Fit and Comfort

Seen above is the right channel of the Custom Art Hybrid 3 Pro CIEMs placed into an artificial ear mold. I mentioned in all my previous IEM reviews how I have average-sized ears, and the ear mold above represents my own experiences well enough as a proxy. As such, I surely had to take a photo of these in my own ears too especially given these CIEMs fit me so well—as they should. If you go for CIEMs then keep in mind that some people have found it handy to use hearing aid lubricants such as Otoferm to help with the insertion and seal from their CIEMs. The way you essentially insert these is by going in from the top and angling into the ear canal until you actually feel the seal in place. Do the same in reverse to extract it, and then see if you need the lubricant, which I ended up foregoing. The CIEMs will also seal better over the next few days as ear wax and your ear canals can slightly conform around them to make for, in an ideal scenario, near-perfect passive isolation that would compete against the best ANC solutions. Comfort should also be at the very top of the scale here, and I know people who sleep with CIEMs/ear plugs in the ears accordingly. The IEMs weigh ~6 g each here to where the larger size makes for relatively low density shells, which also reduces physical fatigue. I would have liked to see flush 2-pin connector and/or angled connector housings on the cable that allow for the pre-formed ear hooks to be more naturally placed above and going around the back of the ears for further support, but it's not a deal breaker by any means.

Audio Performance

Audio Hardware

The Custom Art Hybrid 3 Pro is a new set of IEMs from the brand in that it doesn't build upon an existing product from before. This is also why we have one of the more unique driver configurations in the form of 2 DD +1 planar magnetic drivers here. The bass is handled by a 10 mm PEEK (polyether ether ketone) and PU (polyurethane) composite diaphragm dynamic driver which has the vent in the shell helping with pressure normalization. The vent coupled with the tuning filters also help customize the bass profile from this driver. There is a second dynamic driver, this time a smaller 6 mm unit using a graphene diaphragm, responsible for the mids. The highs are taken care of by the aforementioned planar magnetic driver of which unfortunately we have no details other than the mention of a 3D printed waveguide used internally to fine tune the mid and high frequencies. The three drivers are part of a true 3-way crossover with Custom Art's flat impedance system in place to ensure the frequency response remains the same irrespective of the output impedance of the source you are using. So you can drive it off your laptop or a more expensive dedicated DAC/amp and the overall sound signature will be the same. Driving the set can take slightly more power than the typical set of IEMs owing to the lower sensitivity of 110 dB/0.1 Vrms and the 7 Ω impedance to make it more current-demanding than voltage. A good portable DAC/amp will be fine as long as it has sufficient power off the 3.5 mm output. I used the Questyle M15 and FiiO Q7 for most of my listening.

Frequency Measurement and Listening

I will mention that I have a general preference for a warm-neutral signature with a slightly elevated bass, smooth treble range, detailed mids, and good tonal separation. I also generally prefer instrumental music over vocals, with favored genres including jazz and classical music.


Our reproducible testing methodology begins with a calibrated IEC711 audio coupler/artificial ear that IEMs can feed into enough for decent isolation. Given the CIEM nature of this set, I had to use blutack putty to seal the CIEM nozzle inside my IEC711 couple as shown above. It's not a perfect solution but really it's impossible to accurately measure CIEMs unless you also make a custom coupler attachment based on your ear canals. Removing the stock attachment to couple the CIEMs directly to the mic capsule is possible with some CIEMs but my ear canals were too large to allow this to be done easily and instead made things worse. Testing was done as with any other IEM review thus, such as the Custom Art FIBAE 5, except without the use of the artificial ear mold to test for fit/seal, given these have already passed that test.


