General Information


· Design: In-ear Monitors (in canal)
· Driver: 1 balanced armature
· Frequency range: 10-22000Hz
· Impedance: 40 ohm @ 1KHz
· Sensitivity: 111 dB/mW @ 1KHz
· Cable material: Silver plated copper
· Cable length: 120cm symmetrical design
· Plug Type: 3.5mm straight gold-plated
· Weight: 12g including cable, 3g not counting cable

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100+ Head-Fier
Pros: extremely small
extremely light
fast and likable sound
very nice looking as well.
Cons: not the best sounding IEM
not the most resolving IEM
disappointing soundstage
Binary Acoustics EP1 Single BA In-ear Monitors

First of all, I must admit that I am not too fond of in-ear monitors. My preferences have always been full size open-back headphones and earbuds. I dig full cans because they offer good comfort and the best portable sound; earbuds because they are simple, they offer unequaled comfort and good soundstages. That said, every now and then I will still dip my toe in the water and try out the latest IEMs that are appearing in the market.



Binary Acoustics is an emerging luxury IEM (in-ear monitors) maker from China. They have been producing high end custom monitors and cables for some years now and recently transitioned into making universal IEMs. I was told that Binary Acoustics specializes in BA IEMs and they were responsible for tuning some of the BA IEMs sold under other brands. That is not altogether surprising as the current earphone market in China is in a boom and the audio world is quite a close-knit community.

EP1 is the first universal in-ear monitor produced by Binary Acoustics. As of the end of 2017, they were operating in a studio-laboratory setup. The company did not rely on outside manufacturing plant to churn out the quantity, they currently hand-build each and every piece of EP1 they sell. With the release of a cost-down model in early 2018, things might have changed.

Click below for a stop motion unboxing video.


I received my pair of EP1 as a test sample from Binary Acoustics some three months ago but decided to postpone writing this review because I wanted to have a longer listen to it and I needed some time to digest the sound and the technologies that went into this earphone. As always, I hope my reviews will benefit fellow head-fiers here.



EP1 is tiny and I am not overstating it. Each EP1 weighs 3 gram and has an enclosure volume of 317mm3. While I can’t say for sure if EP1 is the smallest IEM in the world, I am certain that it is the smallest earphones I have ever tested in my life.*

*AAW Q seems shorter in length while having similar diameter.

I was curios so I bench-marked the dimensions of EP1 with similar IEMs. I noticed that EP1 is slightly fatter and shorter than Final Audio Design F3100. Etymotic Research ER4XR, one of the smallest earphone available in the market today is about 50% fatter and two times the length of EP1.

Binary Acoustics claimed that if their sole intention is to create the smallest BA IEM, they probably can come out with an IEM half the size of EP1. They claimed to have beefed up EP1 chamber wall to make it more durable. So I guess EP1 is not small for small sake, the current design is the right size for good sound, durability and comfort.


Instead of having silicon tip on the nozzle, EP1’s silicon tip sits directly on the monitor chamber. The Balanced Armature (BA) transducers literally sit inside my ear canals when I listen to it. I believe the unmistakably forward sounding signature is due to the close proximity of BA drivers to my eardrums.

I also read that Binary Acoustics was able to dramatically shrink down their earphones by eliminating acoustic tubes traditionally used in IEMs. On close inspection, I noticed that the single BA units seemed to sit right behind the metal grills. While I am not entirely sure how that was done (probably with a plastic feature that hold it in place from behind), I believe such unobstructed positioning helped to achieve a clear and natural sound. After listening to EP1 on and off for the some three months, I can confirm that the sound is almost entirely free from chamber resonance.


EP1 looks minimalistic and Bauhaus modernistic. EP1 is an earphone that is striped to its bare minimum and the whole earphone was designed from ground up with basic geometries. There’s no organic curves, fancy ornaments to be seen and Binary Acoustics didn’t even stamp their brand name on this IEM.

