Established in 2017, Fosi Audio is headquartered in Shenzhen, a bustling modern city in China close to the Hong Kong border. The company's name is an acronym for its four core principles: foresight, openness, sincerity, and innovation. Its stated mission is to redefine hi-fi with unmatched value. Fosi recently announced the debut of its new hi-fi 'ecosystem', which includes the i5 headphones reviewed here. It's the company's first such product and lands straight into a hotly contested market sector due to its price point.

UP CLOSE

The i5's machined aluminium frame and lovely suede headband exude quality, as do the gloss walnut ear cup trims. It is a large headphone due to its oval-shaped earcups that measure 130mm high and 105mm wide. The headband slider, which Fosi says is silicon-damped, is stiff but glides smoothly once you put some muscle into it. Physical dimensions are 240x160x55mm (HxWxD), and weight is 550g without cables.

Each planar magnetic driver uses a big 97mm diaphragm that is just 2μm thin. The voice coil is sputtered with silver and positioned between twenty-two N-50 grade neodymium magnets placed symmetrically on both sides, according to Fosi. This is said to enable precise and stable diaphragm vibration for low distortion and fast transient response. The rear metal grilles use a rigid, high-transparency acoustic mesh, which we're told helps to deliver a smooth tonality.

The 1.5m fabric-sheathed connecting cable is made out of 1,120 strands of 4N OFC silver-plated wire and terminated with a 3.5mm jack (with a 6.3mm adapter supplied). There is also the option of 4.4mm balanced cables at an extra cost. The detachable cables connect to the headphones via dual 3.5mm sockets at the bottom of each earcup. The cable is light, flexible and non-microphonic.

Fosi lists the i5's nominal impedance at 28 ohms and recommends at least 100mW of power to drive these, with at least 500mW for best results. These requirements are comparable to other planar magnetic headphone designs, which are generally less sensitive than their dynamic brethren.

In use, I found that my portable devices struggled to properly drive the i5. My Questyle M15 dongle DAC and HiBy R4 DAP lacked grip, especially during loud passages. Using balanced outputs with increased current delivery improved things, but still left room for improvement. As a result, for the purposes of this review, a Chord Hugo TT2 'tabletop' DAC/headphone amp was used – and this gave excellent results.

This pair of headphones is really comfortable to wear, for me at least. Despite being quite a heavy design, long listening sessions present no problem thanks to the wide headband distributing the weight of the i5 evenly across the top of the head. Meanwhile, the headband and earpads' perforations help keep things cool, even in tropical weather. The headband's slider adjuster should have enough range to accommodate most head sizes. The fully swivelling earcups have thick earpads, which are very soft. These factors should result in most users getting a pretty good fit.

THE LISTENING

The wide and spacious soundstage of the i5 impresses greatly, as does its fairly neutral tonality, which has plenty of bass, a pleasantly laid-back midrange and smooth, delicate treble. It's fast enough to carry the music's rhythms convincingly and has strong and impactful dynamics – thanks in no small part to those large transducers, I'd wager. In other words, it showcases all the benefits of a good planar magnetic headphone design.

For example, its tight and controlled bottom end is pleasingly solid. The kick drum and floor toms on Unstatic by Manu Katché sounded punchy and authoritative. Unlike some bass-heavy cans, this was done without blurring out detail, leaving the plucking on double bass tight, textured and detailed. This was mated with well-behaved high frequencies that were clean and silky. Katché's cymbal strikes and the brass instruments had a softer edge that didn't call attention to themselves but resonated and faded gently. Some may prefer a more incisive and spot-lit character, but this will appeal strongly to those allergic to brightness.

The Fosi's midrange is generally laidback and smooth. Tracy Chapman singing Baby Can I Hold You sounded clear, even and grain-free. However, I noticed that the i5 exacerbated sibilance slightly on some vocal tracks. The most obvious culprit was the spoken word, where there could be a hollow and nasal tinge to voices on podcasts. This design is certainly no fan of sub-standard source material.

On good recordings, violin strings sounded natural, with a fine balance between bite and body. Chloe Chua's performance of the finale of Paganini's Violin Concerto No.1 was ably reproduced by the i5 and showcased both her technical expertise and emotional depth. There was also commendable separation between the orchestra and Chua's violin, allied with the retrieval of fine detail, such as the gentle plucking by the string section. Instead of a flat wall of sound, you could hear the various sections as they performed, giving a deep, layered listening experience.

High-tempo songs show that the Fosi can rock with the best of them. Busy tracks like Best of You by Foo Fighters were kept tightly under control with a tidy presentation of vocals, guitars and drums. The sibilance on Grohl's voice was exaggerated here though, giving it some grittiness. The Fire Rises from the soundtrack of The Dark Knight Rises by Hans Zimmer sounded great, complete with all the darkness, suspense and excitement you would expect from one of his cinematic compositions. The opening sounded dynamically impactful and grand, aided by the low-frequency authority of the i5. It was also nimble enough not to be caught out by the fast pace or the changes in tempo as the mood alternated between fast and suspenseful.

The Fosi is fairly unfussy about its musical diet and should handle most genres well. It's pretty balanced in its overall voicing, offering slightly higher resolution than the popular Drop 6xx, along with better bass and superior spatiality. Even against the much more costly Drop 8xx, the i5 acquitted itself comfortably with a more musical and even tuning. However, the former had a wider soundstage presentation and a more prominent and incisive treble. Tonally, the Fosi was in the middle of both, sounding livelier than the cheaper design but not as exuberant as the more expensive one. If I had to make a choice, I could happily live with the i5 in lieu of either.

THE VERDICT

Overall, then, I was left impressed with Fosi Audio's new i5 planar magnetic headphones. It is a meaningful upgrade from any budget design sonically and also offers superlative build quality and finish. Factor in excellent comfort, and it's possible to enjoy its satisfying sound for hours on end. Although it doesn't offer the stunning value of some of the company's other offerings, it's still well worth auditioning.

The i5 Planar Magnetic Headphone is now available on a 40-day Kickstarter campaign starting 22 April; check out the discounts and perks for early birds.

Visit Fosi Audio for more information