Fit and Comfort

Seen above is the right channel of the PMG Audio Apx SE placed into an artificial ear mold with the included black bore size M silicone ear tip installed. I have average-sized ears, and the ear mold above represents my own experiences well enough as a proxy. Size M silicone tips are my go-to for testing, since foam tips are not included by some brands and I generally don't find foam tips agreeable for their sound signature. I used both silicone tip options provided, with the black bore tip being handy to directly compare with the Apx Amber and get the intended house sound, and the clear tips aiding in cutting down the upper treble slightly if you find it fatiguing—more on that below. I'd say the Apx SE is about average in physical size, which in turn means it is one of the smaller tribrid/quadbrid driver IEMs I've tested to date, let alone flagship IEMs which tend to boast large driver counts and associated larger shells too. The inside of the shells is relatively compact without any ridges and a more angled and longer nozzle allowing for a deeper fit in the ear canals. The nozzle should be quite manageable for most people, so there is a higher likelihood of the Apx SE being a comfortable fit for you. But I know the nozzle length and angle might seem daunting at first glance, and some people are also unable to get a good fit owing to the more aggressive insertion angle. If you have tried any of the recent Custom Art UIEMs, then you will already have an idea about how the Apx SE will fare for you. The shells weigh ~5.9 g each to minimize any potential of being physically fatiguing, and the pre-formed ear hooks combined with the relatively supple cable add additional points of contact to support the IEMs in your ears. The thicker cable was a distraction initially though, and I almost went with the more traditional behind-the-back cable routing method before I eventually got used to it. The vent in the shells helps prevent pressure building up in the ear canals to where I had no issues in terms of physical comfort for longer periods of time while still maintaining a good fit and seal.

Audio Performance

Audio Hardware

This section is not going to be that different from the equivalent one previously written for the Apx Amber, because ultimately the Apx SE is based off it and uses most of the same drivers—11 of them in each side. PMG is distinguishing a rectangular planar magnetic driver from a more traditional round planar magnetic one, so it's marketing the Apx SE as a quadbrid set in that it uses four different types of drivers including these two, a dynamic driver and balanced armature drivers. In practice, the type and number of different drivers is less important than what PMG Audio has done with it. As before, the rectangular planar driver is used as a subwoofer, the rest of the bass is handled by a 10 mm PEEK (polyether ether ketone) diaphragm dynamic driver, the mids and highs are catered to by 8 balanced armature drivers in groups of two each, and finally the round planar magnetic driver as a tweeter for the ultra-highs. The net result is a 1+1+2+2+2+2+1 7-way crossover, with each set of drivers positioned carefully inside the 3D printed acoustic chamber and having waveguides for optimal performance. Additionally, there are acoustic filters inside along with the previously mentioned Geometrical Sound Outlet tech to also contribute to the overall tuning. The Apx SE also gets Custom Art's own FIBAE (flat impedance balanced armature earphone) technology, thus providing a flat impedance curve to the IEMs, which ensures its frequency response will not change no matter the source used.

Where the Apx SE differs from its predecessor is that the bass response is increased slightly via reduced damping in front of the subwoofer planar magnetic driver as well as reduced electrical damping for the dynamic driver. PMG audio says the dynamic driver is now electrically less constrained and thus allows for ~1.5 dB more output than the Apx Amber in the mid-bass, while both bass drivers have an "easier" path, so there is more bass presence. The high-frequency BA drivers were also redeveloped—thus making them different drivers from before—and the crossover between these and the round planar magnetic tweeter was also changed such that the lower/mid-treble is attenuated and there should be 3-5 dB extra output after 13 kHz, effectively making the Apx SE less bright and with more air compared to its predecessor. So it's not just a simple re-tuning here, in case people were speculating as much. Thankfully, the Apx SE remains one of the easiest IEMs to drive with a low rated impedance of 5 Ω and average sensitivity of 107 dB/mW (@1 kHz). As such, it is more source sensitive than the average set of IEMs so you should pair it with a decent portable DAC/amp at a minimum. More expensive sources can offer different sound signatures which may synergize with the Apx SE, so your mileage may vary on this front.

