FOSI Audio i5 (Version 2) Review

 

Introduction:

FOSI Audio, an audio company founded in Shenzhen in 2017, has developed a reputation for producing amplifiers and digital-to-analog converters (DACs) often noted for their performance and accessibility. The company has since expanded its product line to include planar magnetic headphones, introducing the i5 model. This review focuses on the i5 Version 2, an updated iteration designed to address issues reported in the initial release. The original Version 1 was noted for concerns regarding sub-bass roll-off and acoustic leakage. These aspects have reportedly been addressed by FOSI Audio through the inclusion of a sound-isolating ring in Version 2. The headphone features a 97mm planar magnetic driver with a 2-micron diaphragm. This review aims to examine the design, build quality, and performance of the i5 Version 2, based on hands-on testing and analysis.

 

Disclaimer:

I would like to thank FOSI Audio for providing the i5 Planar Headphone as review sample. I am not affiliated with FOSI Audio beyond this review and all these words are reflecting my true and unaltered opinions about the product.

 

Price & Availability:

The FOSI Audio i5 planar magnetic headphones currently retail for $549.99 USD. More information’s about the availability can be found under the link bellow;

• FOSI Audio i5 Planar Headphone

 

Package & Accessories:

The i5 Version 2 comes in a premium cardboard box with a magnetic flap, featuring a foamcutout for secure storage.

Inside the box are the following items;

• 1 x FOSI Audio i5 Version 2 Headphone
• 1 x Detachable cable with 3.5mm TRS plugs and 6.35mm jack (1.5m)
• 1 x 6.35mm adapter
• 1 x User manual
• 1 x Sound-isolating ring (pre-installed)
• 1 x Warranty card

 

Design, Build Quality, Comfort:

The FOSI Audio i5 Version 2 features a practical design that prioritizes functionality and durability over flashy aesthetics. The ear cups, measuring 130mm by 105mm, are oval-shaped and finished with a glossy walnut wood veneer, which introduces a natural grain variation across units, though it remains uncertain whether this is genuine wood or a high-quality imitation.

The aluminum frame, crafted via CNC machining, provides a solid structure, contributing to the headphone’s total weight of 550g including the cable. A subtle S-shaped pattern on the ear cup grille serves as a decorative element, adding a minor visual distinction without dominating the overall look.

The open-back ear cups incorporate a rigid, high-transparency acoustic mesh that protects the 97mm diaphragm while allowing sound to disperse effectively. This mesh contrasts with the walnut finish and black aluminum frame, creating a straightforward yet effective design.

The dual-axis ear cup arms enable both vertical and horizontal movement, accommodating different head sizes and improving stability during use.

The ear pads are made with perforated leather and breathable fabric, filled with memory foam to conform to the ear’s shape, though the Velcro attachment may loosen over time with frequent removal.

The headband uses a memory metal core encased in genuine suede leather, offering a flexible yet durable fit that retains its shape after adjustments. The stepless silicone adjustment slider provides a smooth, damped mechanism for precise fit customization, though it can feel slightly stiff initially.

Clamping force is moderate, providing a secure hold without excessive pressure, while the perforated suede top and solid underside ensure breathability and wear resistance.

The 3.5mm TRS connectors at the ear cup bases are robust, fitting snugly with the detachable cable, and support easy replacements, though the connection point may attract dust over time.

The build quality of the i5 Version 2 stands out as successful, utilizing a combination of walnut wood veneer, CNC-machined aluminum, memory metal, and suede leather. These materials contribute to a sturdy yet manageable construction that withstands regular use, with the aluminum frame offering structural integrity and the suede providing a comfortable, durable headband surface.

The use of memory foam in the ear pads and the secure fit of the 3.5mm connectors further enhance longevity, making it a reliable choice for extended use.

 

 

Cable Design and Materials:

The standard cable included in the box with the headphones is constructed from 1120-strand 5N OFC Silver-Plated Wire, renowned for its excellent conductivity and resistance to corrosion. This ensures minimal signal loss and a clean audio transmission. The cable is sheathed in a flexible, tangle-resistant PVC jacket, providing durability while maintaining a lightweight feel. Its design features a twisted + enhanced shockproof mesh braiding, which enhances flexibility and reduces microphonic noise. The connectors are 3.5mm TRS plugs on each end, with a 6.35mm adapter included. These utilize gold-plated aluminum alloy contacts to prevent oxidation and ensure a secure, low-resistance connection. This cable offers good flexibility.

Optionally available is a 4.4mm balanced standard cable. It is also crafted from 1120-strand 5N OFC Silver-Plated Wire with a twisted + enhanced shockproof mesh braiding and gold-plated aluminum alloy connectors. This cable caters to users with balanced-output devices and offers good flexibility.

