ISN Rambo II English Review


Can Rambo Become King?




Construction and Design




  • Huge soundstage.
  • Great mid-range, with excellent voices.
  • Enormous clarity and definition.
  • Soft and delicate trebles, but very detailed and harmonious.
  • Precision, resolution capacity.
  • Very good tonality and realistic timbre.




  • Low zone limited in power.
  • Medium-low depth.
  • Light sub-bass.
  • Lack of body in the mid-low range.


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ISN Audio is constantly surprising the market. After creating some great IEMS, such as the H40, he returns to the scene, bringing out the second version of his Rambo earbuds. The question is: what’s the point of calling these new earbuds, Rambo II, when they are totally different… Maybe it’s because a trilogy is promised… Anyway, Rambo II is the new model of ISN brand earbuds. And its movement has been very much in line with the evolution of the market, moving away from the classic MX500 and PK2 capsules, to mount a new design, which allows the MMCX connection. Its forms have a slight resemblance to the OurArt QJ21, which I analyzed a few months ago, but completely in black and with conical and symmetrical capsules. I have the feeling that ISN wants to turn the market upside down with this new model. And there are plenty of reasons for that, since my initial sensations with this new model, have dramatically increased my expectations of them. Let’s see why





  • Driver Type: 14mm Dynamic
  • Frequency Response: 12Hz – 35kHz
  • Sensitivity: 113dB ± 1dB @ 1kHz
  • Impedance: 32 Ω
  • Connector Jack: 3.5mm Audio
  • Capsule Connection Type: MMCX
  • Cable length: 1.2m





The Rambo II comes in the classic ISN Audio box, whose austerity is frightening. But it’s all because the content offers the best possible. The box is rectangular, 124x78x43mm in size, with the brand logo on the top left, the model name underneath, as well as the small description. In the background, a realistic photo of the product. On the back side, the specifications. Once the cardboard is removed, a turquoise blue box appears, sealed by means of a sticker. Inside, just a black, elongated zippered box containing the following items:


  • The earbuds, with the cable attached and a velcro tape to collect the cable, inside a zippered bag.
  • 3 pairs of donut type foams.
  • 3 pairs of full foams.
  • A clip.
  • A mini hook.


The content is good, it has a decent amount of accessories and its good transport box. The foams come in a zip bag, as do the cable and capsules.

The only thing that can be criticized is the little originality of the box. But, as I say, I prefer that the money be invested in musical quality and construction.



Construction and Design


The capsules have an L-shaped design. They consist of a tube containing the MMCX connector at the bottom. In the upper part, it has a completely conical and regular capsule welded at 90º. The whole piece is metallic and painted in matt black. The cable is matching and even respects the decreasing diameter of the tube. This tube is not completely cylindrical, but has an increasing diameter, from the cable to the union with the capsule, to decrease again at that point, until the end of the piece. Its back is flattened and on it, ISN is written in white letters. There is an O-ring, made of rubber, which secures the MMCX joint. On the connector of each cable, the letters R Y L, in white ink, identify the channel. As I said before, the capsules are conical, ending in a flat edge. The outside, where the sound flows, is also flat and has generous radial openings, which allow the diaphragm to be seen. Its outer diameter is 16mm. Another peculiarity of the capsules is that, on the slopes of their conical part, there are three longitudinal slots, spaced 120º, between them.

The cable is very simple, covered with black rubber, but surprisingly flexible, although susceptible to tangling. It is completely black. It has a plastic pin. The splitting piece is a metal bulging cylinder, as is the 3.5mm gold-plated Jack connector sleeve. It comes with a velcro strip, to collect the cable. On the jack sleeve, you can read «Rambo II», in white letters.

The design is reminiscent of other models, but I appreciate the effort to design something different and very well constructed. Perhaps, the cable, coming from ISN, could have been different. But, it’s possible that the black uniform had something to do with it.