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. The audio coupler feeds into a USB sound card, which in turn goes to a laptop that has ARTA and REW running, and the earphones connected to the laptop through a capable and transparent DAC/amp—I used the Cayin RU7 here. I begin with an impulse measurement to test for signal fidelity, calibrate the sound card and channel output, account for floor noise, and finally test the frequency response of each channel separately. Octave smoothing is at the 1/12th setting, which nets a good balance of detail and noise not being identified as useful data. Also, the default tuning was used for testing, and no app-based settings were chosen unless specifically mentioned. Each sample of interest is tested thrice with separate mounts to account for any fit issues, and an average is taken of the three individual measurements for statistical accuracy. For IEMs, I am also using the appropriate ear mold fitted to the audio coupler for a separate test to compare how the IEMs fare when installed in a pinna geometry instead of just the audio coupler. The raw data is then exported from REW and plotted in OriginPro for easier comparison.


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 PMG Audio Apx SE. 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, so note how the two channels are basically identical across the entire useful 20 Hz to 20 kHz range! Keep in mind that resonance peak matching at~ 8 kHz can introduce some measurement artifacts and yet there was no measured difference even worth talking about, let alone perceived in my ears. This is what I expect to see from flagship IEMs that should be using hand matched drivers and which undergo much more rigorous quality control, so it is good to see PMG Audio meet these high standards. I will mention here for others who plan to measure the frequency response of the Apx SE that it's quite tip dependent, especially on the higher treble. Additionally, not only does the insertion depth change things as expected, but the insertion angle into the coupler also seemed to affect the measurements more than usual. My initial measurements taken on day one showed less upper treble, for example, which was not in line with how I heard the set. I re-measured a few days later for a more representative plot seen above. The response with the anthropomorphic pinna in place is another such example where the Apx SE is quite susceptive in terms of measurements, but ultimately your ears are what matter, even accounting for the part where these couplers are not very accurate in the higher frequencies in the first place. Overall, as with the Apx Amber, PMG Audio passes this section with flying colors.



Here is the average frequency response for both channels of the PMG Audio Apx SE 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 how the PMG Apx SE is tuned—U-shaped, on the warm and bassy side, with a good amount of air in the upper treble.

As with the Apx Amber, the Apx SE is deliberately colored to where it's quite possibly the most engaging set of IEMs I've ever listened to. In fact, such was my first session with it that I just went "oh my!" internally. The Apx SE has been highly anticipated by many, and I deliberately did not listen to it at CanJam London to not affect my review testing. Still, it was impossible to not hear everyone raving about the bass and how clean the set sounded, whereas almost everyone seemed to be in agreement about this being one of the most resolving IEMs ever made. PMG Audio says it took feedback from those who listened to the Apx Amber and made small changes here and there accordingly. The overall changes accumulate to making the Apx SE more amenable to a wider variety of end users, while there will no doubt remain people who prefer the predecessor. Take the bass, for example, which retains the unique pairing of a dynamic driver with a planar magnetic subwoofer. It was already quite satisfying before, but now both have been effectively unshackled. The frequency response is beguiling to an extent here, as the Apx SE sounds bassier and far more dynamic than it already appears. If anything, it was getting close to being a touch too much mid-bass for me, but the Apx SE manages to keep it very tight and controlled and the air in the upper treble helps balance it out too. I previously thought the 64 Audio Volür had the best bass reproduction in IEMs, but I have to now give it to PMG Audio. Sub-bass extension is excellent and has amazing rumble even down to 25-30 Hz from that rectangular planar magnetic driver, whereas the 10 mm PEEK DD has been tweaked further to add a more natural timbre to bass guitars and drums alike while maintaining the expanded dynamic range of the original and the excellent micro- and macro-contrast too. I added a touch more ear gain at 1.5 kHz to further balance the set for my preferences, but I would say the average basshead will be happy with the Apx SE as-is. It gets real close to providing a sense of tactility to the bass notes too, bested perhaps only by IEMs with good bone conduction driver implementations. I suspect the same amount of bass and warmer lower mids with BCDs might have pushed things past my preference though.

