Ultimate Ears In-Ear Reference Monitors (Playback 40)

Earphones and in-ear monitors
Ultimate Ear In-Ear Reference
Ultimate Ears In-Ear Reference Monitors (Playback 40)

Ultimate Ears has been making high-quality, custom-fit, in-ear monitors since 1995, but I would argue their new In-Ear Reference Monitors are the firm’s most significant product to date. Here’s why. Where many in-ear monitors are designed primarily for performing musicians and thus have response curves designed to cut through the din of (sometimes exceedingly loud) onstage performances, the In-Ear Reference Monitors were designed from the ground up with just one goal in mind: sonic accuracy. While other in-ear monitors offer admittedly colorful response curves that may have a certain charm all their own (but that ultimately are not terribly accurate), the IERM’s were designed to provide ruler flat frequency response whose objective is to show you precisely how your favorite recordings really sound, without introducing questionable sonic embellishments, enhancements, or “sweeteners” of any kind. In short, Ultimate Ears’ IERM’s are designed to serve as a transparent conduit for the music at hand—a design goal we think most Playback readers will instinctively appreciate and applaud.

In approaching the IERM design, Ultimate Ears chose to collaborate with the engineering staff at Capitol Studios (of Capitol Records fame), in order to develop the optimally flat, neutral, and uncolored response curves that were required. According to Ultimate Ears the goal was to create an in-ear headphone so faithful to the input signals it is fed that its sonic character will be, “consistent, natural and revealing creating an accurate base line of pro audio reproduction that can be trusted by the professional recording engineer and producer no matter the environment.” Excellent noise isolation was also a prime concern. In short, UE’s intent was to create a versatile and credible in-ear monitor that could reliably be used to monitor and mix recordings both in the studio and at live events—a goal that UE and Capitol collaborators say the IERM successfully meets. And the same qualities that make the IERM a good monitor are also sure to make it a favorite among audiophiles.

From a technical standpoint, the IERM seems comparatively straightforward. It is a three-way, in-ear monitor that uses three high-performance balanced armature type drivers (serving as woofer, midrange driver, and tweeter), which are connected via a passive electronic crossover network. Output from the three drivers is directed through “dual acoustically tuned sound chambers” (which some competitors refer to as “bores,” as in the phrase, “our headphone uses a dual-bore design”) for what UE terms “the ultimate in separation, detail and clarity.” Custom-fit earpieces are made of solid acrylic material, and the IERM’s are fitted with “rugged, low-profile, low-distortion” signal cables.

Unlike most other UE in-ear monitors, whose earpieces typically would be offered in a rainbow-like array of custom colors, the IERM has been given a distinctive look all its own—and one that reflects the product’s design heritage. The IERM earpiece housings are therefore molded in clear acrylic with jet-black outer panels, with the Capitol Studios logo displayed on the right earpiece and the signature “UE” logo on the left earpiece.

How do the In-Ear Reference Monitors sound? You’ll want to read the rest of this review for a detailed answer, but suffice it to say the IERM’s are among the most neutral and evenly-balanced in-ear monitors we’ve yet heard, and they are very revealing. In our view, it is to UE’s credit that the firm had the vision and open-mindedness necessary to think outside the box and to create this studio/audiophile-grade product in the first place.


Consider this custom-fit in-ear monitor if: you have always wanted in-ear monitors that for the most part honestly reveal how recordings actually sound, without injecting interesting but inaccurate colorations of their own. The IERM’s are—as is so often the case with really fine audio components—sonic chameleons, meaning they don’t really have a signature sound of their own, but rather take on the tonal colors of the individual recordings you choose to play. The IERM’s are also very quiet and comfortable to wear for long periods of time

Look further if: you require the most detailed sounding in-ear monitors available (both Westone’s ES5 and the JH Audio JH16 PROs offer stiff competition, here), or the highest degree of noise-isolation possible (where the Sensaphonics 2MAX is our reigning class leader). Note, too, that the IERM’s response can sound very subtly rolled off up near the top of the top octave (which spans the range from 10 kHz to 20 kHz), meaning the IERM doesn’t necessarily capture the elusive sense of “air” surrounding instruments as effectively as some competitors do. But for overall balance and the sheer smoothness of its response curve, UE’s In Ear Reference Monitor is tough to beat.

