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Ultimate Ears Reference Professional Monitors IEMs and UE SoundGuard

07-02-2015 | By Robert H. Levi | Issue 80


The old proverb is false. You can teach an old dog new tricks! After 55 years as an audiophile, I finally have inner ear monitors (IEMs) that are not hearing aids! They are Ultimate Ears Reference Pro Monitors developed for studio recording and mastering use. They fit snugly in the ear just like a baby's thumb in a newborn's lips. They are made just for one audiophile's ears at a time, and laser guided to a flawless fit. 

Reference System

E.A.R. HP4 Headphone Amplifier + UE SoundGuard

Astell&Kern 240 DAP

KingRex Headphone Amplifier

Audeze LCD-X Headphones

Grado PSe 1000 Headphones

The UE Reference Pro's are three-way inner-ear monitors that fit very snugly in one's ears. Consequently, they take a bit of time to get used to them, but with some time, you do become accustomed to them. The firm seal assures excellent linear bass and extreme isolation from outside noise. I have sealed cans which do not isolate as well as the Pro's. I ran them for 50 hours before critical listening on my HP4 in LOz mode. 

The E.A.R. HP4's are not entirely compatible with the Pro's. The impedance of the Pro's varies wildly. Only solid state headphone amps work consistently with them. The HP4 Tube Headphone Amp sounded lumpy and peaky with the Pro's in both the LOz and HIz outputs. To (mostly) fix that, UE has developed a SoundGuard battery powered unit that flattens the impedance curve and allows for very good sound through the LOz output. I recommend the unit if you only have tube gear available.

Even with the SoundGuard employed with tube gear, top solid state gear like the Astell & Kern AK-240 will beat the pants off tube stuff with the Pro's direct in. By the way, the Pro's were developed in conjunction with Capitol Recording Studios engineering requirements for smooth, detailed, linear monitoring. They are the model for audiophiles looking for flat continuous response and ultra-detailed performance.

I am shocked at the dynamic linear power of the Pro's! They sound elegant and sophisticated. They go very low and have excellent dynamic bass power that is spot on for jazz and classical listening. The mid-band is uber detailed and meaty. You will hear tons of air and openness. Imaging is tight and right. The high-band is elegant and very detailed. Lots of space and sparkle. They appear limited only by the source resolution employed. 

With the AK-240 playing double DSD, the Pro's almost equal the Audeze and Grado cans in their ability to achieve full dynamic reproduction. The Pro's isolate better of course, and may slightly beat the big cans in micro-definition. The Pro's put the soundstage squarely between your ears while the cans are more forward, say around your nose. The differences are more subtle than you would think, thanks to the brilliant engineering of the UE team. The laser drawing of your ears also brings the fit to new levels of perfection, and contributes to this effect.

The Pro's are not very forgiving. If the recording is edgy, the Pro's will tell you. They are super neutral and allow for monitoring in the studio with strong accuracy. They certainly fulfill their design parameters. 

While the SoundGuard works well with tube gear making the performance less lumpy and bumpy, I do not recommend you use it with solid state DAPs. In stage use, if an actor may drop the microphone or the like, then the SoundGuard will smooth out the bang. It somewhat muffles detail and is just not necessary with the latest generation of DAPs.

The Pro's take personal listening to a new exalted level. You achieve complete privacy without weight on your head. You hear wondrous definition and suave musicality with great bass.  How wonderful is that?


The Ultimate Ears Reference Professional Monitors IEMs are excellent in-ear monitors for the engineer and audiophile. They are the smoothest, most detailed IEM's I have heard to date, and they excel in neutrality and dynamic range. I recommend only solid state players and sources for best results, though. They are limited only by the maximum resolution of the input, so you'll get more from your best recordings…DSD, SACD, and LP, for example. Once you get used to them, they're very comfortable. The Pro's are light as a feather and designed and installed to perfection. What's not to like?

Highly recommended!

Reference Pro MSRP $999

SoundGuard MSRP $199

For more information:


Contact Emily Gilbert:  [email protected]

[Product photo courtesy of Ultimate Ears]