UE CSX 11 Custom IEM with Fit Kit Hands-on Review: New Way for Custom Earphones

What used to be considered professional audio equipment - the In-ear monitor (IEM) has become a lot more mainstream over the years, making its way into the consumer's earphone segment. The trend is largely attributed to the rise of universal IEMs that use silicone tips, instead of the tedious custom molding process that IEMs originally require.

However, being the company that pioneered the IEM, Ultimate Ears isn't standing idle, but evidently determined to bring custom IEMs to the masses. Lo and behold, this endeavor led to the birth of the Fitkit and the UE CSX series IEMs - a brand new system for getting ear impressions. The new process of obtaining ear impressions can be done alone at home, which is particularly relevant in a season of lockdowns and social distancing.

How does the new IEM measure up against the classic custom In-ear monitors? We dove in to find out.

The Revolutionary Fitkit Experience

The Fitkit experience was an exciting one, as it's something completely new and revolutionary. We were already smittened by the light molding method of the UE Fits, and thought it would be something similar, but it turned out to be something different again.

Receiving the Fitkit, which is a unique package, containing a Bluetooth fitting cable, a small power brick and two sealed packages - containing two sizes of UE's special molding tips.

Since the patented molding process is new and unique, it's exhilarating to go into the unknown. Though it's unknown - I never felt lost, because the Fitkit App leads the user down a step-by-step process with plenty of pictures. The app leads the user through 4 major steps: Taking an ear selfie, Choosing a tip size, Documenting the fit and Molding the tip. It's quite genius as it utilizes the fact that virtually all customers of UE would possess a smartphone that is equipped with a camera: a powerful scanning tool in itself.

After the selfie of my ears with and without the tips in, hitting the 'Start' button began the 60 second molding process. The sensation as described by the app is the tips getting warm, a surprisingly soothing sensation that concludes with the tips making a comfortable and firm seal in the ears.

Once the molding process is done, the molded tips have now taken shape, and the difference can be seen when compared to the unused tips. Returning everything to the package, and sending the whole Fitkit back using the included return label, all that's left is to patiently wait.

UE CSX Fit vs a Classic 'PRO' Fit

The reason the Fitkit's self impression system works is largely because the UE CSX series has a different fit from the classic custom IEM fit. Instead of reaching deep into the ear canal - up to the second bend, the CSX only reaches into the first bend.

The shallower reach results in a more forgiving fit while offering the same sound isolation. What's more, not reaching as deeply into the ear also means it's less intrusive and more comfortable to wear for longer periods of time.

The only downside I found with the CSX fit is that even though it makes a firm seal, since it reaches a shallower depth, it cannot be as secure as a PRO fit. So when making movements, I found the CSX seal more easy to leak. However, this won't be a major issue for those planning to use them at their desk or other sitting situations like on a flight.

The CSX 11 sound: Clearly Amped

Having tested quite a few IEMs before, I was quite interested in how the brand that started it all would perform in comparison. After trying out the UE CSX 11 for a few weeks, I concluded that its strength lies in the expert tuning of its drivers. Even though competing IEM makers can get similar Balanced Armatures or fit more drivers in, the CSX 11's 4 driver, 3-way crossover has superior tuning. UE's expertise makes it more musical than other IEMs that I've heard so far, producing music that sounds more 'alive' and expressive.

If I was to describe the sound characteristics of the CSX 11 with a word, I would say it has a 'forward' sound. Every detail in the song is brought forward like a row of amplified speakers held at equal distance from the listener, not one sound will slip unnoticed. This is most apparent when I pay attention to the reverbs in songs, I can hear them clearly even at lower volume settings - something that other earphones cannot reproduce.

Comparing the CSX 11 with Sennheiser's recently released IE 900 for example, the UE IEM is geared less towards realism, more towards clarity. It's the difference between having an unplugged concert (IE 900), and having Marshall stacks placed around the listener (CSX 11). The sound characteristic is as if every instrument is amplified, sounding more energetic than the instrument being naturally projected across the air. Because of this, the CSX 11 is more suited for synth based and electronically amplified music.

Since the CSX 11 has a closed-back design, the staging is narrower. But it has crystal clear instrument separation. Its sound is perfect as a monitor for live shows, mixing music, and of course for audiophiles who love to catch every little detail in their favorite tracks.

The Mass Appeal in the Accessories

The UE CSX 11 breaks another mold by including two cables with the earphones: a braided IPX 1/8" jack with inline microphone, as well as a Bluetooth cable. These are two accessories that you would least expect from an audiophile level earphone, but it is consistent with the CSX mission: to bring custom IEMs to the masses, to be enjoyed throughout the day instead of only during special listening sessions or professional uses.

Using the CSX 11 cable with my mobile and making a phone call on the inline microphone, I couldn't help but feel it's an overkill to use such a nice set of IEMs while chatting to mom. But you know what? Being able to plug it in the phone means hearing a phone call come, and picking it up straight away. The cable itself is of high quality, and sounds great when connected to a high-tier sound source like the FiiO M11 Plus LTD we recently tested.

The IPX Bluetooth cable pushes the daily-use functionality even further, which again feels like an odd pairing with premium IEMs. The wireless cable even has the Jaybird logo - the sports earphone brand that shares the parent company with UE. In terms of performance, they are decent Bluetooth earphones. I was especially impressed by the pairing speed of the cables, as well as a fast booting and shutdown time.

I have to say though, Bluetooth connection doesn't do the CSX 11 justice, as the resolution of the IEM produces far exceeds any Bluetooth connectivity. But again, this is about providing more opportunities for the custom molded CSX to be used on a day-to-day basis. The wireless set up allows the CSX to be used on public commuting, where its -26db of ambient noise blocking can be utilized.

Personalized Service: Feeling Special

The 'C' in CSX stands for 'custom', and this is something that is common between the CSX and PRO line. Starting from the email from the Ultimate Ears Custom Team when you register for the Fitkit, to the carrying case that literally has your name written on it, to your initials being inscribed on the IEMs themselves - each part of the experience making owning the CSX feel like a personalized service.

What's more, Ultimate Ears now provides a new complimentary service for anyone with a fit inquiry, where you can book a Virtual Fit Assessment. When I wished that my CSX 11 could have a tighter fit, I made a reservation. Little did I know that my video call would be with none other than Noy Soudaly - the first employee of UE who worked with the company founder Jerry Harvey to design the very first IEM. With one look through my webcam, he diagnosed what needs to be done to improve the fit, and ordered a refitting that conclusively made them fit my ears much better.

Final Verdict

The UE CSX IEMs opens a new way for custom molded earphones. By using the innovative process of taking an ear impression using the Fitkit, the CSX is a new breed of custom IEMs that is much easier to acquire. With the shallower reach into the ears, the cable with inline microphone and Bluetooth cable, this is a set of extraordinary earphones that is suited for ordinary uses on a daily basis. UE is an iconic earphone maker that is making owning and using a pair of custom IEMs easier than ever before.

Check out the UE CSX on the Ultimate Ears Website.

Sam is a production engineer turned tech writer who specializes in seeking out gadgets that enhances productivity while still looking sharp. This is a contribution to an ongoing IBTimes review series on gadgets for Business Travelers.