Fosi Audio isn’t exactly the first name most audiophiles think of when it comes to mid-tier planar magnetics. Their amps? Yes. Their DACs? Yes. But a premium open-back headphone? That’s new territory.

The i5 is their shot at the “serious headphone” category — a full-size open-back planar magnetic headphone built with walnut wood, CNC-milled aluminum, and a driver that’s nearly the size of a DVD. And after spending serious time with it, one thing is immediately clear:

Fosi isn’t playing around.

This is a legitimately high-end headphone… with one big catch:
It’s absolutely massive.
One of the largest headphones I’ve ever tested. Buy them on Amazon!

Design, Build & Comfort — Gorgeous, Premium… and Huge

The i5 is honestly beautiful. The mix of walnut wood, precision-cut aluminum, and plush pads gives it a handcrafted, boutique feel. Everything feels dense, tight, and high-quality. The tolerances are clean, the pivots feel strong, and the overall impression is that you’re holding something far more expensive than its price tag suggests.

But let’s talk size.

Because wow — the i5 is huge.

Not heavy to the point of discomfort, but these cups are gigantic. The headphone has the kind of physical presence where you put it on and feel like a deep-sea submarine operator. If you have a small head, this is not your headphone. Full stop. Buy them on Amazon!

Despite the size, comfort is solid for long listening sessions. The pads breathe well, the clamp is moderate, and the weight is balanced. Just be prepared for a headphone that looks and feels “big-boy audiophile.”

This isn’t portable, it’s not subtle, and it’s not the kind of headphone you wear while your partner is sitting next to you watching Netflix.
It leaks heavily — as open-backs do.

Sound Quality — Clean, Fast, Spacious, and Surprisingly Refined

Here’s where Fosi stuck the landing.

The i5’s sound quality is excellent — absolutely competitive with mid-tier planars from well-known brands. Fosi went for a tuning that’s clear, detailed, and open, without going overly bright or clinical.

Bass

The low end is tight, fast, and controlled. It’s super clean, with that classic planar grip. But it’s not a bass-cannon. You’re not getting huge sub-bass rumble or physical slam. This is about accuracy, not impact.

If you love deep, chest-kicking bass, look elsewhere.
If you love clean, articulate bass that never muddies the mids, the i5 nails it. Buy them on Amazon!

Midrange

Vocals and instruments sit in a natural, lifelike zone. There’s a slight hint of relaxed upper mids that gives it an easy-listening character — nothing shouty, nothing in-your-face. Male and female vocals come through with great clarity and space.

Treble

The treble is clean and crisp, with good extension and air. Not overly sharp, not sibilant, but definitely detailed. The i5 gives you that “planar sparkle” without getting fatiguing.

Soundstage & Imaging

This is one of the biggest wins.

The i5 has a big, airy, holographic soundstage — easily above what you expect in this price class. Imaging is sharp, layering is excellent, and instruments occupy distinct, well-carved spaces. Think Grand Canyon level openness.

If you love wide, spacious presentation, this headphone is extremely satisfying.

Source Pairing — Scales Well, but Not Demanding

With an impedance in the high-20s and decent sensitivity, you can run the i5 off portable DAC/amps and mid-range desktop gear, but I wouldn't recommend it. To get that last 20% of sub-bass presence, stage width, and treble refinement, you’ll want a proper desktop amp with some punch.

It doesn’t need a monster amp — but it definitely rewards a good one. I ran them on a SMSL DO400.

Daily Use — Amazing Sound, Big Footprint

This headphone is a “sit down and listen” design. Because it’s huge, open, and leaks like crazy, it’s not meant for:

❌ Offices
❌ Shared living rooms
❌ Traveling (strong no)
❌ Walking around the house

What it excels at:

✅ Music sessions
✅ Late-night audiophile listening
✅ Soundstage-focused genres
✅ Mixing / reference listening
✅ Gaming and cinematic content where immersion matters

Final Thoughts — A Legit Planar Contender if You Can Handle the Size

The Fosi Audio i5 shocked me a little. I expected decent “first attempt” energy, but instead I got:

• Excellent overall sound quality
• A clean, open, wide soundstage
• Fast planar bass
• Fantastic build materials
• A headphone that genuinely feels premium

But the elephant in the room is… the headphone itself.

It’s massive.
One of the largest I’ve ever reviewed.

If you’re cool with a gigantic headphone that leaks sound everywhere and is meant for stationary listening, the Fosi i5 is absolutely a contender in the mid-tier planar space. The sound is excellent, the build quality is impressive, and the price is competitive. Buy them on Amazon!

If you want something smaller, lighter, more bass-slamming, or more closed-in, this won’t be for you.