Fosi Audio i5 Open-Back Planar Magnetic Headphones Review – Superlative Warm Fuzz
Fosi Audio i5 is a $549 USD pair of upper midrange over-the-ear planar magnetic headphones with a really solid design, a large 90mm diaphragm, walnut wood and aluminum frame, and with a genuine suede leather headband. Today we review the Fosi Audio i5, and also compare it with other headphones from a similar price range, including HarmonicDyne Baroque (559 USD), Sendy Audio AIVA 2 (599 USD), and OLLO X1 (539 USD).
Introduction
Fosi audio is getting more daring with their newer poorductors, and Fosi Audio i5 is their latest planar magnetic headphone, a model that rightfully impressed me at High-end Munich 2025, with their exceptional warm, smooth and lush sound. Today we explore the i5, and how Fosi, a company usually focused on entry-level products, made a pair of headphones that can compete with even some of the most popular high-end models that the world has seen to this date.
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Product Link
Amazon – https://amzn.to/45b4Y4X
Aliexpress – https://fosiaudio.com/pages/fosi-audio-i5-planar-magnetic-headphones
Build Quality – Design
Fosi Audio i5 is built around a huge 97mm planar magnetic driver with a 2um nano-level thickness diaphragm. Voice coil is just 1.3um in size, and it has a silver metal alloy deposited on it using the sputter coating technology. Each driver has 22 N50 neodymium magnets arranged symmetrically, to produce a precise sound. This reduces nonlinear distortion, and improves on the resolution of the headphones. Although HIFIMAN recently decided to go for a zero mesh, zero earcup design, in their HIFIMAN Susvara unveiled headphones, Fosi Audio uses a rigid, high-transparency acoustic mesh, which smooths out frequency spikes and reduces nonlinearity, using the earcup as a tuning mechanism.
Fosi i5 follows the natural contour of your head, and it has a Dual Axis Ear Cup Arm, allowing for seamless vertical and horizontal rotation to fit different head shape and size. In fact, it is one of the few headphones that uses a silicone adjustment slider with a dampened smooth feel, allowing for a stepless precise positioning instead of the usual stepped one. Knowing how important earpad quality is for audiophiles, Fosi Audio uses perforated leather and breathable fabric in their earpads to keep the i5 cool and soft, and the memory foam on the inside ensures that those pads feel just right for their users.
Although i5 is launched at an affordable price, we see Fosi using premium materials when building the i5 headphones, including genuine suede leather headband, luxurious walnut wood frame, CNC Machined aluminum frame, S-Shaped decorative accent, and 3.5mm detachable cables, with a 3.5mm cable included in the package of the i5, but compatibility ensured with other premium aftermarket cables.
Subjective Usage
Fosi made some really large headphones and i5 feels like the largest, most tank-ish headphones that I ever tried, but they are not very heavy and instead i5 feels quite snappy and practical on my head. They have large earpads, with real estate available for my ears, and with a soft headband and soft earpads, i5 is super comfortable.
Passive noise isolation is not really existent, although they do offer around 5 dB of isolation or passive noise attenuation. Sound that leaks is quite balanced, if a bit bright, but not very loud relative to the volume you’re listening at. Cable quality is great, but i5 has a 4.4mm balanced cable, at least the pair that I have, instead of a 3.5mm one, so I feel Fosi will update the official information for i5. All in all, Fosi Audio i5 is super comfortable, has a high-quality cable, does not feel heavy and there is no handling microphonic noise coming from the cable.
Sound Quality
Pairings – I decided to pair Fosi Audio i5 with a selection of favorite sources, most of them from the mighty flagship class, including FiiO K17, Burson PlayMate 2, JDS Labs Element III, Singxer Sa-1 V2 driven by a FiiO K15, Rose Technics RT-5000, and Dethonray Clarinet. Fosi Audio i5 eats a ton of power to be driven well, and I find myself using 75% of the max volume that K17 has to offer, which is harder to drive than most headphones I have, even more so than HIFIMAN Susvara unveiled. The signature that Fosi Audio i5 goes for is also partly to blame, because it sounds smooth / laid back and relaxed, which means that you can push the volume far more to achieve a more punchy and vivid sound.
