Fearless Audio S6RUI Review – Pinnacle

Fearless Audio S6RUI featured
Tested at $389

Fearless Audio is a Chinese company that has been around for a while but until recently operated only within China. Luckily for us, they have broadened their target market and today we review the Fearless Audio S6RUI earphones.

The S6RUI has 6 balanced armatures per side with a dual Sonion BA on bass duty and Knowles BA drivers in charge of the mids and treble. I can tell you right now, this is one of the best IEMs I’ve heard in recent times and it has quickly become one of my favourites.

Linsoul Audio official website: https://www.linsoul.com/

This sample was provided for the purpose of an honest review. All observations and opinions here are my own based on my experience with the product.

Fearless Audio S6RUI Review

This is box title
  • Extremely comfortable earpieces
  • Great build quality
  • Good accessory bundle included
  • Resolution, instrument separation and tonality
  • Extensive customization options

This is box title
  • No proper lip on the nozzle means some eartips slip off easily

Package and Accessories

The S6RUI comes in an unassuming but attractive brown box. There is an outline of an IEM faceplate and the brand logo on the front. On the rear of the box are some specifications and a QR code. Inside the box is a plastic carrying case, cleverly secured within an insert that is made from the same cardboard and the main box.

This looks to be more practical and environmentally friendly than the common foam-filled packaging we’re used to and I dig that. The included hard case contains the earphones and all of the included accessories. Let’s break down the contents.

  • Fearless Audio S6RUI earphones
  • Plastic carrying case
  • Shirt clip
  • Detachable 2-pin braided 8-core cable
  • Shirt clip
  • 4 pairs of foam eartips
  • 3 pairs of whirlwind silicone eartips
  • 5 pairs of black silicone eartips
  • Cleaning tool
  • Aluminium information plaque

The unboxing experience is a simple one but the list of accessories is very good. I love to see bundles like this because most of the time the box just gets thrown out after opening anyway. Adding the metal plaque that contains info such as manufacture date and the name of the person who assembled it adds a touch of personalization.

Fearless Audio plaque

Build Quality and Design

S6 faceplates

The Fearless Audio S6RUI is a gorgeous in-ear monitor (in my opinion). Its 3D-printed, transparent shells are flawless and exceptionally clear, giving you a clear view of the internal components. You can clearly see the balanced armature drivers, crossovers and internal wiring.

Shells and internals

There are lots of design options available for the Fearless IEMs, allowing you to choose the faceplates and shells of your choosing. The faceplates are joined to the shells seamlessly and the edges everywhere are rounded and smooth. Those aspects along with the shaping of the inner shells help the monitors fit naturally in your ears.

My only gripe with the design is the lack of a proper ridge or lip on the nozzles. Without a ridge present some eartips with a wider core can slip off easily and get stuck in your ears.

Comfort and Noise Isolation

For me personally, the S6RUI is exceptionally comfortable and fits my ears like a glove (no, my ears don’t have fingers). I can wear these happily all day without any discomfort whatsoever. They’re lightweight and have curves and hollows in all the right places.

Passive noise isolation is considerably above average. The S6RUI housings are non-vented and fill the ear concha much like a custom earphone. So assuming you are getting a good seal, very little outside noise reaches your ears, making these suitable for any environment except places where you need to hear your immediate surroundings.

Noise leak is practically non-existent so you won’t disturb your neighbour on the bus or that grumpy old woman who has a desk next to yours in the office.

Colour-coded 2-pin connectors

The 8-strand braided cable feels just right as a match for the S6RUI. It is an attractive silvery-white colour and looks quite premium. The TPU sheath is supple but robust and it drapes nicely without getting hooked up or dragging on your clothes (assuming you wear clothes you cheeky devil!) On top of that there is virtually no microphonics and it is lightweight.

At the top end are the colour-coded aluminium 2-pin housings, followed by some preformed heat-shrink ear guides. A tasteful aluminium Y-split sits further down the cable and this has the brand logo etched onto one side. Just above this is a matching chin slider with Fearless Audio subtly etched onto one side.

The cable terminates in a straight 3.5 mm aluminium plug with carbon-fibre pattern and solid strain relief. Overall it is a quality cable that most people should be happy with unless of course, you wish to use a balanced source.

S6 cable


Gear used for testing includes the Shanling M5s and iBasso DX120 for portable sources. On the desktop, I fed FLAC files from MusicBee on my PC to the FiiO K3.

The Fearless S6RUI has a warm, resolving character that is balanced and full-bodied. It has detail in abundance, earthy, punchy bass and balanced sound signature.

Fearless Audio S6 frequency response

With a lot of multi-BA IEMs, I sometimes get reminded that there is no dynamic driver. It’s when that bass drop comes or that part in a song where you’re expecting some rumble and it just doesn’t happen. I don’t get that with the S6RUI. It never feels like you’re compromising on the bass and that is a big deal for me. It really sounds and feels like a dynamic driver is on bass duty so those Sonion BA drivers are doing some fantastic work.

