Sound Impressions

Tuning, Pt. 1

At first listen, the NF6 really had me fooled. For the first three songs I was of the impression that the tuning is neutral and flat across the board. But that it is not. However, bass, mids and highs are almost equally present. NF-Audio created an extremely poisonous and addicting W-shape opposed to general popular V-shapes.


The NF6i features a very lively bottom end. Bass extension reaches very low and allows slam in electronic music or necessary atmospheric rumble in Orchestral soundtracks. Yet the bass does not come off as pronounced. The accentuation focusses on the sub-bass allowing an almost dynamic-y body. Luckily, we are still in balanced armature-range and the tightness is enjoyable even with fast Thrash Metal tracks. Warmth is comparably recessed, giving less texture than a neutral response but thus also allowing more musicality without drifting into bassy territory.

The bass elevation is fairly moderate with peaking at around +6 to 7 dB. It is nothing that will woe bassheads but it is also very far from anemic. We are definitely in an era in which people appreciate a mild bass boost over the absurd bass quantities of last gen’s monitors. NF Audio follows recent trends and adds but a little oomph.


The midrange sounds very natural with realistic body and high detail. The presentation from 250 Hz to 2.5 kHz follows the ideal response closely and allows great detail. There is a little bit added edge at around 3.5 kHz but the NF6 don’t sound too forward. Actually, the upper midrange takes a dive after 4 kHz up until the high frequencies from 6 kHz upwards.

The local minimum at around 5 kHz could be a phase issue but it could just as well be intended. I wouldn’t know. Anyway, it takes out any harshness from the midrange while hardly hurting the details. Instead, it allows for a more spheric soundstage. But more on that later.

In the big picture, voices still lack a wee bit presence next to bass and treble. However, this is comparing with studio references only. It is not enough to cast a veil on male voices or to bleed warmth into the body. Electric guitars still have all their energy and neither male nor female voices sound tonally off.

Sadly, my unit is slightly unbalanced between left and right at around 1-2 kHz. That makes one side sound a very tiny bit tinny. It is not an issue that is easily noticed while music is playing, but for professionals that ask for perfection, it could cause some confusion. My ear canals are not symmetrical, however, so I don’t want to over-emphasize the 3 dB difference. (Remember, I also noticed a disparity with my Jomo CIEM in this area.)

High Frequencies

Let’s finally talk about the showstopper here. The high frequencies of the NF6i are absolutely addicting like nothing I have experienced in an IEM before. They are incredibly revealing with a ridiculous amount of detail and clarity. Even though they are very present, they never sound sibilant or piercing. The amount of air and natural space NF Audio managed to reproduce is absolutely fascinating and it makes many earphones sound very compressed and dull in the treble.

In the introduction I mentioned impressions comparing the NF6 with electrostatic earphones and now I can fully understand why. It doesn’t even sound like a CIEM anymore. I cannot even think of any closed supraaural dynamic headphone that manages to create such a convincing treble. Yes, I know that that is a bold statement but I stand by it.

Even though the high frequencies are smooth, should one absolutely detest present treble, one could argue that after prolonged use they could be perceived as hot. 9-14 kHz show a steady level that is very uncommon for balanced armatures – or almost any IEM for that matter. Even more impressive how NF Audio managed to maintain an overall smooth signature. This is a true improvement over the harsh treble peaks we had to accept some years ago.

Tuning, Pt. 2

After having the sound signature picked to pieces, I think it’s fair to make the description whole again and to take a second look at the overall tuning.

Despite not following a natural or neutral frequency response like Etymotic or the recent InEar ProPhile 8, the NF6i sound smooth and still manage to sound natural and musical.

The NF6i are not bright sounding earphones. Quantity-wise, bass, midrange and high frequencies are well-balanced, yet every segmentation has its uniqueness that creates a more lively presentation on its own. The bass focusses more on the very low-end, the midrange has more crunch than edge and finally the treble shies away from sibilance but adds definition and air.

It feels like the NF6 has more of everything: more bass, more mids and more high frequencies. I don’t know any other IEM that tries to achieve the same. The NF6(i) feature a fun sound signature that has neither recessed mids nor sibilance and that makes it even more enjoyable to listen to as an all-rounder.

Soundstage, Imaging and Resolution

The soundstage is very wide and has ample depth. The amount of air and definition from the treble help greatly with separation and layering. A slight suction in the upper midrange/ lower treble pulls voices back maybe just one or two rows. This results in a spheric presentation with the listener sitting in the 4th or 5th row instead of standing in the very front like with the ER4.

I did notice that the imaging is not super precise. Some instruments tend to drift vertically. Especially drums sometimes sounded like they were below in front of me and cymbals hit over my head instead of being on the same height. I used Dr. Chesky’s binaural test tracks for a more detailed analysis, but with such reference material the issue was hardly noticeable.

Treble can carry a lot of information. And in this case, it not only provides great separation and layering, but also amazing clarity. I am trying my best to stay away from the term ‘transparent’, but I know many reviewers would be throwing this around right now. However, the NF6i are not transparent as they have a uniqueness to their sound, somewhat floaty and easy, but they reveal a crazy amount of detail. Even though the bass is tight, the focus lies with mids, treble and their partial overtones.



