FiiO Balanced Cable For Ultimate Ears and M-Audio Earphones (RC-UE2B) - Reviews
Pros: Overall build quality, flexibility, connectors, cinch, aesthetics, fits with some standard 2 pin connections.
Cons: Microphonics, over ear section can initially be uncomfortable, did not fit FLC8S, very difficult to see L/R indicators
For larger (1200 x 800) images, click any picture
(the above photo is one of FiiO's stock images - credit to them for the fine photography)​
I'm pretty much a cable agnostic. I don't believe in magic – I do believe in measurable changes, and do believe they can affect the sound to a certain extent. But the stuff they change can be measured, and as long as we don't try to look for something that's not really there, then I have no issues. I'm usually a sceptic regarding some of the claims that cables can make – and experimenting has helped me a lot with my understanding.
For me – the most important things about a cable are the build, connection/connector quality, flexibility, aesthetics, fit and comfort, level of noise or microphonics. The only real interest I have in sound is that I would prefer it doesn't overly alter the sonics of my earphones. For that I can use EQ, or tip roll. I would never buy a cable because it sounds better. We'll get into that during the review.
You will notice that I've also posted a review on the FiiO RC-SE1B, and that a lot of the review is identical. This is because a lot of the build, packaging etc is also identical. Hopefully you will allow me to reprint same sections in both reviews. In the matter of cables – it is simply not practical to rewrite entire sections when they will contain the same things.
Lastly – my reasons for asking FiiO about the cables was primarily so I could test the new AM3 balanced connection on the X7, and also the Luxury & Precision L3.
By now, most Head-Fi members should know about the FiiO Electronics Company. If you don’t, here’s a very short summary. FiiO was first founded in 2007. Their first offerings were some extremely low cost portable amplifiers – which were sometimes critiqued by some seasoned Head-Fiers as being low budget “toys”. But FiiO has spent a lot of time with the community here, and continued to listen to their potential buyers, adopt our ideas, and grow their product range. They debuted their first DAP (the X3) in 2013, and despite some early hiccups with developing the UI, have worked with their customer base to continually develop the firmware for a better user experience. The X3 was followed by the X5, X1, X3 2nd Gen (X3ii), X5 2nd Gen (X5ii), M3 and X7. They now have a full range of DAPs, DAC/amps, amps, cables and interconnects, and are even starting to release their own earphones (designed and manufactured in partnership with other OEMs).
FiiO’s products have followed a very simple formula since 2007 – affordable, stylish, well built, functional, measuring well, and most importantly sounding good.
The RC-UE2B cable was provided to me gratis as a review sample. I had made it clear to FiiO in the past that I did regard any product they sent me as their sole property and available for return any time at their request.
FiiO have told me earlier this year that they will no longer accept any payment from me for gear I'd like to keep for myself - they have insisted any future review models are mine to keep. So I acknowledge now that the RC-UE2B I have is supplied and gifted completely free of any charge or obligation. I thank FiiO for their generosity. I own and have paid for the E7, E9, E11, E11K, X1, and X5 in the past. I get no form of recompense or payment for these reviews, and I have no other affiliation with FiiO other than as an independent reviewer.
I'm a 49 year old music lover. I don't say audiophile – I just love my music. Over the last couple of years, I have slowly changed from cheaper listening set-ups to my current set-up. I vary my listening from portables (including the FiiO X5ii, X3ii, X7, LP5 Pro and L3, and iPhone 5S) to my desk-top's set-up (PC > USB > iFi iDSD). I also use a portable set-up at work – usually either X3ii/X7/L3 > HP, or PC > E17K > HP. My main full sized headphones at the time of writing are the Beyer T1, Sennheiser HD600 & HD630VB, and AKG K553. Most of my portable listening is done with IEMs, and lately it has mainly been with the Jays q-Jays, Alclair Curve2 and of course the Adel U6. A full list of the gear I have owned (past and present is listed in my Head-Fi profile).
I have very eclectic music tastes listening to a variety from classical/opera and jazz, to grunge and general rock. I listen to a lot of blues, jazz, folk music, classic rock, indie and alternative rock. I am particularly fond of female vocals. I generally tend toward cans that are relatively neutral/balanced, but I do have a fondness for clarity, and suspect I might have slight ‘treble-head’ preferences. I am not treble sensitive (at all), and in the past have really enjoyed headphones like the K701, SR325i, and of course the T1 and DT880. I have a specific sensitivity to the 2-3 kHz frequency area (most humans do) but my sensitivity is particularly strong, and I tend to like a relatively flat mid-range with slight elevation in the upper-mids around this area.
