Pros: Good first earbuds from ISN Audio !
Good vocals and treble.
Good soundstage.
Cons: Low bass presence (especially subbass).
High-mids sometimes a bit agressive.
Huge speakers (meaning average comfort for small ears).
Cable looks a bit fragile.
  • ISN Audio Rambo (earbuds)
Those earbuds can be bought in Penon Audio store (direct link)


A small point and look on the packaging: the box is rather modest but presents the product well with its pretty Rambo style logo on a generally dark blue color, and indicates the specifics of the product.


Inside there are of course the headphones (well wrapped in a plastic bag), a small plastic clip, a set of pairs of black foam, a little strap and a nice little case.


The cable is rather nice, it is soft but is a little memory (nothing very annoying in this area however). It seems a little fragile. The material used is 4-wire silver plated, which therefore remains fairly standard as what can be found in headphones in this price range. ISN Audio is a specialist of cables at very good prices, but which have recently produced very high quality cables at lower cost. Suffice to say that they master this area very well (having already been able to test the brand's S4 and C4 in particular).


The Y-splitter (with the name Rambo engraved on it) is rather simple but does the job, the same goes for the black jack (engraved ISN Audio this time). I chose mine in 2.5mm balanced plug, but also exists in 3.5mm standard.


Note that the Rambos therefore use the very famous “PK” style shells (which Yuin was able to launch fashion), these shells generally include two holes in the rear « ventilation » of the speakers, but on the Rambos, one of the two holes is there, so only the tallest (and therefore the widest) hole remains.


I find that the only negative point on these Rambo is that the speakers are very large and therefore we do not find the usual comfort of PK style headphones (see photos to better understand, but overall nothing to do with speakers PK1 for example). Too bad, especially for small ears (larger ones should not feel discomfort).

  • SOUND :

Note that for this sound part, I burned my pair up to about 150 hours before proceeding to this final verdict.

Overall it is a very good surprise, although the sound is rather made for vocal (like most PK style shells) so high-mids rather sharp (without annoying the ear too much but which can be a little aggressive in some tracks) but I find a good homogeneity of the rest of the spectrum as well. Namely treble is a little "smooth" at the end but properly detailed without going into extreme detail either. The bass is a bit lacking in presence, especially on the subbass, which is almost non-existent, but we can still hear the presence of the mid-bass (if we focus a little). Clearly these are not the kind of headphones that will delight fans of electronic music, but rather instrumental and vocal. That said, the Rambos are a pair that can handle almost any style of music, which remains significant.

The instrumental separation is also quite good. The sound space is not narrow, it is intimate but remains deep. It sounds rather transparent to my ears, without too much coloring. We are not, however, on a completely neutral sound.

I highly recommend the mid-thick foams to fully appreciate these Rambo. Foams with thin thickness will forward too much the mids and trebles and there is already enough like this, soi it may quickly become tiring in the long run.

For the first headphones of the brand, I must say that I am rather amazed, these Rambo will bring your favorite music to life with flying colors. For those who like the prominent vocal and pop music style, these earbuds are for you. The price / quality ratio seems very reasonable especially in view of the performance that these headphones can produce, so congratulations to ISN Audio for this good surprise. Hoping to correct the shooting on the bass (especially subbass) and hope more detailed treble for the next version of the Rambo (2), which according to my sources is about to arrive quickly!

Thank you for reading my review, and as always, happy listening to all of you !

Pros: Well extended and clean treble (!!!); clarity; timbre; separation/layering; high-quality case included.
Cons: Lean on bass.


I have to admit that my knowledge of earbuds such as the ISN Audio Rambo has caught thick layers of dust lately. Starting out my portable experience in the mid 2000s, the second generation Apple earbuds were my one-and-only go-tos…until I sadly lost them more than 10 years ago. A pair of low-end Sennheiser earbuds had to do as substitute, but they were soon replaced by in-ears and small, foldable headphones, that did the job for a long time…until affordable Chifi multidrivers appeared some three years ago.

