oBravo RA C Cu

AMT Technology.

On the surface, RA is a hybrid IEM with a large 16mm neodymium dynamic driver (NDD) and exotic tweeter, but underneath you will find an exclusive AMT-II tweeter driver which offers a technology only found in full size floor speakers. As a matter of fact, this technology competes against electrostatic, ribbon, and electrodynamic tweeters. AMT-II is their next generation driver, featured only in RA model, which is an updated version of the original AMT tweeter found in EAMT models. Even DD driver has been supersized with a bigger and a more powerful neodymium magnet, considering their previous ERIB and EAMT flagships had 12mm and 13mm respectively.

Based on the principle originally developed by Dr. Oskar Heil, AMT stands for Air-Motion Transformer with a design equivalent in surface area to a traditional 7”-8” circular cone type mid-range driver, accordion-folded down to approximately 1” grouping. Being able to shrink it down to such a compact size is the main challenge of the design and the manufacturing of this tweeter, which also explains a premium cost associated with it.


The AMT diaphragm is made of a Mylar ribbon, bonded with conductive aluminum strips which carry the signal current. When current passes through these aluminum strips, it creates bellows-like motion with folded pleats of the diaphragm moving the air at a very fast rate, according to oBravo – 5 times faster than a conventional cone driver. The motion range is very small, but because of this unique folded structure it moves more air than a dynamic cone driver or electrostatic driver of the same surface area. And because of its rapid response rate, it’s suited perfectly for high frequencies, where I even confirmed in my measurements the contributing effect of AMT-II response to be starting around 2.8kHz, covering upper mids and treble.



As I already mentioned, RA features a hybrid design, housing a large 16mm NDD bass driver and 8mm AMT-II 2nd gen tweeter. While Sensitivity (105dB) remained the same as previous ERIB/EAMT model, impedance really changed from a friendly 16ohm to a more demanding 182ohm. And to accommodate a new 16mm dynamic driver (up from their previous 13mm in flagship models), the shell has been redesigned as well.

I was very pleased with ergonomics of the new shell since it’s no longer elongated tear-shaped like in ERIB-1 or EAMT-1 flagships. These previous models accommodated only wire down wear, at least with my medium size ears, while RA (also referred to as EAMT-0) brings the cable connector closer to the shell for a more comfortable fit over ears. Personally, I prefer to wear RA with wire down and the fit feels more secure than ERIB-1C, even though RA is a little heavier (10g vs 6g). Perhaps due to weight distribution, but I found RA to sit more secure in the concha area of my ear, and I was also able to wear them wire up to add extra security when moving around.

Like other oBravo models, it has a beautifully carved acacia wooden faceplate with 8 pinhole vents, as part of its semi-open design. But to my surprise, while ERIB-1C with a similar faceplate design had some sound leakage for others to hear it when being close to the shell, RA had it down to a very minimum level. I confirmed that with a few people, and I even recorded audio by holding my phone next to RA shell while listening to music. Playing the recording back yielded no sound leakage. Proper eartips selection will play a big role in isolation (and bass response), but overall don’t expect a perfect sound isolation, it was just average.

Similar to other oBravo models from ERIB and EAMT series, you have an option of choosing a different combination of nozzle and body material to customize the design which going to affect the sound quality and will reflect in the price.

Available OBravo RA models:

  1. RA-C-Cu (eamt-0c-cu), precision ceramic nozzle, copper body
  2. RA-C-Ti (eamt-0c-ti), precision ceramic nozzle, titanium body
  3. RA-C (eamt-0c), precision ceramic nozzle, aluminum body
  4. RA-W (eamt-0w), acacia wooden nozzle, aluminum body
  5. RA-A (eamt-0a), aluminum nozzle and body

While I spent majority of my time with their top of the line flagship RA-C-Cu used in this review, during CanJam NYC ’18 show I had a chance to take a quick listen to a few other models. For example, while going between Copper and Titanium shell body, I found Ti to give sound a brighter and a more revealing tonality. When trying aluminum body wooden nozzle RA model, I heard a warmer bass with a brighter treble. Ceramic nozzle with Copper body was the best combination to my ears, offering a better balance between a neutral articulate bass and a vivid controlled treble.

