Ultimate Ears Pro Reference Remastered

Editor’s Note: Here’s a comprehensive look at the Ultimate Ears Pro Reference Remastered (UERR), UE’s newest reference product. It’s touted as the successor to the venerable Ultimate Ears Reference Monitor (UERM), a product we love here at CYMBACAVUM. Nearly all of the writers here have the UERM and keep it around as a mainstay reference earpiece. The UERR is supposed to evolve upon the UERM, taking it to new heights. There have been various viewpoints about the UERR; some say it’s a welcome improvement over the UERM and its drawbacks, while others prefer the original. Here, miceblue returns to deliver his take on the UERR.

The inconspicuous in-ear monitor: what is it, and why are they used?

For decades, live-stage musicians used highly directional on-stage speakers (also known as “wedges”) to monitor their performance and adapt how they play to what they hear. As you might imagine, they were not ideal tools to use. Loud, cheering crowds, sound reverberations from the venue space, and the band’s own sounds, all likely drowned out the sounds coming from the on-stage speakers unless the volume was turned past eleven. So, not only were these musicians not hearing what they needed to hear, they were going deaf. Rock concerts (or any concert, for that matter) are loud. It’s not just the audience members who are getting ringing ears after concerts — the musicians are too. Even an orchestral band playing at a venue like the Hollywood Bowl will experience very loud volumes over the course of an evening. These volumes are almost always louder than the Occupational Safety and Health Administration (OSHA) defined limit of 90 dB (A-weighted) loudness exposure levels over eight hours (the typical length of a working day).

Musicians needed a personal tool, one that would isolate their ears from excessive noise but simultaneously allow them to hear their own on-stage music or vocals clearly. Headphones, both over-ear and on-ear, didn’t offer enough isolation (lest they look like the earmuffs worn by airport ground staff). Moreover, they were unsightly; the rockstars weren’t having them. So, pioneering sound engineers turned to hearing aid technology. In-The-Ear (ITE) hearing aids are not the most common auditory assist devices available to the hearing impaired, but allow for the most room for electronics within the ear, as well as cavity-filling noise isolation. They were quickly adapted into custom-fitting earphones designed specifically for performance use. Individualized for a user’s own ear shape and size, custom-molded IEMs rendered on-stage speakers near obsolete. IEMs offered superior sound isolation, and the with the emergence of wireless sound packs, they could feed a musician’s ears with a customized listening experience. A drummer would receive an audio stream from the sound engineer for when to play certain parts, and likewise for the singer and guitarist with separate audio cues.


How does all this tie into the hobby of audiophiles and music lovers? Well, within the last decade or so, the use of in-ear earphones and CIEMs have dramatically increased in the realm of personal audio. As someone who had heard the terms IEM and CIEM well before entering the hobby in 2011, I was thoroughly confused as to why hobbyists were calling in-ear earphones IEMs. To this day, it irks me when people call $20 in-ear earphones “IEMs”. No professional would likely consider using them for in-ear monitoring. For the purpose of this article, I will refer to IEMs as the tool live artists and sound engineers use in a classical sense: in-ear monitoring, while I will refer to general in-ear earphones as, well, in-ear earphones. To put it more plainly, I believe all IEMs are in-ear earphones, but not all in-ear earphones are IEMs.

About Ultimate Ears

Ultimate Ears (UE) is no stranger to audiophiles and professionals alike. They have been around the professional audio industry since 1995 and are still in the professional audio world today. I first heard of UE when I saw live artists using CIEMs on-stage when I saw them on television broadcasts. When I Googled “earpiece live musician“, UE was among the top search results.

Back in 1995, Jerry Harvey, then a touring sound engineer for the rock band Van Halen, founded UE mainly for the purposes of outfitting his band members with custom-fit IEMs. He had done it at the behest of lead guitarist Alex Van Halen, who had been going deaf over the course of their touring days. Armed with a pioneering spirit and ingenuity, but without any manufacturing capabilities, Jerry co-oped his new company name with Colorado-based hearing aid, hearing protection, and defense contractor Westone. It went by the name “Ultimate Ears by Westone“, and was one of the first companies around to offer custom-molded in-ear monitoring products in the US, alongside FutureSonics, Sensaphonics, and ACS.

