Ultimate Ears Personal Reference Monitors (Playback 59)

Earphones and in-ear monitors
Logitech/Ultimate Ears PRM
Ultimate Ears Personal Reference Monitors (Playback 59)

Logitech’s new Ultimate Ears Personal Reference Monitors (PRM, $1999.99) are the most expensive, luxurious, and great sounding in-ear monitor Playback has tested to date and it’s the first one to provide an answer to the eternal question prospective buyer’s always ask; namely, “Will I like the voicing of this monitor?” With the PRM, the answer to that question will almost invariably be “Yes,” and the reason why is that, unlike any other custom-fit in-ear monitor we know of, the PRM provides both a custom fit and a completely customizable sound that can be shaped to suit the owners’ specific needs, wants, and tastes.

How, then, does the PRM sound? The truest answer would be to say it sounds however the buyer wants it to sound—within reason. (UE gives PRM buyers plenty of latitude in creating response curves for their monitors, but there are some practical limits.). Even so, the PRM is the only in-ear monitor that lets each owner custom shape the response curve of the product exactly as he or she sees fit. Indeed, if users need or want to do so, they can even specify separate voicing curves for their left and right ears. No other monitor gives users greater flexibility in terms of shaping precisely the sound they want to hear. That freedom is a big part of what you pay for when you invest in a set of PRMs.

How does Ultimate Ears manage the PRM customization process? Everything begins when a customer approaches UE and is assigned a trained “personal service specialist” who will walk the customer through the process from start to finish. The first step involves the customer spending time at what UE calls a “Personal Reference Tuning Station.” At the station, the customer will listen through a special test-version of the PRM that has been set up for use with universal-fit-type ear tips (a wide range of tips is provided to ensure a good fit). The test PRM, in turn, is plugged into a Personal Reference Tuning Box that provides inputs for the listener’s source component(s) of choice, an output for the test PRM, and two banks of tuning (or voicing) control knobs. One bank of knobs controls voicing settings for the left channel and the other bank controls settings for the right channel.

There are three tuning control knobs per channel—one to control highs, one to control mids, and one to control bass—with precise numerical markings to show what settings have been dialed in for each knob. The settings range from “0”, which denotes maximum emphasis for the given frequency band, to “100”, which denotes minimum emphasis for the frequency band; when settings of “50”are dialed-in for all tuning controls, the PRM will product the most measurably flat (that is, or neutral) frequency response of which it is capable. However, UE is quick to point out that different listeners perceive neutral frequency response in very different ways, so that the “50/50/50” settings are not necessarily “right,” but rather provide a fixed point of reference from which customers can work in creating their own ideal response curves.

Starting out with all knobs in their “50/50/50” positions, customers are invited to play whatever musical material they wish for as long as they wish, while experimenting with different knob settings as they pursue their ideal sound (UE recommends that listeners do this with their eyes closed, so that they aren’t unduly influenced by the numbers on the control knobs). Quite wisely, I think, UE advises listeners to sample a variety of musical materials they know and enjoy and further advises listeners to evaluate a minimum of five different musical selections before finalizing their preferred tuning settings. As an aid to the listener, UE’s Personal Reference Tuning Box is set up with left and right “Bypass” buttons that temporarily restore settings to the “50/50/50” reference positions, which makes it easier to determine whether one’s personal settings have actually improved the sound or not (from the listener’s point of view). Some listeners complete the tuning process in as little as half an hour, while others take much longer (I took around two hours and went through many different reference recordings when choosing settings for my personal pair of PRMs).

It is important to note that the voicing control knobs are not merely level controls. Instead, the knobs continuously adjust crossover network settings for the PRM, adjusting the relative ratio of output between adjacent frequency bands (for example, the ratio of mids-to-highs or the ratio of lows-to-mids, etc.). In my experience, this meant the control knobs seemed to interact with one another to some degree, so that adjusting the bass knob might also lead to further tweaking of adjustments for the midrange knob, and so forth. If the listener is patient and careful, though, I think the PRM Tuning Box gives users the freedom to dial in virtually any response curve they might want (again, with the option of choosing separate settings for one’s left and right ears). Once the listener is satisfied with his or her tuning choices, the personal service specialist records the settings, and then guides the listener through the next step of the process, which is having ear mold impressions taken. After the ear mold impressions are done, the final step involves customers choosing the custom wood finish they want for the ID plates for their PRMs—a selection the specialist once again records.