Despite my review unit being the revised NF6i instead of the original NF6, they are still somewhat power hungry when compared to other multi-BA designs in the same league. For example, hooking the ifi iEMatch up to an iPhone 6S Plus, it is very likely that you will hit the max volume cap on ultra. An even less audiophile device like the Nintendo Switch might not provide enough volume for your needs altogether. The sensitivity is rated at 106 dB. A fullsize orthodynamic like the Oppo PM3 can even achieve higher volumes.

Hugo Pairing

However, the NF6i are not so dependent on the output impedance and they do not tend to pick up hiss easily. Naturally, the Chord Hugo is a great source yet again. This chain creates an ultra-lightweight feel with the music just floating in front and around you. The experience is close to mesmerizing.

Mojo Pairing

The Mojo adds some deeper blacks but takes away some of the magical space in the treble. Going straight to the iPhone 6S output, the NF6i play more forward with heavier and slower bass. The treble luckily doesn’t lose precision, though. My desktop reference RME ADI-2 Pro is fully transparent and got the most natural presentation out of the NF6i. Neither bassy, nor forward but with a realistic treble.

Select Comparisons

Campfire Audio Andromeda

You cannot mention clarity in a review and disregard the reigning popularity king Andromeda by Campfire Andromeda. Based on other user’s reviews, I was expecting the Andromeda to sound similar. However, having already adjusted to the NF6i for a few weeks, the Andromeda left me very underwhelmed. Andromeda’s midrange appeared not only strongly recessed, but voices were a bit muffled in an A/B-test. More noticeably, the Andromeda showed minor sibilance issues – something the NF6i does not have and yet still provides more clarity, more amount of treble and much more air. The Andromeda also sound thicker as they have more bottom-ground.

These are two different signatures with the Andromeda being a warm-bassy monitor with some balanced treble energy. I have to admit that I prefer the more lightweight sound from the NF6i that also features punchy bass and lively treble, yet shows less fatigue and a more natural midrange. Once you get used to the warmth, the Andromeda do have great coherency and a better imaging, but switching back to the NF6 is like surfacing from under water and gasping for air.

Jomo 6 V2

My pair of Jomo6 V2’s are masters of bass texture and they provide string details on cellos that the NF6 cannot render. The 6V2 sub-bass tightness is still amazing. The transition from bass to mids is also more natural and the midrange is more behaved. However, voices sound more alive through the NF6 because of the middle W-signature peak. While signatures can be a preference, I do have to rate the treble performance by NF Audio as much better. The Jomo sound compressed in the treble and lack the air and realistic shimmer of the NF6i.

InEar ProPhile 8

As for natural sounding monitors, the InEar ProPhile 8 are hard to beat at the moment. When put up in an 1on1, the NF6i firstly showed that voices appear a little more distant due to the upper midrange drain. Instead, they put maracas and other high frequent instruments more to the front. But not too much, the timbre remains natural and convincing, even if a little bit fuzzy when challenged by the ProPhile in subpar recordings. Both monitors render male voices well and relaxed. The PP8 are more transparent with female voices, though, which appear a little bit warmer on the NF6.

Bass and dark wood instruments sound amazing on both monitors. The overall bass quantity of the NF6i is more comparable to the PP8 with activated bass boost, but the InEar will show more slam and greater impact than the NF Audio. (This is likely due to comparing a CIEM with a universal.) Surprisingly, the NF6 have a wider and deeper soundstage while boasting equally impressive layering and separation.

In the end, the ProPhile remain a bit more transparent (especially in the lower treble) with similar clarity, flat frequency response, having superior driver matching and thus are more suitable for monitoring. However, the NF6 feature great performance and provide a bit more fun-factor even when the ProPhile has both switches activated. Having minor issues with coherency and transparency, after prolonged use, NF Audio anyway just landed on the number two spot on the list of my favorite IEMs.

Our Verdict

NF Audio caught me by surprise. Based on Chinese local reviews, I was already expecting a solid contender with an enjoyable sound. Obviously, one would expect a newcomer brand to punch the price very low. NF Audio did all that, but that is not even enough to describe the NF6i. This earphone is unique and just as enjoyable as many well-regarded TOTL CIEMs. The high frequencies performance is outstanding. The clarity matches that of an open vented design yet allows high isolation in a custom fit. All without fatigue or sibilance. The NF6i sound fresh and have a unique selling point.

The NF6i are not a new studio reference as their W-signature does not allow the most precise of monitoring across the frequency spectrum. The accurate mid-range floats like an island between present sub-bass and airy upper range. Overall, the NF6 are refined all-rounders that do not let any detail go amiss with any genre. It’s all there, plenty and balanced. They sound fun and hardly colored at the same time. They left me impressed.

Being able to place an order through a Chinese market only will understandably be a huge turn-off for most. But this is a product I advise to put on the watch-list. International dealers or a universal fit might be on their way; at least I hope so, for a more competitive market.

Technical Specifications

  • System: 6 BA, 4-way design
  • Frequency response: 8-30 kHz
  • Impedance: 18 Ω@1kHz
  • Sensitivity: 106 [email protected]
  • Distortion: below 0.5 %
  • Isolation: 26 dB (CIEM)

Leave a Reply

Your email address will not be published.