The IEC711 is such that you can't really compare these results with most other test setups, especially those using a head and torso simulator (HATS). The raw dB numbers are also quite contingent on the set volume, gain levels, and sensitivity of the system. What is more useful information is how the left and right channels work across the rated frequency response in the Custom Art Hybrid 3 Pro. The left channel was separately tested from the right one, and colored differently for contrast. I did my best to ensure an identical fit for both inside the IEC711 orifice but acknowledge the CIEM fit makes this easier said than done. I will say I didn't notice any channel imbalance whatsoever though and the measurements of my review sample show excellent channel matching throughout—anything in the higher frequencies is best taken with a grain of salt anyway. Given that CIEMs are custom made to order, I would not be surprised to see them also getting more individual treatment throughout. Measurements taken after 50 hours of testing, which included these playing a mix of various songs as well as white or pink noise and sine sweeps, showed no difference. There was no perceived burn-in effect thus, and none was measurable, either.


Here is the average frequency response for both channels of the Custom Art Hybrid 3 Pro with all three available tuning filters plotted against my personal target taken from VSG.squig.link, which also gives you an idea of my personal preferences to better correlate any possible biases. The tuning of a set of headphones or earphones does not have to match my target as long as it is tuned with some direction, makes sense, and is executed well. After all, no one set will appeal to everyone, and having different options is what makes this hobby so interesting and hard to quantify. This is in addition to a second graph using a newer target that's based on a more scientific methodology involving a -10 dB tilt (-1 dB/octave) applied to the diffuse field target for the newer, more reliable B&K 5128 but then compensated for my exact 711 coupler instead. Do scroll down to the targets in my database linked above and see the new 5128 section to the left where you can click on the yellow question mark for a brief primer. The bottom line is this target is closer to what many people are likely to prefer out of IEMs and headphones alike. I have chosen to plot this graph with the frequency response normalized/compensated to the target to make it easier to see where the Hybrid 3 Pro deviates from this target. This helps visualize the various elements of the set's tonality—sub-bass focus leading to a warm, clean transition to the mids, forward-facing upper mids and lower treble, relatively recessed treble extension. The nature of the bass and lower mids is contingent on the tuning filters chosen with the default brown filter providing a bass shelf placed between the gray and the yellow filters.

As with the FIBAE 5, the filters can make the Hybrid 3 Pro go from a bassy, punchy set to one that is more leaning towards a warmer sound throughout. I think the yellow filter can definitely help those looking for more accurate mids but at that point you might have as well gone for a neutral set from Etymotic for less. The Hybrid 3 Pro's strength lies in its bass shelf, especially with how it is emphasized in the sub-bass, so the default brown filter is where I would start using and enjoying the set. The gray filter has slightly more bass and this ends up being subjective since I already found the brown filter to be bass-heavy already. Neither have any difference in the mid-bass or lower mids so it really comes down to your music library and preference—if you listen to a lot of electronic music and want that thumping feeling in your ears then go for the gray filter as it will give you more of the same. I ended up sticking with the brown filter for most of my testing and, given it is the default offering with the Hybrid 3 Pro, this means I would not be getting the tuning kit for the optional extra cost if I was a paying customer. The other takeaway here is the Hybrid 3 Pro might benefit from some EQ boost to the mid-bass if you find it potentially lean for drum strikes, although I was fine with its rendition with plenty of detail and dynamics alike.