At present, UE Personal Reference Tuning Station facilities are set up in four nationwide locations (New York, NY; Nashville, TN; Los Angeles, CA; and the UE headquarters in Irvine, CA). UE expects to add tuning station locations in Europe and the Pacific Rim later on.

The build-time for a set of PRMs is about a week (though at extra cost UE can provide a quick turnaround, next-day service, if necessary). UE has specialized expertise in building finished PRMs that precisely match the sound achieved by the test PRM at the tuning station—a construction process that involves substituting various component values in the PRM crossovers and also performing internal mechanical adjustments to make sure your PRMs produce the desired response curves within very tight tolerances.

While the PRMs are in the manufacturing queue, the personal service specialist maintains contact with the customer via email and, in some cases, phone calls, staying in touch up through and beyond the point at which the PRMs ship from the factory. UE is determined that everything about the PRM purchase and ownership experience will be first rate, and they appear willing and able to go to great lengths to make sure PRM buyers are satisfied. This review will attempt to give readers a sense for what the PRM ownership and listening experiences are like.



Consider this custom-fit in-ear monitor if:

•You have always wanted a monitor that could be voiced exactly the way you wanted it to be voiced.
•You have a clear cut idea of what your ideal sound would be, but have not been able to find a standard model that fully meets your needs.
•You want a monitor that offers the ultimate in personalization—both in terms of fit and sound.

Look further if:

•$1999.99 is too rich for your blood. The PRM is very costly, to be sure, but for the right buyer it is well worth the money.
•You want in-ear monitors whose earpieces are made of soft-gel silicone material (in which case you’ll want to check out options from ACS Custom and Sensaphonics).

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

•Tonal Balance: 10 (note: the whole idea behind the PRM is that you dial in its response until it is, for you, a perfect “10”).
•Clarity: 10
•Dynamics: 10 (your ears will cry “Uncle!” long before the PRMs do).
•Comfort/Fit: 9.5
•Sensitivity: 10
•Value: 9


•Custom-fit, earpieces feature outer shells molded from solid acrylic. Note: as with the Ultimate Ears IERMs and UE 18 Pros, the fit of the PRM is significantly better than the norm in this field, which is saying a lot (almost all custom-fit monitors fit reasonably well, but some are better than others). The excellence of the UE fit is not, in our experience, attributable to any one factor, but rather involves UE getting a number of small, fit-related variables right. As a result, UE earpieces are comparatively easy to insert and seem almost to “snap” into place, yielding a firm (but not unpleasantly tight) fit that offers excellent noise isolation and long-term wearer comfort. (I’ve worn my PRMs for listening sessions lasting several hours without discomfort, although one does becomes aware of some in-ear perspiration after an hour or so).
•As a signature detail touch unique to the PRM, this model’s earpieces are molded in clear acrylic and offered with ID plates made of the user’s choice of four exotic hardwoods (options include Cherry, Carpathian Burled Elm, Purple Heart, and Burled Walnut). PRM owners belong to a very exclusive “club,” and those PRM-only wood ID plates are, in a sense, the club’s “secret handshake.”
•“Rugged, low-profile, low-distortion” signal cable fitted with a gold-plated mini-jack.
•Passive three-way crossover, with settings customized to suit the listener’s voicing preferences.
•Five high-quality “proprietary” miniature balanced-armature type drivers.
•Claimed frequency response is 20Hz – 18kHz.
•Impedance is rated at 21 Ohms at 1k Hz
•Sensitivity is rated at 110.6 dB at 1kHz, 50mV and “Efficiency” at 115.6 dB at 1mW —the same as for the firm’s very sensitive UE 18 Pro monitor.
•UE has gone all-out in the packaging for the Personal Reference Monitors, which arrive in a beautiful black presentation case beneath whose flip-open lid you’ll find the user’s manual, plus a padded chamber that protects the road case and the in-ear monitors within.
•The hard shell road case, in turn, features a padded interior with one chamber for the monitors with an adjoining chamber for the signal cable and accessories. As a very cool detail touch, the owner’s name is engraved on the outside of the case.
•As a first from UE, the PRM case comes prominently marked with a RewardTag, which indicates to anyone who might find a lost set of PRMs that a no-questions-asked reward will be paid to and finder who returns the PRMs to the UE factory. (The reward, as I understand it, will likely take the form of a generous UE gift certificate).
•Accessories include a cleaning tool (for removing ear wax, etc. from the monitor’s bore tubes).