In-ears turned out to be better isolating, therefore not affect one’s surroundings, they had a meatier low-end, and they became available with fancy driver arrays that revolutionized detail resolution in the budget sector. But earbuds have always maintained their faithful followers as they are comfortable, typically are pleasant sounding and less prone to fatiguing peaks, you don’t miss the door bell — and one gets their bang for the buck.

Earbuds came lately back to my attention when a hungry however generous fellow Head-Fier provided me with a handful of his DIY models. I was amazed how good they sounded. This renaissance was fuelled further when Penon Audio sent me the ISN Audio Rambos for a review — also rather surprisingly.

I have not heard or read much about ISN Audio other than they specialize in cable development and production including OEM and ODM orders — and the Rambo is their earbud flagship out of two models they offer.


Driver Size: 14.8mm
Frequency: 6-25KHz
Impedance: 32Ω
Sensitivity: 115dB
Plug Type: 3.5mm/2.5mm
Cable Length: 1.2m
Price: $65 (3.5 mm audio edition); $69 (2.5 mm balanced edition)
Purchase Link: Penon Audio


…are the earbuds with attached cable, 2 pairs of foam covers (plus one spare), 4 pairs of donuts covers, short clip, carabiner, and a sturdy high-quality case.



Well, an earbud is an earbud, right? Yes, right, but this one has really small and ergonomically shaped stems that handle very well. Reason for the good haptic is also the hard polycarbonate use which feels good between my fingers. The same material is used for the chin slider, splitter, and headphone jack…the latter has a sturdy rubber strains relief. The braided cable is thin, tangles up a bit easily, but it has no microphonics and rolls up to next to nothing. Handy!


Well, and an earbud fits like an earbud, right? Well, bloody well right, it does. Like all earbuds I know, the isolation is (intentionally) not great, it sits well in my ears and is as comfortable as ever.



The ISN Audio Rambo with their 32Ω impedance need a bit of juice. They can be played with a phone on higher volumes but I got the best results out of the audioquest dragonfly black dac/amp attached to my iPhone SE. I used donuts and full foams as covers and didn’t find a sonic difference between them. Both were equally fine.


The big picture: The ISN Rambo is characterized by warm, bright, clear, and open sound with sugar treble as its outstanding feature.

The details: The Rambo’s most outstanding feature is its textbook quality treble: it is very well extended, yet unobtrusive and not fatiguing and it adds sparkle: high piano notes sound seductively pearly and the opposite of splashy and screamy. High violin tones sound as smooth as butter. Absolutely beautiful. The Rambo has the best treble of any iem or earbud I have reviewed yet.

The bass is nimble, disciplined, it decays at a realistic speed, but it rolls off a bit early and there is no strong sub-bass. The upper bass also does not support the lower midrange well.

The midrange is reasonably intimate but does not get much support from the low end so that voices could be a bit firmer in some tracks. This is enhanced by a very wide soundstage that stretches the image in analogy to widescreen cinema and also by the upper treble which adds much of the air and sparkle. The soundstage is wider than deep but it can have a respectable depth in some tracks. What “bails out” the voices is the great timbre the Rambos offer.

The forward treble and the light bass also result in an outstanding clarity of the image. Layering and instrument separation are great but suffer a bit when the instrumentation gets busy.

As to usage, I am really enjoying classical music with the ISN Rambo because of the timbre, wide stage, and the shiny treble. The unexaggerated bass certainly does justice to an orchestra’s rhythm section. Celli sound great and so do pianos. Jazz also sounds good owing to the good separation and timbre and the bass is sufficient for brass instruments.

When it comes to rock music, the Rambos may be a bit lean on the drums, which can sound a bit tinny in some cases. Obviously, fans of hip hop and drum-and-bass should look elsewhere.

In summary, I’d describe the sound as very refined.


