Let's get the price out of the way. The top of the Ultimate Ears heap, the Personal Reference Monitor costs $1,999.99, placing it in the rarefied realm of super-exotic full-size headphones from Sennheiser, Fostex, Audeze, Stax, etcetera. That is to say, it isn't for everybody. Add to the mix that it's got a unique twist — it's not just a custom-fit headphone, it's a custom-voiced headphone. Say what?
From a hardware perspective, the PRM falls between UE's well-regarded three-way-crossover flagships, the six-driver UE 18 Pro and the four-driver UE 11 Pro. Like those units, the PRM's five balanced armatures per side are packaged in an acrylic shell, outfitted with removable cables that include a stiffened over-the-ear segment for easy fit and removal.
UE had previously turned its tech to the needs of mastering engineers with the Reference Monitor, a voiced-for-accuracey three-driver-per-side model designed in collaboration with Capitol Studios. That model has become a favorite of traveling musicians and recordists, who need a trustworthy reference that provides good isolation — a sort of mastering suite on the fly.
The PRM turns that idea in an interesting direction, away from accuracy and towards euphony — and thus, towards audiophiles. Like a little more sizzle? You can have it? More warmth? Sure. Have a bit of difficulty hearing above 2 kHz on the left after standing stage right of the drummer for too many a bar gig? UE has you covered (and indeed, left-right balance compensation is one of the more interesting potential applications for the PRM).
There are no active electronics within the housings, so adjustments are made the old fashioned way, by adjusting the values of the resistors used in the passive crossover. Given that, the PRM offers a unique fitting and tuning experience, in addition to its grand-luxe fit and aesthetics.
While there are some other user-tunable headphones out there, the PRM gives you an unprecedented level of control over the voicing of the headphones you'll receive.
During the fit process, you get to play around with a three-band stereo EQ (actually not an EQ, but a resistance network) box, helpfully referred to as the "Personal Reference Tuning Box," that lets you choose the final voicing of the headphones you'll receiver by adjusting the relative levels of bass, mid, and treble emphasis. The changes aren't dramatic — as I said, there's no active equalization here — but they are perceptible. A handy null switch next to each big, friendly, stepped knob let's you quickly compare back to a flat setting.
For my fitting, I visited the Manhattan offices of Dr. Julie Glick, who fits CIEMs for a whole lot of boldface names and has a reputation for doing fine work. She's one of the few dealers to get the UE box in, and I was given free reign of the machine for as long as I liked. I played around for the better part of an hour, using my own collection of test tracks I knew well from my own iPod Classic rather than the selection present on the UE box's supplied iPod Touch (which does, by the way, include a set of test tones and a helpful tutorial on the process).
I have to admit, it was a disconcerting process — would I make a mistake? It's easy to get sucked down an audiophile rabbit hole. Did I hear that? What would the results sound like? Was I going too bassy? Am I mistaking exaggerated highs for clarity? Did I have a bit of a cold?
Interestingly, the fitting is done using a modified, universal-fit version of the headphone, with a silicone tip. This, of course, provoked further worries. Was the fit good enough to be making critical decisions? I settled on a medium tip, which gave me an adequate seal, but from experience I recognizedbthat even the best eartip doesn't duplicate the isolation of a custom, so I remained apprehensive.
Was I worrying too much?
In the end, I relaxed, set everything up eyes closed over the course of a few favorites, and felt I had a pretty good setting. Once I looked at the numbers I found that I'd bumped up the bass a tad on the left, a tad less on the right; in addition I'd added a little treble on the right, and cut a bit of mids in both channels. Sounded good...must be good, no? I called in Dr. Glick, who noted my settings, to be sent off with my molds to UE for fabrication. I got a followup call later from UE asking for my preference in exotic wood finishes (you can choose from Cherry, Walnut Burl, Carpathian Elm Burl or Purpleheart — I went with the Carpathian Elm; matched my eyeglasses). Then it was time to wait.
A few weeks later, the headphones arrived.The PRMs are beautiful — fit and finish far outstrip any other custom I've tried. Right off the bat, these slid into my ears with ease, no breaking-in period required — take this as a vote of full confidence in Dr. Glick's casting abilities. The wooden caps blend seamlessly into the plastic, and the facing of the shell for the removable cable jack is perfect. Even the braided cable is lovely, with a soft touch and good resistance to tangling. They're real works of art, these things. I would have liked a pocketable soft puch as part of the bargain, but the metal coffin they ship in is pretty confidence inspiring, so that is forgivable.