I have extensively tested myself (ABX) and I find aac256 or higher to be completely transparent. I do use exclusively red-book 16/44.1 if space is not an issue. All of my music is legally purchased (mostly CD – the rest FLAC purchased on-line). I tend to be sceptical about audiophile ‘claims’, don’t generally believe in burn-in, have never heard a difference with different cables, and would rather test myself blind on perceived differences. I am not a ‘golden eared listener’. I suffer from mild tinnitus, and at 49, my hearing is less than perfect (it only extends to around 14 kHz nowadays).
I need to get this up front very quickly. I personally believe that most of the claims out there about cables increasing things like clarity, sound-stage etc are simply the reviewers who claim it not setting up their comparisons correctly. Let me explain. In my tests, practically all the cables I have tested have had one thing in common, the frequency response does not change, or the changes are so small (mostly a lot less than 1dB – and that is across the whole curve) – so the changes claimed about being brighter or increased bass etc simply are unlikely to be true. I don't doubt that proponents of cable change believe what they are hearing. I am just not experiencing it.
What I can say is that when I have measured, I have often noticed volume changes – and some of these would be very noticeable. In the case of a higher impedance earphone like the MEE P1 – the stock silver-copper hybrid cable actually has a slightly higher impedance that other cables – causing a lower volume. This lower volume is across the whole frequency spectrum though. So for anyone comparing the MEE P1 cable against a FiiO cable – the FiiO cable would be louder. We hear louder things (music) as having more vibrancy, more prominent bass, more detail, more clarity, more apparent sound-stage etc. See where I am coming from? In reality (to me anyway) if I volume match the two cables and then compare – they sound exactly the same.
So why would you bother with an after-market cable? That is actually an easy one. My primary reasons are:
  1. For better fit and comfort
  2. For better connectors (an example is my Fidue A83 which has issues with the stock cable – but these are fixed by an ALO Tinsel)
  3. For better usability – more flexibility, less memory, better microphonics
  4. For alternate connections (e.g. balanced)
  5. For aesthetics – don't discount the pleasure a nice looking cable can bring.
But will a cable never change the sound? Not – it actually can. Often for BA drivers which have an impedance curve with a hump (rather than flat) – if the cable has increased impedance, it can change the frequency response. This is not as common as you'd think though. And if the manufacturer has tuned the earphone – why would I be intentionally looking to change that tuning with an expensive after-market cable, when I could do the same thing easily via EQ?
You may not agree with my stance – and this is not the place for a sermon or a debate. I just thought I'd get my view out there so that if you don't agree, you can stop reading now. Lets also not turn the comments section into a massive debate either. If anyone wants to discuss in the Sound Science section though – let me know the thread and I'm more than happy to discuss further.
This is a purely subjective review of the RC-UE2B cable – my gear, my ears, and my experience. Please take it all with a grain of salt - especially if it does not match your own views.


The RC-UE2B arrived in a small white retail box measuring approximately 80 x 120 x 12mm. On the front is a picture of the RC-UE2B balanced jack, 2 pin connectors, and also a list of compatible IEMs. I didn't have any of the IEMs listed, but I did have a pair of FLC8S which FiiO lists on their website as being compatible.
Retail box front
Retail box rear
Retail box contents
On the rear of the box are full specifications as well as a very good pictorial graphic of the pin and jack configuration. It is simple but clean, clear and informative.
Opening the box simply reveals the wound cable and a white shirt clip.
The table below lists most of the relevant specifications.
Approx cost
30-32 USD
Balanced 2 pin after-market cable
Connector Type
UE 2 pin
Compatibility claimed
UE Fi 10 (Pro), Super. Fi 5 Pro, Super. Fi 3 Studio / M-Audio IE-40, IE-30, IE-20XB, IE-10, FLC8 series (custom or universal)
Conductor material
26 AWG silver plated copper
Teflon FEP (fluorinated ethylene propylene)
0.16 Ω
Individual wires
8 in 4 x 2 configuration
2.5mm gold plated TRRS
Jack config (tip to base)
R-, R+, L+, L-
The RC-UE2B is a really pretty looking cable. Considering it's made of silver plated copper it is surprisingly flexible, and definitely not as unruly to control as the FLC8S cable – which is what I was looking to replace.
If we start at the connector end, the RC-UE2B utilises a EU style 2 pin configuration with an angled connector housing and slight recession in the plug to accommodate this type of socket's bump in the housing. The pins are gold plated and to my knowledge are standard 0.75mm. The housing itself is 6mm by 4mm rectangular shaped and made of clear hard polycarbonate. One negative here – it is extremely difficult to see the L/R indicators and if there was anything I would change from the build perspective – it would be the simple inclusion of red and blue dots on the connectors to make channel identification easier.
2 pin UE type connector
You can just make out the "L" if you magnify it enough
The cable exit from the connectors does not have strain relief, but its unlikely to receive a lot of bending, and given the cable material is so sturdy, should not pose issues. The cable has an 8cm section from the sockets which has a very thin extra layer, and this forms a naturally shaped ear-loop. It's not really a mould-able or form-able ear guide – more of a shaping which naturally loops over your ears.
