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Sound: *********1/2
Value: *********
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Reviewers' ChoiceThe music you listen to is rarely, if ever, recorded straight from the musician onto a recording medium. There are almost always extra steps, most notably mixing and mastering. There’s a sort of black magic to both processes, and the people who do it well are always in high demand. In short, they’re largely what makes a song sound the way it does. A pan here, an EQ tweak there—they let you hear individual instruments (or not), hear the room (or not), and so on.

Typically, these magicians do their work in acoustically treated rooms, with speakers they know incredibly well. During the process, they’ll often check the current mix on a variety of gear. How does it sound on a Bluetooth speaker? How does it sound with tower speakers? Maybe the engineer wants it to sound good on everything, at the cost of sounding amazing on some gear.

Ollo Audio

Other engineers might do some, or even most, of their mixing and mastering using headphones. At the very least, they’ll know these headphones really well. Best case, the headphones themselves will be as transparent and neutral as possible, so they’ll have the best chance of creating a mix that will sound great on the widest range of speakers and headphones.

Enter the S5X 1.1 headphones from Slovenia’s Ollo Audio. The driving factor behind Ollo in general, and the S5Xs in particular, was “flat sound.” Neutrality is the goal, so as to offer a tool for audio engineers that essentially takes the headphones out of the equation. Theoretically, they wouldn’t need to check how a mix sounds on other gear, as this is the best possible option. To further improve neutrality, the S5X 1.1s have an available “USC,” or Unit-Specific Calibration. This plug-in for digital audio workstations will even out the S5Xs’ response even more.

Ollo Audio

At €539 (~$580 USD, all other prices USD), they’re not outrageously expensive, either. How do they sound? Spoiler: pretty impressive.

In the box

In the box you get a small nylon carrying bag, a “backstage pass” that’s basically just a fancy delivery system for a QR code to Ollo’s website, detachable cables with a 3.5mm-to-6.3mm (¼″) adapter, and an envelope with the calibration certificate. This has another QR code and the various info you need to download the USC—more on this in a moment.

Ollo Audio

It’s a small gripe, but the bag’s nylon material doesn’t feel befitting for headphones that cost almost $600. A hard case is available, but it’s an extra $37.50.


Before we get into anything else, I want to point out these are absolutely gorgeous headphones. The dark-walnut earcups and black metal frame are understated, classy business. The soft foam earpads, covered with leather and velour, are quite comfortable. Inside are matched 50mm drivers. At 420gm, the S5Xs aren’t light, but they’re not heavier than larger open-back headphones like the Audeze LCD-5s.

Ollo Audio

The process to get your USC is simple, though accompanied by a bit of ceremony. Following the supplied links and instructions, you “buy” the plug-in with your calibration separate from the headphones via Ollo’s website. There’s no extra charge—as of this writing, the calibration is included in the price of the S5Xs. After “purchase,” you’ll get an email with links to the files you need. From there, you install the plug-in on your digital audio workstation. Then, once the plug-in is open in your DAW, you upload the separate calibration file from the location where you saved it. It’s all easy, and Ollo smartly has a YouTube video that describes every step of the process.

While I understand the S5Xs are targeted at the mixing and mastering market, I would have loved to see a smartphone app that would allow you to use the calibration for more casual listening. Since the calibration is a widely usable (and most importantly, human-readable) XPS file, its settings could be manually added to a third-party EQ app. The lack of a specific Ollo app is not a big deal, but it would have been a cool addition.


Ollo seems to have delivered on its promise of neutrality. I found the overall sound very neutral and flat. I heard great mids, clear treble, and accurate bass during my time with the S5Xs.

Ollo Audio

Molly Tuttle’s “Olympia, WA,” from her 2020 album . . . But I’d Rather Be with You (24-bit/96kHz, Compass Records / Qobuz), is a delightful acoustic singer-songwriter cover of one of Rancid’s best songs. The first thing I noticed was the S5Xs’ impressive soundstage. It was exceptionally wide, with instruments seeming to spread out well over my shoulders. That’s certainly the case with most of the better open-back headphones, but each instrument here seemed like it solidly sat in its place across the soundstage. The center image was a little weak, however. Tuttle’s voice wasn’t down in the mix by any stretch, but wasn’t razor-sharp in the middle of my head, so to speak. No frequency seemed overly accentuated or attenuated.

“Pain” by the War on Drugs (A Deeper Understanding, 24/44.1 FLAC, Atlantic Records / Qobuz) starts with some jangly guitars and percussion. These were exceptionally clear through the Ollos, but not harsh. The snare had a great snap without being overbearing. This track has lots of reverb, and the openness of it came through extremely well.

Ollo Audio

Ollo claims 106dB sensitivity at 1kHz, and I was able to get a decent volume out of them with my meagerly powered Sony NW-A306 media player. However, they sounded a lot better with the Schiit Audio Magni and especially the HiFiMan EF400 (review coming soon) headphone amps. I’d be shocked if there were professional mixers that didn’t have a reasonably powered headphone jack (or amp) at their disposal, so this seems fine.


For headphones to compare with the S5Xs, I first picked the Audeze LCD-Xs, which Ollo mentions as a competitor. At $1199, these are twice the price of the S5Xs, but they are also marketed toward audio engineers. “The Wire” from Haim’s Days Are Gone (24/96 FLAC, Columbia Records / Qobuz) is a fairly straightforward pop rock track. The first thing I noticed was better immediacy of transients on the LCD-Xs, thanks to their planar-magnetic drivers. The Audezes were a little brighter, with more upper midrange/lower treble. They didn’t quite have the same flatness to their sound as the S5Xs, though both are excellent headphones. Subjectively, the Audezes were more “fun” to listen to, but that’s not what a professional is going for. However, the LCD-Xs are just so damn heavy. At 612gm, they’re 50 percent heavier than the Ollos. Personally, that’s too much for me to wear for long sessions.