Overall Signature – Speaking of the tuning and signature, Fosi Audio i5 is super relaxed, smooth, yet revealing of details and information. As it needs quite a bit of power, high gain and a ton of current, when you feed it the power it needs, it also sounds authoritative and controlled, with a strong bass and impact, high dynamic range and a wide, holographic, but relaxed soundstage that tends to blend instruments together, to allow music to sound organic, rich and cohesive. I5 presents a stronger, more forward lower midrange, with a recessed upper midrange, creating less emotion and presence for the female voice, and has a drama-free sound that is lush and a bit bloomy.
Bass – Starting from the low-end, bass extension goes as low as about 30 Hz, with a smooth roll-off below this level. Music generally has most strength at about 80 Hz, with a peaking range up to 120 Hz, so most songs feel warm and dark, instead of sub-bassy and rumbly. Indeed, there is more of a bass presence, warmth and dark bloom rather than there is sub-bass impact usually characteristic of house and EDM music. This marks i5 as a good headphone for Jazz and more mature music instead of the usual EDM and Rap that are great with bassy headphones.
Midrange – Vocals are a bit more forward as presented by i 5, but it is also a bit on the more distant sounding end of things, so it has present, vivid voices, but the whole sound takes a step back as I5 presents music a bit more distant, wide, airy and with a natural level of separation. This helps achieve a more relaxed, laid-back sound, and it lacks aggressiveness, always sounds polite and friendly, open and clear. At extreme volumes, i5 needs power to stay controlled, if it is underdriven, it will distort, but with high gain and proper loudness saturation and power / voltage saturation, it can go very loud, super controlled and impactful.
Treble – With a smoother, more relaxed treble, fosi i5 has extension up to 20 kHz, but the treble energy rolls off above 9 kHz, still remaining audible, but taking a second place relative to the voice and the warmth of the bass. It is generally plenty detailed and crisp up top, but not an aggressive pair of headphones, so you don’t notice treble all that much unless the song really has a ton of high-end, like the first album of Infant Annihilator, but even with that album, treble is audible, not harsh not too forward or too aggressive.
PRaT / Textures / Dynamics – This lack of aggressiveness can be fully attributed to the frequency response, because in technicalities i5 is rather fast, snappy and detailed, and the whole laid back and gloomy sound comes from how it renders frequencies relative to each other, and the relaxed soundstage. I am saying this because the textures are rather crisp and revealing, even a tad grainy at times, but never too smooth, rolled off or absent. It feels like the i5 is a far more detailed pair of headphones than it is allowed to show its true colors.
Loudness Saturation Gradient – I5 sounds similar at all volume levels but it is very sensitive to source power and gain, power and voltage, which makes it hard to accurately recommend sources. Basically, unless you have a few watts of power, it is likely that i5 will sound grainy and loose instead of punchy and vivid, as I heard with sources that do not have quite enough power for them.
Soundstage – Fosi made i5 to sound wide, holographic, but in a relaxed way, with a laid back instrument separation that allows music to blend and breathe, they actually pull the sound away from the listener, giving you some space and room to breathe. This signature is literal perfection with classical and orchestral music, it sounds so natural and lean, detailed yet complete. For rock it can sound distant, and the same can be said for most recent commercial music styles.
Comparisons
Fosi Audio i5 vs HarmonicDyne Baroque (549 USD vs 559 USD) – Baroque has a similar size, but feels smaller on my head, yet both have more or less the same weight and actual comfort. The i5 is better made compared to the Baroque, i5 has a better earcup design, more premium materials and feels more proper for a high-end pair of headphones. Cable quality is a bit better for baroque. Both leak about the same, isolate about the same and both have a similar usage but Baroque is much easier to drive, and less sensitive to source quality and gain. Sonically, I5 sounds far more relaxed, laid back and lean, rich and warmer. Baroque is much more neutral, a bit more aggressive, climbs lower in the sub-bass, rises higher in the treble presence, and sounds more open, brighter, more aggressive and more revealing of imperfections and mistakes, while i5 hides everything. It sounds more distant in the voices while Baroque sounds more intimate and more natural.