The Y split is a piece of solid very clear polycarbonate and just above this sits a really well fitted hard plastic cinch. The cinch slides smoothly, but also keeps its place nicely – and as you'll read later, is really essential.
Y-split and cinch
The very well built 2.5mm TRRS balanced jack
The 2.5mm TRRS jack is gold plated, and a perfect fit for both the X7 and L3's balanced connectors. The jack has very good strain relief and the amazing thing is actually unscrewing the housing. FiiO have encased the wiring in a hard grey plastic mould – I'm guessing this is to further ensure the shielding and separation of the balanced components.
Cable expanded to show all 8 cores
The nice brand below the Y-split
The cable seems to be really well built. FiiO states that the internals consist of:
  1. 11 strands of silver plater copper wire strands (0.08mm each)
  2. these are combined into 8 separate cables which are individually sheathed in Teflon FEP.
  3. These 8 cables then form twisted pairs which have separate L/R channels for each balanced connection
  4. Above the Y-split, each side's cable (2x2 config) is in total <2mm thick.
  5. Below the Y-split, the cable (now 2 sets of 2x2 config) is in total <4mm thick
FiiO's photo showing the cable make-up is imemdiately below - it explains things quite nicely
Apart from the L/R indicators I cannot fault the overall build on this cable. For ~$30 this is really impressive.
I'll start with the good. The cable does have slight memory (most silver plated cables do), but its much better than a lot of copper cables I've tried. It is pretty flexible, and is not overly tangly or unmanageable. I did find the first week of using it could cause sore spots on my ears (where the cable rests). This has dissipated pretty well – but I do wonder whether a slightly heavier cover over this 8cm section could further alleviate some of this. Overall though pretty comfortable.
Where there is a major issue is the choice of outer sheath and the resulting microphonics. The cable noise is really quite noticeable. Touching the outer sheath transmits a lot of microphonics, and wearing it loose outside clothing is simply not an option (if you value your sanity anyway). This is the one single area FiiO do need to do some work on for future releases. To be fair, more expensive cables like ALO's Tinsel also have some issues with microphonics so they aren't alone with this issue. ALO's new Litz cable though is an example of how good a quality cable can be – and personally I'd rather pay a little more for a largely microphonic free cable. Fortunately the cinch works very well, and if I tucked the cable under clothing and used the cinch, noise was kept to a bare minimum, and they were even really good for walking.
Some cable management is essential though.
Sunny sent me the cables after I requested them – mainly for testing the AM3 module, and also because I wanted to try the RC-UE2B with the FLC8S. When I tried them -I could get the first 1-2mm into the socket, and then they were so tight that forcing them further was risking damage to the sockets (I wasn't prepared to risk it). I can't tell if this is just my pair – or if it is applicable to others - but it is worth noting.
Unfortunately my pair of FLC8S were a no-go
Pins slightly too big for the sockets
So my next step was to see if they would work with my other 2 pin IEMs. I first tried the 64Audio Adel U6 – and surprisingly they fit,although the cable was a little loose. I also tried with my Alclair Curve – and had the same experience.
A surprising fit with the U6 (although loose)
And also the Alclair Curve
The solution was simply to modify the polycarbonate connector, and cut out the recessed section to expose the connectors a little more. After this was done, the fit with both IEMs was much better.
Modification (removal) of the polycarb recess/overhang
The U6 now fit a lot better
It's been fantastic to be able to listen to the U6 and Curve balanced and for such a small overall price.
Before I finished, I suddenly realised that I had other 2 pin IEMs I hadn't tried - namely the Delta V2 and Sabre from Trinity Audio.  Amazingly, the fit is perfect - they won't fit the recess, but after modification you can still at least get a flush fit good enough for everyday use.
Trinity Delta - slightly exposed but still snug
And also quite firm 
Trinity Sabre - can't fit the recess
But with recess removed they fit quite snugly
Dilemma how do you measure a cable (to check for differences) without having the possible differences between balanced and single-ended nullifying what you're trying to measure? The good news is that I received a balanced to single-ended adaptor among the cables included with Fidue's new Sirius hybrid IEM – so I could effectively measure and compare:
  1. the stock cable – single ended
  2. the balanced FiiO cable – converted to single ended
In the graphs below I measured both the Alclair Curve and also the 64 Audio Adel U6 with stock cable and also using the RC-UE2B balanced cable converted to single ended. The graphs are generated using the Vibro Veritas coupler and ARTA software. I must stress that they aren’t calibrated to IEC measurement standards, but the raw data I’m getting has been very consistent, and is actually not too far away from the raw data measured by other systems except for above 4-5 kHz where it shows significantly lower than measurements performed on a properly calibrated rig. So when reading the graphs, don’t take them as gospel – or at least remember that the area above 4-5 kHz will be significantly higher in actuality. It is my aim to get this system calibrated at some stage in the near future.