Since earbuds in all price classes can be really good sounding, the underlying question is whether the Rambos are worth their money and where the difference lies with respect to the cheaper competition. I picked the highly rated $25-30 NiceHCK EB2 [review link] for a representative comparison. The Rambos are definitely built better from higher-grade materials which includes the cable. The KB2 has a fuller, darker image owing to more bass, which is a bit cruder than the Rambo’s with lesser treble extension/quality. The Rambos sound more refined with better detail resolution, a wider stage, a better timbre, and their very clean treble. Nevertheless would rock fans probably prefer the “simpler” EB2s, which are also very respectable.


The ISN Audio Rambo is a good sounding and well built earbud that is worth its asking price in my opinion (which would be my personal sweet spot for earbuds). If you own this one, you may not need a large number of budget ones. The Rambos excel over cheaper models by their treble extension, clarity, and wider stage. Particularly the smooth and pearly treble is outstanding. It is a good allrounder that I particularly like using for classical music, jazz, and the odd folk/country music, but not so much for rock. If there are “trebleheads” out there (in analogy to bassheads), this one could be interesting for you.


I thank Penon Audio for kindly slipping the ISN Audio Rambo in with a warranty return of another earphone for the sole purpose of my independent review. I particularly thank them for their quick communication in warranty matters. This review was originally posted at

Pros: Great balance between driver and capsule.
- Balanced and natural sound.
- Comfort.
- Cable, plug.
- Transport box.
Cons: Bass limited in extent and quantity.
- Some lack of depth.

Again another model of the ISN Audio brand. In this occasion it is about earbuds, of controversial name: Rambo. The least you can expect with such a combative name is battle, war ... But really these earbuds are totally harmless, there is nothing that produces an ounce of aggressiveness in them, neither in their design nor in their sound. For this occasion, ISN has chosen to mount one of the classic capsules, but more comfortable on the market, the PK type. My experience tells me that many of the earbuds I own with this type of capsule have a tendency to offer a similar sound: an enhancement in the mid zone, from 250Hz to beyond 1kHz, with a predominance of male voices, soft basses and little prominence and sparkling highs. It's also true that the rest of my earbuds of this type are cheaper. So, you have to see what Ios Rambo can offer, whose price is over 65$.

ISN Rambo 01_resize.jpg ISN Rambo 02_resize.jpg


  • Brand: ISN Audio
  • Model: Rambo
  • Type of Drivers: Dynamic 14.8mm
  • Frequency response: 6Hz - 25kHz
  • Sensitivity: 115dB
  • Impedance: 32Ω
  • Jack Connector: Straight 3.5mm, gold plated.
  • Cable: 4 wires of 1.2m

ISN Rambo 05_resize.jpg ISN Rambo 06_resize.jpg


The Rambo come in a box exactly like the C16 cable, sealed in transparent plastic, dimensions 122x78x38mm. In this case, the box does not have any transparency. On the top there is a black background sticker with the logo and the mark on the top. In the center, with eye-catching red letters, whose font simulates handwriting, the model name: Rambo. Below, a realistic photo of the earbuds and the cable.

After opening the box there is only a black, rigid box, with zipper, very suitable for storage and transport. Inside there is a Zip bag with 6 pairs of full foam, black. A clip for the clothes, a small violet musket and, finally, another zip bag containing the earbuds. The cable of the Rambo comes with a velcro tape.

The packaging is fully functional, simple, without boasts or luxuries. But it comes with everything you need, except donut foam.

ISN Rambo 07_resize.jpg
ISN Rambo 08_resize.jpg

Construction and Design

Describing an earbud that uses a capsule as classic as PK has little history, it can only be summarized in highlighting the details. And actually, these capsules offer several. The first detail is in the cover that encloses the driver. Usually it has a thinner and rounded profile, in this case it is wide and flat. The second detail is found in the horizontal rear openings: there are two notches, but only the top is open, the bottom is sealed.

I have a particular theory (although possibly more than one has also thought about it): I think there is a relationship between the sound/profile of earbuds, depending on the type of capsule used. The PK capsule has some limitations. Starting with the diameter, which restricts the use of larger drivers. There is also a limit in the depth, perhaps this reason has to do with the Rambo cover is wider, to gain something more in this sense. In the end, all these details influence the final sound.

