Fosi Audio was founded in early 2017 by Ryan Huang in the Shenzhen’s Longgang district. Driven by the belief that high-quality Hi-Fi should be accessible to all, Ryan and his partner bootstrapped the company.

This year at AXPONA 2025, they also unveiled their new brand slogan, ‘HEAR THE UNHEARD’ a powerful expression of their commitment to pushing the boundaries of sound quality. It highlights their core philosophy: true innovation begins with understanding and responding to the needs of the user.

The name ‘FOSI’ reflects their core values:

• Foresight: Visionary thinking and proactive solutions for the future
• Openness: Co-creating with audiophiles by listening to users
• Sincerity: Always putting users first with a commitment to quality
• Innovation: Breaking technological boundaries to exceed expectations

‘Our vision is to become a global leader in audio innovation. Fosi Audio will continue to push the boundaries of audio technology based on user feedback, making HiFi not a luxury for the few, but an art of sound that can be enjoyed by audiophiles and music lovers around the world’.

– Founder Ryan Huang

Built on a foundation of innovation and affordability, the brand believes great sound shouldn’t be for the rich and happy few. Today, their products reach buyers in over 100 countries. Backed by a modern Shenzhen facility, which includes a 2,300 m² R&D center, independent production lines and supported by dozens of global patents, Fosi Audio continues to push the boundaries in user-focused audio design.

The company has steadily expanded its lineup to include amplifiers, DACs and audio accessories for both newcomers and seasoned audio fans. Their minimalist design, ease of use and strong performance have earned them loyal worldwide followers.

• In spring 2025, Fosi Audio introduced its Hi-Fi ecosystem at AXPONA Chicago, unveiling the SP601 bookshelf speakers and their first open-back planar headphones; The Fosi Audio i5. The i5 marks the brand’s confident step into high-end personal audio, staying true to their mission of delivering top-tier sound without the premium price tag.

In this review, I’ll take a closer look at their latest and first planar magnetic creation: The Fosi i5

• Test equipment:
  – Sparkos Labs Gemini – Philips 6922 SQ Tube
  – DAC Chord TT2 + Chord MScaler
  – Burson Soloist GT – Burson V7 Vivid opamps
  – Eversolo A8 + LHY LPS

Build quality & design
When held, the i5 gives a robust and strong wel designed impression. It is beautifully designed with a central section made of polished walnut wood. This component isn’t merely decorative, it extends inward to support the internal driver assembly.

Weighing 550 grams, the device exudes a high-end feel, with no visible plastic materials in sight. Its chassis is crafted almost entirely from finely finished aluminum, adding both durability and a level of sophistication that likely helps minimize acoustic vibrations. I’ve seen brands with higher price tags offering lower build quality than the i5, with designs that don’t even come close to this level of craftsmanship.

A friction-based adjustable mechanism is used for the headband, which holds its position reliably after the initial setup. The headband itself is covered in suede and has a generous width, aiding in the even distribution of weight across the head.

The earcups are mounted on a dual-axis hinge system that allows for silent, fluid movement, enabling them to automatically conform to the shape of the head as soon as the headphones are worn.

Comfort levels are generally good, thanks to the substantial and firm cushioning. Additionally, the design of the earcups tends to accommodate glasses wearers more effectively than some other brands, offering a better seal and reduced sound leakage. 

The headband exerts a relatively strong clamping force, only a few headphones have given me this kind of experience, a firm, yet remarkably comfortable fit. Despite the pressure, it never feels intrusive; instead, it delivers a relaxed, almost embracing sensation.

The ear pads are made of a nice vegan leather, filled with a very soft foam, almost similar to soft memory foam. They’re impressively large. The contact area between the pads and the head is substantial, contributing significantly to the overall comfort. Despite their considerable weight, they remain very comfortable to wear. 

The ear pads appear to be attached using Velcro, not the most ideal solution in my opinion, but it works surprisingly well. Since you’re not removing the pads on a daily basis, once attached they remain firmly in place, it’s a practical approach despite initial concerns. 