Ratings (compared to similarly-priced in-ear headphones):

•Tonal Balance: 10 (comes closer to ideal neutrality than anything we’ve heard)
•Clarity: 9.5
•Dynamics: 10
•Comfort/Fit: 9.5+ (UE’s expertise in molding custom-fit earpieces really shows, and the IERM earpieces do a great job in terms of noise isolation and achieving long-term comfort)
•Sensitivity: 9 (not the most sensitive in-ear monitor around, but still quite easy to drive)
•Value: 9.5


•Custom-fit, earpieces feature outer shells molded from solid acrylic, and the fit is noticeably better than the norm in a field where the bar has already been set quite high.
•Distinctive In Ear Reference Monitor earpiece design scheme calls for clear acrylic earpieces with black outer panels that proudly display the “UE” logo on one side and the “Capitol Studios” logo on the other.
•“Rugged, low-profile, low-distortion” signal cable fitted with a gold-plated mini-jack.
•Passive three-way crossover.
•Three high-quality miniature balanced-armature type drivers.
•Comes packed in a hard shell road case whose interior provides well-padded chambers both for the monitors and for accessories. As a cool detail touch, the owner’s name is embossed on the outside of the road case.
•In fact, UE has gone all-out in the packaging for the IERM’s, which arrive in a beautiful presentation case that contains the user’s manual, plus a padded chamber that conceals and protects the road case. Very tasteful.
•Accessories include a cleaning tool (for removing ear wax from the monitor’s bore tubes), a gold-plated mini-jack to ¼-inch phone jack adapter, and a special “buffer jack” cable for use when plugging the IERM’s into portable devices.


The tonal balance of the IERM comes very, very close to the ideal of sonic neutrality, with perhaps the only (minor) deviation being a tendency to sound ever-so-slightly rolled off at the very highest frequencies. What words cannot easily express is how remarkably smooth the IERM’s response curve is, so that you come away with the sense that the IERM’s have done a much better than average job of ironing out the small response curve bumps and dips that most other in-ear ‘phones exhibit,

I found that the IERM’s bass was powerful, well-defined, and deeply extended, yet in no way artificially “pumped up.” For those who are used to listening through earphones that do make deliberate attempt to add extra bass “oomph” the IERM will come as a revelation. I say this because the IERM offers bass weighting that is accurate and highly realistic, yet that holds plenty of bass “thwack” and “slam” in reserve for moments when the recording happens to call for those qualities. And that’s the point: down low, the IERM will do exactly what the music tells it to do—no more and no less, which is how things should be.

Midrange frequencies are the IERM’s great glory, since they are smooth, well balanced and neither overly prominent nor recessed. Instead, the IERM finds the straight and narrow path down the middle, serving up vocal and instrumental timbres that can, on good recordings, display rich, pure, vibrant, and always natural-sounding tonal colors. As I spent time with the IERM’s, listening carefully to vocal and instrumental material, the one-word description that repeatedly came to mind was this: authenticity. These monitors have an uncanny way of keeping faith with recordings, showing you what was done well in the studio (or in the live recording venue), but also reporting any flaws they encounter. In practice this means you don’t so much listen to the IERM’s, but rather listen through them to learn what the recording is all about. As you come to trust the IERM’s overall tonal balance and sonic honesty, you’ll find yourself using them to assess recordings or audio components in the signal chain. In short, through the IERM’s, what you hear is what you get.

The IERM’s treble response is clear and extremely smooth, though I thought there was a touch of roll-off at the very top of the audio spectrum. While the IERM never sounds “dull” or unduly subdued, it does not convey high-frequency harmonics, “air,” or textural and transient details quite as effectively as, say, the Westone ES5 does. Still, if this characteristic represents a small deviation from the absolute sonic truth, then the good news is that it is a minor and subtractive error, which is far preferable to the alternative (excess brightness pretty much sets my teeth on edge).

Overall resolution levels are extremely good, though both the Westone ES5 and JH Audio JH16 Pros offer very stiff competition and may offer even greater resolving power, though only by a hair. But the tradeoff is that no other in-ear monitor I’ve heard can top or even equal the effortless smoothness and overall balance of the IERM’s response curve.

Ultimate Ears did an absolutely masterful job of molding the custom-fit earpieces of my sample pair of IERM’s, so that they achieved an excellent seal in my ear canals, while also serving up a heaping helping of comfort. What makes the IERM so fun to use is the fact that the earpieces are easy to handle and seem simply to “snap” into place with a minimum of fuss and bother (whereas some earpieces can take a fair amount of work to insert properly). Over time, I’ve come to think that translating ear-mold impressions into great fitting custom earpieces involves both science and art, and it’s obvious that UE has mastered both sides of that equation.


