Ollo Audio S4X review : As good as it gets


Ollo uses neodymium drivers which has 2 layered coils with a 25u PET membrane and both the sides are precisely matched.

First statement about the S4X’s sound attributes on its official product page is “Natural and Brutally honest” The burning question is.. How does this beauty sound? First thing first, these are reference type headphones and do not have a lot of lower end grunt to them (Maybe the closed back plates can change the sound signature but I can’t confirm that). Mid range is agile and dynamic with plenty of details, same goes for the treble region.

S4X’s sound signature is slightly on the brighter and crispier side with balanced notes presentation.

Ollo audio dont compromise when it comes to sound quality. In their words:


OLLO headphones are individually tested and measured and come with the frequency response measurements chart in the package.”

“Designed and measured using IEC 60318-1 standard.”


Even when the graph shows a bit of an elevated lower end the S4X cannot be labeled as a bassy headphone by a long shot. The precisely tuned dynamic driver has a controlled and accurate lower end with nice sub-bass extension with required amount of rumble to it. It does not move a lot of air though. Doesn’t matter how it is driven, due to the reference tuning and open back design the sub-bass region doesn’t go boom boom. It does not vanish into thin air but it is just a few DB more than what the ER-4P delivers. The Mid-bass is a bit more voluminous with much better body and slam. It still doesn’t qualify as a “wholesome” but has good amount of body and slam which keeps the party going. The punch is not hard and the rumble is not comparable to other dynamic driver headphones like Sennheiser HD6 mix or even the HD598/599 but it excels with decay speed while maintaining very good amount of texture. The S4X delivers a cleaner and faster response with a slight bit or precipitation. The level of accuracy and precision offered by it is simply class leading.

Should you look at the S4X for its bass thump? Not really, it is tight and precise without much excitement, its has a more analytical tuning to it.

P.S. Equalizing helps (if needed) without messing around. It responds to EQs without any problem.


The Frequency graph shows a slight bit of decrease in volume for the entire mid range but thanks to the open back design the S4X’s bass doesn’t feel heavy, letting the mid range express itself without any restriction. The transition from upper bass to lower mid range delivers plenty of details without losing any energy. The mid range has plenty of micro details with one of the most accurate and precise notes presentation. It manages to find a sweet spot which balances everything while delivering plenty of details and transparency with the juiciness intact.

The vocal region sounds vivid with excellent accuracy while maintaining appropriate amount of fullness. Both male and female vocals have class leading amount of transparency, definition and resolution with a lot of texture. The tonality is accurate and very organic (the wooden housing might be playing a part in this) making the vocals very enjoyable. Male vocals sound throaty while female vocals are aptly sharp with right amount of energy. Instruments have nice shine to them with perfect depth and bite. A bit more might have pushed it into uncomfortable territory. It impresses me by not favoring any part of the spectrum. There isn’t a single instrument that feels dull or over energized. The upper mid is in line with the rest of the spectrum and doesn’t have any anomalies while maintaining equally good amount of energy and transparency.

Ollo S4X separates itself from the crowd with its technicality, the way it manages to deliver micro details of background instruments without tempering with the foreground is praise worthy and the contrasty nature makes the whole experience enjoyable.


The S4X has precise notes presentation across the spectrum and it holds true for the treble section too. It does not have the most liveliest or sparkly treble region. What it has is an aptly energetic presentation filled with good amount of details and transparency, transparency which is not the best in its price range. Some headphones like the HI-X55 exhibit better transparency and clarity with deeper and more energetic notes but the S4X doesn’t belong to that bunch, the open back design helps a lot by dampening most of the shine and sparkle. It delivers the good amount of energy and spark staying clear of any uncomfortable notes. It has very good amount of air between instruments. Thanks to its slightly bright nature it resolves very good cleanliness.

The transition phase from upper mid range to lower treble region is excellent with transparency and clarity. The extension is very good but it starts to lose energy as it goes deeper into the spectrum. Level of details retrieval is very good, it doesn’t miss out on much while keeping the timber close to natural. Cymbals and pianos have good transparency with an organic feel to it. Needless to say that separation and layering is up to the mark with good amount of air and space between instruments. The treble stage is well spread and has good density to it. The bigger stage helps a lot with instrument placements and density.

Is this the best treble? Short answer is no, but If you are coming from a Planar headphone, yes this is better.


