Fosi Audio in recent years has managed to stand out among the countless Chinese companies producing low-cost mini hi-fi equipment: thanks to excellent products sold at fair prices, it has quickly become one of the best-selling brands on Amazon, with notable popularity also in Italy.
In recent months we have had the opportunity to try some of Fosi Audio’s most successful products, including the V3 mono power amplifiers and the ZD3 DAC. Now we have had the pleasure of preview testing Fosi Audio’s first planar magnetic headphones: the Fosi Audio i5.
Planar magnetic headphones, thanks to the use of a diaphragm uniformly suspended between permanent magnetic fields without any physical contact between the parts, are characterized by incredibly fast transient response and extraordinarily low distortion. This technology also has some drawbacks: the weight and total surface area of the required magnets lead to rather heavy and bulky headphones that are difficult to carry around.
They often require a good headphone amplifier capable of delivering a decent amount of current to perform at their best. In recent years, thanks to the arrival on the market of increasingly high-performing and relatively affordable headphones based on this technology, planar headphones have gained great popularity and have driven the success of new companies specializing in their production, first and foremost the Chinese HiFiMan.
The i5 is the first headphone marketed by Fosi Audio and was developed with great consideration for user and hi-fi enthusiast feedback. The headphone project began at the end of 2023 and was funded through a Kickstarter campaign. After months of testing and refinements, the i5 was launched on August 15, 2025, with a launch price of 639 dollars on the official Fosi website, and 599 euros on the Italian market (on Amazon).
The i5 is a large and heavy planar magnetic headphone (550g including cable). The drivers use a diaphragm with a diameter of 97mm and a thickness of only 2 microns. The efficiency of the headphone is quite good for a planar (98 dB/mW) and the impedance is 28 ohms. Fosi Audio recommends pairing it with an amplifier delivering 500mW or more. Among the technical solutions used are the 2μm nanometer diaphragm and stealth magnets.
The construction has been carried out with great care, with the aim of making the headphones durable over time and extremely comfortable. The headband, similar to that used on high-end HiFiMan headphones such as the Arya or HE-1000, is light and flexible, distributing pressure optimally thanks to a wide leather strap and is freely adjustable to fit any head (see photo). The ear pads, large, soft and breathable, do not overheat and ensure maximum comfort. Furthermore, as you can see from the images, aesthetically the i5 is truly very beautiful.
Some technical data:
- Transducer Type: Planar Magnetic Transducer
- Maximum SPL: ≥ 120 dBSPL
- Frequency Response: 10 – 50,000 Hz; THD: < 1% @100dBSPL
- Sensitivity: 98 dB/mW @1kHz; Nominal Impedance: 28 Ω
- Recommended Power: ≥ 500 mW
Thanks to Fosi Audio, we had the opportunity to preview the i5 and experience its qualities. The tested unit is the latest revision, which compared to early pre-production samples features a more extended and linear low-frequency response thanks to the addition of two insulating rings inside the earcups.
The Fosi Audio i5 comes in a high-quality cardboard box, well protected and packaged. In the package, in addition to the headphones, there is a 3.5 mm unbalanced cable, quite robust and well made. The cable is detachable and can be replaced with any cable that accepts 3.5 mm mono plugs on the headphone side, including balanced cables. A 6.35 mm adapter is also included.
Inside the box we also find a well-printed and bound booklet presenting the headphone’s features and describing how to perform certain operations, such as replacing the pads. Taken out of the box, the i5 immediately impresses with a truly exemplary build quality, very rare to find in this price range. Not only does the headphone feel solid and well built, but as soon as you wear it, despite its weight, it is perceived as extremely comfortable.
Let’s now move on to the listening tests: we were very curious to hear how the i5 sounds and we must say it really satisfied us.
From the very first listen, it is immediately clear that this is a headphone with a well-defined sound signature that sets it apart from many other planar magnetic headphones in a similar price range. The i5 delivers a very musical sound, as intended during the design phase by Fosi Audio, which describes the i5 as a headphone made for long listening sessions without fatigue, with a “smooth” and pleasant sound. In particular, the upper midrange never stands out too much, and vocals are never overly forward compared to the rest of the mix. The extreme highs can sometimes sound slightly harsh; however, thanks to the warmth of the bass and lower mids, the i5 remains quite relaxed and musical overall.
The soundstage is definitely good, not extremely wide but with well-positioned instruments and commendable separation between them.
The performance of the low frequencies is also very impressive, well-present but balanced; fast, clean, and with an excellent level of detail.
The pairing with HiFiMan EF400/500/600 headphone amplifiers is particularly good in our opinion, as they complement the character of the i5 and smooth out some harshness in the highs; the sound can vary significantly depending on the DAC, so enthusiasts with a good range of converters will have plenty of fun experimenting with different combinations.
The i5 is relatively efficient but still requires a good amount of amplification power to perform at its best. Although it is possible to drive the i5 with portable devices, we do not recommend it. This is a very large and heavy headphone with virtually no sound isolation, not suitable for mobile use, so pairing it with a portable device makes little sense.
Finally, let’s move on to one last and extremely important aspect: comfort. This factor should never be underestimated: even the best-sounding headphones in the world, if extremely uncomfortable, will end up being used very little and will turn out to be a poor purchase.
The i5 is undoubtedly a very heavy headphone (a full 550 grams), and those used to wearing headphones weighing half as much will certainly need time to get used to it. However, compared to other planar magnetic headphones of comparable or even slightly lower weight, the i5 proves to be extraordinarily comfortable and cool, remaining so even after long listening sessions.
We conducted our tests during the summer period, with temperatures above 35 degrees almost every day. Even with an air conditioner running nearby, under these conditions it becomes more tiring to listen to music with large headphones. Although we have other more expensive planar magnetic headphones, technically excellent and also slightly lighter, during this period we listened almost exclusively to the Fosi Audio i5 precisely because we found them more comfortable and better suited to enjoying music.
In conclusion, the i5 is a planar magnetic headphone with a well-defined character, truly comfortable, very musical and designed for long listening sessions, with excellent dynamics, a good level of detail and very satisfying bass. At the current price (around 599 euros), we can only recommend it to anyone looking for an excellent planar magnetic headphone for home listening. In terms of value for money, the i5 is absolutely worth its cost: if you are looking for a substantial and serious headphone for listening in an armchair or at a desk, keep it in mind! Also because, at the moment, we would struggle to point out planar magnetic headphones with comparable build quality in the same price range.
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