One important note to mention: once you remove the ear pads, the drivers are completely exposed. This leaves the delicate magnetostatic elements vulnerable to damage, so extreme care is required. I would strongly recommend that Fosi consider adding some form of protection. While I understand the design choice, accidents can easily happen, especially during pad changes or handling.

Update
Fosi Audio responded to early feedback of listeners, by addressing a sub-bass issue found in pre-production units. I have to be honest, I was not missing anything, I really like the presentation as it is, smooth and balanced.

They implemented a sound-isolating ring as part of the revision. This updated version offers a more substantial low-end presence, changing the frequency response just a little.

Fosi Audio asked me to install these and  make a comparison. I’ll delve deeper into this update (rev 2) later in the review, including a comparison of the experience with and without the modification. 

Fosi Audio provided, I5 replacement rings, for better seal (REV2)

In the Box:
The set includes both a 4.4mm balanced cable and a standard 3.5mm single-ended version and a 3.5mm to 6.35mm plug.

The supplied cables are constructed from silver-plated 5N oxygen-free copper with an impressive 1120 strands, giving them a robust and high-quality feel.

They’re marked, with a red heat-shrink label on the right channel for easy orientation. While they have a somewhat stiff character, more rigid than I personally prefer, they manage to avoid excessive tangling and present a premium aesthetic overall. It’s possible they may soften slightly with extended use.

The i5 supports standard type third-party cables with 3.5mm dual connectors, if you would like to change them.

Sound
I tested the i5 on several amplifiers, including the Mojo 2, to gauge how it handles a portable source and to my surprise, it ran remarkably well. But the true potential of these headphones only revealed itself when paired with more capable gear.

I’ve seen it many times before: a planar can be quite forgiving when it comes to input power, but pair it with a source that offers real power and control and you’ll understand exactly what I mean.

Switching to the 2-watt hybrid Sparkos Labs Gemini added an extra layer of smoothness and musicality, enriching the listening experience with warmth and finesse. The tube stage introduced a natural, euphonic warmth and fluidity, while preserving the sparkle and air that tubes are known for.

This combination works particularly well with magnetostatic headphones, which are often praised for their speed, detail and neutrality, but can sometimes come across as slightly analytical. The hybrid design of the Gemini balances that out beautifully; The solid-state SS2590 section ensures control and precision, while the tube stage adds emotional depth and tonal richness without sacrificing resolution. It’s a best-of-both-worlds synergy that brings out the soul in the Fosi Audio i5.

The Burson Soloist GT, a powerhouse 10 watt Class A amplifier, fully unleashed the i5’s spatial capabilities, delivering a soundstage with remarkable depth, width and pinpoint precision. The pure Class A topology brought out a sense of effortless dynamics and holographic layering, allowing instruments and vocals to occupy their own distinct space with lifelike realism.

This kind of amplifier excels with magnetostatic headphones, which thrive on stable current delivery and low distortion. The Soloist GT’s ability to provide clean, constant power without crossover artifacts enhances the i5’s already impressive imaging, making the listening experience not just engaging, but truly immersive.

Treble
The upper vocal range carries more energy than the lows, creating a bright and very controlled sound signature thanks to a slight smooth treble roll-off. This prevents any harshness and keeps instruments like brass, clarinet or percussion lively and refined.

Well-mastered recordings truly shine, while compressed or lossy content can occasionally reveal a bit more sibilance and sharpness, particularly in breathy vocals or flutes. That said, this isn’t unusual; the better the headphone, the more revealing it becomes of imperfections in the recording.

Because of the highest frequencies slightly beeing muted cymbals can sound a bit softened, this can be a plus for those that are sensitive to treble peaks. I have heared better headphones and lesser, but in general, the tonal balance of the i5 feels very natural and enjoyable. You can listen for hours and just forget time altogether.

Mid
The mids are clean and agile, with vocals gaining warmth from the low-end and clarity from the lifted upper range. This gives voices strong presence and articulation without sounding overly intimate.

