Though there are literally thousands of different earphones on the market now from hundreds of developers, one way of whittling down the number to “serious players” is to look at the relatively small number that have manufactured earphones with more than one speaker inside per ear, a number that dwindles further when you move the threshold from two speakers per ear to three, then falls into the low single digits when you shift from three to four, and becomes only one when you move from four to six. That company is Ultimate Ears — now a division of Logitech — and its sole six-driver earphone is UE 18 Pro ($1,350), an ultra deluxe model released earlier this year.

It goes without saying that there’s nothing on the planet exactly like UE 18 Pro, but the reality is that there are actually a handful of very similar products, all from Ultimate Ears. The best way to think about UE 18 Pro is as a spiritual successor to the company’s UE 10 Pro, a triple-driver model that used to be the family’s flagship and most expensive product at $900, but has recently been discontinued, leaving the cosmetically identical triple-driver UE 7 Pro as a modestly less expensive alternative. Using the same custom-fit plastic casing described in our UE 10 review—now enhanced with your personal choice of coloration, which we weren’t able to take advantage of for the red model we were shipped as a sample—UE 18 Pro effectively doubles the number of speakers in each ear, and takes what used to be a neutral, reference-quality earphone in a different direction, enhancing clarity somewhat while noticeably boosting the mid-bass. Consequently, UE 18 Pro has its own unique sound signature—one that’s different from the company’s $1,150 UE 11 Pro in being less overbearing in the bass department, and closer in sound to the prototype UE 11 Pro we strongly preferred to the final version.

The thing that’s most striking about UE 18 Pro, and frankly about most super high-end earphones in its general orbit, is the little-discussed but very real subject of diminishing returns: despite the fact that Ultimate Ears has created the world’s first six driver in-ear design, you’d never know that there was extra hardware inside relative to three- and four-driver earphones.
This isn’t a product where the extra parts are expanding the frequency response over prior designs, enabling you to hear thumpy bass or twinkling highs you’ve never heard before; UE 18 Pro instead improves the clarity of the range established by earphones such as the UE 10 Pro and UE 11 Pro, so you’re still getting all the highs, mids, and lows you’d expect to hear in the 11, but the balance and nuances are different. A 2009 remaster of George Harrison’s wall of sound track What Is Life, for instance, sounded pristine in clarity through UE 18 Pro, with a little extra weight in the vocals, while the same track through UE 11 Pro had a push in its lower instrumentation that somewhat muddled Harrison’s voice.

It should be noted that we did our testing over the course of several weeks primarily with very high bitrate files, including 256K MP3s and AACS, 320K MP3s, and lossless tracks, most of which were either recent releases or very recent digitally remastered classics such as the just-released John Lennon Power to the People, the earlier Beatles remasters, Jamiroquai’s new album Light Dust Rock Star, and a variety of vocal, dance, and rap tracks of varying bitrates. Because of the details it’s capable of rendering in songs, UE 18 Pro is—depending on your perspective—either ill-suited or very interesting to use with low bitrate tracks. The best way to explain what it does is as the sonic equivalent of letting you clearly see jagged pixels on a computer screen; here, you’re able to hear all the accidental rough edges in songs, as well as the hiss-like base level of static put out by whatever music player you’re using, and with low-bitrate audio, the compression artifacts, as well.
In highly compressed music, the artifacts manifest as flatness, sizzling and distortion that aren’t there with high-bitrate tracks, so it goes without saying that unless you enjoy focusing on the imperfections in music, UE 18 Pro demands that your music library be in great condition.

So what is it like to listen to a $1,350 earphone with properly encoded audio files? The shortest answer is “smooth.” When playing back high-bitrate tracks through UE 18 Pro, everything just sounds silky—songs that fade in feel as if they’re sweeping gently into your ears, and as a listener, you have the ability to refocus your attention at any given moment to any part of the song that might interest you: 18 Pro produces very full-bodied, highly detailed renditions of tracks that instantly reveal instruments to be in layers rather than just all in a cloud together, so if there’s a drum, a guitar, a foreground or background vocalist, you can listen to everything at once or concentrate on just one of the elements at a time.

While UE 18 Pro has no trouble performing anything you want to throw at it, the midrange definition is particularly impressive, and mids are emphasized enough that we found our focus was generally drawn to the center of songs rather than the extremes. There’s plenty of treble definition, but it’s not sharp in a way that draws the ear towards high-pitched sounds, and though the mid-bass is boosted a little to provide an ear-filling effect, lower bass isn’t, so the thump of rap and some dance tracks comes across here as clear, defined rumbles rather than a flood. UE 18 Pro is stronger in the bass department than the UE 10 Pro was, but doesn’t rumble like the UE 11, a fact that we appreciate but some bassheads may object to.

As a counterbalance, we need to point out that while we very much enjoyed the experience of listening to UE 18 Pro, it’s not mind-blowing in any way; the reality is that the vast majority of music we’ve tested sounds superb through triple-driver SE530 earphones sold for roughly a third the price, and ones that don’t demand custom fitting, either. Beyond a small but noticeable boost in bass definition relative to the SE530, what the price difference is buying you is the custom fit labor, which yields such complete passive noise isolation that you’ll effectively screen out most ambient sounds around you even before your music is turned on, as well as Ultimate Ears’ traditional pack-ins—twin metal cannisters for the earphones and then both your audio player and earphones, plus a cleaning brush, detachable cabling with a more case-friendly connector, and a handsome cardboard shipping box. Though these items have made small evolutions over the years, including what appear to be durability enhancements to the braided cables and their sculpted ear mounts, we’d love to see Ultimate Ears’ talented industrial designers push them further forwards, as they don’t reflect the sleek restyling that the company’s lower-end universal fit earphones have received, and probably should if they want to command this sort of price premium.

Overall, we’d describe our impressions of the UE 18 Pro as very positive, but with caveats: this is as clean and nicely balanced of an earphone as we’ve ever tested, and between the custom fitting process, the color options, and the quality of the included carrying cases, it is likely to become as personalized and individually beloved as headphones get these days.