The bass adds an underlying warmth to the overall tonality and does so without negatively affecting the resolution. It’s mostly balanced relative to the midrange and treble yet it feels powerful and has some real impact.

For a multi-BA earphone, the S6RUI also has very good bass extension with a slower than average sub-bass roll off. This results in a bass that sounds dynamic in nature, weighted with natural attack and decay. Listening to The Cure’s “Lullaby”, the S6 reproduces the meaty kick drum with reassuring impact.


The midrange is full-bodied and inviting. It’s more musical than analytical, and midrange notes have a thickness and density that’s lifelike and very natural. Here is a big part of what makes the S6RUI special. Despite the body and smooth character there’s a tonne of clearly defined layering and detail.

Vocals are engaging and vibrant. Male and female vocals alike sound rich and natural with great articulation. With this monitor, it’s easy to pick up what artists are saying thanks to the clarity and black background.


Treble has just the right density, which along with the right timbre and decay that gives it life and sparkle. The extension is very good but the treble sits a little further back in the mix so it never becomes harsh or too in your face, making the S6 great for long listening sessions. Utada Hikaru’s “Traveling” with its inherent sibilance poses no problem for the S6 and it’s smooth sailing for my treble sensitive ears.

It sounds lifelike, has a nice airiness to it and lifts the overall tonality, counterbalancing the low-end warmth and maintaining the tonal balance. In the mix, it sits slightly behind the midrange and bass but fortunately does not make the earphones sound dark or dull.


The stage that the S6 presents is slightly above average in width and depth. Its instrument separation and layering are superb and work together to paint a 3D holographic image with excellent positional cues. Instruments and vocals occupy their own space on the S6RUI’s stage, ensuring an excellent resolution that is free of congestion.

S6 with case and DAP


Tansio Mirai TSMR-3 Pro ($219)

S6RUI vs TSMR-3 Pro

The TSMR-3 Pro (review here) is another great multi-BA IEM that has great build quality, comfort and sound. I’d say it actually matches the S6RUI in build quality, apart from the dreadful cable that comes with it.

The TSMR-3 Pro has less mid and sub-bass quantity, along with a faster attack and decay. This makes its bass notes thinner in comparison to the S6. There is significantly more sub-bass roll off on the TSMR and overall it has a more typical balanced armature style bass.

Throughout the midrange, the two IEMs share a similar tonality but again the TSMR has faster transients and decay. This gives the TSMR thinner notes and less midrange body. At around 3kHz-5.5kHz the TSMR is more linear where the S6 peaks. Instead, the TSMR puts emphasis at around 9kHz which gives it a little more clarity but also makes it harsher on the ears at higher volume while the S6RUI is smoother.

Resolution is good on the TSMR but cannot quite match the layering and instrument separation that the S6 excels at. The soundstage is comparable in size but the separation and super dark background of the S6 makes things feel more spread out and holographic.

TenHz P4 Pro ($150)

S6RUI vs TenHz P4 Pro

The P4 Pro (review here) is closer to the S6RUI in terms of its physical build and shape. It has more sub-bass roll off with a similar attack speed but faster decay. It’s quite a punchy bass but is more neutral and doesn’t carry the weight or impact of the S6.

The P4 Pro has less body from top to bottom but has A fairly prominent peak in the upper midrange gives female vocals an extra lift. Both IEMs share a similar treble right up to around 18kHz where the P4 gets a second wind in the upper and mostly inaudible (to humans) range.

The P4 Pros stage has less width but a comparable amount of depth. The S6RUI has better imaging, separation and resolution which you would expect since it is more than double the price of the P4 Pro.

S6RUI internal drivers and wiring


The Fearless Audio S6RUI is simply a fantastic in-ear monitor that can go toe to toe with the best in the mid-tier range. It’s one of those very rare earphones that just does everything right. If you’re looking for an exceptional earphone but don’t have deep enough pockets to get TOTL, this is about as good an alternative as you will find anywhere. This one will most definitely be taking a place on our Best Universal IEMs list.

  • Technic Features: 6 BA Drivers, 3-way Crossover, 2 Sound Tubes
  • Drivers: Balanced Armature Driver *6, Including Sonion Dual Bass BA Driver, Knowles Dual Mid-Frequency BA Driver and Knowles Dual Treble BA Driver
  • Sensitivity : 113dB/mW
  • Impedance: 20 Ω
  • Frequency Response: 15HZ-20KHZ

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Howard Olsen
5 years ago

I’ve gotten really interested in this whole Chi-Fi space and your reviews are great. I’ve got set of SE535s and was considering upgrading to the SE846 but now I gotta ask, would the S6Rui or the S8 be an upgrade over the Shure’s? Thanks

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