Additionally, another optional 4.4mm upgraded cable is available. This cable is made from 48-strand CVD Graphene Super Copper, featuring a twisted + enhanced shockproof mesh braiding and gold-plated aluminum alloy connectors. This option offers enhanced flexibility, described as “Soft and Durable,” for improved signal integrity and a more premium feel.

 

Drivability & Pairing:

With a 28-ohm impedance and 94dB sensitivity, the i5 Version 2 is relatively easy to drive. Portable devices like the iBasso DX340 or FiiO M23 DAP can power it adequately via single-ended outputs. For optimal performance, pairing with desktop DAC/amplifiers such as the FiiO K17 or FOSI Audio K5 is recommended, enhancing its dynamic range and detail. High-powered OTL tube amps can also drive it, though careful selection is needed due to its low impedance.

 

Technical Specifications:

• Driver Type: Planar Magnetic Driver with 2-Micron Thickness Diaphragm
• Impedance: 28Ω
• Sensitivity: 94dB
• Frequency Response: 20Hz – 40kHz
• Weight: 550g (incl. cable)
• Cable Material: High-Purity Copper Wire

 

Key Features:

• 97mm Planar Magnetic Driver
• Sound-Isolating Ring for Enhanced Bass (Version 2)
• Open-Back Design with Acoustic Mesh
• Walnut Wood and Aluminum Construction
• Dual-Axis Ear Cup Arms
• Detachable Cable with 3.5mm and 4.4mm Options
• Suede and Memory Foam Ear Pads

 

Equipment’s used for this review:

• Headphones: FOSI Audio i5 Version 2, FiiO FT5
• DAPs: iBasso DX340, FiiO M23
• DAC/AMP & Amplifier: FiiO K17, FOSI Audio K5

 

Albums & tracks used for this review:

• Norah Jones – Come Away With Me (Apple Music Lossless)
• Adele – My Little Love (Apple Music Lossless)
• Sarah McLachlan – Angel (Flac 24bit/48kHz)
• Sertap Erener – Aşk (Flac 16bit/44.1kHz)
• Edith Piaf – Non Je Ne Regrette Rien (Flac 16bit/44.1kHz)
• Diana Krall – So Wonderful (DSF)
• Aretha Franklin – I Say A Little Payer (Flac 24bit/96kHz)
• Michael Jackson – Billie Jean (Flac 24bit/96kHz)
• George Michael – Don’t Let the Sun Go Down on Me (Flac 24bit/192kHz)
• David Bowie – Heroes (Flac 24bit/192kHz)
• Elton John – Rocket Man ((Flac 24bit/96kHz)
• Barry White – Just The Way You Are (Flac 24bit/48kHz)
• Isaac Hayes – Walk On By (Flac 16bit/44.1kHz)
• Sting – Englishman in New York – (Flac 24bit/48kHz)
• Eric Clapton – Wonderful Tonight (Flac 24bit/96kHz)
• Dave Gahan – Kingdom (Tidal Hi-Fi)
• Radiohead – Live in Berlin “Album” (Apple Music Lossless)
• Radiohead – Pyramid Song (Apple Music Lossless)
• U2 – Sunday Bloody Sunday (Flac 16bit/44.1kHz)
• Muse – Hysteria (Flac 24bit/96kHz)
• Red Hot Chili Peppers – Nobody Weird Like Me (Flac 24bit/48kHz)
• Michael Jackson – Billie Jean (Flac 24bit/96kHz)
• Bear McCreary’s – Valkyries (Deezer HiFi)
• Bro Safari, UFO! – Drama (Deezer HiFi)
• Armin Van Buuren – Vini Vici (Flac 16bit/44.1kHz)
• Daft Punk – Instant Crush (Flac 24bit/96kHz)
• Daft Punk – Doin’ it Right (Flac 24bit/96kHz)
• Lorde – Royals (Flac 24bit/48kHz)
• Massive Attack – Angel (Flac 24bit/48kHz)
• Toutant – Rebirth (Deezer HiFi)
• Gogo Penguin – Raven (Flac 24bit/192kHz)
• Gogo Penguin – Murmuration (Flac 24bit/192kHz)
• Portishead – It Could Be Sweet (Apple Music Lossless)
• Hans Zimmer – The Dark Knight OST (Flac 24bit/96kHz)
• Max Richter – On the Nature of Daylight (Flac 24bit/96kHz)
• Charly Antolini – Duwadjuwandadu (Flac 24bit/192kHz)
• Tchaikovsky – Symphony No. 5 (Flac 16bit/44.1kHz)
• Ferit Odman – Look, Stop & Listen (Flac 24bit/192kHz)
• Chopin – Nocturn No. 20 In C-Sharp Minor (Flac 16bit/44.1kHz)
• Clair de Lune – Claude Debussy (Spotify)
• Fazıl Say – Nazım Oratoryosu (Live) (Flac 16bit/44.1kHz)
• Vivaldi – Le QuarttroStagioni “The Four Season” (Apple Music Lossless)
• Pink Floyd – Shine On You Crazy Diamond (Apple Music Lossless)
• Miles Davis – So What (Deezer HiFi)
• Otto Liebert& Luna Negra – The River (Flac 24bit/192kHz)
• Lunatic Soul – The Passage (Flac 16bit/44.1kHz)
• Deftones – My Own Summer (Shove it) (Flac 16bit/44.1kHz)
• Metallica – Dyers Eve (Flac 24bit/96kHz)
• Metallica – Sad but True (Flac 24bit/96kHz)
• Opeth – Windowpane (Flac 16bit/44.1kHz)
• Megadeth – Sweating Bullets (Tidal Hi-Fi)
• Rush’s – Tom Sawyer (Flac 16bit/44.1kHz)
• Slayer – Angel of Death (Spotify)
• Liquid Tension Experiment 2 – Acid Rain (Spotify)
• Yosi Horikawa – Bubbles (Spotify)