As already mentioned in the cable section, connector is mmcx, but it’s a modified design which oBravo refers to as oB-mmcx due to a latch mechanism which prevents cable from rotation, one of the main contributing factor of wear’n’tear. While you can’t use any standard mmcx cable with oBravo iems, you can use oBravo cable or any custom cable with oB-mmcx connectors on other standard mmcx-based iems. Meaning, the PlusSound X-series GPC cable I received with oB-mmcx connector can be used on other IEMs with a universal mmcx connector.

Since the design of RA shell is no longer symmetric like in ERIB/EAMT, and I found the most comfortable way for both wire up/down wear is to have shells with a connector facing away and rounded part of the shell inside of concha area of the ear. Shells are not labeled with L/R marker since you will have to switch then when going between wire up and down, so you need to pay attention to the cable connector where, for example, stock cable has Red/Blue marker. To keep the design clean, PlusSound cable I received had no markers, but you can request your cable manufacturer to customize it.

The fit.

Eartips selection.

Prior to going into the sound analysis, I would like to dedicate a separate section of the review to tip rolling – eartip selection for RA model. This is probably the most important first step before you start listening to RA.

This eartip rolling was done using SP1000 SS and PlusSound X-series cable (as my baseline sound setup). I’m using only the largest eartips to get the best seal, and the focus of this testing was mostly to analyze the quantity/impact of the bass and the brightness/vividness of the treble.

UE Foam – neutral extended bass, revealing micro-detailed mids, crisp sparkly treble, mid-forward signature.

Symbio N – bass has a little more rumble, but treble sparkle went up, being a bit too crisp, while soundstage shrunk a bit. For the reference, normal large Symbio hybrids don’t have as tight seal in my earcanal.

Symbio W – Wide Symbio tips make a better seal in my earcanal, with the sound being closer to UE Foam, though treble has a little brighter sparkle.

Final Audio Type E – holographic soundstage expansion, extended bass with a velvety rumble, yet still neutral quantity, a little more organic, smoother mids, and a very crisp sparkly treble. Interestingly, while treble is very crisp, it wasn’t as piercing as I would have expected.

Comply TSX-500 – deep sub-bass extension with a little elevated warmer bass tonality, more body and smoother mids, sparkly well controlled treble. This is probably the best pair up if you are looking for the least fatigue sound sig, but as a result you lose a bit of transparency and micro-detail retrieval due to a foam “earwax” filter.

SpinFit – very neutral flat bass, bright distant mids (presentation was a bit far out of my head) with a tonality slightly off, crisp vivid treble. I didn’t like this pair up, bass was too flat and something was a bit off with a tonality.

JVC Spiral Dot – very neutral flat bass, bright forward mids, and treble has way too much sparkle/brightness. Wasn’t the best pair up, at least to my ears.

Generic silicone – neutral extend bass with a touch more rumble, revealing micro-detailed mids, crisp sparkly treble, nice holographic soundstage. Reminds me of the sound with UE Foam, but treble is just a little crisper and more vivid.

Generic hybrid silicone – these eartips use a different stem material (thicker silicone, thus I call them “hybrid”), but the sound is very similar to generic silicone eartip above, except I get a little more warmth in the lower end.

Eartip selection is VERY important with RA-C-Cu to have a proper seal of your earcanal to improve the balance between the bass and the upper mids/treble. At the end, I found foam eartips to work the best with RA since they offered the tightest seal, lifted bass impact, and helped to smooth out treble. I ended up using blue Comply T500 eartips because to my ears they offered an ideal micro-tuning of the sound and were less irritating during extended use. Comply TXS were great, but their earwax foam filter dampened the sound and their shallower depth insertion was not as secure to hold RA in my ears.

Just please keep in mind, eartip selection is very subjective due to variation in earcanal anatomy between different people.



Page 3 – Sound analysis, Front vent tape mod, and Comparison.

Page 4 – Pair up and Conclusion.

2 thoughts on “oBravo RA C Cu

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