Ollo Audio

I didn’t have any $600 headphones on hand to directly test, but I had two others that I enjoyed greatly and that are priced closer to the Ollos than those big Audezes. Brent Butterworth reviewed the Beyerdynamic T5 (Gen 3) headphones in 2020 and really liked them—they received a Reviewers’ Choice award. You’d think the Ollos would be outclassed by these $999 headphones, and yet . . . not so much. With Chvrches’ “Over” (single, 24/96 FLAC, EMI Records / Qobuz), the T5s had noticeably more bass, but the Ollos’ bass had better definition, less “thump.” Their treble was also smoother. Of course, being open-back, the S5Xs had a much larger soundstage, so no surprise there.

Going in the other direction price-wise, the HiFiMan Sundara open-back headphones cost $299 and are one of my favorites in that range. This is where things get interesting. The Sundaras are lighter, have that great immediacy of planar-magnetic drivers, and are half the price. They’re a lot harder to drive, and definitely not as balanced. The Ollos have better bass extension (though there’s less bass overall) and better upper treble. Which would I grab for casual listening? The Sundaras. Which would I grab for professional audio work? The Ollos.


Despite graduating with a degree in audio production, and having done some mixing and mastering, I am long out of practice. However, I still dabble in audio recording, so I installed Ollo’s plug-in to Adobe Audition and imported some lossless tracks, starting with Lauren O’Connell’s “Power Out” from Everything Feels Quieter (Acoustic Sessions) (16/44.1 WAV, Sugar Glider / Patreon). This is a folksy singer-songwriter track with vocals, guitar, and some light percussion. You can turn Ollo’s plug-in on and off with a single click. To make this test as double-blind as possible, I closed my eyes, clicked a bunch of times with great rapidity, and then, eyes still closed, attempted to guess whether the plug-in was active or not. I was eventually able to guess correctly 100 percent of the time, but it was extremely subtle. A little more air in O’Connell’s voice was the most notable tell.

Looking at the text in the XPS file, I found it easy to see why. Ollo designs these headphones to be as flat as possible, so there’s not much for an EQ to do. The largest adjustments were a 1.7dB boost centered at 93Hz and a 1.6dB boost centered at 7800Hz. The handful of other tweaks were even smaller. Generally, adjustments of less than 3dB aren’t audible, but if they’re over a wide enough frequency range, they can be, and many of the adjustments in the USC also adjusted the EQ’s “Q”—how wide or focused the adjustment is on the selected frequency. That’s not to say the calibration isn’t useful. It’s a way to improve something that’s already good, and it gives an engineer the peace of mind of knowing that what they’re hearing is as accurate as possible.


To test myself, and to see how far I could tweak the S5Xs, I made my own calibration file, uploading it in the same way as the real one. Naturally, being me, this meant adding some bass. This warmed them up nicely in a way that I’m sure would horrify the folks at Ollo. For some lolz, I also made an EQ I labeled “BAD” and completely jacked all the settings, slashing the bass, boosting a band around 3kHz enough to make dew falling on moss sound like fingernails on a chalkboard, and gave it another go. Shockingly, it was bad. I believe it was THX’s Laurie Fincham, many years ago, who once described EQs to me as “chainsaws in the hands of children.” Clearly, he was presciently talking about me in this very moment. However, this BAD preset was an interesting palette cleanse. The Ollo plugin allows for fast switching between loaded EQs, so I was able to go between it, my bass+ EQ, and the flat one supplied by Ollo. If I had to pick one to live with, honestly (and this will come as a surprise to many), I’d definitely pick Ollo’s neutral option.


Ollo has done such a great job with the S5X 1.1 headphones that the calibration is almost unnecessary. However, if I had followed my degree and gone into professional audio work, I would absolutely want the option to make these as flat as possible. Quite a few people who did go that route, and got very successful at it, seem to feel the same way. Ollo’s website is full of testimonials from engineers who have worked with everyone from David Bowie to Adele, Radiohead to Nicki Minaj, and more. I can see these being a worthwhile addition to any audio engineer’s studio. If that were my life, these would be a tool I’d want.

Ollo Audio

Reviewing the S5Xs as traditional headphones was an interesting exercise for me. They run full speed into my constant balancing act of personal preference vs. accuracy. Would I like more bass in headphones I listen to for pleasure? Yes, a bit. Something more “fun”? Also yes. I can recognize that’s my preference, however, and as a reviewer it’s important to be able to separate that. The Ollo S5X 1.1s are an extremely capable, well-balanced pair of headphones. If that’s what you’re looking for, these are a bargain at $580.

. . . Geoffrey Morrison
This email address is being protected from spambots. You need JavaScript enabled to view it.

Associated Equipment

  • PC: iBuyPower Windows 10.
  • Portable media player: Sony NW-A306.
  • Headphone amplifiers: Schiit Audio Magni, HiFiMan EF400.

Ollo Audio S5X 1.1 Headphones
Price: €539 (approximately $580).
Warranty: Five years (many parts are user serviceable).

OLLO Audio d.o.o.
Sempas 37
5261 Sempas
Slovenia, EU
Phone: 00386 69 712 841

Website: www.olloaudio.com
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

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