As noted at the outset, there is no such thing as “standard” voicing for the PRM; its sound will be whatever your personal tuning settings may dictate. Still, as a means of enabling readers to compare the PRM to other monitors that Playback has reviewed, I thought I might talk about how it sounds when the Personal Reference Tuning Box voicing control knobs are set in their baseline “50/50/50” positions.

With 50/50/50 settings, the PRM sounds very much like an Ultimate Ear In-Ear Reference Monitor (IERM) on steroids. Here’s what I mean by that remark. The PRM (with 50/50/50 settings) has voicing very similar, though not identical, to the IERM, meaning that you hear very smooth and evenly balanced frequency response—a balance where what you hear is pretty much exactly what’s on the record. I did find, though, that with the 50/50/50 settings in place the PRM’s bass output is perhaps just a smidgeon leaner than that of the IERM (this isn’t too surprising when you consider that the IERM was voiced to sound much like the in-room response of a very accurate monitoring-type loudspeaker, where a certain amount of room gain would typically add a touch of bass lift).

Two important differences stood out for me, though. First, the PRM offers a noticeable improvement in resolution—especially on very fine, low-level sonic details—vis-à-vis the IERM. Second, the PRM offers even more stouthearted and explosive dynamics than the already excellent IERM. My point, here, is that UE has managed to take what many regard as a reference quality monitor and build upon its strengths in creating the PRM. In short, the baseline performance of the PRM raises a bar that has already been set very high.

But the custom voicing aspect of the PRM takes performance to an even higher level. The Personal Reference Tuning Box is set up in such a way that you can make anything from ultra subtle adjustments that are just barely audible on up to quite sweeping changes if you so desire. The beauty of the system is that you’re completely free to dial in your ideal sound without having to worry about pleasing anyone else. This, to my way of thinking, represents the ultimate in sonic personalization.

Some Playback readers who know of blogs I’ve written about the PRM have asked if the sound of the finished monitors really does match up with the sound dialed in at the Personal Reference Tuning Station. The answer, at least in my case, is that the match between the test PRM and the final PRM seems excellent, meaning that—as near as I can tell—nothing got “lost in translation.” A UE representative told me that my personal tuning settings were fairly subtle ones, so the fact that those settings were preserved in the finished product speaks volumes for the precision and repeatability of the UE manufacturing/testing procedures.

Interestingly, I found that PRM—much like some of the great loudspeakers I’ve heard and/or reviewed over the years—tends to have a “sweet spot” in terms of playback volume level, where the monitors sound their best with a given response curve applied (I believe some curves will work better for louder averaging listening levels, while others will work better for lower levels). For this reason, I would suggest that prospective customers listen at what are, for them, typical volume levels when picking tuning settings for their personal sets of PRMs.

How do I like my PRMs? Well, they’re the most enjoyable in-ear monitors I’ve ever heard, which comes as no surprise given that they were voiced by and for me alone. The beauty of the PRM system is that it makes “ideal sound” available to any listener—offering a sound that, as UE points out, can be “as personal as your fingertips.”


I could cite example after example of the PRM’s sonic excellence in action, but let me select just a small handful to illustrate the PRM’s capabilities.

