*This blog post originated as a reply to a question on; why choose one of our custom IEMs over a universal fitting IEM of the same model (CIEM vs UIEM)*

We started making in-ear monitors in 2010, focused on building custom IEMs (CIEMs) geared towards musicians. Between 2010-2015 we produced a line of Universal IEMs (UIEMs) that had a direct correlation to our entire CIEM lineup. Although they were manufactured similarly to the CIEMs, these UIEMs were eventually discontinued.

Image of previous generation universal in-ear monitors UIEM referenced in the copy.
Discontinued 64 Audio Universal In-Ear Monitors

In 2016 we focused on audiophile UIEMs rather than competing in the professional UIEM market and made U18t and Fourté. Now we offer nine CIEMs and nine UIEMs. There’s some overlap between the two lines as well as a few models that are either exclusively custom fitting (A2e, A3e, & A3t) or exclusively Universal fitting (Duo, Trio, Fourté). For the six overlapping models here are some of the reasons why you would consider Universal or Custom fit. 

64 Audio custom and universal in-ear monitors. CIEM vs UIEM

Non-Overlapping Models 

Before we get started we’ll briefly touch on those exclusively custom or universal models. The short answer to why we don’t make a Universal version of our A2e, A3e, & A3t is cost. Currently we can’t build those to align with our UIEM build quality at their more affordable prices. We’re continually working on ways to introduce lower cost UIEMs, and hope to have more options soon.

Exclusively Custom fitting IEMs

Our “Tia” models are exclusively made in a universal fitting form. Fourté was our first fully tubeless UIEM. The air volume, internal structures, and passive radiator are crucial to the DNA of Fourté. This is also similarly true for Duo and Trio. They are exclusively Universal because we’re not able to repeatably integrate those variables in custom shapes. Check out our blog post about the development of Tia and Fourté to learn more.

lineup of 64 Audio's Duo, Trio, and Fourté Universal in-ear monitors UIEM
Tia models

Materials and Contents

Although the overlapping IEMs are internally identical, they are still completely separate products geared towards folks with different needs. CIEMs have simpler packaging, custom engraved metal case, choice in socket, almost endless cosmetic customizability, and a 2 year warranty.

A4s custom in-ear monitor packaged contents, comparing CIEM vs UIEM packaging and accessories

UIEMs come with more thoughtful packaging, multiple tips and sizes, leatherette case, premium cable, 1 year warranty, and all three sets of modules. Check out our unboxing video series to get a deeper dive.

U12t custom in-ear monitor packaged contents, comparing CIEM vs UIEM packaging and accessories

Our CIEMs are 3D printed using a hypoallergenic acrylic while our UIEMs are milled out of solid aluminum billet. Of course both are sturdy, but aluminum wins in the contest of material value and structural integrity.

side by side comparison of acrylic custom IEM shells and aluminum universal IEM shells CIEM vs UIEM
Acrylic vs Aluminum shells

The Audiophile’s Pursuit: Resale

Something very characteristic about audiophiles is their relentless pursuit of audio perfection. Upgrading elements in your system is the primary way of driving that chase. Everything from large elements like speakers and amps, to more controversial upgrades like floor spikes and cable raisers. Being able to buy/sell/trade your way into, and up, the hobby is tremendous fun.

64 Audio's U6t displayed next to a hifi system

If resale is important to you then UIEMs are the way to go. This might be one of the most important distinctions compared to the other more subjective ones. Your CIEM is made to your ear shape permanently. You won’t be able to sufficiently transfer your CIEMs to someone without significant physical discomfort. We do, however, offer remold services for those whose ears have changed or grown. Since UIEMs rely on foam and rubber tips, it’s simple for multiple people to enjoy the set throughout its lifespan. 

Functional Differences

There are so many differences and variables when having the CIEM vs UIEM conversation. With UIEMs, each ear canal will resonate, reflect, and dampen audio frequencies differently from person to person. CIEMs consistently sit at the second bend of the ear canal without much variance. Removing that variance makes it easier to compare your observations with others using the same model. It’s one of the reasons why we like to use CIEMs when comparing different cables. UIEM insertion depth and angle will play an exponentially larger role in your perception of the sound. 

UIEMs offer more modularity if that is something you’re hoping to have more of. If you enjoy changing tips, and insertion depth/angle, when going between songs, genres, or devices, you’ll enjoy UIEMs. There’s also the benefit of being able to demo them more accurately than custom. 

If you want absolute sonic consistency, elevated comfort and stable fit the custom IEMs are the way to go. When demoing a CIEM, we recommend using flush fitting silicone tips or foam tips. You’ll want to insert them as deep as they get, holding them in place while listening to your reference tracks. If you push them in too hard or at the wrong angle, you’ll press it into the wall of your canal and it will sound muffled. Just experiment with the angle and you should find the sweet spot. 

The Sound 

The biggest differences are perceived in the highs, when comparing CIEM vs UIEM like our A18t/U18t. This is because those higher frequencies are shorter wave-lengths. Shorter waves have the necessary room in your ear canal to reflect. This causes summation, and even some cancelation, due to their relative phase when arriving finally at the hearing system. The low-frequency differences are oftentimes are attributed to seal but it’s actually less of a factor than you’d think. The seal in both the universal and custom should be pretty close. The differences in bass seem to be a psychoacoustic phenomena. Changes in high-frequencies influence your perception of bass. Although if you truly don’t get a good seal, then that’s a problem for sure.

Wherever you land in the CIEM vs UIEM debate, know that each 64 Audio IEM is a handmade work of art, built by experienced professionals in the USA. Choose wisely!