Adjustment and Ergonomics


The capsules are symmetrical. Thanks to the letters inscribed on the cable, the channel can be identified. They are slightly heavy, due to their metal construction. The adjustment is very free and fast, achieving instantaneous comfort. The downside is that, even with the foams on, it has a tendency to slip and lose its fit. This is a particular situation, because my ear canals are very large. The good thing is that their free form, allows for rotation and can be secured in this way.







The ISN Rambo II has a fairly neutral/balanced character, with a certain mid-centric tendency, where the bass are soft, but noticeable; the mids are quite clear, descriptive and the highs are delicate, expressive and natural. But their great virtue is the enormous scene and the great separation they possess.




The lower zone is characterized by its smoothness, the slots of the cones ensure that its power is contained and that its incidence on the sound is light. Its texture is quite smooth. The depth is easily perceived and it feels like it goes down well, at the beginning of the sub-bass, although with a fairly neutral presence and less so the lower the frequency. Although the driver is perceived as very capable, the design seeks to reproduce the low zone in this way: balanced, with a fast hit, very flexible and effective. There is a slight loss of the natural color and warmth of the timbre in the higher notes of the range. This may be due to the adjustment, but sometimes they can sound a little sterile, which is not the case in the lower tones.

In any case, range is drawn as a good complement to the rest of the sound, rather than as the star of the show. But a very worthy complement, well executed and with remarkable characteristics.





The central territory of the Rambo II, is a great compendium of clarity, balance, equilibrium and naturalness, within a great sound space, open and diaphanous. The result is a very expressive, pleasant and exciting mid-range. In particular, the voices have a very delicate treatment, which fills them with nuances, throughout their execution. In this way, their ornamental richness is enhanced, making their listening very pleasant, as well as detailed. It is as if the voices are reproduced very slowly, giving the listener time to appreciate their entire journey and development. On the other hand, although the voices have that special presence, the rest of the instruments are not omitted, nor are they underestimated. The stage is so big, that they have their own space, just a point behind, always respecting the recording and placing themselves where they have been assigned. Their sonority is natural and balanced, they don’t feel either bright or dull, but rather neutral and with a natural, though delicate, timbre. The body of the notes is not very wide, following the idea of a balanced sound, neither analytical nor blatantly warm, where the weight is precise, although perhaps a little thin. The protagonist is still the detail, the level of resolution, the definition in the execution and the great power of recreation that the Rambo II possess. All of this generates large mids, with a lot of information, which flood the scene and expand three-dimensionally, but with softness, neatness, elegance and refinement.





The treble tuning on the Rambo II is the perfect complement to its huge midrange. Without a doubt, they are not looking to be the protagonists, but to enhance the central range. In that sense, they are responsible for giving a natural, not forced, delicate, precise and fair shine to the whole sound. In this way, the detail feels very neutral, but clear and explicit, with a fair presence, very musical and harmonious. The treble is neither sharp nor incisive, but very much in line with the profile offered. Thus, no sibilance is seen, nor is there any auditory fatigue, even if its use is very prolonged.

And the other great virtue of the upper zone is the amount of air it is capable of generating, which is guilty of the great size and amplitude of the sound.



Soundstage, Separation


The other excellent section of the Rambo II, is its great scene, wide and high. Only the depth feels somewhat more limited. Despite this, it has a good level of length, which makes the separation not only horizontal or vertical, giving the composition a good level of three-dimensionality. In this way, both the instrumental and vocal positioning is perceived as very precise, instantaneous, easy to locate and follow.

Thanks to the amount of air in the sound, the separation is great, the sound is relaxed, but very precise, without being analytical. It is just very delicate, rich in details and nuances, exuberant in its recreation, positioning, definition and resolution.





ISN Rambo


The first version of the Rambo is very different: it uses the classic PK capsule, in a common design. Even the cable and connectors are different. The cable of the first version consists of 4 thin but very flexible strands. In the second version, the cable is interchangeable, with MMCX connectors, but it is made of one rubbery black wire.

