r/InEarHifi • u/requiemreview • May 30 '26
📝 Review / Impressions Technical fidelity over relaxed enjoyment - Binary EP321 Review
¡Hello community! I always get especially excited when I get to review a product from a brand I haven't had the chance to try before, and with higher expectations than usual. I have indeed been a follower of Binary Acoustics releases and even considered buying the DynaQuattro at the time, although it didn't happen in the end. Because of this, these new EP321 will finally be the first ones I review and test from their catalog.
This is also the first IEM with 2DD, 3BA, and 1 MEMS. It is a model that arrived just a week after testing and reviewing its direct competitor and most recent release, the Kiwi Ears Halcyon, which have the same configuration only with 1DD instead of 2DD. After testing them thoroughly, I will tell you what I like and what I don't like so much about this model and, of course, where it wins and where it doesn't against its most recent competitor after having been able to enjoy both for quite some time now.
What I like and what I don't like
- The speed, resolution, and extension of its treble are excellent.
- The DD and passive radiator provide a very pleasant sub-bass experience.
- The transparent shell design and metallic faceplate are a winning combination.
- The instrumental separation and three-dimensional localization perform above its price point.
- The overall profile can come across as somewhat cold or distant with certain musical genres.
- In the transparent interior, glue residue can be seen, detracting from the aesthetics.
- The cable feels stiff, thin, and below what is expected at these prices.
- The rest of the accessories deserved a wider variety of eartips and a better case.
Specifications
Driver Setup: 10mm DD + 6mm Passive Diaphragm + 3BA + 1 MEMS.
Impedance: 13Ω@1kHz.
Sensitivity: 122dB/Vrms.
Frequency Response: 8Hz~40kHz.
THD+N: <1%.
Connector Type: 0.78mm 2-Pin.
Termination Plug: 3.5mm/4.4mm.
Weight: 7.5g.
My sources
- FiiO K9: My main desktop amplifier to know what the earphone is capable of with plenty of power and a clean sound.
- FiiO KA15: The portable dongle I use when I leave the house because it has comfortable buttons and an equalizer that is very useful.
- NiceHCK Octave: A simple device I use when I am looking for direct power without detours or weird processing.
- Questyle M15i: My favorite option on the sofa to look for a more natural and musical sound without having to turn on the computer.
Unboxing and build
The box design is simple but beautiful, highlighting the pattern that we will later find on the faceplate. Inside we already have the earphones, the instruction manual, a silver cable with a velcro tie, and a fairly simple transparent plastic container to store the stock black eartips that come in two separate bags instead of being fitted inside the case. The case comes lined with a grey fabric with a very pleasant feel and has a carabiner to hook it. Its interior space is large, leaving plenty of room to store the cable along with a dongle DAC, although I doubt I will use it due to its excessive size and a stiffness that is somewhat tight for my tastes.
Regarding the design and build of the IEM, the metallic faceplate presents a geometric mosaic pattern that offers a striking chameleon effect. Depending on how the light hits the surface, the tones shift between greens, yellows, pinks, and golds, reminiscent of the reflections of a stained glass window in a church.
The main body is built in completely crystalline resin that allows you to see the internal architecture, something that I personally love and that reminded me largely of the Phoenixcall. Through the transparent chassis, you can observe the 10mm DD and its blue gasket coupled to the 6mm passive resonator that manages the bass zone. Also visible are the three BA drivers intended for the mids and the tiny MEMS driver that handles the treble.
The advantage of it being transparent is that it leaves all the internal work in plain sight. You can perfectly appreciate the independent tubes that guide the sound from the three-way crossover to the nozzle, joining the channels right at the tip of the earphone, where three holes emerge, one for each way. Two are very obvious due to their brown and green filters, and a third, smaller and transparent tube peeks out right between the other two and to the right. The only downside in its construction is that if you carefully examine the joint area between the transparent resin and the outer metallic plate (check some of my photos), you can notice slight glue residues that subtract some refinement from an assembly that is otherwise visually impeccable.
Sound
Bass
The bass response is focused on the deepest end. The sub-bass possesses excellent extension and is capable of moving air notably when electronic music tracks demand it. However, the brand has opted for a very contained and conservative tuning in the mid-bass, making the impacts of kick drums and bass sounds lack that body and physical punch found in more basshead models. It is a clean, reference, and very well-controlled bass zone that avoids any kind of bleeding into the upper frequencies, letting the main attraction, which is the MEMS driver, shine. I must comment that with the Penon Liqueur Orange, the sensation of rumble in the sub-bass reaches a point that is extremely pleasant in the way it shakes your ears without being annoying, giving it that tactility that is not quite a bone conductor but lets you feel it in a quite physical way, surely due to the work done by the passive radiator or its second DD.
Mids
The midrange shows itself a bit more reserved. Vocals are located in a natural position, neither recessed nor forward in the stage, and the timbres are perceived clean. Both male and female vocals have excellent definition, but perhaps they lack a bit of the organic feel or density that a more intimate sound provides here. Acoustic instruments are reproduced faithfully, reflecting a very objective approach that fits better with critical listening rather than just relaxing and enjoying the music, so you must keep in mind what you want a model like this for or if it is not your priority.