In 2002, coincident with the iPod revolution and the explosion of portable personal digital audio, and armed with loyal personnel like Noy Soudaly, UE separated from Westone to become its own entity, lab and all. Despite an initially rocky divorce mired mired in lawsuits for some time, both companies quickly went on to considerable success both in the professional and consumer sectors. UE went from a two-man operation to a multi-million dollar startup, selling both thousand dollar CIEMs and hundred dollar consumer-level in-ear earphones alike. UE gained A-list, celebrity-level clientele, and at one time served well over two-thirds of all road-going musicians. With its success, UE quickly started attracting attention from venture capital firms, and a large holding company bought out the firm in 2007. As part of the deal, Jerry Harvey left the company he helped create (only to turn around and create his own, eponymous company in 2009). But UE ‘s trajectory didn’t stall with the departure of Harvey, as it was acquired by Logitech in 2008 to become a wholly-owned, but autonomous subsidiary of the Swiss electronic peripherals giant.

While the consumer side of Ultimate Ears has since become partially subsumed by Logitech‘s corporate infrastructure, branching out into portable Bluetooth speakers in addition to earphones, the ‘Pro’ side of UE has quietly been fine tuning its operations to become both more streamline and disciplined. It has evolved into a more mature company that quietly serves the professionals in music, but also grooms its consumer clientele. These days, Ultimate Ears Pro is as much about the audiophile’s listening room as it is about the recording studio or the noise live stage.

Fabrication of CIEMs

Rather than explaining what UE does to create their CIEMs, this video is pretty self-explanatory.

The only difference between then and now is that UE trains technicians to use a handheld 3D laser scan gun (sourced from Atlanta’s United Sciences) to obtain digital impressions of one’s ears instead of taking physical silicone ones.

Something I found intriguing is that UE scans clients’ ears with their mouths closed. The typical procedure is to have the client’s mouth open since the ear canal changes shape depending on the position of the mandible.

Anyway, the digital impression is modified in a computer aided design program and is then sent to the 3D printer to be fabricated.

Different materials can also be used for CIEMs. Silicone CIEMs generally offer better isolation due to their flexibility, while acrylic ones generally offer better durability. When I attended the Audio Engineering Society convention event last year, I saw many CIEM companies whom I have not heard of before, and many of them used silicone earpieces.

Ultimate Ears Pro Reference Remastered

Before I jump into the Reference Remastered (let’s call it the UERR), it needs to be stated that UE previously collaborated with Capitol Studios in 2010 to create the predecessor to the Reference Remastered: the In-Ear Reference Monitor, often called the UERM for short. The UERM was made alongside recording engineers within Capitol Studios in Hollywood to create, well, a reference in-ear monitor. The resultant UERM‘s sound was tuned with three proprietary balanced armature drivers, a three-way passive crossover network, and a dual-bore output. The UERM was extremely well-received by audiophiles and music lovers (from what I have seen); while I cannot comment on how it was received in the professional audio industry, CYMBACAVUM has a nice photo library of the UERM here, and multiple writers such as shotgunshane, Mr. T, and kimvictor keep it as one of their main reference earpieces when evaluating other earphones or DAC/DAP products.

Six years later, UE  once again collaborated with the same engineers at Capitol Studios to create the UERRCapitol Studios had just revamped their facilities to accommodate high-resolution audio (better than CD-quality) and wished to redefine the reference sound for this new era of digital audio.

Both the RM and the RR use three balanced armature drivers within the CIEM shell. However, the RR brings some new things along with it.

  1. True Tone drivers
  2. Precision tuned “Sound Engine

The True Tone drivers are touted to be proprietary drivers that allow the CIEMs produce a “flat” response to 18 kHz. Their explanation seems to imply that these drivers were made for high-resolution music and the “flat” response allows the RR to recapitulate the complex harmonics and overtones in music.

This is in accord with the Capitol Studios‘ efforts to capture and deliver music faithfully to the end-listener. Peering through the transparent CIEM shell, it can be seen that two of the three drivers contains a typical balanced armature structure with the drivers wired in the back and a nozzle in the front. The middle one however appears to be special in that it is wired in the front, and the sound tube protrudes from the same side.

The precision tuned “Sound Engine” is a UE patented (U.S. patents #9,042,589 and #9,191,758) structure and manufacturing process that essentially guides the flow of air from the True Tone drivers to the tip of the CIEM. This structure simplifies the manufacturing process since it is kind of like an end-cap that fits onto the ends of the drivers, which can then be inserted into the CIEM shell (figure 25 in patent #9,042,589). For the RR specifically, a three-pronged “Sound Engine” structure is used, and the structure terminates in three sound bores of two different sizes: one large circular bore, and two smaller circular ones.