The mids feel forward, if not warm as I personally prefer my IEMs to sound. Male vocals, be it baritones or rap, continue to be a strong point here as with the predecessor. Helping further is the part where the BA crossover has been changed to where the lower/mid-treble is less energetic. This ensures most instruments and vocals remain in the forefront. It can arguably be a touch too much going on, especially if you have not listened to something this resolving before. You will end up finding new things in recordings that you perhaps did not hear before—percussion mallets hitting and staying on the surface for a touch longer at times, guitar plucks moving on the strings etc. Instrument separation and layering are handled like a piece of cake, and those who primarily listen to Asian pop music with a lot of female vocals will also find the Apx SE to their liking. Female artists, especially higher pitched ones, now can actually be enjoyed on a PMG Audio set without worrying about fatigue or sibilance. It goes without saying then that imaging as a whole is extremely precise in a wide cone up front, although soundstage is slightly narrower than before. Some of this could be down to the tuning changes with the Apx SE not having that ethereal, larger-than-life presentation. This is not to say the Apx SE sounds cramped though as the soundstage depth and height feels effortlessly rendered, and arguably this is the one part where PMG Audio's marketing about the set sounding natural is the most accurate.

I had mentioned in my review of the Apx Amber how I played around with EQ to try and tame the treble without compromising on bass dynamics and details. I failed to do so then, and was hoping the far more talented team at PMG Audio would do it instead. The Apx SE cuts down the 4-8 kHz region, and it did sound tamer and arguably not as fun with my acoustic jazz library, but adds some extra air in the 12-20 kHz region to help with the added bass dynamics and provide a sense of more detail and sparkle too. Given that this increase comes after a more controlled, relatively recessed region before, those sensitive to upper treble presence might find the Apx SE sounding slightly harsh—especially on electronic synth where you perhaps may not be expecting it. On my end, I found the clear silicone ear tips to help manage the upper treble without taking away elsewhere. This extra air also works wonders for my orchestral music library, be it string quartets, brass instruments, or even just relaxing music with harps and triangles—less so for piano keys though, where some fundamental tones felt overly emphasized at the expense of harmonics. I suspect source synergy will have an impact here, as some R-2R DACs seemed to help. Make sure you have a deep and secure fit too, as this alone will play a big role in how you perceive the lows and highs on the Apx SE. I will also say the PMG Audio managed to put together BA and planar magnetic treble better here than on pretty much anything else I've listened to, so it's not just a case of uncontrolled "planar treble" either.

Comparisons

This is the obvious comparison to make, although things are less simple when you realize the original Apx, the Apx Amber as is being referred to now, is long sold out and there were only 25 retail units made. Out of these, at least 8 are in South Korea. So the odds of anyone having listened to one of these is miniscule in the first place, let alone that of someone being able to purchase one from an original owner. For the sake of this review and for those who have heard it, I will still do a comparison. The Apx SE absolutely bests the Apx Amber with its non-acoustic parameters. The accessories are more premium, certainly feel more useful, and do feel like they belong with a flagship product. We also get a new set of ear tips which works better than you might think to help those who would find the increased air in the Apx SE to be on the harsher side. The stock cable also certainly costs more to make, and is selling for nearly twice as much, but this price includes the other accessories too, thus increasing the value proposition. I personally preferred the thinner and lighter Apx cable over the dual-shielded one we get here from a user experience, but I am also not big into cables affecting sound tremendously and here I feel more people will ultimately prefer the new stock cable. Aesthetically, the Apx Amber is special and certainly more unique looking. The story about PMG Audio's founder having picked the amber pieces himself in his younger days and working with his team to develop a new process to assemble them into a faceplate is also touching. The Apx SE is no slouch though, with the shells matching the semi-precious stone hybrid faceplates used here. I personally like the blue Apx SE more, but I can't say if that is because my Apx demo unit had more differing amber pieces which felt less cohesive.

