Fosi Audio i5 Revision 2 Assessment

June 9, 2025

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This time, I’m reviewing Fosi’s revised model of their debut headphones, the Fosi Audio i5 Rev2. It sells for $549,99 USD.

Disclaimer: Fosi Audio isn’t associated to Headfonia. They despatched me the second i5 freed from cost to be featured on Headfonia.com.

Table of Contents

Fosi Audio

The Shenzhen-based model Fosi Audio entered the market in 2017 and has since supplied the audio market with a gradual stream of high-value merchandise, from DACs and headphone amps to devoted speaker energy amplifiers.

The identify “Fosi” embodies the 4 core ideas of the corporate: foresight – considering additional forward; openness – embracing customers’ voices; sincerity – serving you wholeheartedly; and innovation – upholding technical excellence.

Up to now, Fosi Audio have gotten a superb status right here with their V3 monoblock class-D energy amplifiers impressing Nanotechnos sufficient to name them “a steal” for the value Fosi are asking. We’ve additionally reviewed Fosi’s higher-end offshoot Mamoritai Audio’s headphone amp, the Euphony, which, then again, didn’t precisely steal Nanotechno’s coronary heart.

At over USD 500$ retail value, the i5 headphone is one among Fosi Audio’s priciest choices. For now, it’s solely obtainable from the corporate’s Kickstarter marketing campaign.

The first pattern of the i5 we obtained from Fosi confirmed a whole lot of potential, however I agree with my colleagues from different shops – the low-end response suffered from a noticeable roll-off.

Enter the Fosi Audio i5 Rev2

The essential development of the Fosi Audio i5 Rev2 is essentially unchanged. It’s an open-back planar magnetic or orthodynamic headphone with an infinite baffle acoustic formulation. Which means the diaphragm is coupled to the ear. It may be felt when placing the headphones on because the diaphragm flexes subtly when the earcups compress.

Within the earlier model of the i5, the Velcro that holds the pads to the earcups didn’t seal and the working precept was extra akin to an open baffle. Thus the low-end response of the headphones ended up being compromised and rolled off after the driving force’s elementary resonant frequency of round 80Hz.

Based on Fosi, all i5 variations any longer will function the additional sealing ring to enhance the low-end response of the headphones. Which means the bass-lite model will seemingly turn into fairly uncommon because it has principally reached a few tremendous early backers and most reviewers who, like me, must replace their experiences.

Options:

Open-back over-ear headphone, infinite baffle acoustics
97mm, push-pull planar magnetic driver, 2um diaphragm
10 – 50 000Hz marketed frequency response
28 ohm purely resistive load
98dB/mW or 113.5dB/V
Weight: 550g with out a cable
Enter connectors: 3.5mm TRS
Cable jack: 4.4mm TRRRS, 3.5mm TRS (6.35mm adaptor included)
Cable size: 1.5m

Sound Signature and Technicalities

My fundamental testing system for the Fosi i5 was the Topping x Holo Centuarus driving the DROP + SMSL HO150X, Feliks Euforia EVO, and Aune S17 Professional EVO.

The driving force of the Fosi i5 stays unchanged, subsequently, nothing adjustments when it comes to driveability – most headphone amplifiers and all-in-ones will do the trick. OTL tube amps can be utilized, nevertheless, the low impedance means solely essentially the most highly effective will be capable to supply sufficient energy on the 28-ohm load the i5 presents. My Euforia EVO was capable of drive the i5 fairly loudly with out clipping, however it’s not my favourite pairing.

General Tonality

The improved Fosi i5 proves {that a} comparatively easy repair can rework how a headphone sounds. By sustaining a seal all the best way from the driving force diaphragm to the eardrum, the i5 lastly achieves true full-range bandwidth. This has a profound impact on the general sound and makes the response much less top-heavy.

Bass

Beforehand, I acknowledged that the slightly conservative method to the low-end tuning is what dictated the slightly analytical tuning of the preliminary i5. Nicely, this has modified! There’s a bottomless extension I’ve come to anticipate from planars. On the identical time, the i5 doesn’t go full Harman with the sub-bass enhance and retains it slightly tactful.

Make no mistake, that is nonetheless orthodynamic bass with quick and clear transients. There’s nearly no bloom, and decay dies off into the blackness fairly rapidly. With digital performers like Trentemoller, the i5 reveals each its muscle and the potential to activate a dime.

The addition of full-range bass transforms the i5 right into a a lot balanced and fewer introspective listening expertise. Its musical style bandwidth has expanded tremendously, and there’s lastly a superb little bit of coronary heart to the beforehand all-brains tuning.

Midrange, Treble, Technicalities

There are not any adjustments to the remainder of the spectrum, and I’m glad that there aren’t. Usually, bodily modifications to an acoustic system incur unintended adjustments, however not this time. Solely the low-end has been affected, and the remaining stays the identical – a extremely technically succesful window into recordings. Solely the stability has been affected, and now it’s very impartial with each tonal area getting the identical quantity of consideration.

Comparisons

Sennheiser HD6XX

The basic from Sennheiser is the go-to as a tonal stability reference. On the identical time, it’s not an exaggeration to confess that, technically, its 40mm dynamic driver is beginning to present its age. The Fosi i5 highlights it with devastating precision.

With the mounted low-end response, it walks over the HD6XX with regards to low-end extension and technicalities. The HD6XX could be a breathtaking expertise when paired with a succesful setup, however the i5 achieves the identical with out the heroic efforts in accompanying electronics.

Moondrop Para

The entry-level planar from Moondrop took me unexpectedly. It delivers a extremely technical efficiency that’s unprecedented on the value level. Certain, the construct high quality is a bit hit-miss, and its 8-ohm, low-efficiency design is a mainstay in my secure as an amplifier torture system, however I like the hassle nonetheless.

At nearly the identical value because the early-bird deal Fosi i5, the Para seems like a DIY challenge as compared. It’s nonetheless a extremely technical sound with many of the planar advantages, however the improved bass of the i5 is the coup de gras. If it’s a must to select, go for the i5 each time – it improves on each facet of the Para.

HarmonicDyne Baroque

Lastly, a worthy opponent! At $559 USD, it’s a superb bit pricier than the early-bird Fosi i5, however after that deal is thru, the costs turn into nearly the identical. The Baroque is an open-back design with a freshly developed 60mm (!) ceramic-metal diaphragm dynamic driver. It’s additionally fairly well-made and wears slightly cozy.

Each headphones are on par with regards to technicalities. What differs is the best way they’re offered. The Para feels extra ethereal, even electrostatic at occasions, whereas the Baroque hits more durable and delivers a extra visceral efficiency. It’s evident that there’s some bass-boost occurring with the Baroque, however by no means on the expense of the vital midrange.

Conclusion

After I was writing in regards to the first revision of Fosi i5, I used to be THAT near giving it the Headfonia Advisable award. The one factor that stored me was the poor bass, as I knew that many would yearn for extra booty. It’s 2025, and it’s okay for audiophiles to love low-end!

I wasn’t the one reviewer who identified the potential downside within the lows, and Fosi responded with a repair that’s each easy and brutally efficient! Now the i5 really does all of it, and I can safely advocate it for everybody on the lookout for an open-back underneath $1000 USD. It will likely be a superb deal even after the early-bird interval, and I can’t wait to see what Fosi can do sooner or later.

Audeze, Hifiman, DCA, and different planar specialists ought to preserve their eyes peeled!