Ollo Audio S4X

Ollo! It’s a new reference headphone S4X in Tw6 town!

PROS: Boutique brand design and build quality, balanced signature with warm-neutral reference tuning, sub-bass extension, mid-bass presence, midrange tonality and presentation, natural upper-treble extension, detail retrieval and easy to drive dynamic driver open-back design, good reference tool for music industry professionals as well as audiophile enthusiasts who like and prefer their headphones with natural tonality and timbre of instruments.

CONS: Stock tuning is quite good but Nitpicking – Ear pads are a bit small for over-ear design and bigger ears, stainless-steel headband rings loudly when you tap it, a bit more sub-bass and lesser mid-bass will bring it more in line with Harman Target and enable better neutrality as well as sub-bass rumble, perceivable lower-treble dip in 6-9kHz stopping it from absolute neutrality in the range.


I would like to thank Ollo Audio for providing the S4X. Even though the headphones were provided free of charge, I ended up paying almost 100% import duty to import the headphones because of a declaration error. So, it feels like I bought this pair at full price, even though the money went to the wrong people and not Ollo Audio (facepalm). I am not affiliated with the company or any of its sellers and write this review with an unbiased opinion regardless of how the review turns out.

About Ollo Audio.

Ollo Audio is a small and young boutique headphone brand from Slovenia. It was started by Rok Gulic’ and Mitja Sajovic. ­­­Rok, the CEO of the company is an educated audio engineer and his passion of wanting to make headphones started when he was mixing his band’s record and was tired of working late nights on studio monitors in his home studio, with it being highly disturbing for his family sleeping in the next bedroom. So, like every guy in a home studio with family, he tried mixing on headphones but to no avail as mixing on headphones can be very difficult since you can’t feel the bass like you do with full range monitors with a sub-woofer.

One thing lead to another and they finally started developing proper headphones for professionals, tuning them as close to reference as they could through their research. They have 2 models currently,

  • S4 – Closed back recording and monitoring headphone
  • S4X (€399) – Open back reference grade headphones for mixing and mastering

Rok and Ollo run a very nice blog on their website called OLLO LIFE as well as a YouTube channel that I highly encourage everyone to check out if you want to know more about them. They and especially Rok have a knack for creating nice interesting and entertaining videos which are full of knowledge and behind the scenes insight into the world of Ollo Audio.

 Links – Ollo Audio Website | Ollo Life Blog | Ollo Audio YouTube Channel

Ollo S4X Solo 2

Alert! – This is going to be a long and detailed review of S4X with insight into the world of reference. So, brace yourselves and definitely read the review chronologically.

About S4X.

S4X are Ollo’s Open-Back Reference headphones tuned to be ‘neutral and brutally honest’, designed and measured using a GRAS 60318-1 setup.

Technical Specifications.

  • Frequency Response – 20-22kHz
  • Impedance – 32Ω
  • Weight – 350g

HANDPICKED MATCHED SPEAKERS – Ollo measure all speakers in every series and match them together to achieve minimal possible tolerance between left and right channel.

  • Dynamic driver
  • Neodymium magnets
  • 2 layered Coil
  • PET membrane – 25u

NATURAL PREMIUM MATERIALS – They use sustainably sourced woods to make the cups (walnut in my case), stainless steel for headband and luxury nautical leather and velour for their ear pads for maximum comfort.

HIGH PRECISION WOVEN MESH | POWERED BY SATTI – Designed and manufactured to improve acoustics and protect sensitive components.

  • Smooth monofilament fiber
  • Efficient protection from dust, metal particles and liquids
  • Strict airflow control

CUSTOM DESIGNED EARPADS – They are hybrid pleather and velour ear pads with memory foam.

  • Outer diameter: 90 mm
  • Inner diameter: 55mm
  • Hybrid velvet
  • Pleather
  • Memory foam

INDUSTRY LEADING 5-YEAR WARRANTY – The 5 year warranty that Ollo Audio offers on their headphones is class leading and goes on to show how confident Ollo are in their product. 5 worry free years in the asking price of €399 is amazing in my opinion.

Included in the box.

  • S4X Headphone
  • Leather carry pouch
  • 5mm connector cable with 3.5mm jack
  • 5mm to ¼” adapter
  • Graph measurement
  • Warranty card
  • Manual

Build Quality.

S4X are designed with sustainability and upgradability in mind. You can see that S4X oozes of boutique brand build quality right away. The walnut wood cups look premium and are cut, sanded and polished very well. They only use a tiny bit of wood sealer on them and aren’t lacquered because you can feel the wood grains quite nicely. The downside to not lacquering the cups is that the wood can chip and dent if one drops the headphones. The outer metal grill though simplistic looks very nice too. The ear pads are hybrids made of pleather and velour, which feel and look quite good for a headphone in this segment. The leather tensioner headband isn’t padded but is very comfortable on the head and after a while you don’t even feel it pressing on the top of your head.