One disk that highlights a number of the IERM’s strength is the eponymous jazz recording from Floratone (Floratone, Blue Note/EMI)—a band in which eclectic guitarist Bill Frisell and his cohorts figure prominently. As is often the case with Frisell’s projects, the beauty of Floratone not only hinges on angular, otherworldly melodies but also a variety of sometimes dark and brooding and sometimes light and ethereal textures and embellishments. The result, on most tracks, is a densely layered sound that, through some headphones and many loudspeaker systems, runs a serious risk of turning into a complicated and incoherent sonic “mush.” But through the Ultimate Ears IERM’s no such problems occur. Instead, there is real weight, power, and definition on bass passages, while complicated instrumental lines and texture are cleanly presented and beautifully delineated.

Put on the track “Swamped” from Floratone and you’ll immediately hear the round, sweet, and somewhat chime-like signature sound of Frisell’s guitar take up the melody, supplemented by the deep, earthy growl of a syncopated acoustic bass line and a clear, simple rhythmic pattern played predominantly on the percussionist’s high-hats and snare drum. What’s so pleasing about the IERM’s presentation on this track is that each instrument is given its due, so that each sounds full, complete, and three-dimensional—independent of what the other instruments are doing. Nothing is compressed or exaggerated, so the music simply unfolds naturally without any need for embellishment.

Later, on “Lousiana Lowboat”, a different set of challenges arises, as we again hear Frisell’s guitar accompanied by drum kit and bass, but this time with the output of the guitar and bass channeled, in part, through electronics effects boxes. Thus, we hear the natural sound of the guitar and bass overlaid with effects that extend but also fundamentally alter the instruments’ natural voices. The inherent accuracy and clarity of the IERM’s make it easy to tell exactly where natural instrumental timbres leave off and the effects-driven voicings begin. But there is also on further sonic challenge, as the bass drum and tom-toms on this track are very low pitched and tricky to reproduce well (indeed, the voice of the lowest drum is positively subterranean). Here, the IERM really shines as it wades right in and delivers shuddering, ultra low-frequency bass drum thwacks without skipping a beat, and while effortlessly capturing the skin sounds of both the bass and tom-tom drum heads.

Finally, to really appreciate the benefits of the IERM, it’s worth putting on some material whose content is strongly midrange-centric, if only to hear how smooth and suave-sounding the IERM’s mid-band response really is. A good example would be “I Am a Town” from Mary-Chapin Carpenter’s Come On, Come On (Columbia). Two things are gripping about this track: first, the timbre’s of Carpenter’s voice, which are at one breathy sounding yet at the same time earthy and full-bodied, and second, the absolutely gorgeous voice of the acoustic bass (playing way up high in the cello or even viola range) that accompanies Carpenter’s voice throughout the song. The IERM’s do a great job with Carpenter’s voice, capturing both its high, lilting, almost whispered breathy qualities, but also revealing its earthier, lower registers, which carry inflections reminiscent of Southern gospel. But add to this the bass (whose upper register sounds amazingly smooth and evocative) and you’ve got something truly stunning. There is really no other way to put this but to say that the Reference Monitors make the bass sound about as vibrant and realistic-sounding as any headphone possibly can. Through the IERM’s, there is a powerful, you-are-there immediacy to the bass' sound that is truly breathtaking (which is precisely why high-level accuracy is something worth pursuing).


To show you how the IERM stacks up relative to other top-tier custom-fit in-ear monitors, I’ll compare its performance with that of two leading competitors: the Westone ES5 ($950) and the JH Audio JH16 Pro ($1149).

Ultimate Ears In-Ear Reference Monitor vs. Westone ES5 ($950)

•The IERM costs $49 more than the ES5.
•The IERM is a three-way, 3-driver design whereas the ES5 is a three-way, 5-driver design.
•Both monitors are quite accurate in overall tonal balance. However, I would give the IERM the nod for overall neutrality and smoothness of its response curve. That said, however, let me also mention that the ES5’s very subtle touches of tonal emphasis in in the upper midrange and lower treble bands, enable it to reveal delicate low-level treble details a bit more effectively than the IERM does.
•Resolution levels between the two monitors are very closely matched, though in an absolute sense the ES5 may enjoy a very narrow edge. However, the IERM’s superior smoothness and top-to-bottom neutrality make it the more accurate transducer overall.
•One of the biggest differentiators between the IERM and the ES5 involves the construction of their custom-molded earpieces. Ultimate Ears has given the IERM’s solid acrylic earpieces, while Westone uses dual materials for the ES5 earpieces (solid acrylic outer shells with thermally-sensitive, soft feel material for the ear-canal section). Although the manufacturers have taken different design approaches, both monitors offer excellent comfort and very good noise isolation.
•Both the IERM and ES5 earpieces afford a simple, straightforward insertion process where you gently rotate the earpieces until they seem almost to “snap” into position, achieving a very good seal and a comfortable fit in the process. That said, I should point out the IERM is probably “first among near-equals” in terms of overall comfort and ease of use. Note, though, that the ES5’s soft-feel ear-canal sections, which—once they warm up—conform to exact shape of the wearer’s ear canal, yield significantly better noise isolation and quieter backgrounds than most in-ear monitors can provide.