 

 

The Sound:

After about 100 hours of use, the FOSI Audio i5 Version 2 delivers a clear sound. It uses a 97mm planar magnetic driver with a 2-micron thin diaphragm. We didn’t listen to the first version, so all our comments are based on this new Version 2. This updated model includes a sound-isolating ring that fixes reported problems with weak bass and sound leakage from the older version. This change gives it a more balanced sound. The driver’s design, with its balanced magnets and sound-absorbing parts, provides clear sound and low distortion. It also reacts quickly to sounds, which helps show the true quality of recordings. For the best performance, it needs at least 500mW of power from an amplifier.

 

Bass:

The bass on the i5 Version 2 is quite good. It offers fast, clean, and very controlled bass that avoids the boomy or overpowering sound you sometimes get from other headphones. The addition of the sound-isolating ring in Version 2 is a big improvement. Users reported that the first version had weak bass and lost sound due to leaks. This new version lets the headphones produce surprisingly deep bass for an open-back design, especially when compared to many closed-back dynamic driver headphones. So, the bass is precise, handling deep, rumbling tones without sounding slow or muddy. This makes it suitable for many music types. When used with the iBasso DX340, the bass in Daft Punk’s “Doin’ it Right” gives a strong foundation for electronic beats. It stays clear and controlled even at medium volumes, but its deepest bass comes out with a more powerful device like the FiiO K17. The FiiO M23 DAP provides enough sound, but the FOSI Audio K5 makes the bass sound smoother.

In Lorde’s “Royals,” the bassline is tight and punchy, separating well from the vocals and not bleeding into the mid-range. This makes it ideal for pop songs where rhythm is key. The layered and textured quality of the bass is clear in Gogo Penguin’s “Raven.” Fast parts start quickly and fade out at a medium pace, letting each note and its subtle end sound very clear. This detailed sound works especially well for genres like R&B and jazz, where small bass details improve the overall listening experience. Even though the bass isn’t overly warm, its power and clarity are impressive. However, it might not offer the same raw bass power as some closed-back dynamic driver headphones without a very strong source like the FiiO K17. Additioanlly, the planar driver used in the i5 responds well to EQ adjustments, allowing for fine-tuning of the bass response.

 

Midrange:

The midrange on the i5 Version 2 has a clean and natural sound. This updated version was designed to make music sound more natural and engaging. When paired with the iBasso DX340, Norah Jones’ “Come Away With Me” sounds with warmth and emotional depth, capturing the intimate feel of the recording. However, some subtle background details might not stand out as much, suggesting the headphones focus slightly more on the main sounds. The FiiO M23 DAP gives vocals a slightly brighter tone, while the FiiO K17 adds a bit of richness, and the FOSI Audio K5 keeps the midrange clear and balanced.

Adele’s “My Little Love” shows how well the headphones handle a wide range of vocals. They deliver rich and resonant low notes along with clear and sharp highs, with very little harshness in “s” sounds, making the listening smooth and pleasant. However, in more complex songs with many instruments, a slight nasal quality can sometimes appear. Sarah McLachlan’s “Angel” demonstrates how well the midrange reproduces the piano’s resonance and subtle overtones with rich detail. This gives acoustic instruments a full and rich quality, adding body and presence to the sound mix. Despite these strengths, the midrange can sometimes feel a bit less prominent than the bass and treble, especially in complex musical pieces.

 

Treble:

The treble on the i5 Version 2 is bright yet smooth. This new version has been adjusted to avoid overly sharp high notes that could be uncomfortable during long listening sessions, offering an enjoyable high-frequency experience. This brightness boosts the energy of drums, brass, and woodwinds, adding fullness and presence to the sound for a lively feel. When driven by the iBasso DX340, Metallica’s “Sad but True” reproduces high-gain guitar riffs with a sharp attack and clear definition. This allows the song’s complex layers to stand out clearly without tiring the listener, making it a reliable choice for rock fans over long periods. The FiiO M23 DAP adds a touch of sparkle, while the FiiO K17 provides controlled brightness, and the FOSI Audio K5 offers a slightly warmer treble sound.