The stainless-steel headband is mounted on the ear cups with two big screws; both feel quite sturdy and built to last. The headband adds a bit of raw industrial design element to the headphone but sadly, rings loudly when you tap it. Now, this isn’t a problem when you’re listening to music but can be quite off-putting otherwise. I think this is one of the things Ollo should definitely think about fixing in the future.

Cable – Stock cable has L&R 2.5mm TRS terminations for the ear cups and a 3.5mm TRS jack. It has a cloth sheath which splits to red rubbery L&R wires. The choice of red has a very OnePlus feel to it since my DASH charger’s USB cable is exactly the same colour. I do wish they had paired a better UP-OCC cable with the S4X but the stock cable is no slouch. It is better than stock cables of Hifiman and Sennheiser headphones in this price segment,  however I would’ve loved it if they would’ve offered a 4.4mm balanced cable as stock or at least as an option.

Ollo S4X Cable

Case – S4X come with a soft leather carry pouch which fits the headphones and cable easily though it would’ve been great if they would’ve included a hard case to carry and protect the beautiful wood finish from chipping or accidentally drops while travelling or carrying it around.

Fit and Comfort.

S4X are designed to be worn over the ear but the ear pads merely manage to encompass my ears because of the small 55mm inner diameter of the ear pads. That said, even though the hybrid pads and clamping force is rather comfortable and I’ve been using the S4X for production work for several hours without much discomfort, my ears sometimes do start feeling the inner circumference of the ear pads and it does get a bit irritating at times. The headband tensioner on the other hand does not exert a lot of force on the top of my head and I stop feeling it pressing on my head after a while, not because my head goes numb, but because it is well designed. Haha. I’m not the biggest fan of separate headband to attach the ear cups and a tensioner headband for fit, but this does work and enables for an easy and mostly comfortable experience. Even though I can use S4X for hours, I would love to see Ollo workout an even better fit mechanism than the current one. Something along the lines of HifiMan Sundara maybe?

Ollo S4X Solo Earpads

Upgradability and serviceability at minimal cost.

Now, this is one thing that I think differentiates Ollo Audio from all the other headphone manufacturers around the world. Here is what Ollo offer as a brand,

  • The whole headphone is designed in a way that you can open it up and service it at the comfort of your home within a couple of minutes. All the parts you’d need can be ordered from Ollo’s Spare Parts Store individually. The parts are also very reasonably priced with a pair of ear pads being €25 and a pair of matched drivers being €40. That’s amazing in my opinion! They can however repair the headphone for you too if you would like to send them in and have them do it instead.
  • Ollo Headphones are upgradable to new models at a fraction of the cost of the new model. So, if Ollo release a new model and your model is eligible for the upgrade, you can just send in your headphones and they’ll upgrade your headphone with the modifications and ship it back to you. For example, the upgrade from S4 and S4R to S4X is €149 which includes DHL pickup and return and is just €109 if you opt for standard post shipping.

Here’s a video of Rok Gulic’ explaining the same –

Measurements and tuning as per 60318-1 standard vs what others use.

Ollo Audio use a G.R.A.S 45CC using IEC 60318-1 ear simulator with a RA0039 coupler and Dewesoft AD conversion Sirius system. Here is their measurements page where they’ve measured the S4X along with a ton of other headphones – Ollo Audio Measurements

Here is the measurement of my particular S4X unit.

Ollo FR graph

Now some of you who are aware and familiar with headphone measurements and RAW graphs might be wondering why S4X or none of the headphones on Ollo’s measurements page look like the RAW graphs you’re used to seeing with ear/pinna gain. Others might be wondering what these measurement standards are, how and why they differ and the rest of you probably don’t care for any of this. If you’re of the last kind, I envy you for the peace of mind you have in your life not fussing about any of this. Jokes apart, for those who do, let me quickly give you some insight. I’ll try to keep it short and simple without going too deep or digging a hole for myself.

The current commonly used standard is 60318-4 which is also known as IEC 60711 or simply IEC 711. Now technically, there are no hard and fast ‘industry standards’ that everyone adheres to or follows but 60318-4 standard is one of the more commonly adopted and accurate ways of measuring IEMs and headphones, except until the recent development of Brüel & Kjær’s Type 5128 which measures even more accurately but isn’t as widely adopted or used yet.

Oh, before that let me make you aware of a couple of things you might need to know first.

  • ERP = Ear Reference Point
  • DRP = Drum Reference Point
  • Ear Gain (head/pinna gain) = Gain added by the human ear as the sound travels through the outer ear, into the canal and to the ear drum.

If you refer to the Figure 1, you can see that ERP has a microphone measuring the headphone outside the ear canal whereas DRP has the microphone measuring at the ear drum. Since ERP measures the headphone outside the canal, it shows measurements without ear/pinna gain. On the other hand, since DRP measures the sound at the ear drums where the sound has travelled through the canal and has been affected by the ear anatomy’s gain factor, it shows measurements with ear/pinna gain.

Figure 1

Figure 1.