I noticed just a slight emphasis on sibilants and nasal tones, you hear that mosltly with brighter voices, while darker vocals come through naturally. Even sharper, thinner voices stay controlled, though they can sound a touch brittle at times, with some older recordings of Stacey Kent, to give an example.

The presentation avoids real harshness and with minor EQ tweaks, the upper mids can be smoothed out perfectly. In group vocals or choirs, the forward vocal tuning may feel a bit intense, though vertical space and layering are well rendered. A slightly more relaxed upper midrange could improve balance and add openness.

Bass:
The low-end performance is engaging, with a warm and impactful sound signature. In instrumental passages, the bass reveals a satisfying sense of layering and texture, paired with a quick, punchy response. This balance works particularly well with genres like Blues and jazz that feature more intricate bass arrangements.

Bass decay is relatively quick, with an overall clean and articulate presentation. Sub-bass may feel somewhat restrained for some, but I think that is more of a personal taste.

I wasn’t missing anything with rev1 (without modded rings), but some might wish for more in electronic tracks, nothing that can’t be fixed by a little EQ. When it comes to large percussion instruments, there’s a slight roll-off below 80Hz to make an estimate. However, I expect that the addition of the sound-isolating ring will help address this and improve the perceived low-end reach.

Stage
The i5 offers a nice wide soundstage, with a little lift in the bass and upper mids bringing vocals and high-pitched instruments closer to the listener. Vocal placement are clear, with darker and softer voices sitting further back. The planar driver is doing its job well in the i5.

Some high frequency instruments in the upper-register may feel a bit less defined due to the soft top-end, but this also helps avoid harshness. It’s a design choice, which makes the i5 an easier allrounder.

The staging feels like a live set in a small venue, intimate and focused.

To ensure consistency, all evaluations were done using a handpicked playlist of well-known reference tracks that reveal detail, dynamics and spatial cues.

Ibrahim Ferrer – Guaguanco Callejero
Guaguancó Callejero is a rich, streetwise slice of Cuban soul and the Fosi Audio i5 brings it vividly to life. Right from the first notes, the i5 impresses with its ability to render percussive textures with stunning realism, you can almost feel the palm slaps on the conga skins, each strike resonating with lifelike immediacy and presence.

Ibrahim Ferrer’s voice, warm and full of lived experience, is beautifully preserved. The i5 presents it with a natural timbre that captures every nuance, his phrasing, his breath and the subtle grain in his tone. All surrounded by the vibrant hustle of Havana streets.

The soundstage is another standout. The i5 delivers a spacious, airy presentation where instruments are well-separated. Horns flare with organic energy, guitars have a woody warmth and the rhythm section flows with a grounded yet fluid motion. You can almost smell Cuba in the air.

What makes the Fosi i5 so special in this track, is its balance of rhythm and soul. It handles the track with ease and control, never sounding clinical or sterile. Instead, it maintains that essential looseness and humanity that defines Ferrer’s work.

Chris Minh Doky – Scenes from a Dream – All Is Piece
All Is Peace is a quiet meditation in musical form, a composition that breathes with space, emotion and subtle detail. When played through the Fosi Audio i5, the track transforms into an intimate sonic experience that gently wraps itself around the listener.

From the very first notes, the i5 unveils the nuanced textures of the upright bass, allowing Chris Minh Doky’s playing to resonate with both depth and finesse. Each note blooms with warmth, the resonance of the strings rendered with such clarity that you can almost feel the wood of the instrument vibrating through the air.

The piano and ambient elements float effortlessly across the soundstage, but never diffuse. The i5 captures that delicate balance between tone and silence, letting the decay of each note linger just long enough to preserve the contemplative atmosphere of the piece.

You really hear that one of the i5’s strengths lies in the exceptional microdynamics and it’s particularly noticeable in this track. Gentle volume shifts and phrasing nuances are faithfully conveyed, creating an emotional intimacy that lesser headphones often flatten out.

The black background enhances the sense of presence, not just of the instruments, but of the space between them.

In summary, the Fosi Audio i5 elevates All Is Peace beyond a mere listening experience. It becomes a moment of stillness, a deep exhale at the end of the day. It’s the kind of synergy that reminds you why you fell in love with music in the first place.

