Review: OLLO Audio S4X Reference Headphones

If you’ve ever wanted to hear recorded music in its purest form, OLLO Audio might have just the ticket. Hollin Jones road tests the S4X Reference Headphones.  

OLLO Audio is a relatively new company based in Slovenia that designs and builds professional recording, mixing and reference headphones. Its flagship model is the S4X, reference ‘phones designed to be incredibly neutral out of the box, to give the listener an absolutely honest representation of the recorded material. Reference headphones are not really meant for mixing but for checking the accuracy of your finished masters. Or indeed simply enjoying listening to music at the highest quality. OLLO’s list of satisfied customers includes a number of producers who have worked with very big name artists around the world.

Luxury Finish

The build quality is fantastic, with a stainless steel and leather headband combined with 90mm hybrid velvet ear pads and an overall weight of just 350g making them both lightweight and very comfortable for long periods of listening. The ear cups are made of American Walnut and the supplied woven cable has dual mini jack to a single stereo, with a 1/4 inch adapter. There are no electronics and no BlueTooth, with its associated streaming compression. Here, the focus in on fidelity and that means no wireless.

OLLO Audio SX4 reference headphones

The matched 50mm Neodymium drivers offer a frequency range of 20Hz-22kHz with an SPL of 108dB and impedance of 32 ohms. High quality meshes and membranes protect them from dirt and dust without getting in the way. These headphones look and feel beautiful, though OLLO is careful to point out that they must be handled with care. Throwing them in and out of backpacks is to be avoided.

Crank Up the Volume

That’s the specs, but what about real life performance? These are perhaps the most impressively transparent reference headphones I’ve ever used. Their open-backed design means lots of audio spill (hence no good for recording or perhaps even for use in public) but it also makes them wonderfully accurate, with no low-end interference from closed backs on the cups.

OLLO Audio SX4 reference headphones on head

Listening to a wide range of commercially produced music reveals the disparity in production and mastering techniques. Not that one is better than the other, but you can really, really hear the soundstage and separation going on. Bass is tight and solid but never overwhelming, mids are pin-sharp and crisp, and highs sizzle with life without ever becoming tiring. It did occasionally feel like the upper mids, somewhere around a higher snare frequency, were a fraction more prominent than they should be at high volumes, but since this happened with some tracks and not others it may be more of a reflection of the original mixes than the hardware itself.

OLO Audio SX4 reference headphones. Credit: Ari Takahashi.

OLO Audio SX4 reference headphones. Credit: Ari Takahashi.

Digging Deeper

Listening with such incredibly flat ‘phones makes you realise how much other models - even your favourites - do colour the sound at least to an extent. Of course they may well not be reference models, and better suited to recording or mixing. But the S4Xs made me want to go through my music library looking for songs I knew to be particularly well produced, to hear new details - and they didn’t disappoint. From jazz to rock, dub to dance, they revealed every detail. And I mean that in a good way.

In the world of audiophile hardware, the asking price is actually very reasonable and the company offers both a 5-year warranty and a 30-day money back guarantee. My guess would be that this generous offer doesn’t see much uptake because once you have listened on these, you’ll not want to go back.

Price: 399 Eur

Pros: Gorgeous build quality. Lightweight for long listening sessions. Incredible sonic accuracy. Unbelievably flat. Reveal every detail of music tracks. Money back offer (not that you’ll likely need it).

Cons: Tons of audio spill makes them accurate but also best used in private, and not for recording.




Hollin Jones was classically trained as a piano player but found the lure of blues and jazz too much to resist. Graduating from bands to composition then production, he relishes the chance to play anything with keys. A sometime lecturer in videographics, music production and photography post production, Hollin has been a freelance w... Read More


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