The reason why none of the headphones on Ollo’s measurements page have ear/pinna gain is because the RA0039 coupler that Ollo uses is an ERP coupler which measures the headphones outside the ear canal.

Now, you might be wondering why Ollo Audio use the 60318-1standard/RA0039 coupler which is an ERP coupler and not the 60318-4standard/RA0045 coupler or one of the newer RA0401/RA0402 couplers which are all DRP couplers. I had the same questions and emailed Rok for his take. Here is a summary of our exchange –

After having long discussions with Bang and Olufsen engineers, then GRAS and Dewesoft about the best option as per their requirements, they decided on the 60318-1 setup to measure their headphones mainly because DJs and artists are a major of chunk of their customers and they like to see flat line graphs without ear/pinna gain. Unless people are familiar with and know how to read RAW graphs with ear/pinna gain, it can be difficult to comprehend – which is true. Flatline graphs helps make stuff easier for the layman but are not the best for people like us who like 60318-4 style RAW graphs and want to focus on the details that are available in those 60318-4 style RAW graphs.

Another thing is that Ollo Audio don’t want to use compensation curves either. So, a RA0039 coupler, which is an ERP coupler, is the best way to measure when you don’t want ear/pinna gain in your graphs. Also, Rok says that 60318-1 is way easier for them to handle on the production floor, is more consistent with quick back to back measurements and doesn’t have as big a learning curve. They need ease of use and consistency because they measure every headphone and put its individual graph printout in the box with each headphone, which I think is very cool for a headphone that sells for just €399.

My personal take – I personally think the best way to do flat line measurements ideally is to use the industry standard 60318-4 (711) DRP setup or even better, the new Type 5128 (more accurate but also more expensive), to measure a RAW graph and then compensate with popular target curves like Diffuse Field or Harman Target and specifically specify the compensation publicly. This way you can offer both graphs for people to check out. But I can imagine it taking more time, having a bigger learning curve to keep the measurements consistent one after the other at the production floor and confusing people who don’t know how to read 60318-4 style RAW graphs.

Another observation of Ollo’s headphone measurements I had was that their 60318-1 graphs of some headphones on their measurements page weren’t consistent with 60318-4 (711) graphs or my experience of having tested them in real life, particularly in the upper-midrange and lower treble. Now, that could be because of a number of reasons, with setup and software differences being the primary one and driver differences between samples and all being secondary. Rok too switched to REW software instead of Dewesoft after me having pointed this out to him and noticed that S4X with REW measured quite differently from Dewesoft even with the same measuring setup.

This is why you see a lot of people around stressing on having an industry standard way of measuring headphones so that everyone can cross-refer measurements between different brands, companies and hobbyists easily and without confusion.

Recently, Brüel & Kjær have come out with a newer and more accurate measurement standard called Type 5128 but it hasn’t been adopted by the masses yet. Also, it is quite expensive and many enthusiasts wouldn’t want to spend so much money for a hobby. But frankly, we do need an industry standard for consistency and cross-referencing and I can only hope that one day we can have an industry standard measurement setup that doesn’t cost an arm and leg so that every brand and enthusiast can own one. #wishfulthinking

Nevertheless, Ollo Audio’s method works well for their intended purpose and their target audience, and that graph does translate mostly in case of their own headphones S4X. Also, as you get to know more and more about Ollo Audio as a brand and team, you’ll see how knowledgeable they are and how aware they are of what they are doing or wanting to do. It definitely shows in the product they’ve made as well as the enthusiasm, ideas and insight they share in their YouTube videos and blog.

Page 2 – Sound analysis, Comparison, and Conclusion.


4 thoughts on “Ollo Audio S4X

  1. Thanks for this review, very deep explanations.
    In your opinion S4X are valid headphones for music in which the bass is fundamental ? ( for example techno, drum n bass, etc.)
    Can work well paired with an UMC404HD ?


    1. Hey! It has really good extension down low but it is tuned neutrally flat. If you like a lot of bass for those genres, you should go for a bass boosted headphone. If you want the songs to sound close to flat (reference-neutral) like flat studio monitors, then you should look at headphones like Ollo S4X, Sennheiser HD6XX, HifiMan Sundara 2020, etc.


      1. Sorry, i forgot to specify the purpose: production and mix (and master when i will learn how to properly do it).
        Can confirm that these cans have precision on the low end ? (Now i’m using akg k240 mk2, nice for newbie but zero bass freq). And, sorry if i repeat the question, the impedance of S4X is good enough for the phone’s output of UMC ? I think [ load impedance = 8x source impedance ] isn’t observed but i don’t know if is a problem.


      2. I mainly use studio monitors for mixing but I like HD6XX and Ollo S4X both for cross checking my mix decisions. They’re both much better than AKG K240 MK2. Ollo S4X is slightly easier to drive, is mostly neutral and has slightly better bass extension. HD6XX has a more realistic and natural midrange and treble presentation as well as better separation. I’ve never used the Behringer UMC404HD, so I have no idea about its power or driving capability.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s