Finally there's the cable. The first impression it gives is that it is something fine and delicate. It consists of four braided wires, of small thickness, covered with transparent plastic, which shows a dark silvery material. But in the end the cable is very light and manageable, has very little tendency to get tangled and does not offer any microphones. On the other hand, there are the metal parts. Both the plug and the splitting piece are two almost identical black cylinders with a double notch ring, which makes them much easier to use and ergonomic. The plug has a thick piece of plastic, which protects the cable junction. The name of the brand is written on it. The connector is 3.5mm gold-plated Jack. The name of the model is written on the splitter. Finally, the cable has a small sphere with a through hole, which is used to adjust the cable under the chin.

In my opinion the cable is almost perfect for these earbuds, it does not weigh, it is not bundled, it is highly flexible, the connectors are comfortable, of great quality and ergonomics. In addition, it comes with a piece of adjustment. Everything I usually ask for.

ISN Rambo 10_resize.jpg

Adjustment and Ergonomics

The PK capsule is one of my favorite capsules in terms of fit and ergonomics, its small diameter and its thin spike represent an achievement in design, between minimalism, simplicity and practicality. In this case, the detail I mentioned earlier, about the thickness of the cap, is the only thing that could be susceptible to limit the comfort of these capsules.

Another point that facilitates comfort is the cable. In this case, the fact that it is made up of four fine, braided threads is an advantage, because it is not binding, it has no rigidity at all, it is highly manageable, it is very easy to pick up. In addition, all the metallic pieces that compose it do not do more than to facilitate any task. The design of the plug, the splitter and the adjustment sphere form an excellent whole.

ISN Rambo 11_resize.jpg



The ISN Rambo are warm but balanced earbuds. They have a rather neutral low zone, well balanced mids and a good spark of brightness at the top.

ISN Rambo.png


The low zone of the earbuds with a PK capsule I've always found conflictive. But the Rambo solve the problem better than the rest. The sub-bass below 40Hz is light, providing a moderately limited depth. From there its presence improves and rises, but to stay at a fairly contained point. The mid-bass hit enjoys a soft forcefulness and decays moderately. Its texture is smooth and the definition is not very accentuated. Globally, the presence of the zone remains one point below the rest of the ranges. As a result, the lower zone is, as a whole, balanced. However, the Rambo have a certain warm face, with a hint of darkness.

ISN Rambo 12_resize.jpg


Things change here. The ISN have the best mids of all the PK earbuds I have heard. The trend with this capsule is to get a range of 200Hz up to 1kHz quite pronounced and present. The Rambo manages to invert this particularity and its curve descends from 300Hz, allowing to compensate the effect on the mid zone with this capsule, lightening the response in that zone. This is a very clever choice, because some negative peculiarities are avoided, such as the presence of male voices, with their consequent large dose of mud, nasal and even metallic sound. None of this is perceived here. The Rambo have a very balanced vocal range between male and female voices, without one prevailing over the other. In addition, the naturalness improves enormously, offering a very balanced texture, that conjugates warmth and certain darkness, with a light brilliant spark, that contributes clarity, detail, separation, space and air, but without contributing any sibilance.

It is true that the voices are in a closer plane than the rest of the instruments, which makes it very suitable for genres with vocal predominance and few instruments. But the rest of elements also enjoy all the virtues that voices have, but with a point of distance. Thus, they are also a delight for rock or pop.

ISN Rambo 13_resize.jpg


The upper area has the typical PK flash, but it occurs earlier and is narrower. Thus its incidence is noticed something different but in a beneficial way. The brightness is observed, noticed and perceived in a quite complete way, but wide, extended and not very sharp, free of fatigue. It offers a good dose of air, good level of detail and brings good clarity and separation to the sound.

