ToTL Madness! 24 Top-of-the-Line Custom In-Ear Monitors Reviewed

This story originally appeared at

Photo Credit: John Grandberg

(Ed. Note: I want to thank John Grandberg for writing the Introduction and the company capsule profiles for this article. Lots of tidbits in there I didn't know. Thanks, mate.)

Custom in-ear monitors—often referred to as custom IEMs or just CIEMs—are a rapidly growing segment of the headphone industry. You don't have to go too far back to find a time when there were only a handful of companies making a few models each. Most of those went to industry folks—musicians and sound engineers and the like. Somewhere between then and now, a funny thing happened: consumers figured out that custom IEMs sound really great, and demand went through the roof, resulting in massive growth in the segment. The companies who were there since the beginning such as Ultimate Ears and Westone responded with an increasingly broad selection of models ranging from the somewhat affordable to the very high-end. As if that wasn't enough, custom IEM "founding father" Jerry Harvey left Ultimate Ears to start his own competing firm, JH Audio. Numerous startup companies have since appeared on the scene, ranging from small brands mainly focused on their local market to large companies with plenty of financial backing. The result of all this growth? Lots and lots of choices.

So what exactly is a custom in-ear monitor? Conceptually, they are similar to standard universal in-ear monitors, but with a key distinction: Rather than taking a one size fits all approach, custom IEMs have an outer shell custom molded to the shape of the user's ear. This requires ear impressions to be taken—a process that may soon be done with a 3D scanning system but for now requires a trip to the audiologist. The process looks like THIS—it's an unusual but not particularly unpleasant experience, and getting it right is critical for a proper end result. A few videos showing the actual process for building the CIEM are HERE and HERE. Some enthusiasts have had success by using DIY impression kits like this one. The CIEM companies will vary in their attitude about this method, but the bottom line is that it should only be used by experienced hobbyists—when in doubt, see a professional. Try to find an audiologist with experience taking impressions for custom IEMs if at all possible. CIEM makers are a great resource for finding qualified audiologists in your area.


A few companies—mainly Future Sonics and Aurisonics—utilize dynamic drivers in their custom IEM models. Nearly every other brand out there uses balanced armature drivers instead. As with universal designs, a single armature driver tends to run out of bandwidth and headroom before covering the entire frequency spectrum at decent levels. A few custom IEM brands make budget single driver models but most skip directly to a dual driver configuration and go up from there. A new trend is to offer what's known as a hybrid—a dynamic driver covering the low end, augmented by multiple armature drivers for the mids and highs. The intent is to capture the best of both types, and chances are good we'll see more of these in the near future.

Why Customs?
The benefits of a custom monitor are extensive. Fit is obviously a major factor—a properly fitting custom IEM will be far more comfortable than any universal model could hope to be. Most of the options use acrylic for the shells, with a few brands offering silicone instead, and one offering acrylic shells augmented by soft vinyl tips (Westone). We'll discuss the differences between these but ultimately they all have the potential to be exceedingly comfortable for many hours of use. Some readers may be thinking "What's the big deal? Universals are comfy enough." Many people suffer from moderate to intense fit issues with universals, but even if that's not a problem, I'd say you really don't know comfort until you've experienced a custom fit. Those universals may seem great for 30 minutes or an hour, but try a 4 hour train ride or a 12 hour flight—the ear canal simply does not respond well in the long term to an expanding material exerting pressure to create a seal, it doesn't matter if it's a stock silicone tip or a foam Comply tip. Universals can arguably achieve superior noise isolation—deeply inserted Etymotic triple flange tips anyone? But they do so at a cost, and for many of us that's simply not a long term option. A properly fitting custom will isolate very well and last for a seemingly indefinite amount of time.

Beyond a potentially perfect fit and the benefits associated with that, custom IEM designers just have more room to work with. Literally. Universal IEMs tend to be very compact and don't leave a lot of room for drivers inside their shells. Designs top out at 3 or occasionally 4 drivers per side. Customs, on the other hand, can usually accommodate 6 or even 8 drivers in each earpiece. More drivers don't necessarily equate to better sound in every case, but it does allow more freedom for the designer to tune response to their desired goal. Custom shells can better accommodate driver placement, different lengths of sound tubes with different diameters, and even different tube angles, all of which are factors in the resulting sound. This requires each set to be hand-built but the end result is definitely worth it for serious audiophiles.

