ISN Audio Rambo Review – Delightful Treble Treble Treble

Pros — Well extended and clean treble (!!!); clarity; timbre; separation/layering; high-quality case included.

Cons — Lean on bass.

INTRODUCTION

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.

SPECIFICATIONS

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

IN THE BOX…

…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.

PHYSICAL APPEARANCE, HAPTIC, AND BUILD QUALITY

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!

ERGONOMICS, COMFORT, ISOLATION, AND FIT

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.

SOURCE AND EARPIECE COVERS

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.

TONALITY

JK’s tonal preference and testing practice

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.

VALUE

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.

CONCLUDING REMARKS

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.

DISCLAIMER

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.

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