Ultimate Ears In-Ear Reference Monitor vs. JH Audio JH 16 PRO ($1149)

•The IERM costs $150 less than the JH 16 PRO.
•The IERM is a three-way, 3-driver design, while the JH 16 PRO is a three-way, 8-driver design.
•Up to this point, the JH 16 PRO has been Playback’s reigning neutrality champ, so we were eager to compare the IERM to what we considered our gold standard. Here’s how that comparison plays out. Both monitors offer excellent neutrality and overall balance, though their voicing is not, strictly speaking, identical.
•The IERM offers powerful low bass and remains almost perfectly balanced from the bottom end all the way up through the midrange and lower treble regions, with just a hint of top end roll-off.
•In comparison with the IERM, the JH 16 PRO also offers potent bass, but with perhaps not quite as powerful a low-end presentation as the IERM; the JH 16 PRO’s mids and highs therefore sound just a hair more prominent than its low-end does. The JH 16 PRO’s treble response is beautifully extended and shows no signs of roll-off at all.
•If you consider the response curves of the IERM and JH 16 PRO side-by-side, the IERM sounds beautifully smooth and balanced, but just a touch more warmly balanced (because of its subtle treble roll-off). In turn, the JH 16 PRO sounds nearly as smooth and equally well-balanced, but with a subtle touch of midrange/upper-midrange forwardness, which I attribute to the fact that the JH 16 PRO’s bass range response is pulled back ever-so-slightly vis-à-vis its midrange and treble response.
•So which is the neutrality champ? I’d give the nod to the IERM, by the slightest of margins.
•Resolution: In terms of ability to resolve fine, low-level textural and transient details both monitors are good, but the JH 16 PRO enjoys a narrow edge (in part because its extended but unexaggerated treble response makes details easy to discern, yet without imposing any sort etched or artificially “spotlighted” sound).
•The earpiece designs of the IERM and JH 16 PRO are conceptually similar, as both use solid acrylic earpiece designs. Yet in terms of execution the IERM and JH 16 PRO earpieces are—at least in the case of my review samples—functionally different. My JH 16 PRO are extremely easy to fit and remove (the best custom-fit models I’ve tried in this respect), but they do not offer the last word in noise isolation, which suggests to me that the earpieces may fit a bit more loosely than some competing custom-fit earpieces do. In contrast, the IERM’s offer a subtly tighter fit (yet one that is still quite comfortable, once you get them properly inserted) and concomitantly better noise isolation (UE claims -26 dB for the standard versions with acrylic housings, though a special-order, soft-silicon version boosts isolation to a whopping -32 dB). So good is the UE fit that I would rate it second only to the Sensaphonics 2MAX monitors in terms of noise isolation, which is most impressive.


Recognizing that accuracy is at times an elusive goal, I would say that Ultimate Ears’ In-Ear Reference Monitor is arguably the most accurate and neutral sounding in-ear monitor Playback has tested to date, which is a terrific achievement. In our view, sonic honesty is one of those rare gifts that keeps on giving, and it’s a gift you can enjoy every single time you put a set of IERM’s in your ears and settle back to enjoy your favorite recordings. We might also mention that the IERM makes a very useful tool for those of us who work as equipment reviewers, because this trustworthy monitor makes it easy to assess what other components in the signal chain are doing.


Ultimate Ears In-Ear Reference Monitor
Type: Three-way, 3-driver (balanced armature), custom-fit in-ear monitors
Accessories: Hard shell road case (custom labeled with a padded interior), cleaning tool, mini-jack to ¼-inch phone jack adapter, portable “buffer jack” cable.
Frequency response: 5Hz – 20 kHz
Weight: Not specified.
Sensitivity: 112 dB @ 1 kHz, 1mW
Impedance: 35 Ohms
Warranty: 1 year, parts and labor.
Price: $999

Ultimate Ears
(800) 589-6531 English
(800) 963-3479 Spanish

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