Are there downsides to consider? Of course. Obviously you can't share your new custom IEM with a friend, which is kind of a bummer. The trip to the Audiologist for impressions is a minor hassle and adds about $50-$80 to the total cost. Then there's at least a few weeks of wait time for the initial build, followed by the potential for fit issues which means sending the IEMs back for adjustments—some people go through this several times before achieving a perfect fit. Instant gratification this is not. It's also hard to demo a custom IEM prior to buying, though some firms have demo units available at shows or might even ship them (deposit required, naturally). Lastly, the resale value of a custom IEM also tends to be lower, percentage wise, than a universal design, because the buyer needs to pay to have the IEM reshelled. None of these downsides are overwhelming but it's worth considering all aspects before jumping into a big purchase.

IEMs present an interesting scenario with regards to equipment—they have different requirements than a typical full-sized headphone. One certainly doesn't need a high-powered amp to drive them. Instead, the focus shifts to areas like noise floor, where IEMs can be brutally revealing of any hiss or grunge, and channel tracking, where IEMs can reveal even the smallest imbalance. They also demand a very low output impedance. You'll generally see an impedance spec listed in the 20-40 ohm range for custom IEMs but that doesn't tell the whole story. Take a look at some measurements of universal models like AKG K3003, Shure SE535, Ultimate Ears UE700, or Westone 4R. Note the wild impedance swings and dips into the single digits, which would be problematic for an amp with an otherwise acceptable output impedance of 5 ohms or so. Custom IEMs tend to be used on the go at least some of the time, yet surprisingly you'll find plenty of portable amps with far too much gain, lots of hiss, and unacceptably high output impedance. Desktop amps tend to fare better, and honestly there's nothing wrong with using custom IEMs at home—it can be a very rewarding experience and is rather affordable compared to some monster amp driving an HE-6 or HD800.

The typical headphone review process at InnerFidelity involves detailed measurements combined with subjective evaluation, hopefully with some degree of correlation between the two. But the measurement gear doesn't play well with custom-molded shells, so our coverage of custom IEMs thus far has been severely limited. Last year we got together and decided that this category was simply too significant to overlook. With no measurement data available, we decided to shoot for the next best thing: experience, and lots of it. Between Tyll, John Grandberg, ljokerl, Dinny Fitzpatrick, and Steve Guttenberg, the team has extensive history using custom IEMs. We all owned multiple sets already, but also reached out to the various brands for their latest and greatest. The result is a massive collection of 40+ sets of 24 models from 15 different brands, the retail value of which is easily equivalent to that of a brand new, well-optioned BMW. All of these models are positioned either at or very near the top of the current line up. Most brands do offer budget models but that's a topic for another day—for now we wanted to see just what each company was capable of when cost was not a limiting factor.

Early on in the project Jerry Harvey agreed to set us all up with his newly redone JH13 FreqPhase model. Since the original JH13 was considered by most to be something of a benchmark, we decided to use the new FreqPhase as a reference against which all others would be compared. This gave us all some common ground to use when describing the various competitors. That's not to assume the JH13 FreqPhase would automatically come out as a winner in this comparison—but it does make sense to describe things in comparison to a well known reference as opposed to a lesser known model, even if that model ends up being superior. Subsequently, both Westone and Sensaphonics provided models for the entire team, to enhance our common experience. The InnerFidelity team, and readers, I hope, are deeply appreciative.

In each writers section he had the opportunity to decide which cans were strong enough performers to get a strong recommendation. In those cases, the products have been given the "Stuff We Like" award. After the review process, we had some dialog in the writer's private forum area to discuss which headphones would achieve "Wall of Fame" status. Those awards are given on the last page of this article.

Note that there do exist some custom IEM companies which aren't represented here. A few of them declined to participate, a few just never answered our requests at all, and a few had problems getting us a set in time for our deadline. Our list is fairly complete but there are always alternatives and by all means if something looks appealing you should research it further. Unfortunately there are still some custom IEM firms out there with bad reputations and poor customer service so please check carefully before handing over your hard earned money. These are expensive bespoke products and you deserve a correspondingly high level of service when making a purchase. Thankfully the forums are a great resource for this type of thing since people who have a terrible experience tend to be very vocal about it.

Let's have a look at the companies that participated with this effort...