And these big differences are also found in the sound. So much so, that it makes one wonder why this new model has been called Rambo II. Mainly, the profiles are different. Version 1, is warm and a bit dark, comparatively speaking. In version 2, everything is light and clarity, open space and more advanced and detailed mids. The lower area of version 1, in general, cannot be considered for bassheads, but its incidence on sound is greater, as well as its presence and power. It is slower, deeper, darker, wider, less defined, less compact and with poorer resolution. The texture in version 2 is more perceptible and richer, with more detail and agility. The hit is faster and more contained, with better recovery. In contrast, its tone is cooler and its sound is somewhat coloured towards the high side, making it sound less realistic and less low.

In the middle zone, version 1 retains some incidence of its lower zone, being warmer and darker, softer and less detailed. Version 2 exudes clarity and draws the voices throughout its performance, sounding more natural and richer, both tonal and timbral. In addition, the details are clearly perceptible, giving both voices and instruments a descriptive capacity that version 1 lacks. The mids sound more dull in the first version, with a softer and less defined, pleasant and musical development. However, in the second version, the resolution has been increased, providing a more agile and fast sound, with a greater richness of nuances and naturalness.

The high zone has a similar presence in both earbuds, but its timbre, definition and resolution is different. The first version offers wider and smoother trebles, less fine. Meanwhile, the new version does not offer a sharp version, but a more delicate one, with a more realistic and brilliant timbre, freer, calmer, but at the same time, brighter. This higher resolution generates a more detailed and precise sound, without sounding sharp, but more faithful and fast, very attached to the sound, complementing it in an excellent way.

The scene is a new revolution in the second version. The Rambo 1, has a recreation with a medium-high width, with a good feeling of depth, but without too much height, nor much separation. Version 2 improves all these aspects (except the depth), raising the amount of air, gaining in separation, giving more three-dimensional space to the instruments and voices, placing them more precisely, within a more ethereal and spacious environment, where they can perform with greater freedom and projection. In short, the scene has grown, it has become more enveloping and more spherical, gaining in separation, air and global positioning.



Ourart Ti7


Rambo II has returned to the war and this time his rival is Ourart Ti7, an old acquaintance of the scene, who maintains his reign in the middle zone. Rambo II, has learned and now has similar weapons: MMCX cable, some metal and ergonomic capsules, as well as large openings in its front, to win on stage and amount of air. Ti7 is a tough competitor and its cable proves it, displaying its powerful L-shaped connector, big and golden, in addition to its 4 braided strands. Rambo II, has a more limited arsenal in this sense: its cable is thinner and rubbery, but has good flexibility. Rambo II has felt inferior in this respect and has retracted, to rethink the strategy:

  • «It will be necessary to start at the low end… At the bass!»

He shouted Rambo II.

  • «Here I wait for you!»

Ti7 answers. And the bass of Rambo II start to play:

  • “I think I lack power, but I trust the wisdom of my new diaphragm. It may not be as powerful, but it is agile, fast and recovers easily”.
  • “Where are you going, young Rambo II? My bass still imposes…”
  • “You’re wrong Ti7, your reproduction has lost its naturalness and can no longer stand the passage of time, your diaphragm can’t withstand the onslaught of electronic music like mine, you need to reduce the volume to resist the pressure …”
  • “Damn it! Rambo II has discovered our weak point: lighten the load on the lower zone and shore up the middle flank. Everyone knows where the true power of Ti7 lies…”

What King OurArt did not expect, is the study of his enemies, which Rambo II has done, in the battlefield. Now, not only has he improved his lower zone, making it more resistant and permeable, gaining precision and detail, but he has also raised the realism, without damaging the middle zone. They are not the best bass, but they are great warriors, very useful to reproduce any genre. Rambo II has come out confident and has raised his voice:

  • “To the mids!”

At this moment, Ti7 is waiting, calm, listening to the war noise of his enemy… The first musical onslaught has fitted it in, the first chords have started to sound… Rambo II is offering his best strategy: The mids starts to play freely, openly, clearly and cleanly. The instruments are described with neatness and definition, natural and neutral. Details flow like light arrows, nuances are shot like lethal, ultra-fine and unstoppable darts. Ti7 protects itself and withstands the onslaught.