The technical skill of the treble is clear in Max Richter’s “On the Nature of Daylight,” where the delicate shimmer of string sections is captured smoothly and airily. This creates an immersive orchestral feeling, especially when used with the refined sound of the FiiO K17. However, sounds above 9-10 kHz show a noticeable drop-off. This means very high-pitched elements like cymbals or whistles might sound a bit quieter at the very top end compared to more analytical headphones. This drop-off is balanced by a gentler fade-out above 10 kHz. This design choice makes the sound more open and wide, prevents harshness, and ensures comfort during long use across all tested sources. The treble’s good speed and detail further show the driver’s technical abilities, providing quick and precise responses. However, the warmer tone of the FOSI Audio K5 might soften some of the finer details.

 

Soundstage:

The i5 Version 2’s open-back design creates a noticeably spacious soundstage, giving music an engaging sense of breadth. Sounds are well-separated, allowing instruments to be distinctly heard and layered, much like a live performance. The ability to place individual sounds in the space is accurate, though it may not achieve absolute precision with the most intricate recordings. Overall, the sound presentation remains unified and clear. While it offers a good sense of open space, it doesn’t reach the extreme depth found in some top-tier headphones, even when used with the FiiO K17

 

Comparison:

FOSI Audio i5 versus FiiO FT5:

The FOSI Audio i5 Version 2 and FiiO FT5 present distinct approaches within the mid-range planar magnetic headphone category, catering to different listener preferences. The i5 Version 2 leans toward a balanced to slightly warm and musical response, with the sound-isolating ring boosting its bass, making it a great fit for pop, electronic, and jazz where a fuller low-end drives the rhythm. The FT5, however, favors a neutral and analytical tuning, excelling in classical and rock where detailed instrument separation and a transparent midrange and treble are key, offering a cleaner, more clinical response for critical listening.

In terms of construction, the i5 Version 2 uses a walnut wood veneer with a CNC-machined aluminum frame, resulting in a 550g weight that might feel noticeable during long sessions but supports its sturdy build. The FT5’s all-metallic design is lighter at 492g, and while ergonomic, its weight might also be noticeable over time. Drivability favors the i5 with its 28-ohm impedance compared to the FT5’s 36 ohms, allowing it to work well with portable devices like the iBasso DX340 or FiiO M23 DAP. The FT5, however, scales better with high-end desktop amps like the FiiO K17, revealing greater dynamic contrast and refinement. The soundstage width is similar, with both providing an open and spacious presentation. The i5’s warmer tone creates a cozy feel for casual listening, while the FT5’s neutrality offers a precise, expansive stage for detailed analysis. The FT5 edges out in treble clarity with a crisper, more detailed high-frequency response, appealing to audiophiles seeking micro-details, whereas the i5’s smoother treble prioritizes comfort during prolonged use. The choice depends on preference: the i5 for a warmer, bass-enhanced experience, or the FT5 for a neutral, detail-focused profile.

 

Conclusion:

The FOSI Audio i5 Version 2 is a compelling choice in the sub-$600 headphone market, offering a practical design and a refined response that suits diverse preferences. The sound-isolating ring in Version 2 enhances the bass, making it powerful yet controlled for genres like pop, electronic, and jazz. Its build, with walnut wood veneer, CNC-machined aluminum, memory metal, and suede leather, ensures durability and comfort, though the 550g weight may be noticeable during long sessions.

Performance shines with desktop amplifiers like the FiiO K17 or FOSI Audio K5, which unlock its full potential, while portable devices like the iBasso DX340 and FiiO M23 DAP provide adequate drive. The headphone benefits from EQ adjustments to fine-tune the response. Minor issues include the lack of a hard case and potential dust buildup at the connectors. Overall, it’s a strong option for users seeking a balanced, driver-focused headphone with good comfort.

 

Pros & Cons: 

• + Surprisingly deep bass for an open-back, precise and clean (V2)
• + Vocals and instruments sound natural and engaging
• + Bright without being harsh, comfortable for long listening
• + Good sense of breadth and instrument separation from its open-back design
• + Responsive to EQ: Planar driver allows for effective sound customization
• + Durable construction with aluminum, wood veneer, and suede
• + Works well with portable devices, though benefits from a good amp
• + Improved Design (V2): Sound-isolating ring addresses V1’s bass and leakage issues.

 

• – At 450g (without cable), it might feel noticeable during extended use
• – Accurate, but not ultra-precise for extremely complex tracks
• – Lacks robust protection for travel
• – Velcro Ear Pad Attachment may loosen over time

 

Thank you for the Read!