY board, DIY chassis, and an array of DIY kits. These meticulously crafted offerings embody our commitment to exceptional sound quality and innovation.
Established in China in 2017, Fosi Audio was founded by a team of devoted audiophiles. Our products have gained significant popularity within the Chinese DIY audio community, amassing a large and dedicated following. To expand our reach beyond borders, we launched this website in 2017 and began offering a selection of products on Amazon under the name "Fosi audio." However, please note that many of our outstanding products are not yet available on this website or Amazon. If you cannot find what you're looking for, simply reach out to us via email, and we will be delighted to assist you in finding the perfect product to meet your needs.
At Fosi Audio, we are not just a brand; we are your partner in achieving audio excellence. Join us on this immersive sonic journey and experience the true essence of Hi-Fi audio.
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OUR HONEST REVIEWS FROM THE CO-FOUNDERS & AUDIOPHILES
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from 7467 reviews
If you are planning to buy your 1st IEM around 1k then you must go with this one no other options are valid against it. And Big thanks to Audio store for quick delivery.
its really good
I’ve been genuinely impressed with this IEM The sound signature feels well-balanced and refined, making it enjoyable across different genres. What stood out most to me is the controlled bass it has enough punch to keep the music engaging It stays tight and clean, which adds depth without sacrificing clarity
Just one cosmic issue which I had is the right shell's rubber has got yellowish I don't know the reason but it is yellowish since I unboxed
The Tanchjim Bunny is a lightweight, premium-looking upgrade cable that prioritizes portability and comfort.
Build: High-purity silver-plated copper with a soft, tangle-free texture.
Ergonomics: Excellent flexibility with zero "memory" (no kinks) and very low microphonics (cable noise).
Sound: Provides a clean, transparent signal with a subtle "perceived" boost in treble clarity.
Best For: Users who hate stiff cables and want a minimalist, comfortable aesthetic for daily commuting.
Verdict: A great buy if you want a "disappearing" cable experience, though the white finish requires extra care to keep clean.
This s my first iem. When i used it first i didnt like tht much . But aftr using this i used my tws i was really shocked to c the diff. Nw this is part of my daily wear.
Make sure to selct ear tip according to ur size. It s really importnt.
Pretty good
I am using it with TANGZU - Waner SG 2 - Red Lion Edition -Type C. I replaced my type C cable with this and now its the beat thing I have done, Obviously with a external DAC
What a great great experience.
Clean and fast bass, balanced mids and crisp highs, loved the bunny. Also, good mic quality.
comfortable to wear. clean, layerd , detailed sound.
This adds wireless convenience to IEMs. Paired it with KZ Castor Pro.
ANC : 3/5
it is an added plus but people using IEM do not usually care about ANC. The passive NC depends on the IEM itself.
Sound quality: 4.5/5
With LDAC support, works pretty good with supported devices. I even tried it with Iphone, works really good. Most normal people wont feel any difference over wired. Audiphiles may feel subtle loss of details. But thats what you compromise for convenience. Gain may seem a bit low compared to a DAC+IEM setup but 70-80% volume is sufficiently loud. The audio tone is neutral and balanced
Comfort: 4.5/5 As comfortable as the IEM itself. Gives a Open Wireless earphone feel in terms of comfort. I have wore it over 8-9 hours intermittently playing songs - didnt feel any bulk.
Case: 1/5 Extremely bulky. Forget about keeping in the pockets when you decide to buy this. But treat it like a IEM case. The feel is plasticky and not premium. The adapter themselves feel premium but not the case.
Battery: 4/5 Decent battery backup.Adapters themselves give around 5-6 hours playback at 70-80% volume.
Overall a worth purchase if you are looking for tws convenience with your IEM.
I never thought I'd ever buy an on-ear headphone considering the nature of these headphones sitting on the ears, but I was pleasantly surprised by how comfortable they are. The delivery was snappy, received way earlier than expected.
Sound wise I'd say these are great, very open and natural sounding with a flat profile but reacts well to EQ. These are not for Hip Hop listeners straight out of the box but the drivers can get boomy with bass boost. I use these with a DAC/Amp and if you are planning to buy them then you truly need one. I'd suggest to get a warm sounding DAC/Amp dongle to bring out the best in these and make them sound musical.
They look nice too. Go for it. But as expected they leak sound, so outdoor usage is not recommended, but if you want natural ambient sound while listening to music on a jog and hate in-ear earbuds then these are perfect.
Really appreciatethe quality of this product as it is really a premium quality product with a touch of nice red led ring light. I have paired this DAC with Moondrop chuu 2 IEM. The sound quality is phenomenal. Worth buying and in my opinion its a value for money.
Hi Team, great product , impeccable service, at reasonable cost. Thanks Audio Store.
Just visited an audio store and finally picked up the Moondrop Golden Ages 2, and honestly, the experience was great from start to finish.
The staff were knowledgeable and actually understood what I was looking for instead of just pushing random products. They let me try out different audio gear properly without rushing, which made a big difference in making the right decision.
The overall vibe of the store was clean, organized, and very audio focused. You can tell they cater to enthusiasts, not just casual buyers. Pricing was fair, and they were transparent about everything.
Ended up going with the Moondrop Golden Ages 2, and I’m really happy with the purchase so far.
Definitely recommend this store if you're into good audio gear and want a proper listening experience before buying.













