Fosi Audio i5

Package Contents

The Fosi Audio i5 arrives in sturdy packaging with a custom-moulded foam insert for secure storage. Two high-quality cables (3.5 mm and 4.4 mm balanced) are neatly stored in separate pouches. A 3.5 mm to 6.35 mm adapter is included for immediate compatibility with various devices. No dedicated headphone carrying case is provided.

Technology

97 mm Diaphragm

An ultra-thin (2 µm) nanomaterial diaphragm promises fast transient response and high accuracy. The large surface area is said to enhance detail retrieval, dynamic extension, and transient handling compared to smaller drivers.

Target Sputtering Technology

A 1.3 µm silver voice coil is deposited onto the diaphragm, increasing conductivity, reducing distortion, and ensuring long-term performance stability.

Magnet Array

Each planar driver houses 22 symmetrically arranged N50 neodymium magnets, creating a strong, even magnetic field for stable diaphragm movement and reduced distortion.

Acoustic Mesh

A rigid, highly transparent rear mesh regulates air pressure and reduces unwanted resonances, producing an open, airy sound with minimal resistance.

Rear Chamber Damping

The rear acoustic chamber uses airflow management to control resonance and improve spatial precision.

Open-Back Over-Ear Design

The open construction of the Fosi Audio i5 provides a natural sense of space and reduces the “in-head” effect.

Specifications

• Driver: Planar magnetic
• Frequency range: 10 Hz – 50 kHz
• Impedance: 28 Ω
• Sensitivity: 98 dB/mW @ 1 kHz
• THD: < 1% @ 100 dB SPL
• Max SPL: > 120 dB
• Recommended power: > 250 mW (minimum > 100 mW)
• Weight: approx. 550 g

Comfort

Despite weighing around 550 g, the i5 is surprisingly comfortable.

• Dual-axis earcup arms: Allow vertical and horizontal adjustment, ensuring a precise fit without pressure points.
• Stepless silicone slider: Enables smooth, precise headband adjustment.
• Memory-metal headband: Retains shape, evenly distributes weight, and maintains gentle clamping force.
• Breathable earpads: Memory foam covered in perforated fabric keeps ears cool over long sessions.

Even during multi-hour listening, the fit remains secure and comfortable, with no discomfort for glasses wearers.

Build Quality

The Fosi Audio i5 exhibits premium craftsmanship, with perfectly aligned aluminium, walnut, and leather elements. There are no sharp edges or assembly flaws. The S-shaped decorative plate on the earcups, inspired by musical notes, adds visual appeal.

Dual 3.5 mm connectors in each earcup securely hold the supplied cables, which are both flexible and robust. The Fosi Audio i5’s overall build feels like it will withstand years of use without visible wear.

Sound Impressions

Low Frequencies

Sub-bass and bass are slightly restrained out of the box, giving an analytical, controlled presentation. A 3 dB EQ boost adds welcome weight. Mid-bass is clean, fast, and well-defined, making basslines tight and articulate.

Midrange

Mids are neutral and detailed, with natural vocals and instruments. Slight forwardness in the presence region can occasionally introduce sharpness, which can be reduced with a 2–3 dB EQ cut.

High Frequencies

Treble is detailed and airy, providing excellent resolution. In some tracks, it can lean analytical or slightly bright; EQ adjustment can add warmth if desired.

Soundstage & Imaging

The open design delivers a wide, natural stage with precise imaging and convincing depth. Instruments and vocals are well-positioned without sounding artificially stretched.

Overall Sound Character

The Fosi Audio i5 shines with acoustic genres like jazz, classical, and singer-songwriter material, offering neutrality, dynamic subtlety, and a lifelike presentation. For electronic, rock, or metal, bass boost via EQ can add the needed punch. Treble smoothing can also help tame sharp masters.

Conclusion

The Fosi Audio i5 is a serious planar magnetic contender, combining technical precision with premium craftsmanship.

Key Takeaways:

• Analytical, precise bass; easily boosted with EQ
• Neutral, well-detailed mids with natural timbre
• High-resolution treble that benefits from occasional smoothing
• Expansive, realistic soundstage
• High comfort despite its weight
• Outstanding build quality with premium materials

Now available as a late pledge: Fosi Audio i5 planar magnetic headphones

The brand new Fosi Audio i5 planar magnetic headphones are currently in the late pledge phase on Kickstarter. The official market launch date is scheduled for September 2025 – but if you don’t want to wait that long, you can secure one of the limited packages now.

• i5 Basic Pledge – £229
• Includes headphones, detachable cable, carrying case and 2 pairs of ear pads.
• i5 Kit Pledge – £269
• Basic package + replacement velour ear pads & a symmetrical 4.4 mm cable.

Tip: Both pledge levels are limited – secure your set while stocks last.