The Fosi Audio i5 was kindly provided free of charge in exchange for an honest review. I didn’t receive monetary or any other kind of compensation and I don’t use affiliate links.
The retail price of the Fosi Audio i5 planar magnetic headphones is $639.99 and they go live on the 15th of August. A special promo 15% discount applies till the 15th of September. Use the code: FAI5MKT15. You can purchase them from Fosi Audio and Amazon.
Important note
The first pre-production units of the Fosi Audio i5 planar magnetic headphones, that were sent to reviewers and didn’t reach the public, had an internal sealing defect that made the bass roll-off below 80Hz. Fosi Audio immediately acknowledged the problem and sent replacement units or an easy DIY installation kit that resolved the issue.
The reviewed headphone is the revised version without the bass roll-off issue and identical to the final production model.
Fosi Audio
Founded in 2017 in Shenzhen, China, Fosi Audio specializes in making compact, high-performance audio gear that brings audiophile-quality sound to budget conscious listeners. Driven by a user‑centered philosophy, Fosi Audio co‑develops nearly half of its product line with direct input from users, blending customer feedback into award‑winning designs like the V3 and ZA3 amplifiers.
Fosi’s lineup encompasses compact Class‑D amplifiers, preamps, DACs, headphone amps, speakers, and accessories, all built with premium components sourced from brands like Texas Instruments and Cirrus Logic.
You can read further Fosi Audio reviews here.
Fosi Audio i5
The Fosi Audio i5 marks the brand’s first foray into making headphones. An ambitious start as the i5 is a planar magnetic headphone that incorporates a 97mm ultra-large diaphragm that is crafted with 2μm nano-level precision.
Using advanced targeted sputtering technology, an ultra-thin 1.3μm silver voice coil is precisely applied to the diaphragm. Each driver unit incorporates 22 symmetrically arranged N50 grade neodymium magnets, ensuring precise and stable diaphragm movement that minimizes nonlinear distortion. Additionally the use of a high transparency, rigid rear mesh structure, ensures stable air pressure damping, linear airflow control and minimizes nonlinearity.
You can read more about the Fosi Audio i5 here.
Design and build quality
The Fosi Audio i5 is exceptionally well made, featuring premium materials and great attention to detail that reflect superior build quality, far surpassing its asking price. The i5 is sturdy and durable, it has premium looks and doesn’t make any noises during use or adjustment.
The oval shaped enclosures are made from real walnut wood in combination with CNC-machined aluminum outer frames that have a smooth black finish. They are decorated with an S-shaped accent that has the Fosi Audio logo printed in orange color.
The natural grain patterns of the brown wood, that are unique to every pair, blend ideally with the black and orange colors of the outer frame in a beautiful looking and aesthetically pleasing appearance.
The ear-cups are attached to the headband with metallic arms that rotate both vertically and horizontally. The attaching slider has smooth action and allows for precise adjustments of the headband length that can be permanently fixed by tightening the screw.
The hybrid headband consists of an elastic metal outer frame and a genuine sheepskin suspension strap that has large perforations for better ventilation of the head.
The detachable ear-pads are made of perforated protein leather both at their outer perimeter and inner circumference while the face side is from breathable velour. They are generously stuffed with memory foam and get attached to the ear-cups with velcro stripes so they are easy to remove but the velcro might deteriorate after frequent use.
Wearing comfort
The Fosi Audio i5 has large and roomy ear-pads that are exceptionally comfortable to wear. They have a soft feeling and engulf the whole ear, not letting it touch the driver, while staying cool even after hours of use.
However, the Fosi Audio i5 is a huge headphone even at the minimum setting of the headband length so it may not fit well people with small faces or heads. Additionally, weighing a whole 525g, it is a heavy headphone and there is no way for the user not to start feeling the weight after some time. The headband strap is generously wide and effectively distributes weight to prevent pressure points or hot spots. However, the headset’s overall heft and weight eventually takes a toll, and you’ll likely need to take a break after extended use.
One last thing to consider is that the Fosi Audio i5 leaks quite a lot of sound so you might annoy people sitting around you.
Cable and accessories
There are no other accessories included except for the cable and a 6.35mm adapter. The Fosi Audio i5 comes packed in a high quality cardboard box with a magnetic lid that can serve as a long time storage solution but it is missing a high quality case or at least a velour pouch to help carry it around.
The stock detachable cable is made from 5N OFC silver-plated wire and is reinforced with an outer PVC sheathing that also helps reduce microphonic noise. It is a sturdy and well made cable with aluminum plugs but it is thick, stiff and difficult to handle. The cable is rather heavy and pulls the already heavy headphone downwards. Thankfully it supports the dual 3.5mm mono interface so I immediately swapped it for a Lavricables pure silver cable that offers a much better handling experience.
The package includes two identical cables, one with a 3.5mm plug and another with a 4.4mm, each one stored in its own velour pouch. Fosi Audio also makes a higher quality 4.4mm upgrade cable that is softer and easier to handle than the stock one.
Efficiency and associated gear
The impedance value of the i5 is 28Ω with a sensitivity of 98dB/mW so while it might not be that hard to drive, it is not an easy load either. The manufacturer recommends at least 500mW per channel but it needs more to reach its full potential. The i5 can get loud enough with 500mW but it sucks current like a leech and needs more juice to get alive. Using an inadequate source will make the treble distort and the soundstage collapse.
High quality desktop sources like the Aune S9c Pro or powerful DAPs like the iBasso DX340 are ideal to make it sing. The i5 also scales unexpectedly well so make sure to use the best equipment in your arsenal.
As per usual practice, the Fosi Audio i5 was left playing loud music for more than 100 hours before listening evaluation.