Official UE Press Release Photo

Package Contents

The UE RR comes with a machined aluminum case that is held together with a rubber gasket, not a screw lid. Although this is not an ideal closing mechanism, it does the job. Also included is a cleaning tool that has a metal pick and brush, a 3.5 mm to 6.3 mm gold-plated adapter, and a UE Buffer Jack. The UE Buffer Jack supposedly self-adjusts to match the electrical impedance of the item it is plugged in to. Subjectively, it just seems like an attenuator.

Subjective Impressions

I find the UE RR to sound pretty good overall. It seems to have a warm-tilted frequency response to me, so the lows are slightly elevated while the treble is slightly soft. I would say this CIEM matches the Harman target response fairly well given that it sounds similar to the OPPO PM-3 I have at hand, which also follows the Harman target really well. The overall tonality of the UE RR is, as you can imagine, rich-sounding due to the warm-tilted sound signature.

As mentioned above, the bass of the UE RR sounds slightly elevated to me. It is not the cleanest bass response I have heard (it sounds a bit slow to me), but it does have good extension and texture.

Moving up the frequency spectrum to the midrange, the lower-midrange frequencies (200-1000 Hz) take a rich tone from the elevated bass. Many of the soul, R&B, and funk songs I listen to sound really pleasant to the ear from this effect.

To me, the upper-midrange (1-6 kHz) is a bit laid-back, but that allows the UE RR to play back sibilant songs without sounding too harsh. Although I personally find this tuning to sound colored in the sense that it is altering the original sound, I think it works extremely well for female vocalists in particular. Combined with the enhanced tonality of the lower-midrange, and fundamental frequencies, sounds from the upper-midrange are rather thick-sounding. They do not have a bit or edge, which may detract some listeners who prefer that kind of sound.

Finally, in the treble region, I do find the UE RR to have very good extension for an in-ear earphone. What I like about the treble is that it sounds smooth, but it does not lose its ability to pick up textures and it strangely reminds me very much of an electrostatic headphone’s treble response. I do not hear a large spike in the treble region that I often hear in in-ear earphones, or headphones for that matter. Maybe these True Tone drivers are really doing something for the sound in this region.

Switching over to the UE RR‘s ability to image (and with it, instrument separation), I think the UE RR has solid imaging capabilities. However, again perhaps due to the slow-sounding bass, the images appear to sound a bit fuzzy. Listening to self-recorded binaural recordings, all of the images are there, but they are not as well-defined as what they were in reality.

In terms of the soundstage presentation, the UE RR takes a rounded soundstage. It is neither too wide nor too deep, nor is it too tall. For an in-ear earphone, I think the soundstage sounds about average in size.

When I use the included UE Impedance Adapter, the perceived volume seems to be cut in half, and the sound becomes a little warmer overall. I do not prefer this sound, but if an amplifier has too much gain, the extra attenuation is nice to have.

As a whole, I really like the UE RR as an in-ear reference monitor. It reminds me very much of my STAX SRS-2170 system, which is my current reference monitoring system. When looking for a reference in-ear earphone, the UE RR and the Etymōtic Research ER4-series were on my radar.

Objective Measurements

As a disclaimer, the subjective impressions above were all made before I had the UE RR measured. For the following measurements, as with any kind of data, please be sure to take the time to read the axes and labels carefully. Also, do note that these measurements are made from one pair of CIEMs with very specific measurement systems and may not necessarily reflect everyone’s UE RRs, or other sets of measurements.

During CanJam SoCal 2017, I had the opportunity to get my custom UE RR measured by Audio Precision as well as Brüel & Kjær. Although my CIEMs did not fit into the Head And Torso Simulator’s (H.A.T.S.) silicone ears, both companies had in-ear couplers available for in-ear earphone measurements. For my UE RR measurements, I used a sacrificial pair of large Comply foam eartips and attached them to the tips of the CIEMs, ensuring the three bores of each earpiece were not occluded. From this, I jammed the UE RR into the coupler and held the earpieces in place with my hands as the software did its test sweeps. The earpieces were too large to fit into the couplers and be held in place with the Comply foam eartips, so although this is not the ideal measuring setup, it is the best method I could think of doing.

Audio Precision‘s AECM304 Coupler

Audio Precision could not get their impedance measurements to work, so I will assume the UE RR has a nominal impedance of 35-ohms based on their official specifications. During the test, they initialized the system to measure at 94 dB sound pressure level. I asked what the voltage reading was for the UE RR to reach that level and they said 25 mV RMS, or 0.0178 mW of power (assuming the impedance of my UE RR is 35 ohms). To reach 100 dB SPL then, it would take 0.0714 mW of power (double the power for an increase of 3 dB SPL). This is well below UE‘s specifications of 1 mW (187 mV RMS) to reach 100 dB at 1 kHz. When the measurement system was trying to initialize, the software recorded the voltage outputs and at 192.6 mV RMS (1.06 mW), it was measuring my UE RR at 111.879 dB SPL.