On the sound front, things are more different than they seem looking at the graph above. I would say the Apx SE can be conceptualized as a more mainstream take on the Apx, but this is only because PMG Audio took feedback to heart and addressed the common issues raised, thus making the Apx SE more likable to the target audience. The Apx SE is not only bassier, but it has better quality bass too. It's more dynamic and timbre overall is improved too. Likewise, female vocals are now almost perfected compared to before. There's also no potential for sibilance and the brighter tonality is gone in favor of something you can listen to for hours on end thanks to the Apx SE being a lot more balanced sounding to my ears. On the other hand, between the upper treble presence and the Apx SE effectively throwing everything in a recording at you, you may find the Apx SE not working well with poorly recorded/mixed tracks. The Apx SE also feels less wide, but taller and deeper, sounding than the Apx Amber, and plays better with some instrument classes over others that were handled better by the predecessor. As such, there will certainly be a subset of people who prefer the Apx Amber. I would like to think the vast majority will prefer the Apx SE though, and knowing it costs less while being more widely available with better accessories will help clinch this comparison.


Stepping outside PMG Audio, there are a lot of IEMs now which are in the same price range as the Apx SE. I have heard plenty of them over the past few months—the Empire Ears Raven, the Fatfrequency Grand Maestro Anniversary Edition, the Elysian Acoustic Labs Annihilator, the Noble Audio Ronin, the Unique Melody Multiverse Mentor/Mason Fusang/Amber Pearl, the Canpur CP622B, and many others, although these have been primarily at shows and at retail demo locations to where it's not easy to talk about them given the different listening environment and other variables involved. It's also understandably less common to have flagship IEMs on hand for review comparisons, so I will say right away that you should definitely read other reviews of the Apx SE for other valid comparisons. In my case, I went back to some I had previously compared to the Apx Amber since I had freshly heard them again with my own sources/ear tips in a quiet environment. The Noble Audio Viking Ragnar is a $4000 tribrid set which is going to be quite divisive owing to its more colored tonality. The Viking Ragnar also has very good bass and resolution but is a set that really needs EQ to bring down the treble mountain which pierces my ears over time. It uses metal shells with intricate carvings, and is paired with one of the better cables I have used to date. The accessories are less premium perhaps than what the Apx SE comes with, but are certainly competitive on the practical front. I took the Apx Amber over the Viking Ragnar before, and I personally think the Apx SE is a better set than the Noble Audio offering in even more ways. It's more resolving, has a more dynamic bass, and is just more fun and engaging without ever feeling like I had to take it out for a break every so often. Then there's the Campfire Audio Trifecta which currently sells for $3300 in a few different colorways. It uses three full-range dynamic drivers without any crossover, meaning the three compete with each other and have phase issues even beyond what the tonality shows up like on the measurements. Campfire Audio's unboxing experience is.. interesting too, and I give props for its wackier nature. I also know many who swear by the Trifecta, but I really don't understand it. If you like the Trifecta, then I feel we simply differ too much in our audio tastes. There is no way I would pick the Trifecta over the Apx SE, and certainly can't recommend it over the PMG Audio flagship either—even accounting for the significant price difference.

Once again the toughest competition here comes from the Subtonic Audio STORM, although now things have changed to where no one knows when it will be available for sale in its "regular" edition. People were generally left unimpressed with the faceplates shown off on the prototype unit earlier this year and I understand the regular edition will come with less extravagant accessories compared to the $5000 launch version while costing $6000 or more too. This actually makes the Apx SE now less expensive than the Subtonic STORM and available for purchase as of the date I write this review too. The STORM is a special set of IEMs though, scaling tremendously to where I heard them off speaker amplifiers—yes, it is also notoriously hard to drive—and it actually gave me an experience akin to a set of properly calibrated speakers in a well-treated room. You will have to pay for that experience in multiple ways though; the STORM is not an easily portable set thus. The Apx SE has also closed the gap in terms of being an all-rounder, and I know first hand multiple people prefer the Apx SE for its bass and treble over the STORM. I personally think the STORM has more accurate mids and generally sounds smoother too, but it's tough to say how the true value will be without knowing what the regular version will be like and how much it will cost, let alone when it will be available for purchase. As and when more relevant IEMs come in for review, I'll be sure to compare them to the Apx SE too since PMG Audio has kindly allocated this demo unit as a longer-term loaner.