Eva Cassidy with the London Symphony Orchestra – I can only be me – Autumn leaves
Eva Cassidy’s Autumn Leaves , Already hauntingly beautiful in its own right, becomes something truly transcendent when paired with the Fosi Audio i5, very intimate and warm.

From the first orchestral swell, the i5 showcases its ability to render orchestral depth and layering with breathtaking clarity. The strings of the London Symphony Orchestra are lush yet controlled, spread across a wide and natural soundstage. Each section has space to breathe, with fine detailing in the violins and a rich foundation in the cellos and basses.

Eva’s voice, fragile, pure and soul-stirring. The i5 captures every nuance; the air in her breath, the subtle shifts in her dynamics and the raw emotion that made her so beloved. There’s a sense of intimacy here that feels almost tangible, as though she’s singing in the room with you, just a few feet away.

What sets the Fosi Audio i5 apart in this track is its organic tone and emotional transparency. It simply lets the music unfold naturally. The decays linger gently. The room reverb of the orchestra feels real. And in those quiet pauses between lines, you can hear the weight of silence, not as absence, but as part of the storytelling.

Herbie Hancock – Gershwin’s world – The Man I Love
Herbie Hancock at the piano and Joni Mitchell on vocals, The Man I Love becomes more than a Gershwin standard; it becomes a quiet confession wrapped in jazz. Through the Fosi Audio i5, this performance is unveiled in all its emotional and sonic nuance.

Joni Mitchell’s voice, weathered and expressive, is rendered with breathtaking intimacy. The i5 doesn’t beautify or smooth it out, it presents her raw ‘almost smokey’ timbre faithfully, letting every crack, breath and hushed syllable fall exactly where it should.

Herbie Hancock’s piano is full of restraint and soul. The weight of the grand piano is revealed, the soft attack of each note, the lingering decay and the space between the chords. You can sense the studio air, the tension in the pauses and the reverberation of a phrase just after it’s been sung.

With the i5, The Man I Love becomes a deep personal moment; a late-night exchange in a jazzy bar between piano and voice.

Patricia Barber – Clique! – This Town
Patrica Barber’s This Town is a masterclass in jazz minimalism, dry wit, noir tension and late-night swagger all wrapped in a smoky groove. Through the Fosi Audio i5, the track becomes an immersive, almost cinematic experience.

Barber’s voice is presented with striking immediacy, cool and controlled. The i5 captures every nuance; the whispered consonants, the subtle vibrato and the delicious irony in her phrasing. There’s a sense that she’s right in front of you, leaning on the piano, telling the story with a raised eyebrow.

The bass lines are another highlight, resonant and full of texture. The i5 locks them in with precision and weight, anchoring the track while still allowing the groove to breathe. You feel the pluck of the strings, not just hear them. 

The percussion and cymbal work shimmer with air and space. The i5 handles the transient detail with finesse no splashiness, just crisp, natural decay. It’s the kind of clarity that reveals the drummer’s restraint and touch, not just the rhythm. The i5 gives each chord body and weight, with a harmonic richness that never feels exaggerated. 

The Fosi Audio i5 delivers a neutral transparency with a hint of warmth, a wide soundstage that makes every instrument feel anchored in space.

 

Pros:

• Detail & Transients: Crisp, precise, revealing subtle nuances in every track
• Soundstage: A wide stage with excellent layering and placement
• Premium Build Quality: Solid, refined construction that looks as good as the headphone sounds
• Bass-Seal Ring: Enhances bass linearity while gently smoothing the treble for a more balanced presentation
• Flagship-Level Fidelity: Delivers top-tier sound performance at a fraction of the price

Cons:

• Slightly heavy: Though not uncommon for larger planar designs

• Included cables: Are a little too stiff and less flexible than I would have hoped

• Exposed drivers when pads removed: Removing the pads fully, exposes the planar magnetic drivers, which may increase the risk of damage, so caution is advised.

Fosi Audio i5 product page