EP1 monitor chamber is made of chrome-plated copper and it is reminiscent of an empty bullet casing. There are altogether three openings on the monitor chamber, one for sound to pass through, a cable outlet and a tiny hole for air flow balancing. Overall EP1 is a tasteful design and it screams elegance!

The EP1 I received is a special edition that came with silver plated copper (SPC) cable. A basic EP1 will come with black rubbery cable. I believe Binary Acoustics sourced the SPC cable (OD 2mm) from Lyre Acoustics (I happen to have a similar 3.5mm MMCX cable from Lyre Acoustics). While the SPC cable is springy, it is tangle free and feels soft to the touch. The cable has no memory effect and most importantly I never had an issue with it being microphonics. The left and right sides of EP1 are identical but the left cable is wrapped with a tiny black rubber ring. That is quite a genius touch as it means a lot to me to be able to distinguish left from right by feel in the dark.

Probably due to space constrain, the strain relief had been omitted from EP1. Some people might fret about the the absence of a strain relief, I am not a careful person so I was naturally one of them. I broke some of my earphones the first day I had them, thankfully I am blessed with good soldering skill. I have yanked EP1 cable a couple of times by accident, luckily it is still functional at the time of writing this review. EP1 might look delicate but it is actually quite durable since it had survived the last three months with possibly one the clumsiest person on earth and that is saying something!



I had a very positive experience unboxing EP1. EP1 came in a black box made of sturdy cardboard material. The box was filled with abundant accessories: two sets of silicone flange tips in three sizes, a pair of earhooks, a lapel clip, a faux leather pouch, a piece of cloth, some cable ties, a warranty card and a manual.


· Design: In-ear Monitors (in canal)
· Driver: 1 balanced armature
· Frequency range: 10-22000Hz
· Impedance: 40 ohm @ 1KHz
· Sensitivity: 111 dB/mW @ 1KHz
· Cable material: Silver plated copper
· Cable length: 120cm symmetrical design
· Plug Type: 3.5mm straight gold-plated
· Weight: 12g including cable, 3g not counting cable

Total Harmonic Distortion THD is not offered by Binary Acoustics.
EP1 delivers decent volume through most portable devices.


Acoustic Design

Prior to the golden age of IEMs (~2008-now?), BA transducers were mainly used in hearing aids. They were later appropriated into IEMs thanks to acoustical improvement over the years.

In this day and age, it is not uncommon for a custom IEM to have 2-10 balanced armature and dynamic drivers. It has even became a norm for a sub-30dollar earphone to have up to 3 drivers (Xiaomi Hybrid Pro HD and Knowledge Zenith KZ being the prime examples) and that makes the single BA EP1 seems almost primitive on paper.

In general, a single Balanced Armature (BA) IEM tends to be flat sounding and tiring to listen to (usually metallic sounding because the sound comes from a moving metal piece inside the unit). The most common trick to get a BA IEM to sound right is to pack a few BA units together and have each BA handles a part of the sound spectrum. Audio companies also usually achieve a relatively flat frequency response chart by stuffing multiple BA drivers in an IEM. Theoretically speaking, a flatter frequency response chart is a more balanced sound.

Unlike dynamic drivers, BA drivers tend to create a less powerful bass response since less air is moved during sound production. More air movement almost always means stronger bass sensation because in reality we tend to equate good bass with what we can feel and not actually hear.

Binary acoustics obviously modeled EP1 after some single-BA IEMs in the market today, notably those from Final Audio Design (FAD) and Etymotic Research. A typical IEM is sealed but there are some that are not, for examples those FAD earphones with BAM system. The description of BAM on FAD site is quite vague. BAM is a fancy acronym (Balanced Air Movement) coined by Final Audio Design to describe airflow optimization through creations of apertures on BA transducer and the monitor barrel. To me, BAM is essentially a bass response port that allows BA drivers to move at a higher amplitude and have a faster return. EP1 has a similar BAM port of about 0.5mm in diameter. It is located directly opposite the cable outlet. I did not and do not intend to break open my EP1 so I can’t confirm if the BA driver in it has a port as well. Alternating through the few IEMs that I have, it became obvious to me that EP1 sounds bassier and faster because of this technology.