Fosi Audio i5 vs Sendy Audio AIVA 2 (549 USD vs 599 USD) – AIVA 2 is more compact overall, it is tighter on my head, but not less comfortable, both headphones have softer earpads, and AIVA 2 has a thinner, more flexible cable that feels more high quality. Both headphones have a similar build quality, both have wood and metal, AIVA 2 leaks much less than i5, and isolates far more from the outside noise. AIVA 2 is also easier to drive in general, while i5 requires more raw power. Sonically, AIVA 2 is the first really natural sounding pair of headphones that Sendy created, and they sound very natural, while i5 has a signature that really reminds me of the Sivga Audio Peacock. I5 sounds more distant, less focused, wider, more relaxed and richer, while sounding darker and more lush too. Aiva 2 sounds more neutral, more natural, and a bit cleaner, but with a tighter soundstage, stronger instrument separation, stronger sub-bass extension and presence, stronger treble sparkle and less bloom.
Fosi Audio i5 vs OLLO X1 (549 USD vs 539 USD) – OLLO X1 is far more compact, but i5 feels more comfortable with larger earpads, a lower perceived weight, and a more standard cable. This being said, both headphones have wood and metal in the build, both have perforated earpads, both have soft texture surfaces for contact with your ears and head, and X1 is the more compact, travel-friendly option while i5 is both harder to drive, leaks much more, isolates less and has a more premium but less flexible cable. Sonically, X1 is more dry, more precise, more vocal centric, but with a much smaller soundstage and focused sound. I5 sounds bloomier, wider, more rich, darker, and more lush. I5 is also more relaxed, and smoother in general, a much better listening pair of headphones, but not made for studio usage like X1.
Value and Conclusion
Although i5 is not very expensive, it offers a nice package, good cable, reliable build quality, and a novel, warm, bloomy sound that is super enjoyable with classical music, orchestral and jazz, mature music, and generally what a mature audiophile would listen to. They also work really well with rock and older, slower music, but EDM and slower pop too, being a uniquely relaxed listening experience that is totally worth the asking price from a technical point of view.
At the end of the day, Fosi delivers a completely new tuning, new sound, new product and all for a convenient price point, Fosi i5 being an excellent choice for those who want to step away from the fatiguing more energetic headphones that the market usually offers in the price range, and someone who wants a darker, more lush, richer and more relaxed listening experience. This is the perfect pair of headphones for classical, jazz, cabaret and more mature music styles, and fully recommended for those relishing listening to those styles.
PROs
- Rich and acoustically relaxed signature
- Dark and bloomy, full and warm sound
- Very high build quality and beautiful design
- Balanced cable included in the package
- Excellent price performance ratio
Cons
- Quite hard to drive, sensitive to gain levels and it requires a good source to truly shine
Product Link
Amazon – https://amzn.to/45b4Y4X
Aliexpress – https://fosiaudio.com/pages/fosi-audio-i5-planar-magnetic-headphones
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Full Playlist used for this review
We listened to more songs than those named in this playlist, but those are excellent for identifying a sonic signature. I recommend trying most of the songs from this playlist, especially if you’re searching for new music! The playlists are different for Spotify, Tidal and Youtube, and based on the songs I enjoy and are available on each!
https://www.youtube.com/playlist?list=PL_cjBXGmwSHSdGcwuc_bKbBDGHL4QvYBu
https://open.spotify.com/playlist/5J3oloz8Riy9LxEGenOjQ0?si=979ba4f082414be7
https://tidal.com/browse/playlist/330fd544-8e5b-4839-bd35-676b2edbb3d5
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