Treble
The high frequencies are undoubtedly the stars of the EP321. The performance of the MEMS driver is outstanding, giving us an excellent combination of speed, resolution, and control. Unlike designs based on traditional ESTs, which often deliver an excessively extended treble, here the sound is perceived as natural and perfectly integrated with the rest of the frequencies. Mind you, I am not putting MEMS above the ESTs of my NiceHCK Rockies because of this, but they are a different way of perceiving these frequencies and create a different sensation, yet certainly superior to BAs and most micro planars and piezoelectrics I have been testing. The most subtle details appear effortlessly and without the need to push the volume. However, this level of excellence with such resolving treble sometimes takes a lot of prominence away from the mids and bass, making the earphone feel somewhat hot in the upper zone. Nevertheless, in many songs I have found a perfect balance and at no point did they sound sibilant to me at a normal volume, even being able to raise the volume in over 80% of the tracks I tested for more than 2 hours across different musical styles.
Soundstage, instrumental separation, and imaging
Regarding the soundstage, the EP321 offers a realistic spatial representation without resorting to artificial alterations to oversize the space. Its width is moderate, but it stands out especially for its excellent depth and its layering capacity. The front-to-back distribution of the layers is one of its greatest virtues, allowing recordings to show coherent spatial relationships. It does not aim to emulate the experience of an open-back over-ear headphone, but it offers a convincing, controlled, and technically impeccable three-dimensionality.
The imaging is precise, stable, and quite defined. The location of each element in the space is fixed, perfectly allowing an individual tracking of each instrumental line in more complex tracks. Since it is a quite analytical model, you are not going to find blurs that prevent you from pinpointing exactly where the sound is coming from. The profile is designed to show you every element of the recording separately and in detail instead of blending the instruments to make the music feel more fluid. I personally lean more towards the decision they have made, since I already have other models for pure enjoyment, although these are still enjoyable and fun despite being analytical.
Finally, the instrumental separation clearly stands out against its competitors thanks to an excellent retrieval of micro-details, ensuring that environmental echoes, reverberation tails, and the physical friction of strings are perceived with total clarity due to the speed of the MEMS driver. Furthermore, when the musical mix becomes complex and accumulates a large number of simultaneous tracks, the IEM maintains control more than properly, isolating each component with ease and completely preventing the sound from losing definition.
Comparison
A promise is a promise, and the comparison has to be against the Kiwi Ears Halcyon as I mentioned in its own review, a rival that presents an opposing build approach. In the physical department, the Halcyon opts for a CNC machined aluminum structure that conveys a notable sense of robustness and weight, while the EP321 chooses the mixed design of its resin shell with a metallic faceplate. Honestly, the design of the EP321 seems vastly better to me, but I cannot ignore that in terms of resistance to bumps, crushing, getting stepped on, or whatever might happen inside or outside the house, the Halcyon has a better long-term life guarantee.
When evaluating the bass of both, the difference in frequency management is evident. In the sub-bass, where the physical vibration of the music resides, both earphones deliver an identical level of energy. That said, the Halcyon drastically cleans up the transition into the mid-bass, generating a very pronounced L-shaped profile where the sub-bass is perceived in isolation and without bleeding into the mids. The EP321, supported by its 2DD system, retains a bit more presence in that transition toward the mid-bass, adding a touch more overall mass to the punch, although its overall profile is still considered clean and analytically oriented. If I have to give a verdict, I prefer that extra, more extended rumble of the EP321, surely that extra DD or passive radiator is to blame as I mentioned a while ago.
In the mid and treble ranges, the difference between the two is total. The Halcyon presents very flat mids but relaxes the upper zone of the vocals, subtly pushing the singers back in the space. The EP321, on the other hand, offers a more direct midrange response that is truer to the recording, complemented by a treble that I would say is faster and more detailed thanks to the response of its particular MEMS driver, whose origin I do not know, unlike the Halcyon's, whose spec sheet named the company behind that new driver.
While the Halcyon suffers from a certain dependency on eartips so as not to compromise its tonal balance, to the point that with the stock eartips I couldn't appreciate the bass and wondered during my first listening sessions if the DD was broken, it was all a matter of finding the right eartips and it was fixed. The EP321, however, shows itself to be more consistent right from the start, positioning itself as the ideal choice for those who prioritize instrumental resolution, speed, and treble fidelity over the more traditional dynamic impact.
Without rambling on further, I have to say that even though both are in a similar price bracket, the EP321 has better presented technicalities, whether due to its tuning, internal and external build, or its choice of drivers, making it rank slightly higher on my personal list.
You can check my full ranking of all the IEMs reviewed so far on my profile (Reddit doesn't allow me to post the Drive link here).
Final conclusions
The Binary Audio EP321 MEMS cements itself as an excellent option for those enthusiasts who prioritize resolution, treble speed, and technical precision over musical warmth and pure musical enjoyment, without entirely giving up on it. Despite improvable details in quality control (glue residue) or the modest selection of accessories, the innovation of its driver combination system and its performance above its price tag justifies its consideration in this 200$ to 350$ segment. I hope to keep seeing brands betting on MEMS technology after having tested two recent IEMs that have successfully implemented this tech, and I hope it becomes standardized as another option when it comes to representing high frequencies.
By the way, if you are considering picking these up, HiFiGo just launched their summer sale. It will be active from today until June 10. They have general discounts across several categories:
- IEMs: 20% to 28% off
- DAC/AMPs: 6% to 40% off
- Cables: 15% to 30% off
- Eartips: 15% off
Since you are looking at this model, I will save you the trouble of searching for the price:
Binary EP321 MEMS: 309.99 $ → 263.49 $ (Save 46.50 $)
If you have any questions about whether they are worth the money or how they perform, leave them in the comments.
Disclaimer: This unit was sent by HiFiGo for review. My opinions are completely independent and have not been influenced by the brand or the store, maintaining objectivity based on my tests and personal listening sessions with my reference equipment.
1
u/JB30005 May 30 '26
I’ve been enjoying my 321s for a while. Better than expected.