ISN Rambo 14_resize.jpg

Soundstage, Separation

The ISN Rambo have a wide enough scene for earbuds. The feeling of three-dimensionality is limited by that certain lack of depth, but still offer a good feeling of recreation spherical and quite zenithal. The positioning is good, but with a closer predominance of voices over the rest of sounds. The level of separation is appreciable, within the parameters of naturalness and equilibrium that characterize these earbuds, without being either excessive or unreal.

ISN Rambo 15_resize.jpg


DQSM Z & W Panda PK2s

The comparison is necessary, because the Panda are so popular, but they are not at the same level. The Panda have that over-emphasized sound in the lower section of the mids, which characterizes some models with a PK capsule. They sound clearly muddy, congested, muffled, nasal, unnatural. Moreover, in this case, the Panda has a very smooth treble and less extension, which also helps to muddy the sound in that mid zone and to turn off its profile more.

In terms of scene, separation, instrumental recreation, three-dimensionality, etc., the differences are just as great. And it is true that the Panda cost a third of what the Rambo, but in this case the price difference is totally justified.

PK2 Earbuds.png

Ourart Ti7

The Ourart Ti7 are a worthy rival for the Rambo. Although in the lower zone the Ti7 have clearly less global presence, the impact of the bass is faster, drier and more contained. The Rambo offer a more complete zone, with more body, punch and incidence in the rest of the sound. In the Ouart, the global absence of the lower zone frees the sound, but depending on the genres and/or songs, it is somewhat orphaned.

In the mid zone the differences are maintained, the Rambo have a warmer profile, sweet, natural, more compact and homogeneous. Meanwhile, the Ti7s are colder, more analytical and, although the graphics do not reflect this, their sound is brighter, with higher resolution, cleanliness and separation. The presence of the voices is similar in both and both give them special attention and emphasis, but each one focuses them from their profile.

The trebles feel more present in general, in the Ti7, although locally, the Rambo offer a more crunchy hit in the lower area of the trebles.

In terms of separation, the greater openness, clarity, air, definition and resolution of Ti7 is above the Rambo. The scene feels bigger in Ti7 too, while Rambo offers a more intimate and compact ensemble, not so ethereal or open, but also more realistic and natural.

In short, Rambo has a warmer, analogical, compact, balanced and natural profile, as opposed to the cold, analytical, brilliant, ethereal and open profile of Ti7. They are two profiles rather complementary than opposite.

ISN Rambo vs Ourart Ti7.png
ISN Rambo 16_resize.jpg


The ISN Rambo is a candy inside a PK capsule. Intelligently tuned to conjugate the sonic characteristics of this envelope, with a driver designed to use, obtaining the best synergy to offer a natural sound, organic, analogical, balanced in bass, with great voices and a wise dose of brightness. A charming man, this Rambo.

ISN Rambo 17_resize.jpg

Sources Used During the Analysis

  • Burson Audio Playmate
  • Xduoo X3II
  • F.Audio S1

ISN Rambo 18_resize.jpg


  • Construction and Design: 75
  • Adjustment/Ergonomics: 85
  • Accessories: 70
  • Bass: 75
  • Mids: 85
  • Treble: 75
  • Separation: 80
  • Soundstage: 80
  • Quality/Price: 85
Purchase link

You can read my full review in spanish here:
Pros: Good Build quality,
Sweet Midrange,
Sparkling Highs,
Soundstage and Imaging,
Cons: Cable could have been better,
Bass shy.
A cup of basil tea and some favorite BLUES always rejuvenates me after a hectic day in office. I prefer Earbuds more than an IEM or Headphone, when my body is totally exhausted and crying only for the bed. So as of now I have collected more than twenty Earbuds and use them periodically. Today for review I got the ISN Audio Rambo from Penon Aduio and after using it almost a month writing this review. The unit completed almost 100 hours of controversial burn-in and I have used normal thin foam for this review. Dount foams are not suitable with Rambo.