With the Alclair Curve – a dual BA – the two frequency curves are for all intents and purposes identical. The actual difference was 0.5 dB between the two. And if I had been doing a blind test on the two cables without volume matching, the FiiO cable may have sounded slightly more detailed and slightly clearer. The benefit of being able to measure and show the 0.5 dB difference is invaluable in this situation.
Measuring the U6 was just as enlightening. This is a 6 BA per side with appropriate crossovers – so there is plenty of room for impedance miss matches and changed frequency responses. But with the cables, all you'll see are some very minor changes – most of them well under 1 dB, and some of them will be attributable to reseating the IEMs. Is there a possibility for change in frequency response – in some cases definitely yes. But in the two I've shown you (and the U6 one would have been closer if I'd adjusted the stock cable down by about 0.2-0.4 dB instead of leaving it as measured).
For the record, when actual listening – I couldn't tell any real differences. It could be that my hearing isn't as acute as some people who report such sound variations. All I can do is present you what I hear and what I measure, and leave you to draw your own conclusions.
Unfortunately this was one exercise I couldn't perform with my U6. My right side has developed an imbalance – so it is due for RMA next week (BTW great service from 64Audio – they are brilliant to work with). So the only configuration I could check was with the Alclair Curve. I volume matched and used Fidue's Sirius adaptor, and swapped back and forth. It was a sighted test – so bear that in mind.
For my hearing I would not be able to tell the two apart in a blind volume matched test. I know the crosstalk is better and distortion is lower in the balanced measurements. But for me personally – the benefit of balanced would be the ability to drive harder loads a little more easily. In the case of my Curve, this is not applicable – but with an IEM like the MEE P1 (see my RC-SE1B review), the use of balanced can be really handy.
Now just in case some of you are thinking “Brooko should maybe stop reviewing – his ears are getting shot”, I thought I'd back up the test with a direct comparison of the balanced and single ended output of the L&P L3. For this I used the FiiO cable and also the adaptor from the Sirius. In the graph below you will see the curve from the single ended raw output, the balanced raw output and the comparison when you apply ~ 6dB of volume adjustment to match them. The reason they look slightly different from the other graphs is that this time the L3 was used as a DAC and it has a noticeable filter roll-off compared to the “flat” sound-card I use for most of my testing. There was also a few days between testing, and it's practically impossible to get the tips on the coupler exactly the same.
Anyway – my ears aren't fooling me. The outputs are essentially audibly identical once volume matched.


For a cable agnostic like me, this was going to be an interesting exercise. I wanted this particular cable because it was cheap, had a balanced connection, and so I could use it with my FCL8S. As the song goes, two out of three ain't bad (not fit on the FLC8S), but I was lucky enough to be able to test with the U6 and Curve instead.
There are a lot of positives with the RC-UE2B. It is extremely well built, looks fantastic, and has pretty low impedance – so its not going to be adding its own flavour. It is also very affordable which is an absolute bonus for those looking for a balanced cable but don't want to spend big bucks.
On the negative side with this one is the high microphonics (can be mitigated through use of the cinch and sensible cable management), and the fact that I couldn't use it for the FLC8S. If you are particular about the need for low microphonics and aren't open to use of cable management, my advice is to steer clear of the FiiO cables for now.
Overall though I have no problems giving a 3/5 for the RC-UE2B. The value and build quality is hard to fault. If FiiO could refine it a little more with a different sheath material, and better R/L markings it would make it even better value.
Once again thanks to Sunny at FiiO for giving me a chance to try the RC-UE2B.
This cable cost $31 from amazon and given the price I wanted to give it a try to experience the balanced output. After getting ak100ii, I was using it single ended mode for a week before trying this cable. I've a u12 (with MAM) and the cable fit perfectly without any modifications. I didn't need to do the "removal of the polycarb recess/overhang" step that Brooko did. 
The sound: I wasn't expecting any big difference. But the combination of balanced output and this cable really takes the sound, the soundstage to a new level. The treble has a sparkle too. The overall sound is more airy and the sound stage is wider with good separation. To my ears, it is heaven.
​I've to have the volume at a higher level in balanced mode that I do with while in single ended mode. Even if the price isn't $31, this cable is providing amazing listening experience and with the $31 price, this is outstanding. Extremely happy.
Good to hear you having a positive experience with it
When searching for a review, I had a feeling, if one was out there, it would be yours.  Thanks for another solid review, you and I share similar thoughts on cable swap claims!  Looking at picking up a balanced DAP as well as the P1, already own the UE TF10 so this is pretty much a no brainer given the minimal investment.