Also noteworthy in my opinion is the tubeless design of EP1. I am quite sure Binary Acoustic is not the first company to come out with such a design as I have read about the Tubeless In-ear Audio (TIA) technology used in Audio 64 earphones and the Acoustic Expansion Chamber (TAEC) used in Campfire Audio earphones, I believe EP1 runs on the same acoustic principle. At least judging from the exploded views, Audio 64 and Campfire Audio seems to have similar driver placement.



I relaxed my EP1 with at least 100 hours of burn-in to ensure that I was hearing the optimal sound during my review.

The one weakness of EP1 is almost predictable given they use a single tiny balanced armature driver. EP1, not unlike other single BA IEM struggles to present grand, powerful orchestral arrangements that can go toe-to-toe with more powerful multi-driver earphones.

EP1 isn’t neutral, it is in fact a little aggressive sounding for my pallet. It is forward sounding with a U-shaped sound character. The resolution of EP1 is good, but it is far from being the most analytical earphones I have heard. EP1 is obviously not reference-tuned, it has this easy-going sound that is almost tailored for contemporary pop and rock music. The treble and bass of EP1 are clearly lifted above the mid. Although EP1 does not sound extremely smooth across the frequency spectrum, I have not heard any disconnection (a sudden dip or bump in the spectrum) when I used it for some complex tunes.

I am actually quite impressed by the clarity of EP1 as it is clean and clear even at the lower volume. The tiny bit of sparkle in the sound adds some excitement to a song. Enough with the praise, I think EP1 is not suitable for listening to youtube, audiobook or podcast. The forward and aggressive character became a curse for spoken audio. I couldn’t stand the shoutiness of the earphone and I often find myself changing to other earphones when I listen to an audiobook.

Overall there is a lot of energy in EP1’s sound and I find the sound signature to be quite unique for a single full-range BA IEM. It is meant for engaging listen and I do not think it is for analytical listeners.



Coming from full size headphones and leaky earbuds, I am truly disappointed by EP1’s soundstage. The soundstage is neither tall nor it is wide and the spatial spread of EP1 is slightly narrower than an average IEM. I guess the tiny port does nothing to expand the soundstage.

Vocals are front and intimate and they sounded very near probably due to the driver placement and the absence of an acoustic tube. Sound imaging is okay, I could distinguish different sound sections without a problem. Still, it is almost wrong to use EP1 for orchestral or classical music due to its cluttered stage.

All in all, the soundstage of EP1 leaves a lot to be desired. If you want an expansive soundstage, get yourself other IEM or better still get something else that is not an IEM.


Oddly enough, what surprised me the most is the bass of EP1. The midbass is thick and punchy but not exceedingly so. I can hear or feel a good amount of sub-bass as well. To me, EP1’s bass quality is spandex tight and the attack is impactful, It is something not often seen (or heard) in an IEM, more-so in an IEM of this size.

While the bass quantity is good, It is by no means bloated or boomy. The bass texture is awesome and it is far from sounding murky. EP1 defies my expectation of the lower frequency in a single-BA IEM. If Binary Acoustics aimed to create IEMs with good lower frequency that can match that of a multi-drivers IEM, they clearly had succeeded.


The mid of EP1 is nothing to write home about. It is mildly recessed while being smooth and natural, but there’s really not a lot going on here. Female vocals usually sounded great and male vocals tend to sound younger than they should be. Being tuned as a musical IEM rather than a reference IEM, the mid is really not EP1’s strongest suit but hey, you can’t have it all!


EP1 is adequately bright. For the last three months listening to EP1, I spotted no hint of sibilant. I think the treble is well defined but not entirely soft. It is well extended but a tad bright for my liking.

