Fosi i5 Headphone Review: Transparency Taken To The Max

For midrange open-back headphones, there are quite a few options that allow you to enjoy premium audio at a great cost. Hifiman's Ananda Unveiled, the Meze 109 Pro, Beyerdynamic DT 1990 Pro MKII: all these headphones are great options for a sub-$1000 listening experience. Fosi Audio comes in with a new contender to add to your collection. The Fosi i5 is a headphone that retails for $549 and promises immersive and transparent sound. It's a sound that has people wondering: Is this the best new open-back to hit the market?

• Device Type: Open-Back Wired Headphones
• Transducer Type: Planar Magnetic Drivers
• Maximum Sound Pressure Level: >120 dB SPL
• Frequency Response: 10Hz - 50kHz
• THD: <1% @ 100 dB SPL
• Sensitivity: 98 dB/mW @ 1kHz
• Nominal Impedance: 28Ω
• Recommended Power: ≥ 500mW
• Minimum Recommended Power: 100mW
• Weight: 550g

SOUNDSTAGE & IMAGING

Now we move onto the i5's sound profile. The Fosi i5 invites you to be completely immersed in your listening. The soundstage has a lot of stereo width and expands backwards to give you just as much depth. The layers allow you to focus clearly on each instrument in a track, with decent separation that is placed expertly around you. The level of detail across the entire frequency range is clear to hear, and the transparency in the midrange is a highlight. The i5's sound is pretty grounded, not really getting to high up in height, but the placement of everything makes me think this could be a great addition to a gaming setup. 

The i5's sound signature is interesting because of how transparent it is. The midrange has a clarity that makes it almost invisible, so you have a lot of clarity and drive coming from the bass and treble. This V-shape makes critical listening take on a new form, where you listen mainly for instrument placement rather than exact tonality. The sound signature on the Fosi i5 is fun and dynamic, so you can pass a lot of different genres through these headphones and be entertained by each track. 

BASS FREQUENCIES

On open-back headphones, the bass is normally pretty relaxed and takes a backseat in the signature. This remains pretty consistent when listening to the Fosi i5. With the i5, you get a laid back bass repose that is punchy and driving without being overwhelming and the entirety of the sound signature. It is deep and grounded, giving you a nice foundation that everything will build up from. The bass is certainly thick with color and character, but it doesn't overwhelm the sound signature completely and become the only thing you notice. The sub-bass rumble isn't quite there, but it doesn't need to be since you get a nice level of clarity in the bass to make guitars, drums, and low-register vocals all distinct and separate. 

MIDRANGE FREQUENCIES

The Fosi i5's midrange is quite forward, so you get this section at the forefront of your mix. This makes the i5's sound signature take on the classic V-shape. At the same time, the transparency made this section sound so thin and nearly invisible. The sound reproduction was effective of giving you natural timbres and dynamics, and you get distinct coloration between different instruments for a memorable sound. Vocals sounded like they were in the room with me, and other instruments filtered around it to create total immersion. 

Listening to this section on the i5 was a bit of a battle because of how transparent the frequencies got. There was some distinct characteristics that almost faded to the background because of how clean things sounded. It was interesting to see how the i5 handled those midrange instruments layered backwards and filtered around you, creating an ultra-immersive listening experience that was unlike anything I'd heard. It almost had a thin quality to it, which made it an odd complement to the more grounded bass. 

TREBLE FREQUENCIES

I really liked the treble response of the Fosi i5 the best. There is an airy quality about them to really open up the top end of the signature, allowing frequencies to air out and dissipate naturally. The top doesn't hit any shelf or have an awkward cut-off, so you are able to listen smoothly and have frequencies blend into their natural environment. I definitely noticed how the i5's top end maintained clarity and detail without leaning into the piercing range; there was enough overall brightness that it wasn't too sharp to listen to. High strings and brass instruments were well reproduced, and the treble made sure to take a step back so the midrange could be the focus. It lined up well with the bass, creating pristine balance that worked across multiple genres. 

During my time with the Fosi i5 headphone, I used a few different DACs and amplifiers to see what would be out there. Luckily, the i5 is not hard to drive with a 28Ω impedance, but having an additional amplifier and DAC certainly cleans up the sound. Fosi Audio has a few amplifiers that they make themselves, and I used a few during my time with the i5. With the i5, I used the following: 

• Fosi MC331 Tube Amplifier
• Fosi DS-2 Portable DAC/Amp
• FiiO QX13
• iFi GO Blu

Out of all the amplifiers used in my setup, I found myself leaning towards the tube amplifier the most. The clear sound of the i5 paired well with the warmth from the MC331, creating a nice, laid-back listening experience that I could really immerse myself in. The FiiO QX13 was also a great pairing to the i5, complementing the clarity and detail heard across the sound signature and giving it an extra boost.