Lower mids being handled by another dynamic driver is not typical and yet this works beautifully with this warmer tonality. Male vocals have weight behind them as do a lot of instruments with natural-sounding timbre for guitars and acoustics alike. Mids don't feel recessed either and imaging is spot on in a wide cone around the ears and in the front. It's fairly easy to discern instrument classes as well, although I immediately noted the soundstage to be on the narrow side—perhaps as a result of the lacking air presence in the upper treble here. While this doesn't result in that psychoacoustic larger-than-life feeling if you close your eyes, I can see it being handy for prosumers using the Hybrid 3 Pro for music mastering and mixing given the narrower stage to operate in spatially. The upper mids have an ear gain beginning relatively early which has a side effect of making the mid-bass potentially lean to some ears as aforementioned, but it also means more energy for acoustic guitars, trumpets, horns, piano keys etc. Female vocals may come off a bit shouty by comparison though although fans of Asian pop music featuring female artists may adore this. This continues with the treble where, unlike what the measurements suggest, the Hybrid 3 Pro is on the brighter side and can be fatiguing given the highs are otherwise on the darker side. CIEM measurements don't translate well to the higher frequencies in general but in my ears I found the Hybrid 3 Pro to be overly energetic from 5-8 kHz before it gets darker and I found myself missing out on what that planar magnetic driver was supposed to achieve. There's also the part where the lower treble feels a bit spicier than I'd like, especially for percussion hits. I ended up adding a couple of EQ filters which helped enough to reduce any potential sibilance and fatigue although more time and effort might be necessary to personalize the highs to your liking. In general I see the Hybrid 3 Pro more handy for pop and jazz genres rather than classical music.


The Custom Art Hybrid 3 Pro operates in one of those weird price ranges where there isn't a lot of market presence relatively. A lot of Asian IEM brands tend to focus in the <$200 market with many going up to $500 before suddenly jumping up to $1000 and higher. On the other hand, most established Western IEM brands will see the tough competition from Asia in the budget space and try to specialize their offerings which can end up costing 4-figures to start with. This leaves the $600-900 market for the likes of the Hybrid 3 Pro to explore although pricing is such that Custom Art's own FIBAE 5 isn't that far away. If you are saving up for a set from the Polish outfit and were wondering which is the way to go then things are not as simple as they might feel. The Hybrid 3 Pro is a sub-bass beast compared to the FIBAE 5 that is more V-shaped with added mid-bass and treble presence. Removing the tuning filter the FIBAE 5 comes in further accentuates the bass shelf and it is far from neutral, which the Hybrid 3 Pro can come close to being with the yellow filter. The FIBAE 5 can be a more exciting set for some and far too energetic and I suspect fatiguing for many others but there's also the part where the FIBAE 5 has a more relaxed ear gain compared to the Hybrid 3 Pro. So depending on your HRTF and where you are more sensitive, these two sets have different strengths and weaknesses which can make one more amenable to you and certainly earn both a spot in Custom Art's IEM lineup. I prefer the FIBAE 5 more although the FIBAE 7 Unlimited's tonality is still my favorite from Custom Art to date.

The DUNU ZEN PRO is an older set which can be found for less than MSRP these days on sale but it sells for nearly the same, if not slightly more, as the Hybrid 3 Pro most of the year. This is a single dynamic driver set which was DUNU's flagship for a couple of years too and makes use of its patented independent driver/surround platform resulting in one of the most impactful bass reproductions I have heard to date. I also like the smaller all metal shells with excellent accessories to help on the comfort and value front. It doesn't have the best extension on either side though and comes off more like a one-trick pony these days with the tougher competition than I'd like. I'd say the Hybrid 3 Pro is more specialized and is better suited for multiple genres although not as safe as an all-rounder. Still, I would be more likely to take the Hybrid 3 Pro and a $30 balanced/neutral set of IEMs rather than just the ZEN PRO on its own which usually costs about the same as that combination. I also recently got my hands on one of the most ludicrous sets in the form of the FATFreq Scarlet Mini which is all about that bass and then some. I'll have more to say about it soon but in summary—the Scarlet Mini is smaller and more comfortable in UIEM form, is best treated as a basshead-only set, and yet somehow it does have fairly clean upper mids and treble. While I can absolutely see people loving the Scarlet Mini, and I personally know some of them, it's not a set I can personally enjoy for more than 10-15 min and is highly, highly subjective to where even the Hybrid 3 Pro comes off quite tame by comparison. I wish I had the 7th Acoustics Supernova on hand since it gets rave reviews too, but I can't speak for it without having even heard it. Also, it may seem obvious but I need to point out that CIEMs can sound slightly different from UIEMs and most IEMs on the market don't even have a CIEM option.