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Description
Binary EP321 MEMS Tribrid IEM – World’s First Direct Drive MEMS Hybrid In-Ear Monitors
The Binary EP321 MEMS Tribrid IEM marks a major breakthrough in in-ear monitor technology. Designed by Binary, the EP321 is the world’s first IEM to feature Direct Drive MEMS driver technology, delivering an ultra-high-resolution listening experience with exceptional speed, clarity, and tonal accuracy.
At its core, the EP321 uses a six-driver tribrid architecture per side, combining the physical impact of dynamic drivers, the precision of balanced armatures, and the lightning-fast response of a MEMS driver. Every element is carefully tuned using a professionally engineered three-way frequency crossover, resulting in a sound signature that is detailed, rich, engaging, and effortlessly musical.
Powerful, Clean & High-Resolution Sound Performance
The Binary EP321 features a meticulously arranged 321 driver configuration—three Balanced Armature drivers, two Dynamic-based drivers, and one MEMS driver—cleverly reflected in its name.
Each driver plays a dedicated role, ensuring outstanding separation, accurate imaging, and an immersive soundstage. Whether you’re listening to acoustic recordings, electronic music, or complex orchestral arrangements, the EP321 reproduces sound with authority and finesse.
Direct Drive MEMS Technology – A True Industry First
The highlight of the EP321 is its Direct Drive MEMS driver, engineered with a built-in energizer that eliminates the need for external amplification. Designed specifically for the ultra-high-frequency region, this MEMS driver delivers:
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Super-fast transients
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Exceptionally clean treble extension
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High micro-detail retrieval
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Zero harshness or fatigue
The result is a treble response that audiophiles crave—airy, precise, and incredibly natural.
Dual-Driver Bass Module – Dynamic + Passive Radiator
For the low frequencies, Binary integrates a 10mm dynamic driver paired with a 6mm passive diaphragm, forming a powerful bass module. This configuration produces:
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Deep, textured sub-bass rumble
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Punchy and controlled mid-bass
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Excellent speed with minimal distortion
Bass remains impactful yet clean, never bleeding into the mids.
Three Balanced Armature Drivers for Natural Mids & Detail
Supporting the bass and treble performance are three high-performance Balanced Armature drivers:
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One full-range BA for detailed, natural mids
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A composite dual-BA setup for smooth and extended high frequencies
Working in harmony with the crossover network, these drivers ensure seamless integration across the entire frequency spectrum.
Premium Design & Ergonomic 3D-Printed Shells
Visually, the Binary EP321 is just as striking as it sounds. The IEMs feature CNC-machined stainless steel face panels with irregular geometric patterns that shimmer and change colour under different lighting angles.
The shells are crafted using high-precision 3D printing, offering excellent structural integrity and long-term wearing comfort—ideal for extended listening sessions.
Technical Specifications
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Driver Setup: 10mm Dynamic Driver + 6mm Passive Diaphragm + 3BA + 1 MEMS
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Impedance: 13Ω @1kHz
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Sensitivity: 122dB/Vrms
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Frequency Response: 8Hz – 40kHz
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THD+N: <1%
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Connector Type: 0.78mm 2-Pin
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Termination Plug: 3.5mm / 4.4mm
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Weight: 7.5g (per side)
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5 star iem but deducting 1 star due to tuning
Have to put a low shelf filter in bass region to make it forgiving of poor music recordings.
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Pairing this Harman Target Version with a Samsung A17 playing Apple Music and FLAC files and Fiio X1 DAP as a secondary source with FLAC files. When tuned to give preference to Mids as i prefer to hear the voices more than anything else, this comes out as a sweet sounding combination and tracks like Racy Chapmans Fast Car and Massive Attacks Teardrop shine beautifully. The Castor Pros are best listened at about 40% volume and and infact they do actually sound amazing at a high volume for bass heavy tracks such as EDM but for Trance and Rock the cymbals and snare drums sound better at 40%. This pair of iems and the combo sounds like money well spent so far and next i want to try analytical IEMs like the 7Hz. Thanks to the Audio Store for the rushed delivery.
Great purchase... excellent product
Good Product as expected
Worth every penny! This is not for bassheads as it lacks just a bit on the bass department, but the separation is awesome and the sound stage is also huge. Awesome for gaming as well! (Apex Legends, Arc Raiders, PUBG)
This is the replacement for my purchase of moon drop dsp chu2 which I bought in aug 2025 i don't know how it got damaged from last it stopped working on left side buds and after a few days mic also stopped working and i forgot to claim the warranty for it . So find this spare cable very helpful since I love these IEMS for real Tq AUDIO STORETEAM FOR THE smooth delivery
Great job on packing of the product. As a gamer I can say that, for fps games like PUBG , CS2 etc., Castor Pro is the best in under ₹2000
I recently bought this and am incredibly impressed with it. The build quality feels solid and premium right out of the box.
When it comes to performance, the amplification is fantastic—it delivers a clear, noticeable boost to the audio power and volume without sacrificing clarity. It is also incredibly easy to use; completely plug-and-play with zero hassle.
An awesome bonus is the inclusion of the Type-A to Type-C dongle/adapter. It makes it incredibly versatile to connect to different devices right away without needing to buy extra accessories.
Overall, it's a great purchase and definitely worth the money. If you are on the fence, just get it!
As an all rounder it fits my taste quite well,the only problem it really has is the male vocals being a bit recessed (not terribly recessed if you use vocal eartips),they are a tad bit overpriced seemingly,divine planar might be better,but for people looking for a fun entry into iem's,it's worth the price (some people say it's included DAC isn't enough,it works well enough as a temporary solution,yet to test if a dac makes a big difference or not).
Unsure if this is how most iem's are but the cable felt a tad bit short.
I had never used an IEM before, so this was my very first experience and I was genuinely impressed. As someone who loves music, I can confidently say this is one of the best investments you can make for audio quality. The sound is exceptional and absolutely worth the price.
To get the best possible audio experience, I would also recommend pairing it with a good-quality DAC, as it significantly enhances the overall output. ....
This is the most balanced sounding IEM I've used in this price. I am using the Type C variant, and I haven't experienced any issue regarding the playback whatsoever. It is equipped with the DAC chip CX31993, which is found on the dedicated DACs around the price of 1K. The cable is also a 4-core silver plated copper one, with really nice build quality. These are also really responsive to EQ Settings, tweaking the audio balance using a 10 or 31 band EQ makes the experience even more versatile.
The only cons I have noticed are regarding the in-box ear tips, I didn't find them to be very comfortable, so I had switch them with some other ear tips. Although, the metal built of the IEMs give them a really premium feeling, the glossy surface is extremely prone to scratches and they still get scratched even after using cautiously.
It is good but could be a bit sharp sometimes may be balanced by EQ. But one problem in my type C unit, after 3 days it stop sound out of nowhere, while listening music, or watching movie/yt. Have to plug out plug in to get the audio back.
This is a magical DAC, I don’t believe ki isne mere headphones main jaan daal di ho
Really the quality of aurora ultra is out of the box , literally if you never use an iem and experience first time you feel actual music. Aurora ultra give life best experience.
This is only possible because of the audio that my first experience and the audio store surve there best to just create my best experience thanks a lot for protective, timely delivery and
Again thanks for giving that service and seamless experience to the team
AUDIOCULAR DAC Recommend asome sound quality it's pushing
Aswome experience with kz castor pro harman target Bass edition I never heard that quality of
Bass My second experience with iem aswome