EP1 is one of the crispiest sounding earphones I have. It is capable of delivering some of the most realistic string and cymbal renditions I have heard so far.


EP1 is not picky. I used it with my ipad, phone, laptop and lossless player. EP1 did not sound very different on different devices and I don’t think EP1 will scale with better sources or amps. I was told that Binary Acoustics designed EP1 to be played through iphone or ipad (Cirrus Logic DAC) and that meant it was optimized for other smartphones as well.


Comfort and Isolation

In the end, even the best audio quality equates to nothing if an earphone is not comfy. No matter how great a pair of headphones is, if it hurts my head I will not be able to listen to it.

I do not consider EP1 the most comfortable earphones I have ever used. First, like any other IEM, EP1 requires a getting-used-to period, which is typically a few days. It is an invasive fit after all, it took me roughly 4 days to be able to use EP1 for a long listen. If you are a seasoned IEM user, you might find EP1 quite comfortable.

Also, my ears suffered air pressure in-balance when using EP1, that is an inherent shortcoming of an IEM. Air pressure builds up in a blocked canal after an hour or so. Most IEMs give me that same claustrophobic feeling if I use them for more than an hour. Using EP1 is quite straight forward. I didn’t have to fight EP1 to get it to fit right on me. When I use EP1 for a normal listening session, I usually push EP1 into my ear canals until I hear a pop or I get cut to a total silence. I generally do not have noise isolation problem with EP1.


When it comes to single BA IEM, most audiophiles will certainly think of Etymotic Research ER4. Final Audio on the other hand also released a line of single BA IEMs, that they labeled as the F series (F7200, F4100 and F3100). So I think it makes a lot of sense to compare EP1 to them because they share the same design.

Etymotic Research ER4XR is the latest and greatest of the ER4 series. Compared to ER4XR, EP1 has a much narrower soundstage with worse imaging, it is bassier, brighter and has a thinner mid. I find EP1 to be more engaging to listen to but it is less balanced compared to ER4XR. EP1 simply does not have the same resolving power of ER4XR. The treble control, dynamic and articulation of ER4XR are better than EP1 but not by a mile. Overall EP1 has a different emphasis compared to ER4XR: ER4XR is more of a balanced-mid IEM and EP1 is a bassier IEM. EP1 can’t compete with ER4XR solely on the sound department but as an overall package it does hold its own ground, especially if you take into account of its styling, portability and fit.

Final Audio Design F7200 has a flatter but finer sound compared to the more accentuated EP1. Now that I listen to EP1, I consider F7200 an earphone that sounded similar to ER4XR. Also worth mentioning is the Final Audio Design E series because from afar, EP1 looks undeniably similar to FAD E3000 but they are actually very different. It is unfair to compare EP1 with E3000 because E3000 is a budget single dynamic driver IEM. Zero Audio’s Carbon Tenore (the one everyone raved about) is another single dynamic driver IEM that looks similar to EP1. In a short listening session, I concluded that both Carbon Tenore and E3000 were outmatched by EP1 in most aspects. Carbon Tenore’s mid is remarkable, it is silky smooth but overall the earphone does not sound as lively as EP1. E3000 is a decent dynamic IEM. It is a great IEM for the price but the bass sounded loose and lacking to me, the decay and return is slow compared to EP1.


Overall Thoughts

I must admit that I greatly underestimated EP1 because of its size and simplicity. EP1 ticked off many boxes and does many things right. If you want a pair of earphones that sound great, look nice and are highly portable then look no further, you will not go wrong with EP1.

EP1 is a very well-made earphone with no major flaws. While the sound didn’t blow me away nor it has the most drivers, EP1 is a refreshing take in this somewhat convoluted Ear-Fi world.

To me (a mild alcoholic), EP1 is like a pint of craft beer: fine, exclusive and exquisite.

Thanks for Reading.