In general an open back headphone has to have a wider, deeper and open field of sound compared to most of the closed back headphones and that holds true here. The open back design grants a lot of dynamism and sonicalities. Depending on the track the stage can stretch, if the stage feels a bit narrow near the head with one track, with the right track it feels wider. Overall the stage is well extended in every direction, one might complain that it does not have the height some other headphones like the HD598 but it is much more deeper, wider sonically superior than that. It can place cues much further and precisely. All of the vocals are placed inside the head and most of the instruments are placed outside.


VS Fischer M12s:

The M12s used to be my favorite headphone under 500 euros. It too has a wooden enclosure with a open back design. It has only one in and cannot be sued with balanced cables. The 5mm larger cups are a bit more comfortable on the head as it doesn’t press on my ears.

Sound wise it has a slightly more rumble with similar body, the decay is slightly slower. Unlike the S4X the M12s is a bit less colored and more accurate. The S4X has brightness to it across the spectrum and feels a bit colored where the M12s is much more neutral. M12’s notes feels a bit sharper with finishing and less forgiving. It too is a lot precise and accurate, what it does better is the tingling feel. It has excellent contrast and the shine of the instruments are more perceivable. Where the S4X doesn’t have anything sharp, the M12s doesn’t try to hide them which adds a bit of extra character.

Sonically it is equally good but has overall taller and less deep stage.

Which is better.. If you like tingling instruments the M12s will rock, if you like a bit more overall attacking sound with everything sounding eager and forward the S4X is excellent.

VS Austrian Audio HI-X55:

How dare I compare a closed back headphone with open back? I can, because both are a lot similar than different. Both are from Europe and have a balanced sound with excellent build quality. The X55 has slightly bigger and thinner ear pads which are more comfortable on the ears.

Sound wise, the X55 has bigger lower end and feel a bit more complete, it still is not bassy but has better slam and rumble. The sub-bass have a bit more heft to it. Mid range is similar to the M12s, it favors vocals a bit while other instruments take a step back, managing to deliver a slightly less aggressive sound. Timber is equally natural but the S4X is a bit more colored thanks to its slight brightness. Treble is a bit more extended with much better energy till the end of the spectrum, the S4X sounds dull in front of the X55. Layering and separation is better than the S4X with treble notes. The x55 has much deeper notes, the S4X feels smaller here, when I A-Bed both headphones the difference with the treble energy and notes depth took me by surprise.

Stage wise, the X55 is much wider and taller than the S4X, one might doubt that this closed back HP might not sound open and grand but the X55 manages to wow me. The depth is slightly lacking but still then it is around 20% bigger than the open back S4X which is surprising.

Which one to pick.. Both are excellent headphones but if you don’t want to leak anything and want a bit more flexibility then the X55 is the one to go for as it can deliver a bit more rumble and can take heavy metal without sounding tiring. If the need is for an open back headphone with a reference sound the S4X nails it.


So.. This is the end of the S4X review, an excellent sounding headphone which looks gorgeous at the same time. It is a reference headphone which will appeal to those who want details over anything else. It has everything balanced but there is some roll off at both the extreme ends. It does not pump much bass and is kind of small too but that does not stop me from recommending these over any other headphones in its price range. The open back design gives it a big stage and added sonicality. The dynamic feel is intriguing.

S4X is an excellent headphone, but if you want a bit of lower end rumble and don’t want to compromise with treble region, even when the x55 is a closed headphone, you can look into that.

Improvements I would like to see:

1. Slightly bigger cups. This 90mm is neither on-ear nor over-ear and feels a bit less comfortable.

2. The mid range can be a bit less forward and the treble can be a bit more forward.

3. A bit more sub-bass will make it more enjoyable.

Before you decide to go..

Make yourself busy with this interesting bit of comparison graphs from Ollo:



Suman Sourav Meher

Suman Sourav Meher

My humble audiophile journey started in 2010, when I was in college, where I fell in love with the elements, nuances, and variations of this mesmerizing world. The ability of tiny earphones to recreate amazing sounds made my bad days tolerable and good days better! Now I am a full-time audiophile with a preference for musical tracks, especially vocals and engaging ones. I must admit I am addicted, but not to drugs or alcohol, but to earphones. Come join me as I share my experiences, bad or good, and let’s have some fun!


Leave a Reply

Your email address will not be published.

Recent posts