  • “So you will not defeat me, my midrange possess the same or more, than what you have offered. You don’t surprise me.”

Meanwhile, Rambo II smiles and mutters to himself:

  • “Let’s sing …”

Suddenly, the voices appear and stand in front, demonstrating all their power. Riding between the instruments, coming out from the front and the back, left and right… boasting of their gentle omnipresence. Their wake is bright, but sweet, lush and elegant. In this way, the vocal riders have trapped the enemy voices, they have not been able to go out to the battlefield, because the instruments were not separated enough, nor did they possess the total freedom and clarity that Rambo II does.

  • “It’s not possible that my voices don’t go in front of the instruments… Go on!”

Shout Ti7. But the battle has begun to fade. Not only do the voices feel more delayed, mixed, less clean. They have perished to the greater resolution and power of Rambo II’s better definition. The vocal riders have risen majestically, perfectly drawn, exposed and proud. And the rest of the mids has celebrated the victory of the central range.

Ti7, maintaining his pride, has clenched his teeth and raised his arm, has said:

  • “Swords Up: Battle of the Treble.”

Rambo II, attentive, has whistled and the treble has begun to shine. Their brilliance is not blinding, but vivid and effective, they always accompany the mids, finishing their actions, leaving a subtle, delicate, harmonious and pleasant trace.

In the face of such an attack, Ti7’s high notes have been disappearing rapidly, its career is shorter, fading among the rest of the notes, without defining its edges, leaving them withered, orphaned, unarmed… It is a minor battle, but Ti7 has run out of air. Meanwhile, Rambo II expands his sharp soldiers to the higher areas, where Ti7 cannot attack them.

It’s the moment of truth. Ti7 has set up the board and challenges Rambo II:

  • “Welcome to Our Art.”

The final battle for the scene and the separation, where Ti7 has reigned in all its forcefulness, is about to begin.

Ti7 arranges its warriors across the battlefield, with a good lateral separation, but forgets to access higher places, losing perspective and three-dimensionality. Meanwhile, Rambo II surrounds the enemy in a circular manner, with a closer presence, but with less depth. Aware of this fact, he rushes to gain height, climbing hills and small mountains, in order to offer a more adequate vision and better positioning of his warriors on the battlefield. In this way, his sound grows and expands over the gaseous plain of Ti7.

  • “Ti7, give up, you’ve lost your aural sound…”
  • “Never, warriors, surround him.”
  • “You’ll never be able to do it, my soundstage is bigger than yours and my soldiers are better placed and trained, they are able to reproduce the sound with more precision, detail and resolution. Their positioning is concise, not like your soldiers, who wander ethereal, but less defined. Give up, you have nothing to do. If you retreat now, you can still retain the dignity as a great earbud that you have been.”

Finally, Ti7 has come to his senses, giving up, admitting the superiority of Rambo II, in those aspects where he had previously triumphed…

And so it was that, like Rambo II, he conquered the Middle Kingdom…





Rambo II has returned to conquer and won the battle, becoming King. But he has not achieved this by the way of war, but by using strategy, which is also peaceful.

Version II is a revolution, both in design and sound. It joins the great initiative of using MMCX cables and creating a new capsule. This, allows it to generate a new sound, much more free, open, defined, rich, detailed and clear. A neutral and balanced sound, where the midrange stands out, qualitatively speaking, for its technical level, resolution capacity and richness of timbre, tone and nuance. And for dessert, its high zone: the perfect ally that generates sparkle, brilliance and detail. To top it off, the Rambo II has a very large and airy stage, which enjoys an excellent instrumental positioning, where the voices receive a very special treatment.

Yes, Rambo II can reign and with much delicacy, too.



Sources Used During the Analysis


  • Burson Audio Playmate.
  • JWD JWM-115.
  • Tempotec Sonata iDSD Plus.
  • Tempotec Serenade iDSD.
  • HiBy R3 Pro.