Buying Link –


Driver Size - 14.8mm,
Shell – Yuin,
Frequency - 6-25KHz,
Impedance - 32Ω
Sensitivity -115dB,
Plug Type - 3.5mm/2.5mm.
Cable Length: 1.2m.


What’s inside the Box
Rambo Earbud,
6 pairs of Eartips,
Shirt Clip,
Metal Carabiner Clip Snap Hook Key Ring,
Velcro cable tie,
1 durable Carry case.



Rambo needs good amount of power to shine. As per specification its 32 Ω and sensitivity is -115dB still need powerful sources to open up. I have used my Fiio 1 mk2+ Topping NX3s, Fiio Q5 + Fiio A5, IFI XDSD as sources for this review.

Presentation, Design & Build Quality

The presentation is simple. A 120cm X 75 cm cardboard box and inside that a hard earphone case. Brand name and specifications clearly printed on the box. Earbud and accessories securely packed inside that carry case. Rambo is a Hand crafted Earbud with Yuin shell, beautifully braided silver cable and matching non bulky 3.5 mm jack & Y splitter. We know that Yuin shells are best in terms of fit and comfort. Thankfully ISN Audio has used a good quality Yuin shells here but I am concerned with the cable; it’s a bit softer side and may not last long after daily torture. The chin slider is small and a bit tight. Supplied hard case is very good in quality, so overall ISN Audio managed to maintain quality for their first Earbud.


Before proceeding to the sound part I want to clear a point i.e. the contradiction of name. Sylvester Stallone’s Rambo (John Rambo) is nothing to do with ISN Audio Rambo but the first impression may go to a buyer that this Earbus is for bass lovers which is actually opposite. Sonically ISN Rambo is a bright sounding Earbud. But there is a catch, ISN Rambo proved how beautiful a bright sounding Earbud can be. Give Rambo at least 100 hours of burn in and let it rock and roll.


Out of the box Rambo is a bit Bass shy but after burn-in it improved a lot, still quantity is not that much for a bass lover to appreciate. Surprisingly quality of lower frequency is at least good. Bass is tight, punchy and texture is there. Sub-bass region is not that emphasized and also Speed is not that fast and accurate. For example in tracks like ‘Dreams’ by Fleetwood Mac and ‘Billie jean’ by M. Jackson you can feel the punch but slower decay also can easily noticed.


Now things going to change because Midrange is the strongest part of Rambo, midrange is definitely forwarded in Rambo. Upper Mids are more emphasized than lower Mids. Both male and female vocals are crisp, clear and full of texture. Midst are totally transparent, songs like ‘Bennie And The Jets’ by Elton John, ‘Talking To The Moon’ by Don Henley and ‘Don't Let Me Be Misunderstood’ by Nina Simone sounds just natural and mesmerizing.


Treble is the cream of Rambo. Upper frequency part is well extended, clean, and airy; no noticeable harshness is there. With treble demanding tracks like ‘The chain’ by Fleetwood Mac the sparkle also can be noticed. Both quality and quantity is top notch. Personally didn’t expect such polished treble from Rambo but it managed to impress me.


Soundstage & Imaging
Soundstage is very good in terms of width and depth, even better than some IEMS and headphones I have heard before. Imaging is above the average still managed to bring the imaginary stage with complex tracks.


For 65$ I don’t think there is much to think before buying ISN Audio Rambo, unless you are a die heart bass fan. Sufficient Bass, clear Mids and sparkling Treble if this is your requirement then Rambo is a perfect one. For Jazz, blues, country music Rambo is one of the best Earbud I have heard till now but ‘Romeo’ could be a better name for it.
Thanks. I have already mentioned the sources earlier in this review. For comparison in this price point I have used only OUTART ACG. I will update this review with a comparison part soon .
Otto Motor
Otto Motor
Concise and to the point! I am about to open mine...
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Otto Motor
Otto Motor
I am not an earbud guy but...this one is really good: warm, good intimate mids, and the well extended treble you described. It also has a fantastic timbre....couldn't get enough of that Chopin cello sonata.
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