But, you are doubtless wondering...how do they sound?
Well, they sound fantastic. They're clearly not flat (they deliver the sort of warm sonics most associate with UE's previous high-end models, such as the six-driver 18 Pro), but they're very exciting to listen to, keeping pace sonically with the unbelievably comfortable fit. They have (well, my set has) a bit of a bass-forward character, without as much warmth as the ACS A2 I'd written about some months back, but with enough additional oomph to make sense walking around New York City. They handle classic Blue Note sides and extreme metal with equal aplomb, and overall compare favorably to the sonics, though not the stereo imaging, of full-size exotics like the HiFiMan HE-500 and Audeze LCD-3. I paired the PRMs with a range of portable sources, from various Android and iOS devices to the HiFiMan HM-801 and 602 Slim portable high-resolution players, and found the UEs efficient enough to provide a good experience with just about any source — no need, as I'd pointed out earlier, for particularly expensive portable amplification to get a truly high-end listening experience on the road.
One caveat. That extra low end I'd dialed in did, in the end, give me some pause about the process, or at least contributed to some continuing anxiety about the PRM tuning process. Maybe I'm imagining it, but I do feel, after spending several months with the PRM, that I might have over compensated for the fit of the universal testers by exaggerating the bass a tad. On certain tracks featuring solo acoustic instruments with a considerable amount of low end and good dynamic range, the phones had just the slightest bit of bass excess. I noticed this while checking out the high-rez FLACs of the Rolling Stones' Let it Bleed, where the acoustic guitar intro to Love in Vain" had a hint of boom; I noticed similarly when listening to Andras Schiff's recent ECM recording of The Well-Tempered Clavier, where I felt that the piano sounded ever so slightly bigger than it needed to be in the bottom octaves.
This was the sort of stuff I only noticed — and even then just barely — when doing critical listening in a very quiet environment, and in any case, performance across the rest of the frequency spectrum is, to my ear, as good as promised (and really about as good as I can imagine from an IEM), and imaging is quite impressive for an in-ear monitor, barring the presence of some sort of speaker simulation or cross feed circuit. Kudos to Ultimate Ears for making it hard to really screw these up!
That warmth served the PRM quite well with ensemble recordings, however — I gave the FLAC release of the Eroica Quartet's reading of the Debussy and Ravel string quartets (on the Resonus label, available from HDtracks) a listen, and found the PRMs did a great job of setting the Eroica's gut-strung sonorities in acoustic space; the warmth, in this case, read as room tone. Maybe the experience wasn't as much like being there as with the HE-500s, but very close for an in-ear monitor.
But you'll have to take my comments on the sound signature of my set of PRMs with a gigantic grain of salt. Obviously I tuned the darned things myself, and to be honest, even mentioning what I'm hearing is at a level of nitpicking that I wouldn't even mention with a headphone that came in at a less stratospheric price point. And in any case, should you choose to take the plunge, your pair is likely to sound completely different!
I suppose the big downside to the Ultimate Ears Personal Reference Monitor and the tuning process (which is a big part of the appeal, obviously) is that you don't get to perform the voicing with the headphones you'll end up with, and given the paramount importance of fit for in-ear sound (indeed, for the sound of any headphone), this seems like it might be significant in some cases. I'd much rather see some sort of tunable-after-the-fact model — adjustable via DIP switches, perhaps, or mini pots accessible via a removable panel. Or some sort of two-stage process where you're fitted first and then tuned later. Perhaps anything along these lines would add too much to the bulk of the housings, or be even more prohibitively expensive, but I'd much rather see consumers test the sonics of these in the form factor they'll be worn in.
With the Personal Reference Monitor, Ultimate Ears isn't just selling a product — they're selling an experience, offering the dedicated headphone audiophile a chance to create the in-ear-monitor of his or her dreams. It just happens to wrap that experience in about the most luxurious IEM package I've encountered. If you've got the cash to burn, it's hard to go wrong here — so long as you take care with your fitting and tuning session, of course.
Since the process is designed as it is, what I'd suggest is that those interested in the PRMs make sure to show up at the fitting and tuning session well rested, well hydrated, and prepared with a library of well-known favorites loaded up on the player of your choice. Be prepared to spend a lot of time — an hour or more, checking out a wide variety of material at a range of volume levels. You're paying for the right to choose your sound, so you should be prepared to choose as wisely as possible. The PRM will pay you back with a uniquely customized listening experience that you just can't get anywhere else.