On “Freddie Freeloader” from Miles Davis’ classic Kind of Blue [Columbia], the ride cymbal that does so much to supply the song’s wonderful “late night in a club” feel sounds essentially perfect: delicate, shimmering, and clear, yet in no way overstated. Similarly, the acoustic bass has the expected “woody” tonality and exhibits a just-right touch of gravitas for a sound that is weighty, but not overpowering or boomy. But the real piece de resistance is the lovely sound of Miles’ trumpet: it is perfectly clear, has appropriate levels of detail (you can hear mouthpiece/embouchure noises and the subtlest of modulations), and shows that indescribably captivating, melancholic quality that has won the hearts and ears of jazz enthusiasts for decades. The only thing I think would compare to the PRM’s performance on this track would be a very, very expensive pair of high-end loudspeakers or perhaps an also expensive set of high-end full-size headphones (think Audeze LCD3 or Stax SR-009).

Now let’s turn to “Joanni” from Kate Bush’s Aerial: A Sea of Honey [Sony]. The song makes a bit of a bellwether test in that it can sound terrific through truly excellent transducers, but can also give variable (and sometimes borderline unpleasant) results through merely good or “run-of-the-mill” earphones and speakers. As you might expect, though, the PRM passed this test with flying colors. The song opens with synth washes and a percussion figure, where at least one of the percussion instruments is very low-pitched (so low-pitched, in fact, that some earphones lack sufficient bass reach to show you what’s really going on). With the PRM, however, those low-pitched percussions “thwacks” are fully present and accounted for, with real weight, punch, and depth. But happily, even when reproducing powerful low frequencies, the PRM remains clear sounding and well controlled—never succumbing, as some monitors do, to bass overload.

When Bush’s vocals enter the mix, another difficult test arrives. Bush’s voice is not easy to reproduce, partly because it is inherently high-pitched, but also because Bush often applies angular touches of emphasis and inflection—touches that can wind up a little bit edgy or even “squeaky” through monitors that have excessive upper midrange emphasis. But through the PRMs Bush’s distinctive voice sounds beautifully expressive, albeit a bit unorthodox at times. The PRM’s just show you what the record is capable of, without editorializing or overcooking vocal elements in a way that might shatter the mood of the recording. Finally, “Joanni” features a number of delicate but definitely grooving high percussion accents—accents that, on some monitors, can either sound way too hot or else go missing in action. Once again, the PRMs found the ideal middle path, letting the high percussion notes ring out with natural shimmer and sustain, yet without becoming overpowering or overwrought. Again, the only times I’ve heard the track handled as well have been instances where I was sampling (very) high-end speakers or full-size high end headphones.

Would the voicing settings I chose for my PRMs work for you? Probably not, but then they aren’t meant for that (my settings are unique to me and my ears). But if you acquire a set of PRMs, your set would—like mine—have custom settings geared to work perfectly for you and your ears. Isn’t that kind of personalized perfection all that one could ever ask of a high-quality in-ear monitor?


Logitech’s Ultimate Ears Personal Reference Monitors takes the concept of a truly personalized in-ear monitor further than ever before; it’s the first product of its kind to offer both a custom fit and a fully customizable voicing that can be adapted to fit the needs and/or desires of most any listener. One key to the PRM, though, is that it starts life with a monitor platform whose baseline performance capabilities are very, very high, so that custom-tuned voicing becomes a matter of enhancing what is already a “gold-standard” product. What is more, Ultimate Ears’ customer-centric mindset promises to make the PRM ownership experience a joy. Though admittedly expensive, the PRM is arguably the finest in-ear monitor presently available.


Ultimate Ears Personal Reference Monitors
Type: Custom-fit in-ear monitors with fully customizable voicing curves.
Driver complement: Three-way system featuring five proprietary balanced armature-type drivers.
Accessories: Hard shell road case (custom labeled with a padded interior), cleaning tool.
Frequency response: 20Hz – 18 kHz
Weight: Not specified (weight can very considerably depending on the size/shape of the owners’ ears)
Sensitivity: 110.6dB @ 1kHz, 50mV (Efficiency rated at 115.6dB @ 1mW)
Impedance: 21 Ohms @ 1kHz
Noise Isolation: 26dB
Warranty: 1-year limited hardware warranty
Price: $1999.99

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

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