Listening impressions
Neutral and balanced are the first two words that spring to mind after testing the Fosi Audio i5. This is a headphone with a reference neutral tuning that shows exceptional tonal balance throughout the whole frequency range. A high quality planar magnetic headphone with a monitor-like tuning that doesn’t follow the Harman target curve and is not too bright as other monitoring headphones.
The i5 is ideal for critical listening but it doesn’t sound clinical or sterile either. It is musical and engaging enough, able to extract all the fun elements from your favorite tunes. Still, the i5 is to be considered primarily as an audiophile headphone made to offer class-leading tonal precision and not for setting the party mood. This doesn’t mean though that the i5 is not suitable for listening to all kinds of music but the listener should be prepared to hear the truth and not the headphone’s version.
The low-end has great sub-bass extension and easily reproduces the lowest audible tones without adding any extra emphasis. The bass has a linear and neutral tuning without any mid-bass lift or any other kind of unwanted coloration as it happens with more casual tunings. The i5 has excellent tonal precision and all instruments are reproduced with lifelike accuracy and impressive realism. The i5 is one of the best headphones in its respective category for listening to classical music or doing mastering applications.
More listening impressions
The technical performance is also impressive for the category and can easily compare with more expensive planar magnetic headphones. Given that you are feeding it with plenty of current, the bass can sound exceptionally dynamic and impactful, as well as fast, tight and controlled with outstanding clarity and separation.
The i5 can easily handle the most intricate bass lines without losing composure or lacking in resolution and layering. The textures are clearly defined but not fragile or thin. Typical for a planar magnetic headphone, the bass isn’t as weighty and visceral but in the case of the i5, you wouldn’t call it dry or lacking in elasticity either. The bass is also free from any cup resonances or any hint of audible distortion.
The mid-range also follows a neutral style of tuning but it manages to stay musical and engaging all while retaining good clarity and articulation. The timbre is quite natural and realistic, voices and instruments don’t sound artificial or fake. The mids are evenly tuned without too much upper mid-range emphasis or lower-mids recession.
And some more
The immense transparency of the i5 guarantees that it can easily capture the harmonic richness and the intricate sound colors of a capable source but it also means that it will not do any favors to lower quality recordings and it cannot fill the missing harmonies of a sterile source.
The treble is brilliant and energetic but not bright or sharp and ideally balances smoothness with transparency. Honesty is the governing rule, so depending on the source and the material the i5 can vary from sounding pleasant to quite sharp and harsh.
The overall presentation is lively and clean with satisfying detail retrieval and definition. The only things that hold it back from competing with higher-end headphones are some lack of texture refinement and ultimate resolution while there is a mild audible ringing in certain frequencies.
The i5 avoids the typical behavior of other monitoring headphones and doesn’t sound clinical or analytical. It is a cohesive sounding headphone throughout the whole frequency range without artificial or metallic timbre in the higher registers.
Speaker-like experience
The soundstage is really impressive in how well it handles the music material and sounds more like speakers than headphones. With the i5 you won’t hear the typical left to right soundscape, the various sound elements are so naturally mixed and projected both on the horizontal and vertical planes that it is like someone has applied crossfeed from the source.
The stage is wide, spacious and holographic with precise imaging and good depth layering, while it easily adapts to the scale of the music, from a single performer to the full symphony orchestra. The only thing missing in comparison with flagship models, is that they are much more focused and layered than the i5.
Vs the competition
The Fosi Audio i5 has a lot of tuning similarities with various Hifiman headphones or even the FiiO FT5. The Hifiman models have an almost identical neutrality and tonal precision but they are a little brighter sounding, while on the other hand the FT5 is slightly warmer and more colored on the low-end.
The technical performance of the i5 is comparable with the HIFIMAN Arya Stealth or the Ananda Nano models which are a little more resolving and produce less ringing on the treble. The i5 has a bigger and more holographic/immersive soundstage but it doesn’t image as sharp as the Hifiman’s.
The Fosi Audio i5 is better made and uses more premium materials throughout while It is also equipped with two higher quality cables. The i5 is at least as comfortable as the Arya and the Ananda but it is somewhat heavier.
In the end
The Fosi Audio i5 is so good sounding and technically accomplished that it easily competes with headphones considerably more expensive than it. The only thing that holds it back from reaching high-end level performance are some lack of texture refinement and absolute resolution, as well as the tiny bit of ringing glare in the treble.
For people looking for reference tonal accuracy with competitive technical performance backed by a speaker-like soundstage, the Fosi Audio i5 ticks all the boxes and more at a fraction of the cost relative to the competition.
Except for its excellent sonic performance, the i5 is also exceptionally well made with premium materials and very comfortable to use despite its slightly increased weight. An outstanding achievement and a strong debut by Fosi Audio that enters the headphone market with confidence and promises a brilliant future.
Copyright – Petros Laskis 2025.
+ Neutral reference and balanced tuning
+ Impressive tonal precision
+ Strong technical performance
+ Natural and realistic timbre
+ Doesn't sound clinical or sterile
+ Excellent clarity and transparency
+ Present mid-range and polite treble
+ Speaker-like and immersive soundstage
+ Scales very well with higher quality sources
+ Well made with premium materials
+ Comfortable and roomy ear-pads
+ Comes equipped with two high quality cables
+ Great price to performance ratio and good value
- Small amounts of treble ringing
- Doesn't image as sharp as higher-end models
- Not as resolving and refined as the class-leaders
- Huge size may not fit people with smaller heads
- Heavier than the average
- Stiff and heavy cables
- Needs plenty of current for optimum performance
- No carrying case
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