From Audio Precision‘s “Technical Library” (basically a glossary of the measurements their products can make):

For THD+N Ratio, the rms level of the measured distortion plus noise (the signal with the stimulus tone removed) is divided by the rms level of the total signal. The result displayed on a bar meter or as a point on an XY sweep graph. THD+N ratio is most often stated in as a percentage or as a decibel value, where 0 dB represents the total signal.

In the various THD and Distortion Product ratio measurements in APx, the rms level of the measured distortion is divided by the rms level of the fundamental, unlike the THD+N ratio results discussed above, where the ratio is to the total signal. The difference is negligible for all reasonable distortion levels.

RMS Level and Distortion Free-Field-Compensated (1/6 Octave Smoothed):
Level and Distortion 1 Free-Field-Smooth

RMS Level and Distortion Diffuse-Field-Compensated (1/6 Octave Smoothed):
Level and Distortion 1 Diffuse-Field-Smooth

Relative Level Free-Field-Compensated (1/6 Octave Smoothed):
Relative Level 1 Free-Field-Smooth.PNG

Relative Level Diffuse-Field-Compensated (1/6 Octave Smoothed):
Relative Level 1 Diffuse-Field-Smooth.PNG

Left/Right Tracking:
LR Tracking 1 Diffuse-Field.PNG

Phase 1 Diffuse-Field.PNG

Impulse Response:
Impulse Response 1 Diffuse-Field.PNG

THD Ratio (1/6 Octave Smoothed):
THD Ratio 1 Diffuse-Field-Smooth.PNG

RMS Level and Distortion Free-Field-Compensated (1/6 Octave Smoothed), with UE Impedance Adaptor:
Level and Distortion 2 Free-Field UE-Smooth.PNG

Relative Level Free-Field-Compensated (1/6 Octave Smoothed), with UE Impedance Adaptor:
Relative Level 2 Free-Field UE-Smooth.PNG

Impulse Response, with UE Impedance Adaptor:
Impulse Response 2 Free-Field UE.PNG

THD Ratio (1/6 Octave Smoothed), with UE Impedance Adaptor:
THD Ratio 2 Free-Field UE-Smooth.PNG

RMS Level and Distortion Free-Field-Compensated (1/6 Octave Smoothed), with iFi Audio iEMatch (Ultra Sensitivity Setting):
Level and Distortion 2 Free-Field iFi-Smooth.PNG

Relative Level Free-Field-Compensated (1/6 Octave Smoothed), with iFi Audio iEMatch (Ultra Sensitivity Setting):
Relative Level 2 Free-Field iFi-Smooth.PNG

Impulse Response, with iFi Audio iEMatch (Ultra Sensitivity Setting):
Impulse Response 2 Free-Field iFi.PNG

THD Ratio (1/6 Octave Smoothed), with iFi Audio iEMatch (Ultra Sensitivity Setting):
THD Ratio 2 Free-Field iFi-Smooth.PNG

RMS Level and Distortion Free-Field-Compensated (1/6 Octave Smoothed), 3 Graphs Combined:
Level and Distortion 2 Free-Field Native-iFi-UE-Smooth.PNG

Relative Level Free-Field-Compensated (1/6 Octave Smoothed), 3 Graphs Combined:
Relative Level 2 Free-Field Native-iFi-UE-Smooth.PNG

THD Ratio (1/6 Octave Smoothed), 3 Graphs Combined:
THD Ratio 2 Free-Field Native-iFi-UE-Smooth.PNG

Unfortunately, the only data that was saved from Brüel & Kjær‘s measurement session was from the H.A.T.S. system. On the plus side, this can give you a good indication of what a very poorly-sealed CIEM measurement looks like. A CIEM is obviously made for one specific pair of ears, so getting a proper seal with a set of artificial ones is not going to happen.

RMS Level and THD Diffuse-Field-Compensated [Generated by Brüel & Kjær]:

Screen Shot 2017-04-21 at 02.26.33_mini

I re-plot the data into MATLAB to change the scales of the axes.

RMS Level Diffuse-Field-Compensated (x-axis is on a linear scale to emphasize the “normal-looking” data after 2.5 kHz):

MATLAB Handle Graphics

THD (linear-scale x-axis, logarithmic-scale y-axis) [100 = 1, 10-1 = 0.1]:

MATLAB Handle Graphics



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